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Technology Comparison for Spark Ignition Engines of New Generation.

INTRODUCTION

Figure 1 shows the macro-trends that are shaping the future of the automotive industry. Some of them have a considerable impact on the vehicle propulsion system. The most significant ones are:

* sustainability, namely the simultaneous reduction of C[O.sub.2]/ fuel consumption and emissions;

* autonomous driving;

* powertrain electrification.

In this scenario, as shown in Figure 2, internal combustion engines will still have a key role, as confirmed by many studies [3,2].

In long-term scenarios, it is still assumed the presence of a thermal unit in most powertrain configurations, albeit with varying degrees of electrification. The pure electric propulsion can mitigate the problem of the cost of fuel, as shown in [5,6,7], and the local emission of vehicles, even though it does not seem to solve the problem of fine dust, mainly due to asphalt wear, tires and brakes, and as such directly linked to the weight of the vehicle, as shown in [12].

In purely electric vehicles, it is necessary to replace functions that are not closely related to propulsion, which are carried out by the thermal unit, as described in Figure 3, namely:

* production of electricity for devices on board the vehicle;

* mechanical energy production for the air conditioning system [8,9,10];

* production of thermal energy to heat the passenger compartment.

In the absence of an internal combustion engine that converts chemical energy stored in the fuel, the additional functions [9,10] require an electrical energy storage on board possibly much larger than what is necessary for traction only, with negative impacts on cost, weight, range and charging times.

The effectiveness of a purely electric powertrain for the global reduction of C[O.sub.2] is another item that poses some doubts. Indeed, the most correct way to evaluate the environmental impact is to consider the so-called Well-to-Wheel (WTW) [13,14,15] efficiency, which is the product between the production yield from the primary source and distribution of the fuel (or energy carrier), said Well-to-Tank (WTT) and the conversion efficiency of the fuel/ energy carrier into energy for propulsion, said Tank-To-Wheel (TTW):

WTW = WTT x TTW (1)

Considering this approach, the effectiveness of the pure electric propulsion becomes significant when the energy production comes mainly from renewable sources [14]. In addition, as already mentioned above, to consider the real use of the vehicle, TTW should also include useful energy not used for traction, leading to a more significant variable, that is the Tank-To-Use (TTU) efficiency:

TTU = [Energy Used in Vehicle/Energy Taken from Tank] (2)

Moreover, a more detailed evaluation should include both the production efforts and the user scenario, such as the proportion of short/long distances, the intermediate charging as well as the supply of raw materials and recycling [15].

The analysis of the impacts on C[O.sub.2] emissions of different types of powertrain using the approach just described, will be presented in a future work.

After highlighting the importance of powertrains that include an internal combustion engine, it is necessary to evaluate how they can cope with the more and more stringent regulatory constraints, relating to C[O.sub.2] emissions and toxic gases, as detailed in [4]. It should be considered that there are significant differences in the various world markets, and after year 2020 the scenario is still uncertain, as summarized in Figure 4.
Figure 4. Trend of CO2 emission legislation (dashed lines are only
forecast)

Years   NEDC eqiv. CO2 emissio limit g/km

2015    130
2020     95
2025     75
2016    154
2025     97
2015    167
2020    117
2025     96
2030     72

Note: Table made from bar graph.


Lower C[O.sub.2] emissions may be achieved by reducing fuel consumption, or by using fuels with smaller carbon content, such as bio-fuels or natural gas [14]. Furthermore, the efficiency increase should proceed in parallel with the reduction of toxic emissions, both during regulated driving cycles and real driving conditions [4]. These constraints are the main challenges confronting the design and development of new internal combustion engines, together with safety, comfort, drivability/performance, and costs.

Downsizing concepts, including turbocharging in combination with direct injection, have significantly contributed to the recent improvements of internal combustion engines [15, 16, 17, 39]. Among these, gasoline engines, operated with stoichiometric mixture, appear particularly promising for the simultaneous reduction of fuel consumption and toxic emissions. The Three-Way-Catalytic converter is a well-proven, affordable and very efficient after-treatment system. Diesel engines are more efficient, but N[O.sub.x] and PM reduction is much more complex, expensive and potentially highly impacting on end user use since the SCR system will be used more frequently to respect the new N[O.sub.x] limits under real driving conditions, thus requiring urea refills more often [18,19].

Nonetheless, SI engine efficiency is still to be significantly increased to respect the next and future C[O.sub.2] regulations. To better identify and understand the most effective technologies that could be introduced or adopted, one should firstly focus on the main limiting factors affecting efficiency and transient response. Referring to Figure 5 and [34, 35]:

* pumping losses at partial loads in zone n.1;

* limited thermodynamic efficiency due to reduced compression ratio, to avoid knocking damages at high loads, mainly in zones 2 and 3;

* combustion chamber and exhaust system thermo-mechanical stresses at high loads load in zone n.4 where an enrichment of the mixture is necessary to protect the engine components such as the turbine;

* turbo-lag for turbo-downsized engines, in zone n.2 where scavenging strategies should be adopted with negative effects on the Three-Way Catalyst (TWC).

This paper presents a conceptual comparison among the most promising technologies for SI engines, considering their effectiveness, their technological maturity and their impact on powertrain production costs. The considered timeframe horizon is 2025, and for brevity, this work will focus on powertrains designed for C-segment vehicles, which constitute the largest portion of the market, both in European and emerging markets.

The main investigated technologies are related to combustion management and air charging systems, the key elements for improving the previously mentioned limiting factors. To develop an objective comparison of the possible benefits, the evaluation criteria have been defined based on the requirements described in the previous paragraphs, and considering the most promising powertrain architectures. Different powertrain electrification levels have also been considered, thus implying different operational requirements for the internal combustion engine.

Below, a general overview of this work is provided. The main objective is twofold: technological assessment for SI ICEs, and definition of a methodology to objectify the comparison between technological solutions for complex powertrain architectures.

The first section presents a detailed analysis of the powertrain requirements, using a Quality Function Deployment (QFD) with a modified and personalized approach [20, 21]. Two vehicle concepts have also been considered, namely human-driven and computer-driven, by integrating and providing more details than what has already been published, for example in [23]. Indeed, semi-autonomous and autonomous driving systems will be progressively introduced in the market, and therefore the analysis of their impact on future powertrains cannot be ignored. The following section introduces the key powertrain architectures to achieve the desired targets, and focuses on their impacts on the internal combustion engines. Finally, evaluation criteria for a quantitative comparison are defined.

Then the different ICE technologies are described and critically analyzed, highlighting their effectiveness versus the main requirements. Such considerations are mainly based on the most significant technical and scientific literature.

The subsequent section introduces a simplified ICE-Vehicle model, which has been used to validate and integrate bibliographic data, and to further extend the analysis, to consider technologies and vehicle-powertrain architectures that could not be found in the literature. The attention is then mainly focused on technology costs, with a 2025 timeframe constraint.

A comparison among the most promising technologies for SI engines is finally presented, by making use of a selection matrix that defines the overall ranking based on benefits/costs ratio.

NEW POWERTRAIN AND ENGINE REQUIREMENTS

To define the requirements of the new powertrain architectures, a modified QFD approach has been used. QFD is an effective way to link the requests and needs perceived by the end-user point of view to the technical features of a product. Specifically, needs are evaluated by the users at the vehicle high level, therefore a multi-level QFD approach, as in [20], is used, until the powertrain level is reached, where engine and other powertrain components are evaluated. A brief illustration of the process is given in Figure 6.

User's needs and their priority (1-low, 7-high), can be obtained from market research and they represent the inputs for QFD. Specifically, in HoQ1 (house of quality, level 1), driver's needs are evaluated in an objective way by means of engineering variables. For instance, the demand for high performances can be objectified by the maximum vehicle speed, its acceleration or the time from 0 to 100 km/h. Table1 shows the measurable requirements, which, in turn, represent the inputs for the second level, coming from driver's point of view.

Furthermore, requirements can be divided in two sub-groups, both for standard and autonomous vehicles:

* explicit requirements by end-user;

* requirements from legislation related to C[O.sub.2] and toxic emissions, which are considered implicit by the end-user.

Legislation requirements are clearly of great importance because vehicle needs to fulfill them to be saleable. They are not explicitly considered by the user although their impact on customer's choice is becoming greater due to the driving bans imposed in many cities to the vehicles complying with old legislations.

Furthermore, the requirements for autonomous vehicles change, as already shown in [23]; specifically, the requirements related to performances (such as vehicle speed or acceleration time) become less important. The opposite is true for those related to comfort, such as NVH, torque regularity, vibration.

However, the constraints on C[O.sub.2] and toxic emissions remain at high priority and are the main driver of the technological change requested to new vehicles and powertrains.

The priorities and requirements targets in Table1 depend on the vehicle segment, legislation standards and the manufacturer position among the competitors. Moreover, it is important to underline that costs are not considered here. The reason is that cost is one of the main requirements for the end-user and its weight would not be enough important if considered at this level. It instead will be considered by means of the Technology Value Ratio, as defined in the section Results of Engine Technology Comparison.

As mentioned before, this work refers to a C-segment vehicle and regulation standards on emissions and fuel consumption by 2025 as shown in Figure 4. The priorities were introduced based on the study [22], adjusted with Magneti Marelli internal analysis.

On QFD level 2, in HoQ2.1, the requirements and priorities for the powertrain, described in Table1, are mapped with their technical characteristics in Table 2, with appropriate specifications to effectively satisfy the requirements. In Appendix 3, the HoQ2.1 correlation matrix is illustrated. In Table 2, the priority specifications in case of driver or driverless vehicle as well as the most significant differences between the two cases are reported. The relevance of the different characteristics is highlighted by the green histogram on the left. Among all, the powertrain weight, including the contribution of the energy storage system, represents the most important factor in addition to the energy generation efficiency for the propulsion. Among the technical characteristics with higher ranking, it must be noted that the energy refilling time is critical for pure electric powertrains but not for hybrid ones. Clearly, emissions still have a crucial role. In case of vehicle with autonomous driving, the powertrain characteristics related to the performances are less important, whereas the comfort features are more relevant. This is true in case of the vehicles being used exclusively in driverless mode.

The reported characteristics and their targets are the inputs for the next phase of definition and selection of the powertrain architecture.

POWERTRAIN AND ENGINE ARCHITECTURE

ICE technical features and powertrain requirements depend on the architecture chosen for the analysis. As shown in the previous chapter, efficiency (tank to wheel) is one of the key features of the powertrain and electrification is one of the most effective ways to improve it. Several architectures exist [24], however the main ones are summarized in Figure 7. From B to F, the degree of electrification of the powertrain increases, which implies a greater availability of electrical power with respect to the total power used for traction and an higher pure electric mileage range. In hybrid vehicles, the electric machine can be mounted in different positions and can be used for different functions. In Figure 7, the electric machine positioning and the power flows for propulsion and kinetic energy recovery during braking, which represent a key feature to improve the efficiency of the vehicle, are highlighted. Electric machine positioning is denoted by P0/P1/P2 or P3. P0 means that the Electric Motor (EM) is coupled to the crankshaft via a belt in a configuration known as Belt Starter Generator (BSG). When the EM is in P1 position, it is directly coupled to the crankshaft by a toothed wheel or a chain. P1 configuration allows reaching a higher maximum torque than the belt driven electric machine, due to the higher power from recuperation and the more robust connection. In P2 configuration, the EM is located upstream the transmission between two clutches, in parallel to the ICE. P2 configuration allows the functionality of pure electric driving, with higher fuel consumption saving than P0/P1 architectures. The torque delivered by the EM is limited mainly by the maximum torque of transmission, hence in case of contemporary use of ICE and EM, the gearbox must transmit the sum of the torques delivered by the two machines. In the P3 architecture, the EM is connected in parallel to the ICE downstream the gearbox, without any adaptation, and typically a BSG (> 4 kW) is also adopted in P0/P1 position to charge the battery during engine stops. In all previous hybrid configurations, the worse efficiency regions of ICE at part load can be avoided, leading to a lower fuel consumption. Furthermore, braking energy recovery can be performed.

In the so called Mild Hybrid powertrain (typically P0 and P1 configurations), the EM cannot drive the vehicle in pure electric mode, however it can support the internal combustion engine. P0 configuration main advantage is low cost integration, however P1 allows higher torque density.

In Full Hybrid powertrain, the most effective solutions are P2 and Power Split. In Power Split (configuration E), ICE is connected at the same time to the generator and the electric motor by a planetary gearbox, and the motor shaft is connected to the wheels with a final gear reduction. Power split concept combines features of both series and parallel hybrid. Full hybrid can be obtained also in P3 configuration (scheme D), with the highest energy recuperation potential.

Scheme F in Figure 7, describes a serial hybrid, where ICE operates as a range extender of the autonomy. The battery capacity allows to cover, without recharge, a longer distance than for a parallel hybrid (>250 km). ICE and generator have typically very high efficiency in a limited operating area [43] and rate power lower than 50% of the electric traction motor, depending on vehicle class and battery capacity.

The architectures from C (only P2) to F can be plug-in, with the possibility to recharge the battery like a pure electric vehicle. The functions of each described architecture are summarized in Table 3.

Using the selection matrix, described in Table 2, a comparison among the most interesting variants of the proposed architectures is performed using the technical requirements described before as selection criteria. In the selection, the values of the technical specifications have been disregarded, considering the capacity of each architecture of satisfying the requirements. Focusing on C-segment, the reference powertrain consists of a 4-cyilinder GDI turbocharged engine with a 6-speed DCT gearbox.

In [61], a comparison between P2 hybrid and Power Split architectures is shown and it is considered to define the selection matrix. In Table 4, architectures from 2 to 6 have a growing score due to the electrification, however they are characterized by rising costs due to the increased complexity and the larger size of the battery, which is necessary to ensure a long range in purely electric mode.

Moreover, as underlined by the high score, electrification affects not only the overall efficiency of the powertrain but also NOx as well as Soot/PN emissions. Indeed, the required torque is shared between electrical motor and internal combustion engine, and EM may relieve ICE during transient phases, where EGR management (internal or external) is critical, allowing the reduction of NOx peaks. Clearly, the impact of the electrification is higher when the proportion of the torque assigned to the EM is higher, which happens for HV configurations. As a matter of fact, the presence of TWC when ICE operates in stoichiometric conditions reduces the global ranking in the selection matrix.

The plug-in penetration in C-segment is expected only after 2025 to fulfill the C[O.sub.2] requirements. Indeed, as it will be shown in the next sections, C[O.sub.2] targets to 2020 and 2025 can be reached for C-segment vehicle by improving internal combustion engine efficiency and by a 48V electrification.

ENGINE TECHNOLOGIES DESCRIPTION AND ANALYSIS

This chapter summarizes the most relevant technologies for SI-ICE highlighting their advantages and the main drawbacks. The considered technologies can be classified according to the engine subsystem, as described in the following table:

The aforementioned technologies have been chosen for their degree of maturity with respect to the horizon of year 2025; moreover, they are considered the most effective for overcoming the limits of SI-ICEs, exposed previously.
Engine Subsystem    Technologies

Combustion System   GDI Lean Combustion
                    Miller/Atkinson Cycle
                    Variable Compression Ratio
                    Water Injection
                    Cylinder Deactivation
Air System          External EGR
                    Multistage Air Charging


Furthermore, the technologies to reduce ICE mechanical friction and the power from auxiliaries, especially in the regulated cycles when the system starts from cold conditions, can be considered already state-of-art in many applications. They can be summarized as follows:

* electrification of coolant and lubricating systems, allowing to optimize pumping requirements for the coolant and oil, depending on the real needs of the engine, in contrast with non-variable mechanical pumps; furthermore, the combination of the electrification with split cooling, allows the engine to achieve warm conditions sooner, while the charge air cooler is kept colder in order to keep the filling efficiency at an appropriate level.

* crankshaft offset adjustments, bearings design or steel pistons (instead of aluminum).

After-treatment systems are not considered in this work because the options are quite defined; in case of stoichiometric combustion, the after-treatment system is composed of a three-way catalytic converter (TWC) in addition to a gasoline particulate filter (GPF); in case of lean combustion another catalyst to reduce N[O.sub.x], such as SCR or LNT must be added. Furthermore, the benefits achievable with biofuels are not considered in this work and they will be investigated in future works.

GDI Lean Combustion

Lean combustion in gasoline engine has proven to significantly increase the overall efficiency [35]. Unfortunately, expensive exhaust after-treatment is necessary because the three-way catalyst cannot reduce N[O.sub.x] in case of excess of oxygen in the exhaust gas. To mitigate the catalyst cost increase, engine has to operate in extreme lean conditions (e.g. lambda > 1.8), thus obtaining a drastic reduction of engine out N[O.sub.x] emissions and further engine efficiency improvement, thanks to the higher ratio of specific heats and lower heat losses to the cylinder walls. Figure 8, from [32], is an example of the operating modes of a lean concept in the engine working points, highlighting the operating range in the WLTC cycle.

In addition to the increased demands on the charging system, further challenges arise with the extreme lean operation. The ignition of the diluted mixture is strongly hindered by the poor thermal boundary conditions that might lead to misfiring, therefore ignition system technology development is often required. An additional limitation under lean conditions is the increased cycle-to-cycle variations (CoV) due to the slower combustion. CoV can be minimized with higher turbulent combustion velocity by enhancing the in-cylinder charge motion. Hence, port and combustion chamber design as well as the spray pattern layout play a key role in the development of extreme lean combustion concepts. Furthermore, the transient operations including the switching between operating modes, e.g. from stoichiometric to lean air/fuel ratios or vice-versa, have to be properly managed. As for all lean gasoline engines, the control of N[O.sub.x] emissions remains a challenge, therefore LNT or SCR solutions are needed. LNT was already employed at end of the '90s in the first vehicles (Toyota, Mitsubishi, VW) equipped with GDI lean engines, and in the recent years it has been widely adopted in diesel engine applications.

In [33], Ricardo shows a lean burn combustion concept that uses spray guided lean stratified operation. N[O.sub.x] emissions control is carried out by means of a Lean N[O.sub.x] Trap (LNT) catalyst. The study highlights the BSFC improvement achievable in stratified lean burn conditions (2.0 L turbo, 200 kW rated power) for a D-segment vehicle. Over NEDC, the solution has been simulated producing a 14% reduction of C[O.sub.2] emissions compared with the equivalent stoichiometric turbocharged GDI engine, considering LNT regeneration. Over WLTC, the fuel consumption reduction is 12%.

Miller/Atkinson Cycle

Miller-Cycle describes a combustion system with early or late intake valve closing [30, 41, 47, 49, 51, 63]. Figure 9 illustrates the two possibilities used to perform the Miller cycle.

Miller cycle is based on Otto cycle, having an expansion stroke which is longer than the compression stroke. In late intake valve closing Miller cycle (LIVC), the intake valve is kept open during a significant part of the piston movement during compression, so that part of the mixture contained in the cylinder is sent back to the inlet manifold, allowing the reduction of mixture mass that is "trapped" in the cylinder. Moreover, pumping losses are reduced, and the volume of the 'trapped' mixture corresponds to the cylinder volume at the closure of the intake valve. In early intake valve closing Miller cycle (EIVC), the descent of the piston creates a vacuum inside the cylinder, achieving the manifold pressure somewhere during compression, near the position where the intake valve was closed on the downward movement of the piston.

The major benefits of Miller cycle can be obtained in combination with boosting and charge air cooling, with an higher compression ratio (which increases part load operation efficiency). Moreover, in medium load conditions, lower peak pressure and temperature are reached, leading to a lower knock tendency.

Atkinson-Cycle is instead a combustion system with increased expansion stroke realized by a different crank train, which involves a system redesign. Atkinson, as Miller, has a lower effective compression ratio compared to the expansion ratio.

On the other hand, both for Miller and Atkinson cycles, depending on the gasoline engine configuration, a turbocharger upgrading or installation might be necessary to ensure the specific power and the low-end torque. In naturally aspirated engines, the lower engine power and torque might also be compensated by an increased displacement which in turns increases the friction losses.

In [30], FEV estimates that the Miller cycle reduces fuel consumption by 3.9%-5.7% over a baseline, 1.0 L downsized turbocharged engine with variable valve lift and timing. Part of the efficiency increase is due to the increase of geometric compression ratio from 10:1 to 12:1.

VW recently implemented the Miller cycle concept in EA211 1.5L TSI EVO engine family [47] and the claimed average efficiency improvement is 10% compared with the previous generation engine (1.4L TSI), including also a VGT (variable geometry turbocharger), cylinder deactivation and other in-cylinder improvements to increase engine efficiency. However, the reduction of BSFC, due to the Miller cycle implementation, was estimated to be at least half of the overall benefit. The new engine shows a reduction in fuel consumption between 5-10%, compared to the previous generation over most of its engine map. Furthermore, for a significant portion of the low loads region, Miller cycle enables 10-30% reduction in fuel consumption.

In [51], Audi shows a significant fuel economy improvement for the 2.0L TFSI with Miller cycle, implemented by means of the EIVC, in which, some additional gas expansion occurs, which helps reducing in-cylinder temperatures. In this configuration, engine compression ratio was increased from 9.6:1 to 11.7:1. Compared to the previous generation, fuel consumption is reduced up to 21% (on the NEDC), while power output is increased up to 25%.

Variable Compression Ratio

Increasing the compression ratio is an effective way to improve the combustion efficiency, as clearly stated by Equation (3) in the Powertrain System Model section of the paper. However, this solution is limited by high peak cylinder pressures and temperatures, which affect the powertrain design (friction and materials) as well as increasing knocking tendency in gasoline engines. Alternatively, the reduction of compression ratio helps solving the problems mentioned before, reducing the overall friction, but also getting some improved powertrain efficiency at full load operation. However, this possibly leads to cold start problems, combustion stability issues and worse efficiency at part load.

Currently, in the market, both tendencies of increasing and decreasing the compression ratio can be found, requiring different side measures, as shown in Figure 10.

To get the best from both trends, a variable compression ratio (VCR) system should be employed, using a higher CR at engine part load operations and a lower CR at higher loads. Two possible VCR technical solutions have been recently developed:

* a 2-step compression ratio [30,52] that improves full load performance, reducing emissions and friction with lower compression ratios, while it increases the combustion efficiency at lower loads with higher compression ratio;

* a fully variable VCR [30,44,53] that allows adjusting the optimal CR for each operating point, using the full potential of this technology.

In addition, there are no significant disadvantageous interdependencies with other technologies. Compared to the fully variable VCR, the cost of the 2-step VCR is much lower [52], and at the same time more than 80% of the fuel consumption reduction potential of the continuous system can be achieved in gasoline engines. Moreover, in 2-step VCR, the compression ratio can be maximized at lower loads without redesigning the different systems which are subjected to high stresses, e.g. piston or crankshaft, with important advantages in terms of packaging, modification of production and friction. Clearly, theoretical potential will not be fully available; indeed, due to the piston design for maximum compression ratio, disadvantages in the combustion efficiency and knock limit arise. Moreover, the modified conrod is usually heavier than the original one.

In [52], AVL presents its 2-stage VCR system based on the connecting rod length variation. The concept allows modular integration in the existing architecture without significant modifications, with only minor adaption of the production lines and thus it represents a highly attractive solution with respect to costs. Depending on the vehicle class, the load profile and the power rating, a C[O.sub.2] reduction between 5% and 9% in the WLTC is achievable.

In [44], Hyundai presents its fully variable VCR system and evaluates its benefits in 1.6L inline 4-cylinder gasoline engines both NA PFI and TC DI. VCR, by the combination of four valve timings (IVO, IVC, EVO, and EVC), has the potential to improve the fuel efficiency by 4 to 5 %. Low speed torque, in the NA PFI engine, is increased by more than 5 to 10%, while in the TC DI engine, it is increased by more than 10%.

Water Injection

Water injection (WI) is a cost-effective solution to minimize knocking in (downsized) gasoline engines, especially with high compression ratio. This technology is already well-known because it has been used in motorsports and aviation industry. The current trends in legislation related to the automotive sector make it particularly relevant for serial production in passenger vehicles. Water injection can be exploited as a solution to reduce fuel consumption and C[O.sub.2] emissions, especially at medium and high load, as well as to increase the engine power output [36, 37, 38, 39, 59]. The main concept is to inject water and to use its high latent heat of vaporization to reduce gas temperatures before their combustion. In fact, the addition of vaporized water would result in an efficiency decrease due to the reduction of [c.sub.p]/[c.sub.v] ratio. However, the evaporation of water results in a significant temperature reduction of the mixture of air or air/fuel and water, permitting the adoption of an higher spark advance, thus possibly reaching the optimum MFB50 position. This effect can overcompensate the efficiency decrease expected when adding gaseous water. At the same time, the dilution of the mixture with water and the reduced temperature level in the combustion chamber have minor influences on the losses due to unburned fuel and the losses due to heat transfer.

Furthermore, the cooling effect may be utilized in different ways according to the desired benefits:

* knock tendency reduction[right arrow] higher compression ratio enabled/advanced spark ignition permitted[right arrow] fuel efficiency increase at the same desired brake torque;

* reduction of exhaust temperatures under full load operation[right arrow] mixture enrichment can be avoided[right arrow] fuel efficiency increases at the same desired brake torque;

* knock tendency reduction[right arrow] advanced spark ignition[right arrow] torque increase at the same fuel consumption.

The ability of WI to lower the exhaust gas temperature is also of interest since it may be used as an enabler for employing turbochargers with variable geometry turbines (VGT) even in gasoline engines, thus allowing further downsizing potential. Alternatively, it may be used to reduce material costs on the turbochargers, due to reduced thermal stresses on the component.

As shown in Figure 11, three different implementations of water injection systems are possible:

1. Port Water Injection (PWI). In this approach, water is injected on the inlet side with a low-pressure system (5/20 bar). The advantage of this solution is its simplicity because it includes a simple pressure supply with an electrically driven water pump. Furthermore, corrosion and freezing issues caused by water are relatively easy to handle.

2. Direct Water Injection Mixture (DWI-M). Water is mixed with gasoline and it is directly injected via a modified high-pressure injector. Water quantity is metered based on the intake air mass measurement; the water-fuel mixture is compressed to an emulsion by the high-pressure pump after which it is injected via the high-pressure water-fuel injectors directly into the combustion chamber. While the amount of water required is slightly lower than PWI, the system suffers from several technical challenges and risks. Firstly, the presence of high-strength steels in such high-pressure systems is not trivial and thus magnifies the challenges associated with corrosion damage. This implies a major and complete overhaul of the existing high-pressure fuel system. Secondly, to enable a quick availability of water in the system, the connecting pipes and components need to have small cross-sectional areas and volumes, respectively. This creates high pressure pulsations and thus high-pressure peaks in the injectors and in the high-pressure pump. Therefore, a completely new and complex high-pressure system is required, which has a negative effect on costs and risks. Furthermore, when the engine is stopped, water needs to be removed from the fuel system by running the engine and flushing it with pure gasoline. This makes the solution less effective when used together with hybrid powertrain solutions and start-stop technology. Finally, the challenges associated with freezing and corrosion are magnified in such a high-pressure system.

3. Direct Water Injection Separate (DWI-S). A high-pressure water injection system is installed in parallel to the existing high-pressure fuel injection system requiring additional high pressure direct water injectors to be integrated in increasingly smaller and complex cylinder heads. Component costs are then higher than the equivalent low-pressure variant. As in the previous case, the presence of high-strength steels magnifies the problem of corrosion damage, while keeping the robustness against freezing, i.e. due to anomalous water expansion. In addition, reversing the flow through the high pressure mechanical pump is achieved only with additional valves and a high system complexity which adversely affects weight and costs.

As a result of the previous considerations, the Port Water Injection concept is the best candidate for series production. Its main drawback with respect to the other possible solution is the higher water consumption.

The general limit of WI is the availability of good quality of water (deionized) on-board the vehicle. Three possible solutions are under investigation; refilling by the user, A/C condensation and rainwater harvesting, exhaust gas condensation. The first one is the most promising because it is cheap and accepted by the end-customer, as reported in the survey [36]. The other solutions are considered to be developed to minimize the end-user impact and refilling costs.

In [36], the benefits of PWI with a CR increased by 2 points were studied, resulting in 4% of fuel saving on WLTC, 13% in real word conditions and up to 20% in full load. Water rate related to fuel was up to 60%, with a water consumption under real world driving conditions between 1.3-2.8 L/100 km, considering a large family car equipped with a turbo GDI engine with 115-130 kW rated power.

In [37], the DWI-S technology combined with Miller cycle, cooled exhaust gas recirculation and variable compression ratio was investigated. After a single cylinder experimental investigation, driving cycle simulations were carried out in order to understand both the fuel and water reduction potentials. The combination of water injection with the Miller cycle and cooled EGR has allowed to improve the indicated specific fuel consumption up to 197 g/kWh together with a significant enhancement of the region of very attractive efficiency values, especially at low engine speeds and high loads. Increasing the VCR up to 10.7/14.7 from 9.5/13, the resulting fuel consumption benefit in WLTP was up to 6.7 %. At the same time, water consumption was up to 3 l/100km. Therefore, onboard water generation or, at least, the utilization of tap water for a refill tank are required, in order to ensure an affordable cost also from the ownership's perception.

Cylinder Deactivation

Cylinder Deactivation (CD) allows a significant reduction of the pumping as well as heat transfer losses at lower engine loads, by reducing the number of active operating cylinders. The active displacement is reduced, increasing manifold pressure and reducing pumping losses. The requested load on the cylinder (BMEP) is also increased, which reduces the relative heat transfer to the cylinder walls with respect to the available heat. Since other technologies (e.g. downsizing or VVT) can reduce pumping and friction losses, the coupling of CD with other technologies could be not so effective.

There are two possible main solutions to implement cylinder deactivation:

1. A variable valvetrain is used to shutoff the intake and exhaust valves of the deactivated cylinders.

2. Electronic Cylinder Deactivation; in which, the exhaust system is duplicated (for instance, each cylinder pair 1-4 and 2-3 has a dedicated exhaust line) and the injection is switched off for one cylinder group.

Mode 2 is an alternative method without the need for additional flexibility in the valve train and it additionally offers the chance to utilize the deactivated cylinders with the characteristic sound of the engine. The main drawback is the packaging impact of the exhaust line.

The conventional cylinder deactivation, especially the first solution, is normally applied only to large engines with an even number of cylinders. In this way, the cylinders deactivate symmetrically in order to avoid intense torque fluctuations and vibrations. Furthermore, higher improvements can be attained with the dynamic deactivation of individual cylinders. Regarding this particular technology, many systems are being currently developed. These systems continually change the active cylinders and have many potential advantages over conventional cylinder deactivation, such as:

* Maintaining uniform engine operation temperatures;

* Allowing the throttle to remain nearly fully open by controlling the engine power by varying the firing cylinders;

* Handling noise, vibration and harshness by dynamically controlling the active cylinders, allowing the adoption of cylinder deactivation at lower engine rpm;

* Expanding the range of applicability to smaller engines, even to 3-cylinder engines or with an odd number of cylinders.

An example of this new CD system is the DSF (Dynamic Skip Fire) system, described in [62], that claims to achieve a fuel benefit between 10/20%, depending on engine type.

In [45], the benefits achievable with the Electronic Cylinder Deactivation in a 4 Cyl 1.4L TC GDI engine are shown. In the NEDC cycle, fuel consumption improvements are up to 7%, with small penalty in comparison with a 2 Cyl 0.9L TC GDI engine.

External EGR

The external exhaust gas recirculation (EGR) [59] is an alternative to the internal one, made using VVA systems. It can be carried out according to the three layouts described in Figure 12:

* High Pressure (HP-EGR)

* Low Pressure (LP-EGR)

* Dedicated EGR (D-EGR)

High pressure and low-pressure split is also possible. In the HP-EGR solution, exhaust gases are recycled from upstream the turbine to the intake manifold; in the LP-EGR version, exhaust gases are recycled from downstream the catalyst to the compressor intake. In both cases, gas is cooled with an air/water cooler before entering the control valve, typically driven by a DC-motor. For the LP-EGR case, a lower pressure ratio for the gas flow is available, however, the main advantage is the lower temperature in the manifold [43]. Indeed, exhaust gases are cooled both in LP-Cooler and turbocharger intercooler, which is designed for the maximum engine power, a faraway condition from the operating area of LP-EGR. Furthermore, LP-EGR leads the compressor to work in an area with greater efficiency, with benefits on fuel consumption for the lower exhaust pressure at turbine upstream due to the reduced compressor requested power. In SI engines, EGR can be used also for the reduction of N[O.sub.x] emissions, the de-throttling at partial loads and knock mitigation. An additional benefit is at high engine power, thanks to the avoiding of the enrichment of the mixture with advantages on BSFC and PN.

The main EGR drawbacks are the reduction of maximum power with a given turbocharger layout and the negative impact on transient response at low engine speeds because of the increased turbocharger size to compensate for maximum power loss with EGR. Furthermore, cooling capacity of the engine cooling system as well as for the charge air intercooler (for LP-EGR) has to be adapted and integrated to the front end of the vehicle. The third variant for the external EGR is called "dedicated EGR", as shown in Figure 12. Dilution of the intake charge, with the traditional EGR, provides benefits in terms of cycle efficiency and knock resistance. However, it also poses challenges in terms of combustion stability, condensation and power density. With D-EGR, one cylinder, which operates in rich condition, produces EGR for all four cylinders of the engine, introducing reformates such as CO and H2 into the intake charge by means of a mixer installed upstream the intake manifold, bringing back some of the stability lost for EGR dilution, leading to a higher ratio of specific heats and a benefit on effective RON of the fuel. To enable the technology, in addition to the high-pressure EGR loop and EGR cooler, a supercharger with a bypass valve and an after-cooler is used. A cold start valve is installed as alternative path for exhaust gases when the EGR valve is closed. A PFI injector can be added to the intake manifold which allows flexibility in the way the extra fuel to the 4th cylinder is delivered.

In [34], the following advantages with the adoption of LP-EGR are shown:

* 1% BSFC improvement at partial loads;

* more than 4% BSFC improvement, with the same PN-emission, by shifting the 50% MFB50 to the optimum in knock limited engine operating points.

In [55], an extreme downsizing from a 3.7L V6 NA engine to a I4, 2.5L turbocharged engine is allowed by a cooled HP-EGR in combination with scavenging, achieving an increase in the low-end torque and maximum efficiency by more than 30%, as well as a significant weight and size reduction.

In [60], D-EGR improves the knock resistance of a 2.L GDI engine allowing a compression ratio equal to 11.7. In this configuration, the improvement in engine efficiency was at least 10% across the whole performance map, with substantially higher improvements for certain engine operating points. For instance, BSFC @ 2000 rpm/ 2 bar BMEP improved from 385 g/kWh to 330 g/kWh and the lowest BSFC in the engine map was 212 g/kWh compared to 236 g/kWh of the original engine. The addition of 2-stage boosting also allowed the engine to meet its BMEP target of 17 bar from 1500 to 5500 rpm while maintaining good transient response and low engine-out emissions. The main drawbacks of D-EGR are the need to control combustion stability and the complexity due to a second stage of air boosting to recover the power loss at high loads.

Multistage Air Charging

The most effective way to reach a higher specific power output is increasing the boost pressure. This allows more air (oxygen) into the cylinders. Furthermore, increased boost pressure is necessary in combination with increased EGR and the application of Miller Cycle to avoid reduced volumetric efficiency and reduced full load torque.

The extension of boosting operative range can increase the low-end torque, which is a critical issue especially in extreme downsized engines [59], with fun to drive benefits and/or possibility to implement down-speeding strategies. Furthermore, the use of complex charging systems is necessary to fulfill the new European RDE standards where scavenging strategy will not be implementable, because it can cause the decrease of TWC efficiency.

The extension of the boosting range is possible employing VGT turbochargers, as long as exhaust gas temperature is low enough, however better results can be attained employing multistage charging layouts, according to two main solutions:

* 2-stage turbochargers;

* mechanical supercharger or electric turbocharger in addition to the first turbocharger stage.

In the first solution, two differently sized turbochargers are used and chosen to be operative in different areas of the engine map. This solution has huge impact on cost and layout. In the second solution, the tendency is to use an electric turbocharger (or an e-booster only), that can deliver air at maximum boosting pressure within 300-1000 ms [42,57]. This technology is particularly suitable when used in conjunction with a 48 Volt BSG, allowing to achieve a fuel economy improvement over 10% and a significant gain in the fun to drive, as shown in [16,57,58].

Summary of Technology Benefits and Drawbacks

The evaluated technology benefits, drawbacks and the influences in the main zones of engine map referring to Figure 5 are summarized in Table 5. Moreover, in Appendix 1, a detailed summary of the outcomes from literature analysis is reported.

POWERTRAIN SYSTEM MODEL

Much information to evaluate new technologies relating to the powertrain can be found in literature; however, the effects due to the technology mixing for various powertrain configurations and in different vehicle segments can be predicted only thanks to the simulation approach.The adopted models must be at the same time adequately accurate and fast, to carry out evaluations on long driving profiles and to be used for system optimization. In [29, 30], several examples of simplified models used for evaluations are considered. In this study, 0-D models, whose scheme is depicted in Figure 13, are used.

The outputs are fuel consumption, emissions and performance, evaluated on different driving profiles (e.g. NEDC, WLTC, etc.). The details of the model have already been the subject of other works [25, 26, 27, 28], to which some of the authors have contributed; therefore, in this section, only specific parts related to the impacts given by the engine technologies under consideration are shown. Specifically, the brake effective torque and the brake specific fuel consumption (BSFC) have been evaluated using the Willan's line method, as described in [27].

The definitions and the mathematical steps leading up to the torque model can be found in Appendix 2.

Specifically, brake effective torque ([T.sub.e]) can be expressed as follows (3):

[T.sub.e] = e * [[eta].sub.idc] * [H.sub.LHV] * [[??].sub.f]/[omega] - [p.sub.loss] * [V.sub.d]/4[pi] - ([p.sub.exh] - [p.sub.intake])[V.sub.d]/4[pi] (3)

where: e is the product of thermodynamic and combustion efficiencies, [H.sub.LHV] is the fuel lower heating value, [[??].sub.f] is the fuel rate, [omega] is the engine speed in rad/s, [p.sub.loss] takes into account the mechanical losses for friction and auxiliaries, [V.sub.d] is the engine displacement, [p.sub.exh] and [p.sub.intake] are the exhaust and intake pressures, respectively.

Moreover, [[eta].sub.idc] is the ideal efficiency which is theoretically dependent on compression ratio only. However, in this work, a modification to ta[k.sub.e] into account the Miller cycle is considered, as proposed in [47]:

[[eta].sub.idc] = 1 - 1/[r.sup.[gamma]-1.sub.g] * ([sigma]) (4)

where [sigma]=[r.sub.g]/[r.sub.tr] is the expansion - compression ratio, with [r.sub.g] geometrical and [r.sub.tr] trapped compression ratio, respectively. Moreover, f([sigma]) takes into the account the effect of the Miller cycle on the theoretical efficiency; its formula can be found in Appendix 2.

Introducing [lambda], the volumetric efficiency [[eta].sub.v] and the air density p, (3) can be re-written as:

[T.sub.e] = e * [[eta].sub.v] * [[eta].sub.idc] [rho] * [V.sub.d]/[lambda] * [alpha] * [H.sub.LHV] - [p.sub.loss] * [V.sub.d]/4[pi] - * ([p.sub.exh] - [p.sub.inta[k.sub.e]])[V.sub.d]/4[pi] (5)

From (5), the bra[k.sub.e] specific fuel consumption BSFC, which is correlated to the C[O.sub.2] emission, is calculated:

BSFC = [[??].sub.f]/[T.sub.e] * [[omega].sub.eng] (6)

Notice that, the first term of the equation (5) is the indicated gross torque, the second is the torque term for friction and auxiliaries and the third is the component due to the pumping losses. To consider the effects lin[k.sub.e]d to the applied technologies, the generating torque equation can be modified through several coefficients. In particular, the effects of the technologies investigated can affect all the terms of Equation (5) that can be corrected as follows:

[T.sub.e] = [k.sub.e] * e * [[eta].sub.v] * [[eta].sub.idc] [rho] * [V.sub.d]/[lambda] * [alpha] * [H.sub.LHV] - [k.sub.f] * [p.sub.loss] * [V.sub.d]/4[pi] - [k.sub.p] * ([p.sub.exh] - [p.sub.inta[k.sub.e]])[V.sub.d]/4[pi] (7)

Where [k.sub.e] takes into account the correction on the thermodynamic efficiency (e.g. for lower/higher heat losses, MFB50 position, knock phenomena), [k.sub.f] is the correction for the friction losses (e.g. for heavier/lighter cranktrain, bigger/smaller bearings, etc..), [k.sub.p] is the correction for the pumping losses (e.g. for part load operations throttle adoption or not, turbocharger improvements, VGT or WG adoption, etc..).

The corrective parameters [k.sub.f], [k.sub.e] and [k.sub.p] have been evaluated starting from literature analysis and by means of a 1D engine model, calibrated and validated against experimental data, as described in [39]. A 1.4L - 4 cylinder - Turbo- GDI engine with VVT and CR =10 has been chosen as baseline engine. Specifically, the 1D model contains, in addition to the air path with turbocharger and supercharger, a predictive combustion modelling, which can also predict MAPO statistical distribution. In case of water injection, as an example, the corrective parameters can be found by firstly establishing a trade-off between MAPO percentile and indicated efficiency for knock limited engine operating points [36].

Subsequently, water injection is simulated and the new trade-off can be defined; [k.sub.e] is therefore calculated and extrapolated for the nearest points, obtaining the static map to be used in the 0D model. In Table 6, the effects of the ICE investigated technologies on the parameters are illustrated:

In Figure 14 and Figure 15, the BSFC map and the correlations between measured and estimated values of BMEP and BSFC for the baseline engine are shown, demonstrating the feasibility of the approach.

The advantage of the approach is its modularity. Indeed, from the baseline case, the BSFC curve derived for any combination of technologies can be estimated. As an example, Figure 16 shows the BSFC map for the baseline case, adding the Miller cycle with an increased CR (12.5), cylinder displacement and friction reduction of 20%. The results are quite similar than those shown in Figure 17, describing the measured BSFC map of the evolution of the baseline engine with the technologies investigated in [47].

The cumulative trends in fuel consumption on NEDC cycle for a C-segment vehicle equipped with the baseline engine and with some of the technologies studied are shown in Figure 18; moreover, in Table 7, all the most meaningful technologies and their combinations are analyzed; their savings in fuel/C[O.sub.2] both in NEDC and WLTC are shown. The C[O.sub.2] estimation by means the model is 125 g/km in NEDC cycle against 123 g/km of the real emission of the reference vehicle. The mass of the vehicle in the baseline configuration (only ICE) was considered equal to 1350 kg, whereas it was increased by 60 kg for a 48 Volt 22kW hybrid in P2 configuration and 1 kWh of battery capacity (source: MM data).

From Figure 18 and Table 7, it is clearly shown that the benefits given by each technology are not additive, and that the contribution of the electrification decreases with increasing the efficiency of ICE, especially in the WLTC cycle which is characterized by a higher average load.

As it can be observed, the estimation of the improvements related to the analyzed technologies is aligned with the values highlighted in the bibliography.

ENGINE TECHNOLOGY COST ANALYSIS

Cost estimations for powertrain manufactures during the early phase of technologies investigation or product development are subject to several uncertainties. These uncertainties are related to information concerning the product and production including the production process and its resources. Nevertheless, especially when developing a new technology, the assumed product costs must be tracked in order to lead the product to a successful market introduction.

The main sources of technology costs are [16, 30, 46, 52]. Information coming from these works was reviewed and integrated with Magneti Marelli data. The estimated costs at 2025 for the technologies considered for C-segment vehicle are summarized in the following Table 8.

RESULTS OF ENGINE TECHNOLOGY COMPARISON

The engine technologies studied in the previous chapters by analyzing the literature and using the models, can be compared both in terms of C[O.sub.2]/energy consumption on the reference cycles and, in a more effective and complete way, in terms of fulfillment of the design criteria and priorities coming from HoQ2.1, taking into account not only the GHG emission or fuel consumption but also other technical characteristics linked to the purchase reasons of the vehicle (e.g. performance, fun to drive, etc.). In addition to the individual technologies, some interesting combinations among them and some powertrain architectures listed in the previous chapter are considered in this work. The combinations and architectures have been chosen considering the time horizon of 2025 and certain assumptions on the emission legislation. The comparison was made with the selection matrix shown in Table 9. The values shown in the matrix depend on the technology effectiveness in satisfying the different design criteria. In the lower part of the matrix, the technology ranking can be found. The ranking expresses the effectiveness of the technology and it is graphically summarized by the green and light blue histograms for human and autonomous driving, respectively.

As it is clearly shown, the powertrain characteristics that impact on C[O.sub.2] and emissions are still the most important both for human and autonomous driven vehicles. Conversely, the characteristics linked to the performances are more relevant for the human driven vehicles. The most effective technology combinations include a mix able to improve the limits of gasoline engines shown in the previous chapters. In particular, the downsizing from 4 to 3 cylinders, with a second turbocharger stage (e.g. electric type), in conjunction with Miller and port water injection is a particularly interesting solution. This best engine configuration has been assessed in terms of C[O.sub.2] reduction by means of the simulation, obtaining the results shown in Figure 19. Starting from the engine and vehicle baseline, the European limits at 2020 are achievable, with a slight electrification (BSG) that can ensure a margin. Instead, to face the limits of 2025, assumed to be set to 75 g/km, the introduction of a full hybrid P2 48V 22kW architecture is not enough. Other improvements should be introduced, for example a vehicle mass reduction ( -20%), even though other technology alternatives will be explored in future works.
Figure 19. Technological path to face CO2 requirements, without penalty
on engine performance and emissions. Technologies are additive,
excluding the path highlighted by the arrows where the adoption of BSG
or P2 48 V layout are considered as alternative.

                CO2 [g/km] in NDEC

1.4L 4Cyl TC    125
GDI S&S
Miller          117
(CR+2)
VGT
1.0L 3cyl        98
MT6+ WI
DCT 7            91
BSG              85
e-sc
P2 48 V          82
-20%             74
Vehicle
Mass
Reduction

Note: Table made from bar graph.


However, another essential aspect is the value analysis (cost/benefit), where the benefit is weighted by means of the costs, summarized in the previous chapter. The Technology Value Ratio describes the relationship between the satisfaction of a requirement (benefits) and the use of resources (costs):

Technology Value Ratio = Function Effectiveness/Cost (8)

For this aim, the Function Effectiveness is measured by means of the ranking in the selection matrix, Table 9, whereas the costs are evaluated according to Table 8. By this procedure, the function/cost value, for each technology and their combinations, can be obtained. In Figure 20, the comparison of the technologies is shown both in terms of ranking from the selection matrix and of Value Ratio. According to the last index, water injection, Miller cycle and cylinder deactivation are very promising technologies. However, to achieve the C[O.sub.2] emission target a mix of engine technologies are needed even if these combinations (right side of figure) have a lower value, showing a growing powertrain cost in order to meet the legislation limits.

Alternatively, the technologies value can be defined as ratio between the percentage of C[O.sub.2] savings and cost. This evaluation is depicted in Figure 21. Assuming that 1% of C[O.sub.2] saving is slightly above 1 g/km, considering the baseline engine (125 g/km), it can be observed that all technologies and their mix are below the cost of the penalty (95[euro] /g) foreseen by the legislation. It is also important to remark that the affordable cost per gram of C[O.sub.2] saving depends on the distance of the powertrain emissions from the legislation limit. This means that the application of the technologies at higher cost could be mandatory to achieve the legislation limits, as long as the cost itself remains lower than the legislation penalty.

CONCLUSIONS

Future C[O.sub.2] scenarios represent a great challenge to the automotive industry. However, other end-user requirements (e.g. fun to drive, performance) have to be ta[k.sub.e]n into account. Many technological opportunities are available to improve the current powertrain, including not only electrification but also several technologies for ICE, especially for SI engines. A structured approach to link end-user requirements to powertrain technical features was proposed. In this way, an objective comparison of architectures and technologies can be carried out. The effectiveness of the technical solutions must be weighted taking into account the cost, which is one of the main purchasing drivers. The case study was a C-segment vehicle, for which a possible technology path to fulfill customer requirements and C[O.sub.2] limits in the timeframe of 2025 was presented. From the analysis, some technological improvements, like downsizing/down-speeding increase, Miller cycle, and water injection can help to achieve the 2020 standards, without an high grade of electrification. To face the further steps of C[O.sub.2] reduction at 2025, an higher electrification grade is needed; however it does not seem to be enough without other vehicle improvements (i.e. mass reduction). Moreover, other powertrain improvements, considering for instance bio-fuels or plug-in hybrid architectures, can be introduced, however these topics will be analyzed in future works.

FUTURE WORK

To complete the analysis of future powertrain scenarios, the following topics will be investigated:

* improvement of the models to ta[k.sub.e] into account all significant vehicle loads (e.g. HVAC) for real driving conditions, with the aim to evaluate also the Tank To Use;

* analysis of the natural gas and bio-fuels impact [64], in term of performance and C[O.sub.2]/consumption;

* analysis of the benefits coming from new Low Temperature Combustion concepts (e.g. Gasoline Compression Ignition [65]), that could improve emissions and overall fuel efficiency up to 25%, greater than state-of-art of gasoline engine, but at lower cost than a diesel with similar efficiency;

* analysis of benefits of engine Heat Recovery systems [26,27,66], especially in hybrid electric architectures.

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[58.] Stapelbroek, M., Birmes, G., Thewes, M., Espig, M. et al., "Fuel Consumption Reduction and Performance Improvement by Electric Driven Supercharger", 25th Aachen Colloquium Automobile and Engine Technology 2016

[59.] Bevilacqua, V., Jacobs, E., Grauli, G., Wust J. Future of Downsizing: Fuel Consumption Improvement in NEDC as well as in Customer Operating Conditions, SIA Technical paper 2013, R-2013-06-30

[60.] Chadwell, C., Alger, T., Zuehl, J., and Gu[k.sub.e]lberger, R., "A Demonstration of Dedicated EGR on a 2.0 L GDI Engine," SAE Int. J. Engines 7(1):434-447, 2014, doi:10.4271/2014-01-1190.

[61.] Kapadia, J., Kok, D., Jennings, M., Kuang, M. et al., "Powersplit or Parallel - Selecting the Right Hybrid Architecture," SAE Int. J. Alt. Power. 6(1):68-76, 2017, doi:10.4271/2017-01-1154.

[62.] www.delphi.com/manufacturers/auto/powertrain/gas/valvetrain/delphi-tula-dynamic-skip-fire-cylinder-deactivation-system

[63.] Osborne, R., Downes, T., O'Brien, S., Pendlebury, K. et al., "A Miller Cycle Engine without Compromise - The Magma Concept," SAE Int. J. Engines 10(3):2017, doi:10.4271/2017-01-0642.

[64.] Darlington, T., Herwick, G., Kahlbaum, D., and Drake, D., "Modeling the Impact of Reducing Vehicle Greenhouse Gas Emissions with High Compression Engines and High Octane Low Carbon Fuels," SAE Technical Paper 2017-01-0906, 2017, doi:10.4271/2017-01-0906.

[65.] Sellnau, M., Foster, M., Moore, W., Sinnamon, J. et al., "Second Generation GDCI Multi-Cylinder Engine for High Fuel Efficiency and US Tier 3 Emissions," SAE Int. J. Engines 9(2):1002-1020, 2016, doi:10.4271/2016-01-0760.

[66.] Arsie, I., Cricchio, A., Pianese, C., Ricciardi, V. et al., "Modeling and Optimization of Organic Rankine Cycle for Waste Heat Recovery in Automotive Engines," SAE Technical Paper 2016-01-0207, 2016, doi:10.4271/2016-01-0207.

CONTACT INFORMATION

Matteo De Cesare

matteo.decesare@magnetimarelli.com

Nicolo Cavina

nicolo.cavina@unibo.it

Luigi Paiano

luigi.paiano@magnetimarelli.com

DEFINITIONS/ABBREVIATIONS

AD - Autonomous Driving

AFR - Air-Fuel Ratio

AMEP - Available Mean Effective Pressure

AMT - Automatic Manual Transmission

BMEP - Brake Mean Effective Pressure

BSFC - Brake Specific Fuel Consumption

BSG - Belt Starter Generator

CO - Carbon monoxide

CoV - Coefficient of Variation

C[O.sub.2] - Carbon dioxide

CR - Compression Ratio

DCT - Dual Clutch Transmission

DSF - Dynamic Skip Fire

DWI-M - Direct Water Injection - Mixture

DWI-S - Direct Water Injection - Separate

EGR - Exhaust Gas Recirculation

EM - Electric Motor

FR - Friction Reduction

GDI - Gasoline Direct Injection

GPF - Gasoline Particulate Filter

HC - Hydrocarbon

HD - Human Driving

HLHV - Fuel Lower Heating Value

HoQ - House of Quality

HP - High Pressure

ICE - Internal Combustion Engine

LP - Low Pressure

LNT - Lean N[O.sub.x] Trap

MR - Market Research

NEDC - New European driving cycle

N[O.sub.x] - Nitrogen Oxides

NVH - Noise Vibration Harshness

OEMs - Original Equipment Manufacturers

PM - Particulate mass

PN - Particulate Number

[p.sub.exh] - Exhaust Manifold Pressure

[p.sub.intake] - Intake manifold pressure

[p.sub.loss] - Mean effective pressure lost

PWI - Port Water Injection

PWT - Powertrain

QFD - Quality Function Deployment

r - Compression ratio

RDE - Real Driving Emissions

SCR - Selective Catalytic Reduction

S - Piston stroke

SI - Spark Ignition

Te - Effective torque

TTU - Tank to Use

TTW - Tank to Wheel

TWC - Three-way catalyst

VCR - Variable Compression Ratio

Vd - Displacement

[V.sub.pist] - Average piston speed

VVA - Variable valve actuator

WLTP - Worldwide harmonized light vehicles test procedure

WHR - Waste heat recovery

WI - Water Injection

WTT - Wheel to Tank

WTW - Well to Wheel

[[epsilon].sub.tr] - Trapped compression ratio

[[eta].sub.idc] - Thermodynamic efficiency

[gamma] - Specific heat ratio

[sigma] - Expansion - Compression ratio

[omega] - Engine angular velocity

APPENDIX

APPENDIX 1

APPENDIX 2

BMEP can be expressed as:

BMEP = [[eta].sub.cv] -AMEP-[p.sub.loss] - [p.sub.pumping] (9)

where:

BMEP = 4[pi]/[V.sub.d] * [T.sub.e] (10)

AMEP = 4[pi][H.sub.LHV]/[V.sub.d] * [[??].sub.f]/[omega] (11)

the available mean effective pressure 'AMEP' represents the available chemical energy granted by the fuel flow rate [[??].sub.f]

[p.sub.loss] = [p.sub.loss]([v.sub.pist])

[P.sub.pumping] [p.sub.exh] - [p.sub.intake] (12,13)

the [[eta].sub.cv] is the global engine conversion efficiency as function of the 'e' energy conversion efficiency parameter, which is the product between the thermodynamic and combustion efficiency and [[eta].sub.idc], the corrected theoretical efficiency:

[[eta].sub.cv] = e([v.sub.pist],amep) * [[eta].sub.idc]

(14)[v.sub.pist] is the average piston speed defined as:

[v.sub.pist] = S/[pi] * [omega] (15)

where S is the engine stro[k.sub.e]. The term [[eta].sub.idc] is corrected to ta[k.sub.e] into account the Miller/Atkinson cycle:

[[eta].sub.idc] = 1- 1/[r.sup.[gamma]-1.sub.g] - f([sigma]) (16)

where, as described in [47]:

f([sigma]) = [[sigma].sup.[gamma]]([gamma]-1)-[gamma]*[[sigma].sup.[gamma]-1]+1/([gamma]-1)*[[sigma].sup.[gamma]-1]*B (17)with

(B = [H.sub.LHV]/1+AFR/[RT.sub.air])

(18)and [sigma]=[r.sub.g]/[r.sub.tr], where [r.sub.g] and [r.sub.tr] are the geometric and trapped compression ratios, respectively.

By replacing (10), (11), (12), (13) and (14) in (9) it is possible to obtain the effective torque [T.sub.e]:

[T.sub.e] = e[[eta].sub.idc][H.sub.LHV][[??].sub.f]/[omega] - [p.sub.loss] [V.sub.d]/4[pi] - ([p.sub.exh]-[p.sub.intake])[V.sub.d]/4[pi]

APPENDIX 3

Matteo De Cesare

MAGNETI MARELLI SpA - Div. Powertrain

Nicolo Cavina

University of Bologna

Luigi Paiano

MAGNETI MARELLI SpA - Div. Powertrain

doi:10.4271/2017-24-0151
Table 1. Measurable Powertrain Requirements and Priority from HoQ1

                                                             Priority
                                                             from MR
            Needs/              Measurable Needs             Vehicle
            Requests            and Request                  Controlled
                                (from HoQ1, Vehicle Level)   by Driver

End-User    Low Noise       1   Noise Emission Level         4
            High            2   Accel.Time 0 -->100 Km/h     3
            Performance
                            3   Accel.Time 80 -->120 Km/h    3
                                (elasticity)
                            4   Max Vehicle Speed            3
            High            5   Accel. Time 0 -->50 Km/h     4
            Comfort             (direct transmission)
                            6   Time w/o acceleration        4
                                during load Req,
                            7   Low Vibration                4
                            8   Cabin Comfort                4
            High            9   Mileage w/o failure          4
            Reliability
            Easy to use    10   Energy Refilling autonomy    5
                           11   Maintenence intervall/cost   4
                           12   Energy Refilling Time        4
            Low Fuel       13   Fuel Economy                 4
            Consumption
Standards   Low Emission   14   Toxic Emission according     7
                                to Standard (WLTP and
                                RDE)
                           15   EOBD/OBD2 compliance         7
                           16   CO2 according to Standard    7
            Safety         17   Mileage w/o critical event   7

                           Priority
                           from MR
            Needs/         Autonomous   Unit
            Requests       Driving


End-User    Low Noise      5            [dB]
            High           2            [sec]
            Performance
                           2            [sec]

                           2            [km/h]
            High           2            [sec]
            Comfort
                           5            [ms]

                           5            [dB]
                           5            [[degrees]C] & [hum]
            High           5            [km]
            Reliability
            Easy to use    5            [km]
                           5            [km]
                           4            [min]
            Low Fuel       5            [km/l]
            Consumption
Standards   Low Emission   7            [mg/km]

                           7            [mg/km]
                           7            [g/km]
            Safety         7            [km]

Table 3. Functions in hybrid electric powertrains

Functions           ICE    P0 Belt  P0 Belt  Hybrid  Hybrid   Range
                           12V      48V      P2/P3,  Plug-in  Extender
                                             Power            EV
                                             Split

Cold Start          Y               P        Y       Y        Y
Stop & Start        Y      Y        Y        Y       Y        Y
Coasting            Y (*)  Y        Y        Y       Y        Y
High Efficiency            Y        Y        Y       Y        Y
Electric Power
Generation
Regenerative               P        Y        Y       Y        Y
Braking
Torque Assist              P        Y        Y       Y        -
Electric Take-off                   Y        Y       Y        Y
Electric Driving                             Y       Y        Y
Plug-in Electric                                     Y        Y
Charging

(*) with e-clutch or AMT/DCT Y=Yes P=Partially

Table 4. Selection Matrix for Powertrain Architectures

      POWERTRAIN                      Relevance  1            2
      ARCHITECTURES                   (0/100)
                                                 ICE GDI      Hybrid
                                                 Turbo + DCT  P0/P2 48V
      Powertrain Charcteristics       Human
      (from HOQ2.1)                   Driving

 1    Powertrain Noise Level          10          1            2
 2    Powertrain Time to Full Power   15          3            5
 3    Low-end Torque (at wheel)       20          3            7
 4    Speed Range of High Torque      16          5            7
 5    Maximum Power                   21          9            9
 7    Time w/o Torque delivery        18          5            7
      during load Req.
 8    Powertrain Vibration            13          1            2
 9    Tank to Wheel Maximum           25          5            5
      Efficiency
10    Tank to Wheel Efficiency at     29          3            7
      part/low load
11    NOx Emission according to       14          1            3
      RDE
12    HC/CO Emission according to     16          5            7
      RDE
13    Soot/PN according to RDE        15          1            3
14    CO2 on WLTC                     23          5            7
15    Heating Power                    5          9            9
17    Efficiency of Electric Power    21          5            5
      Gen.
18    Energy Storage Capacity         15          7            7
19    Energy Refilling Time           14          9            9
25    % Braking energy recovered      23          0            5
26    PWT Size                         5          7            5
27    PWT Weight                      38          7            5
                                      -
PWT Architecture Ranking [0/100]                 55           72

      POWERTRAIN                      3       4
      ARCHITECTURES
                                      Hybrid  Hybrid Power
                                      P2 HV   Split HV
      Powertrain Charcteristics
      (from HOQ2.1)

1     Powertrain Noise Level           3       7
2     Powertrain Time to Full Power    7       9
3     Low-end Torque (at wheel)        7       9
4     Speed Range of High Torque       7       9
5     Maximum Power                    9       9
7     Time w/o Torque delivery         7       9
      during load Req.
8     Powertrain Vibration             3       7
9     Tank to Wheel Maximum            7       9
      Efficiency
10    Tank to Wheel Efficiency at      9       9
      part/low load
11    NOx Emission according to        5       5
      RDE
12    HC/CO Emission according to      9       9
      RDE
13    Soot/PN according to RDE         5       5
14    CO2 on WLTC                      7       7
15    Heating Power                    9       9
17    Efficiency of Electric Power     5       7
      Gen.
18    Energy Storage Capacity          7       7
19    Energy Refilling Time            9       9
25    % Braking energy recovered       7       7
26    PWT Size                         5       3
27    PWT Weight                       5       5

PWT Architecture Ranking [0/100]      82      93

      POWERTRAIN                      5                6
      ARCHITECTURES
                                      Hybrid P2/Power  Range Extender
                                      Split Plugin     EV Plugin
      Powertrain Charcteristics
      (from HOQ2.1)

1     Powertrain Noise Level           7                7
2     Powertrain Time to Full Power    9                9
3     Low-end Torque (at wheel)        9                9
4     Speed Range of High Torque       9                9
5     Maximum Power                    9                9
7     Time w/o Torque delivery         9                9
      during load Req.
8     Powertrain Vibration             7                7
9     Tank to Wheel Maximum            9                9
      Efficiency
10    Tank to Wheel Efficiency at      9                9
      part/low load
11    NOx Emission according to        5                5
      RDE
12    HC/CO Emission according to      9                9
      RDE
13    Soot/PN according to RDE         5                5
14    CO2 on WLTC                      9                9
15    Heating Power                    9                7
17    Efficiency of Electric Power     7                9
      Gen.
18    Energy Storage Capacity          5                7
19    Energy Refilling Time            5                3
25    % Braking energy recovered       7                7
26    PWT Size                         3                3
27    PWT Weight                       3                3

PWT Architecture Ranking [0/100]      89               90

Table 5. Summary of Technology benefits and drawbacks

ICE            Advantages                         Influenced
Technology                                        Engine Zones (Fig. 5)

GDI lean       - Pumping losses reduction at      All engine
Combustion     low loads                          operating area
               - Higher ratio of specific heats   with
               - Knock mitigation                 higher impact
               - Lower heat losses towards        on 1, 2 and 3
               cylinder walls

Miller         - Pumping losses reduction at      All engine
Cycle          low loads                          operating area
               - Higher geometric CR enabled      with
               - Knock mitigation                 higher impact
               - Lower peak pressure and          on 1 and 2
               temperature
               - VGT enabling with higher
               cylinder displacement
VCR            - Higher efficiency at low loads   Zones 1 and 3
               due to the high CR
               - Very effective coupling with
               Miller
Water          - Very effective way to            Zones 2,3 and 4.
Injection      mitigate knock phenomena           If higher CR is
               - CR can be increased              adopted,the
               - Lower exhaust temperature        impact is on the
               in full load avoiding              whole engine
               enrichment and enabling VGT        operative area
Cylinder       - Pumping and heat losses          Zone 1
Deactivation   reduction
               - Higher efficiency at low loads

External EGR   - Knock mitigation                 Zone 2,3 and 4
               - Lower heat losses
               - De-throttling at partial loads

Multistage     - Low end torque increase          All the engine
Air Charging   - Downsizing and down-speeding     operative area
               enabler
               - Scavenging reduction or
               elimination
               - Drivability improvement

ICE            Drawbacks
Technology

GDI lean       - Expensive exhaust after-treatment
Combustion     - Higher cycle-to-cylce variation
               - Higher boosting demand
               - Combustion chamber and
               piston re-design
               - More advanced ignition system
               requirements
Miller         - Lower volumetric efficiency,
Cycle          more boosting required
               - Displacement needs to be
               increased to recover the engine
               power leading to higher friction
               losses

VCR            - High cost and complexity
               - Complex handling during
               switching from high CR to low CR

Water          - Water consumption leads to
Injection      the need of producing it on
               board
               - Corrosion needs to be handled

Cylinder       - Torque fluctuation, vibrations
Deactivation   and noise to be handled
               - Low effectiveness in coupling
               with other technologies
               - Cost and packaging impact
External EGR   - Reduction of maximum power
               with a given turbocharger layout
               - Negative impact on transient
               response
Multistage     Cost and packaging impact
Air Charging   Added complexity for the engine
               control

Table 6. ICE technologies and main parameters

ICE Technology               Linked Parameter

Cylinder deactivation (VVA)  [V.sub.d] [k.sub.f],[k.sub.p] in part load
                             operations
Cylinder deactivation        [V.sub.d] [k.sub.f],[k.sub.p] in part load
(2CATs)                      operations
Miller/Atkinson Cycle        [sigma] and therefore [[eta].sub.idc],
                             [k.sub.p] in the part load operations,
                             [[eta].sub.v], [k.sub.e] depending on the
                             strategies used
External EGR                 [k.sub.e] for the lower heat losses and
                             knock mitigation, [k.sub.p],[gamma]
Lean Combustion              [k.sub.e], [k.sub.p] especially at part low
                             operations and knock resistance
Water Injection              [k.sub.e],y and knock resistance
                             [right arrow] higher [r.sub.g] allowed
                             [right arrow] higher [[eta].sub.idc]
Variable Compression R.      [[eta].sub.idc], [k.sub.f]
2stage-Air Charging          Extreme downsizing [right arrow] [V.sub.d]
                             and [pme.sub.req]

Table 7. Fuel benefit of ICE technologies vs. reference engine
estimated and from literature data

Technology                    CO2/Fuel Saving in NEDC
                                          [%]
                              Model         Literature

BaselineTC, GDI, S&S           1.4L, 4Cyl    1.01/2.01, TC, 3/4 Cyl
Miller Cycle (CR+2)            6             5/12
VCR- 2stage (CR+2)             4             4/9
Port Water Inj. (CR +2)        4             4.4
Electronic Cyl Deactivation    5             7
Cylinder Deactivation          7             -
LP-EGR/ HP-EGR                 3.5           -
Miller Cycle+Wl               10             -
Miller Cycle+VCR              10             -
2st.-Turbo (3cyl + downsp)    12            12/18
eBooster (3cyl + downsp)      12            12/18
BSG                            8             5/10
BSG+e Booster+                14            12/18
3 cyl+ downspeeding
BSG+eBooster+WI (CR +2)       15             -
3 cyl+ downspeeding
P2 48Volt 22kw                20            15/20
P2 48V22kw+Miller+WI          28             -

Technology                    CO2/Fuel Saving in WLTC
                                          [%]
                              Model        Literature

BaselineTC, GDI, S&S           1.4L 4Cyl    1.0L/2.0L, TC, 3/4 Cyl
Miller Cycle (CR+2)            5            5/12
VCR- 2stage (CR+2)             5.5          4/9
Port Water Inj. (CR +2)        6.0          4/6.5
Electronic Cyl Deactivation    5
Cylinder Deactivation          6           10
LP-EGR/ HP-EGR                 3            3/4
Miller Cycle+Wl                9            -
Miller Cycle+VCR               9            5/9
2st.-Turbo (3cyl + downsp)    12            -
eBooster (3cyl + downsp)      12            -
BSG                            6            5/6
BSG+e Booster+                10            6
3 cyl+ downspeeding
BSG+eBooster+WI (CR +2)       12            -
3 cyl+ downspeeding
P2 48Volt 22kw                18            -
P2 48V22kw+Miller+WI          24            -

Table 8. Cost of analyzed technologies

Technology             Baseline                 [DELTA]   Remark
                                                Average
                                                Cost
                                                [[euro]]

GDI Lean               1-stageTC, GDI, 4 Cyl     385      including LNT
                                                          catalyst
Miller Cycle           1-stage TC, GDI, 4 Cyl,   200      considering a
                       VVA                                2st of TC or
                                                          desplacement
                                                          increasing
VCR- 2stages           1-stage TC, GDI, 4 Cyl    125
VCR- Continous         1-stageTC, GDI, 4Cyl      350
Port Water Injection   1-stage TC, GDI, 4 Cyl     95
DWI - Separate         1-stage TC, GDI, 4 Cyl    180
DWI - Mixture          1-stage TC, GDI, 4 Cyl    130
Electronic Cyl Deact.  1-stage TC, GDI, 4 Cyl    100
Cylinder Deactivation  1-stage TC, GDI, 4 Cyl,   200
                       WA
LP-EGR                 1-stage TC, GDI, 4 Cyl    115
HP-EGR                 1-stage TC, GDI, 4 Cyl    115
2stages-Turbo          1-stage TC, GDI, 4 Cyl    200
eBooster               1-stage TC, GDI, 4 Cyl    400      including Li
                                                          battery
BSG                    1-stage TC, GDI, 4 Cyl    700      including Li
                                                          battery
BSG+eBooster           1-stage TC, GDI, 4 Cyl   1000      including Li
                                                          battery

Table 9. Selection Matrix of Technologies to ICE improvement (2025
timeframe)

                                                      SELECTION MATRIX
                                                      COMBUSTION
                                                      TECHNOLOGIES
                                                      1
     ENGINE                         Relevance         Port Water
     ARCHITECTURES                  (0+100)           Injection


     Powertrain Charcterlstics      Human    Auton.
     (from HoQ2.1)                  Driving  Driving
 1   Powertrain Noise Level         10       13
 2   Powertrain Time to Full Power  15        9        3
 3   Low-end Torque (at wheel)      20       14        7
 4   Speed Range of High Torque     16        9        3
 5   Maximum Power                  21       14        7
 7   Time wlo Torque delivery       18       15
     during toad Req.
 8   Powertrain Vibration           13       16
 9   Tank to Wheel Maximum          23       22        5
     Efficiency
10   Tank to Wheel Efficiency at    29       24        3
     part/low load
11   NOx Emission according to      14       16        3
     RDE
12   HC/CO Emission according to    16       18
     RDE
13   Soot/PN according to RDE       15       17
14   CO2 on WLTC                    23       19        5
15   Heating Power                   5        5
26   PWT Size                        5        8       -1
27   PWT Weight                     38       35
                                     -        -
     Tecnology Ranking [0/100]                        25
     - Human D.
     Tecnology Ranking [0/100]                        21
     - Auton. D.

                                               SELECTION MATRIX
                                               COMBUSTION
                                               TECHNOLOGIES
                                     2          3        4     5
     ENGINE                          DWI-       DWI-     GDI   Miller
     ARCHITECTURES                   Saparate   Mixture  Lean  /Atkinson
                                                               Cycle

     Powertrain Charcterlstics
     (from HoQ2.1)
 1   Powertrain Noise Level
 2   Powertrain Time to Full Power    3          3        5
 3   Low-end Torque (at wheel)        7          7             -1
 4   Speed Range of High Torque       3          3
 5   Maximum Power                    7          7              7
 7   Time wlo Torque delivery
     during toad Req.
 8   Powertrain Vibration
 9   Tank to Wheel Maximum            5          5        3     9
     Efficiency
10   Tank to Wheel Efficiency at      3          3        7     7
     part/low load
11   NOx Emission according to        3          3       -1     1
     RDE
12   HC/CO Emission according to                          3
     RDE
13   Soot/PN according to RDE                             1    -1
14   CO2 on WLTC                      5          5        7     9
15   Heating Power
26   PWT Size                        -1         -1       -3    -5
27   PWT Weight                                          -1

     Tecnology Ranking [0/100]       25         25       17    25
     - Human D.
     Tecnology Ranking [0/100]       21         21       15    22
     - Auton. D.

                                              SELECTION MATRIX
                                               AIR DELIVERY
                                               TECHS.
                                     9         10        11
     ENGINE                          3cyl +    3cyl +    Cylnder
     ARCHITECTURES                   2-stage   2-stage   Deact.
                                     TC        TC        (VVA)
                                     (BMEP     (BMEP
                                     27 bar)   35 bar)

     Powertrain Charcterlstics
     (from HoQ2.1)
 1   Powertrain Noise Level          -1        -1        -1
 2   Powertrain Time to Full Power    3         3        -1
 3   Low-end Torque (at wheel)        5         7
 4   Speed Range of High Torque       3         7
 5   Maximum Power                    7         9
 7   Time wlo Torque delivery         1         3
     during toad Req.
 8   Powertrain Vibration                                -1
 9   Tank to Wheel Maximum                                5
     Efficiency
10   Tank to Wheel Efficiency at      7         9         9
     part/low load
11   NOx Emission according to
     RDE
12   HC/CO Emission according to                          1
     RDE
13   Soot/PN according to RDE         1         1
14   CO2 on WLTC                      7         9         5
15   Heating Power
26   PWT Size
27   PWT Weight                                -3        -1

     Tecnology Ranking [0/100]       25        31        15
     - Human D.
     Tecnology Ranking [0/100]       20        24        14
     - Auton. D.

                                          SELECTION MATRIX
                                     AIR DELIVERY  TECHS. MIX
                                     TECHS.
                                     12            13       14
     ENGINE                          Electronic    1+9+11   1+5+9
     ARCHITECTURES                   CD

     Powertrain Charcterlstics
     (from HoQ2.1)
 1   Powertrain Noise Level                        -1       -1
 2   Powertrain Time to Full Power                  5        7
 3   Low-end Torque (at wheel)                      7        7
 4   Speed Range of High Torque                     5        5
 5   Maximum Power                                  7        5
 7   Time wlo Torque delivery                                1
     during toad Req.
 8   Powertrain Vibration                          -1       -1
 9   Tank to Wheel Maximum            5             5        9
     Efficiency
10   Tank to Wheel Efficiency at      9             7        7
     part/low load
11   NOx Emission according to                      3        3
     RDE
12   HC/CO Emission according to      1             1        1
     RDE
13   Soot/PN according to RDE                       1        1
14   CO2 on WLTC                      5             7        7
15   Heating Power
26   PWT Size                        -1            -1       -1
27   PWT Weight                      -1            -1

     Tecnology Ranking [0/100]       16            32       37
     - Human D.
     Tecnology Ranking [0/100]       15            26       31
     - Auton. D.

                                     SELECTION MATRIX
                                     TECHS. MIX

                                     15        16
     ENGINE                          5+6+8+9   4+6+9
     ARCHITECTURES

     Powertrain Charcterlstics
     (from HoQ2.1)
 1   Powertrain Noise Level          -1        -1
 2   Powertrain Time to Full Power    5         5
 3   Low-end Torque (at wheel)        5         5
 4   Speed Range of High Torque       5         5
 5   Maximum Power                    5         5
 7   Time wlo Torque delivery
     during toad Req.
 8   Powertrain Vibration            -1        -1
 9   Tank to Wheel Maximum            9         5
     Efficiency
10   Tank to Wheel Efficiency at      7         7
     part/low load
11   NOx Emission according to        3
     RDE
12   HC/CO Emission according to
     RDE
13   Soot/PN according to RDE         1         1
14   CO2 on WLTC                      5         5
15   Heating Power
26   PWT Size                        -1        -3
27   PWT Weight                      -1        -1

     Tecnology Ranking [0/100]       31        25
     - Human D.
     Tecnology Ranking [0/100]       25        20
     - Auton. D.

Table 10. Summary of technology impact from literature analysis

Analyzed     Reference   Vehicle   Engine               Other Engine
Technology   Work        Segment   Refernce             Modification

Port Water   30                    TC,GDI,              CR=+2
                                   130 Kw
Injection    50                    1.0LTC,GDI,          SA optimizatin
                                   CR=11 6
Direct       32          E         1.6L,TCGDI,          VCR 14.7/10.7
Water                              VCR 13/9,5
Injection                          AT 8-speed
GDI Lean     29          D         2.0 L, TC, GDI,
                                   200KW
             27          c         1.0L.TC,GDI,         CR=12
                                   WL,CR=10
             44                    1.4L,TC,GDI          1.5L,CR-12.5,
                                                        VGT,CD
Miller       46          D         2.0 L, TC, CR- 9.6   CR-11.7
Cycle
             58          D         2.0L,TC,GDI          CR=13.1 4 Cyl
                                   4cyl, CR=10.5        Supercharger
                                                        CR=13.1. 3Cyl,
                                                        Supercharger
             37          c         1.4L.TC,GDI          1.6L, CR=13.
                                   RC=10,S/B=l.17       S/B=1.35,
                                                        Friction
                                                        Reduction
LP-EGR       30          C         1.2L,TC,GDI
                                   RC = 10.5
Dedicated    54                    2.0 L,TC             Supercharger
EGR                                                     added, CR=11.7
HP-EGR       49          SUV       3.7L,V6, NA,CR=13    2.SL,TC,Scav.
                                                        GDI,CR=10
Variable     47                    2.0L.TC, GDI,        Miller. 2step
Compres.                           CR=9.5               VCR=9.5/14
Ratio
             40                    1.6L,TC.GDI,CR=10    Continous VCR=11
             27                    CR=13.1              2 step VCR=12.1
Cylinder     41          c         1.4L,TC.GDI          Electronic
                                                        Cylinder
                                                        Deactivation
Deactiv      57                                         Dynamic Skip
                                                        Fire
48V BSG      14
             51          B         NA,PFI
             14
             14          c         2.0 L, 4 cyl, PFI    1.01, 3 Cyl, TC,
                                                        GDI
48V BSG +    14          c         1.01, 3Cyl,TC, GDI   Combustion &
eBooster                                                Thermal opt.
             14                                         1.7EL,TC,ODI
             14                    TC, GDI
             51          Sport     TC, GDI, AT

                          Engine Characteristics
Analyzed     Low-end            [DELTA]   [DELTA] Tank   [DELTA]Tank
Technology   Torque             Maximum   to Wheel       to Wheel
             Improvement        Power     Maximum        Efficiency at
                                          Efficiency     part/low load
                                          [%]            [%]

Port Water                                13

Injection                                  1.8

Direct
Water
Injection
GDI Lean

                                           5              10/30

Miller                          25
Cycle
                                                           1.8/9.4

                                                           5.3/21.8

                                           2

LP-EGR                                                     1

Dedicated                                 10
EGR
HP-EGR       30                           30

Variable
Compres.
Ratio
             10                                            4/5

Cylinder

Deactiv

48V BSG

48V BSG +
eBooster
                                                         200 g/kwh

                                50

             Engine Characteristics
Analyzed     CO2 Benefit   CO2 Benefit
Technology   in WLTC       in NEDC

             [%]           [%]

Port Water    4

Injection

Direct        6.5           4.4
Water
Injection
GDI Lean     12            14

              3.8           4.4

             10

Miller                     21
Cycle
              6.3

             12.5

LP-EGR        4

Dedicated
EGR
HP-EGR

Variable      5/9
Compres.
Ratio

              4.2/6.2
Cylinder                    7

Deactiv                    10/20

48V BSG       5.1/6.2
              4
                           10
                           50

48V BSG +                  17
eBooster

              6            15

Table 11. House of Quality 2.1

                                              Priority

                                              from MR
Needs/                     Measurable Needs   Vehicle
Requests                   and Request        Controlled
                           (from HoQ1,        by Driver
                           Vehicle Level)
            Low Noise      1                  Noise Emission Level
                           2                  Accel.Time 0-->100Km/h
            High           3                  Accel Time 80->120 Km/h
            Performance                       elasticity)
                           4                  Max Vehicle Speed
                           5                  Accel. Time 0-->50Km/h
                                              direct transmission)
End-User    High           6                  Time w/o acceleration
            Comfort                           during load Req,
                                              Low Vibration
                                              Cabin Comfort
            High           9                  Mileage w/o failure
            Reliability
                           10                 Energy Refilling autonomy
            Easy to use    11                 Maintenence intervalt/cost
                           12                 Energy Refilling Time
            Low Fuel       13                 Fuel Economy
            Consumption
Standards                  14                 Toxic Emission according
                                              to Standard (WLTP and
                                              RDE)
            Low Emission   15                 EOBD/OBD2 compliance
                           1G                 C02 according to Standard
            Safety         17                 Mileage w/o critical event
Powertrain
characteristic
ranking
- Human
driving
Powertrain
Characteristic
ranking
- Autonomous
driving

Needs/                     Autonomous   Unit
Requests                   Driving

            Low Noise      4            5      [dB]
                           3            2      [sec]
            High           3            2      [sec]
            Performance
                           3            2      [km/h]
                           4            2      [sec]

End-User    High           4            5      [mo]
            Comfort
                           4            8      [dB]
                           4            5      [[degrees]C] & [hum]
            High           4            5      [km]
            Reliability
                           5            5      [km]
            Easy to use    4            5      [km]
                           4            4      [min]
            Low Fuel       4            5      [km/l]
            Consumption
Standards                  7            7      [mg/km]

            Low Emission   7            7      [mg.'km]
                           7            7      [g/km]
            Safety         7            7      [km]
Powertrain
characteristic
ranking
- Human
driving
Powertrain
Characteristic
ranking
- Autonomous
driving

                           HoQ2.1 Powertrain Level
                           Traction Power
                           Generation/Control
                           1             2                3
                           Powertrain    Powertrain Time  Low-end Torque
                           Noise Level   to Full Power    (at wheel)

                           [down arrow]  [up arrow]       [up arrow]

Needs/Requests

            Low Noise       9
                                          9                9
            High                          3
            Performance

                                          9                9

End-User    High                          3                1
            Comfort

                            9
            High
            Reliability

            Easy to use

            Low Fuel                      1                5
            Consumption
Standards                                 1                1

            Low Emission
                                          1                5
            Safety
Powertrain                 10            15               20
characteristic
ranking
- Human
driving
Powertrain                 13             9               14
Characteristic
ranking
- Autonomous
driving

                           HoQ2.1 Powertrain Level
                           Traction Power
                           Generation/Control
                           4             5           6
                           Speed Range   Maximum     Max Amplitude
                           of High       Power       of jerking
                           Torque                    Oscillation

                           [up arrow]    [up arrow]  [down arrow]

Needs/Requests

            Low Noise
                            9             9
            High            5             9
            Performance
                            5             9
                            9             1

End-User    High            1             1           9
            Comfort

                                                      9
            High
            Reliability
                                          5
            Easy to use
                                          5
            Low Fuel        1            -5
            Consumption
Standards                   1

            Low Emission
                            1             6
            Safety
Powertrain                 16            21          10
characteristic
ranking
- Human
driving
Powertrain                  9            14          11
Characteristic
ranking
- Autonomous
driving

                           HoQ2.1 Powertrain Level
                           Traction Power
                           Generation/Control
                           7            8              9
                           Time w/o     Powertrain     Tank to
                           Torque       Vibration      Wheel Maximum
                           delivery                    Efficiency
                           during load
                           Req.
                           [up arrow]   [down arrow]   [up arrow]

Needs/Requests

            Low Noise                    5
                            5                           1
            High            5                           1
            Performance
                                                        5
                            5                           1

End-User    High            9
            Comfort
                                         9
                            9            9             -1
            High
            Reliability
                                                        9
            Easy to use
                                                        1
            Low Fuel                                    9
            Consumption
Standards                   1                           1

            Low Emission
                                                        9
            Safety
Powertrain                 18           13             25
characteristic
ranking
- Human
driving
Powertrain                 15           16             22
Characteristic
ranking
- Autonomous
driving

                           HoQ2.1 Powertrain Level
                           Traction Power        Emissions Control
                           Generation/Control
                           10                    11
                           Tank to               NOx Emission
                           Wheel                 according
                           Effieteney            to RDE
                           at part/low
                           load
                           [up arrow]            [down arrow]

Needs/Requests

            Low Noise
                            5                    -1
            High            5                    -1
            Performance
                            1                    -1
                            5                    -1

End-User    High
            Comfort

                           -1
            High
            Reliability
                            9                     1
            Easy to use
                            1
            Low Fuel        9                     1
            Consumption
Standards                   1                     9

            Low Emission                          9
                            9                    -1
            Safety
Powertrain                 29                    14
characteristic
ranking
- Human
driving
Powertrain                 24                    16
Characteristic
ranking
- Autonomous
driving

                           HoQ2.1 Powertrain Level
                           Emissions Control

                           12               13             14
                           HC/CO Emission   Soot/PN        CO2 on
                           according        according to   WLTC
                           to RDE           RDE

                           [down arrow]     [down arrow]   [down arrow]

Needs/Requests

            Low Noise
                           -1               -1
            High           -1               -1
            Performance
                            1                1              5
                           -1               -1

End-User    High
            Comfort

            High
            Reliability
                           -1               -1              9
            Easy to use

            Low Fuel        1               -1              9
            Consumption
Standards                   9                9

            Low Emission    9                9
                            1               -1              9
            Safety
Powertrain                 18               15             23
characteristic
ranking
- Human
driving
Powertrain                 18               17             19
Characteristic
ranking
- Autonomous
driving

                           HoQ2.1 Powertrain Level
                           HVAC                        eGen.
                           15            16            17
                           Heating       Mech Power    Efficiency
                           Power         for Cooling   of Electric
                                                       Power Gen.

                           [down arrow]  [down arrow]  [up arrow]

Needs/Requests

            Low Noise
                                          3             1
            High                          3             1
            Performance
                                          3             1
                                          8             1

End-User    High                          1
            Comfort

                            9             5             5
            High
            Reliability
                                          5             5
            Easy to use
                                          5
            Low Fuel       -1             5             5
            Consumption
Standards                   1             8             8

            Low Emission
                           -1             5             5
            Safety
Powertrain                  5            29            21
characteristic
ranking
- Human
driving
Powertrain                 5             24            18
Characteristic
ranking
- Autonomous
driving

                           HoQ2.1 Powertrain Level
                           Energy Storage            Self-diagnosis
                           18          19            20
                           Energy      Energy        PWT hours
                           Storage     Refilling     w/o failure
                           Capacity    Time

                           [up arrow]  [down arrow]  [up arrow]

Needs/Requests

            Low Noise
                                        3
            High                        3
            Performance
                            1           3
                                        3

End-User    High
            Comfort

            High                                      9
            Reliability
                            9          -3
            Easy to use
                           -1           9
            Low Fuel                    3
            Consumption
Standards                               1

            Low Emission                              5
                            9           3
            Safety                                    5
Powertrain                 15          14            15
characteristic
ranking
- Human
driving
Powertrain                 13          12            15
Characteristic
ranking
- Autonomous
driving

                           HoQ2.1 Powertrain Level
                           Self-diagnosis
                           21            22            23
                           Firing        Extra         PWT on board
                           Risk          Torque        Failure
                           Recovery      Recovery      Detection
                           time          Time          Time

                           [down arrow]  [down arrow]  [down arrow]

Needs/Requests

            Low Noise                                   1

            High
            Performance

End-User    High
            Comfort
                                                        1

            High                                        5
            Reliability

            Easy to use

            Low Fuel                                    1
            Consumption
Standards                                               1

            Low Emission    7             7             9

            Safety          9             9             5
Powertrain                 16            16            20
characteristic
ranking
- Human
driving
Powertrain                 17            17            23
Characteristic
ranking
- Autonomous
driving

                           HoQ2.1 Powertrain Level
                           Self-diagnosis   eBrake
                           24               25           26
                           Fuctions         % Braking    PWT Size
                           /Components      energy
                           failure          recovered
                           prevention

                           [up arrow]       [up arrow]   [down arrow]

Needs/Requests

            Low Noise       3
                                                          1
            High                                          1
            Performance
                                                          1
                                                          1

End-User    High
            Comfort
                            3

            High            5                3
            Reliability
                                             9           1
            Easy to use

            Low Fuel        1                9           1
            Consumption
Standards                   1                1           1


            Low Emission    9
                                             9           1
            Safety          5
Powertrain                 22               23           5
characteristic
ranking
- Human
driving
Powertrain                 25               21           8
Characteristic
ranking
- Autonomous
driving

                           HoQ2.1 Powertrain Level
                           eBrake
                           27
                           PWT Weight

                           [down arrow]

Needs/Requests

            Low Noise
                            5
            High            5
            Performance
                            3
                            5

End-User    High
            Comfort

            High
            Reliability
                            9
            Easy to use
                            1
            Low Fuel        9
            Consumption
Standards                   9

            Low Emission
                            9
            Safety
Powertrain                 38
characteristic
ranking
- Human
driving
Powertrain                 35
Characteristic
ranking
- Autonomous
driving
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Article Details
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Author:De Cesare, Matteo; Cavina, Nicolo; Paiano, Luigi
Publication:SAE International Journal of Engines
Article Type:Report
Date:Dec 1, 2017
Words:15954
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