Performance analysis of a modified 4-stroke engine using biodiesel fuel for irrigation purpose.Introduction
The demand for mobility, automobiles and cultivation of land in India has been growing with the increase of population along with the economic progress. The country faces problem in regard to the fuel requirement for increased transportation and irrigation demand and import about 70% of its petroleum requirement. The current yearly consumption of diesel is about 40 million tones forming 40% of the total petroleum product consumption. This is expected to reach 55 million tones and growing at about 6% annually.
In India 70% of the population continues to earn its livelihood from agriculture. Improper land use, lack of irrigation facility at cheaper rate and population have resulted an extensive degradation of agricultural land. The high cost of irrigation facility, higher electricity prices, costly seeds and other equipments have resulted in a large number of suicidal case of the farmers in different parts of the country. The answer to the above problem is to search for an alternative fuel at a cheaper rate.
The fossil fuels, especially the petroleum oil, are depleting at a fast rate year after year and are bound to get exhausted in coming future. Therefore, petroleum oil is always under threat of supply instabilities and cost escalations. This has led to growing concern for petroleum oil throughout the world, more so in the petroleum importing countries like India. The oil prices have increased alarmingly. Since the last decades, the oil consumption is increasing at an alarming rate due to the economic progress and it might create a major crisis if its alternate sources are not evolved or exploited. There is an urgent need for suitable alternative fuels for use in diesel engines for transportation and irrigation purposes. As it is known there is a crisis of energy all around the world and there are limited recourses of conventional energy sources. Therefore, there is a large focus on alternative fuels. Alternative fuels should be easily available at low cost, be environment friendly and fulfill energy security needs without sacrificing engine's operational performance. Now bio-fuels are getting a renewed attention because of global stress on reduction of green house gases and clean development mechanism and may be suitable for rural mass. In view of this, vegetable oil is a promising alternative because it has several advantages as it is renewable, environment-friendly and produced in rural areas, where there is an acute need for modern forms of energy for irrigation. Therefore, in recent years, systematic efforts have been made by several researchers to use vegetable oils as fuel in engines. Obviously, the use of non-edible vegetable oils compared to edible oils is very significant because of the tremendous demand for edible oils as food and moreover, they are too expensive to be used as fuel as present.
It has been reported that in diesel engines, crude plant oils can be used as fuel, straight as well as in blends with the diesel. It is evident that there are various problems associated with vegetable oils being used as fuel in compression ignition engines, mainly caused by their high viscosity. The high viscosity is due to the large molecular mass and chemical structure of vegetable oils, which in turn leads the problems in pumping, combustion and atomization in the injector system of diesel engine. Due to the high viscosity, vegetable oils normally introduce the development of gumming, the formation of injector deposits, ring sticking as well as incompatibility with conventional lubricating oils in long-term operations. Therefore, a reduction of viscosity is of prime importance to make vegetable oils a suitable alternative fuel for diesel engines. The problem of high viscosity of vegetable oils has been approached in several ways, such as preheating the oils, blending or dilution with other fuels and transesterification.
The fuel of bio-origin may be alcohol, vegetable oils, bio mass and biogas [1,3,6], which may be largely used for rural people for irrigation purposes and cultivating their lands. Some of these fuels can be used directly while others need to be formulated to bring the relevant properties close to conventional fuels. For diesel engines, a significant research effort has been directed towards using vegetable oils and their derivatives as fuels [2,4,5,7].
A lot of research work has been reported in various literature sources in the past two decades on the production methodology and performance analysis of bio-diesel. The commonly used alcohol for transesterification is methanol because of its lower price than that of other lower alkanols. Use of absolute ethanol was found essential to produce ethyl esters successfully, which was characterized by the production of two liquid phases: ester and denser glycerol phases at the end of the reaction.
Vegetable oils can be used directly or blended with diesel to operate compression ignition engines. An experiment using of blends of vegetable oils with diesel has been conduced by various researchers in several countries [9,12,13]. Caterpillar (Brazil) used pre-combustion chamber engines with a blend of 10% vegetable oil while maintaining almost same power output without any engine modifications. It has been reported that use of 100% vegetable oil is also possible with minor fuel system modifications . Short-term engine performance tests have indicated good potential for most vegetable oils as fuel. The use of vegetable oil results in increased volumetric fuel consumption and BSFC . Study reveals that emissions of CO, HC and S[O.sub.x] were found to be higher, whereas N[O.sub.x] and particulate emission were lower compared to conventional diesel.
However, there are many problems reported related to utilization of vegetable oil such as severe engine deposits, piston ring sticking, injector coking, gum formation and lubricating oil thickening [22-24]. These problems are primarily attributed to high viscosity and poor volatility of straight vegetable oils due to large molecular weight and bulky molecular structure. High viscosity of vegetable oil creates problems of unsuitable pumping and fuel spray characteristics as compared to mineral diesel. Larger size fuel droplets are injected from injector nozzle instead of a spray of fine droplets, leading to inadequate air-fuel mixing. Poor atomization, lower volatility, and inefficient mixing of fuel with air contribute to incomplete combustion. This results in an increase in higher particulate emissions, combustion chamber deposits, gum formations and unburned fuel in the lubricating oil. Since raw vegetable oils are not suitable as fuels for diesel engines directly, they have to be modified to bring their combustion related properties closer to the diesel. For the diesel engine, seed oil bio fuels have been widely examined across the world, as a suitable alternative in field trials and laboratory tests. It has been found that these fuels render similar performance and emission when compared with conventional diesel fuel, particularly when blended with diesel fuel or emulsified with ethanol or water. This fuel modification is mainly aimed at reducing the viscosity by transesterification process to eliminate flow/atomization related problems. Several other techniques used to reduce the viscosity of vegetable oils are mainly heating, dilution/blending and microemulsion [25-28].
Transesterification is well accepted and best suited method of utilizing vegetable oils in CI engine without significant long-term operational and durability issues. However, this process relieves the operator of the need to subject the fuel to costly treatment to reduce viscosity and degumming to reduce injector deposits. Maximum population of India leaves in rural and remote areas, where electric power is not available. Jatropha seed's oils can play a major role and may be used for irrigation and electrification. In these remote areas, jatropha plant can be grown and biodiesel of jatropha oil can be produced locally to fulfill their needs. The results described in present work are obtained from a single cylinder CI engines running by Jatropha seed oil bio fuel. The objective is to asses the satisfactory performance for relatively low power requirement in rural masses, which cannot afford the costly fuel resources using local made bio fuel. Keeping these facts in mind, a set of engine experiments were conducted using biodiesel of Jatropha oil on modified engine, which may be used for agriculture, irrigation and electricity generation. Heating and blending of fuel is required to lower the viscosity of Jatropha oil in order to eliminate various operational difficulties. The aim of the present study is to explore the technical feasibility of Jatropha based Biodiesel in direct injection compression ignition engine with slight modifications of the engine, which may further be used by rural masses for application in the irrigation sector.
Relevant properties of the test fuels used from Jatropha seed in the reported work are listed in Table-1.
Design Modifications and Fabrication of test rig
There are several design modifications of normal diesel engine to engine compatible with B100 fuel, as there are many problems in the diesel engine, when it is run on B100 fuel due to its high viscosity. There are many problems in the engine due to high viscosity. Some of them are Impact atomization of the fuel being injected into the engine combustion chamber, large drop of fuel caused by high viscosity affect to combustion quality, burn not clean, build up a layer in the engine, around valve, injector tips and on piston sidewall and ring. Moreover, fuel does not flow properly through filter and engine injection system. To overcome these problems it is very essential to reduce the viscosity of biodiesel fuel by heating method. This is due to the reason that in liquids the cohesive forces predominates the molecular momentum transfer, in the closely packed molecules and with increase in temperature, the cohesive forces decreases as a result of decreasing viscosity.
As the high viscosity of bio diesel creates a lot off problems in the conventional diesel engine; therefore it requires some modifications in the design of engine. In the proposed design modification, the exhaust gases of the engine are utilized to pass through the biodiesel tank so that the heat of the exhaust gases may be utilized to increase the temperature of biodiesel, which finally reduces the viscosity of biodiesel as viscosity of biodiesel is inversely depends on temperature as shown in Fig. 1.
[FIGURE 1 OMITTED]
Following problems are apparent in the engine, when it is run on B100 bio-diesel fuel of high viscosity: impact atomization of the fuel being injected into the engine combustion chamber, large drop of fuel caused by high viscosity affect to combustion quality, burn not clean, build up in the engine, around valve, injector tips and on piston sidewall and ring and Fuel does not flow properly through filter and engine injection system.
To avoid these problems, design modifications as shown in Fig. 2 has been suggested in the 4-stroke vertical single cylinder compression ignition engine, so that the viscosity of biodiesel may be reduced. Several designs modifications done in the 4-stroke vertical single cylinder compression ignition engine are to utilize the exhaust heat for reduction of viscosity of biodiesel. Experiments show that viscosity decrease with increase in temperature as shown in Fig. The viscosity decreases very sharply with increase in temperature upto 40[degrees] C. However, further increase in temperature after 40[degrees] C, the viscosity decreases very slowly. It has been found from the results that viscosity of biodiesel at 40[degrees] C is close to the viscosity of diesel fuel. It is suggested by experiments that biodiesel at 40[degrees] C may be used directly in the compression ignition engines.
[FIGURE 2 OMITTED]
The another arrangement, which has been done in CI engine is that, a second biodiesel fuel tank has been attached with bracket opposite to the first diesel fuel tank. A combination of two knobs also gas welded with a T-joint mounted on the filter of the diesel engine as shown in Fig.2. The biodiesel knob allows biodiesel to flow into the engine when heated up to a 40 [degrees]C temperature. A second diesel knob also has been attached to allow the diesel fuel into the engine at the time of starting and closing of the engine. In starting diesel knob is kept in opening position and biodiesel knob is in closed position. The engine is started on the diesel fuel first and run for a short duration while the bio-diesel in the second tank is warmed up by the exhaust gases from engine's exhaust system. When the oil gets to the appropriate temperature, the engine is switched from the diesel to the bio-diesel and experiment shows that the engine will run perfectly on just the bio-diesel fuel alone. Before switching off the engine, the engine is switched back to the diesel tank and the bio-diesel purged from the fuel system.
In this design modification, the exhaust pipe of the diesel engine is made to pass through the bio-diesel fuel tank. A light duty gate valve is used to bypass the exhaust emission to maintain the 40 [degrees]C temperature of biodiesel by heat transfer from flue gaseous to the biodiesel fuel.
A separate thermometer arrangement is used over the bio-diesel fuel tank for temperature measurement. Bypassing the exhaust emission by use of gate valve whenever the temperature of bio-diesel exceed from certain safe limit i.e. 40[degrees] C. A second gate valve may also be used to restrict the exhaust emission completely through bio-diesel fuel tank. Two separate silencers have been used in this arrangement. Gas welded technique with brass filler metal is used to make a leak proof fillet joints. One three phase elbow, one socket, two silencers, one gate valve, one two phase elbow and one 2.5" nipple is used in this arrangement as shown in Fig. 2. Few photographs on design modifications are also presented in Fig.3 (a)-(h).
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Performance Analysis of Engine
A four-stroke vertical single cylinder compression ignition engine was modified so that it may be run on B100 fuel. Specifications of the engine are presented in Table.2. The experiment facilities used for CI engine test are shown schematically in Fig. 1. A Kirloskar variable compression ratio research engine with dynamometer, pressure display and processing system was employed.
The other physical parameter used in the experiments may be given as:
Drum diameter = 300 mm
Rope diameter = 15 mm
Orifice diameter = 1.52mm
Calorific value of diesel = 45000 KJ/Kg
Density of diesel = 0.84 g/cc.
Calorific value of bio-diesel = 35000 KJ/Kg
Density of bio-diesel = 0.890 g/cc.
Tests were performed on a modified 4-stroke CI engine at different applied load. Initially, the engine was run for conventional diesel fuel only. However, at a later stage, different blends of biodiesel fuel B20, B40, B46, B80 and B100 was used. A range of load settings up to maximum power was used at various engine speeds, at constant compression ratio of 16:1 for each of the fuel examined. Conventional diesel fuel and biodiesel fuel wit different blends were tested. Tests were made at steady conditions after the engine had reached normal operating temperature with diesel fuel.
Results and Discussions
Figure. 4 shows the brake specific fuel consumption of the different blends of biodiesel and conventional diesel fuel, indicating that the brake specific fuel consumption (b.s.f.c) for the different blends of bio diesel fuels. The b.s.f.c decrease very sharply up to 4 Kg load and at slow rate thereafter. The b.s.f.c is defined as the ratio of the fuel consumption rate to the engine brake horsepower output. It may be noted that the conventional diesel has the lowest brake specific fuel consumption value among the other used fuels and needed the lowest fuel consumption rate for achieving the brake horse power output as the other blends of fuels.
The brake thermal efficiency for the different blends of biodiesel fuel (B20, B40, B60, B80, B100) and conventional diesel under constant engine torque and varied engine speed are shown in Fig. 5. The brake thermal efficiency is defined as the brake horsepower output divided by the rate of heat released from the fuel brings power. Fuel (B20, B40, B60, B80, B100) had larger brake thermal efficiency than other blends as the oxygen contents of the biodiesel improved their fuel burning characteristics. The Fig. 5also indicates that the engine speed decreases very sharply, when 100% biodiesel is used in comparison to the other blended fuels.
From the test results, it is observed from Fig. 6 that the brake thermal efficiency increase with the load applied. However, the maximum thermal efficiency is obtained at 8 Kg load in case of 100% biodiesel and the thermal efficiency decreases beyond 8 Kg load. There is a considerable increase in efficiencies of different blends of biodiesel, but the BTE of the bio-diesel is lower than that of conventional diesel fuel through out the entire range. The reason behind this drop is attributed to the poor combustion characteristics of the bio-diesel due to their high viscosity and poor volatility.
It is shown from the Fig. 7 that fuel consumption increases with the load for the different blends of biodiesel fuel. For 100% biodiesel fuel, the fuel consumption increases very rapidly with increase of load beyond 8 Kg. This is due to the low heating value and incomplete combustion of the biodiesel fuel.
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It becomes very clear from the previous sections that biodiesel may be commercial used as an alternate fuel in the existing diesel engine with slight modifications. The main aim of this research was to run the modified compression ignition engine on pure biodiesel made from jatropha curcus oil for engine performance analysis, which may find large applications in irrigation sector. For this purpose, the viscosity of jatropha curcus was reduced and making it close to that of conventional fuel so that it may find suitable use in a C.I. engine for transportation and irrigation for the rural mass. Following results have been obtained:
* Fuel consumption increase with increase of load.
* Fuel consumption also increases with increase of blended Fuel.
* Brake power increase with increase of load.
* Brake power slowly increases with increase of blended Fuel.
* BTE increase with increase in load applied.
* BTE slowly increase with increase of blended Fuel.
* Engine gives considerable Brake thermal efficiency (31%), when 80%-blended fuel was used.
* When 100% Bio Diesel was used Brake thermal efficiency was reduce to 23%.
Jatropha biodiesel may be commercially used with 20% diesel blending. But to run an automobile engine on pure biodiesel (B100) prepared from jatropha oil, temperature variation is the only viscosity reduction process that can be used. For this purpose, pure biodiesel (B100) prepared from jatropha must behave similar to conventional diesel in various physical characteristics and other combustion related properties.
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Indraj Singh received his Post Graduate Degree from Punjab technical University, Jalandhar. He is presently working as Senior Lecturer in Mechanical Engineering Department at Sant Longowal Institute of Engineering and Technology, Punjab. His research areas are alternative fuels, Combustion and automobiles.
Vikas Rastogi received his Ph. D. degree from Indian Institute of Technology, Kharagpur. He is presently working as Assistant Professor in Mechanical Engineering Department at Sant Longowal Institute of Engineering and Technology, Punjab. His research areas are Lagrangian-Hamiltonian mechanics for general class of systems, study of symmetries for discrete and continuous systems, bond graph modeling, and simulation. He is also doing research in alternative fuels and Hybrid vehicles.
Indraj Singh and Vikas Rastogi *
Department of Mechanical Engineering, Sant Longowal Institute of Engineering and Technology, Longowal-148106, Punjab, India
Table 1: Properties of diesel and biodiesel. S. Fuels Flash Fire % N Point Point Carbon ([degrees]C) ([degrees]C) Residue 1. Diesel 80 88 .04 2. Bio 162 170 .003 Diesel S. Calorific Density Cloud N Value (kg/[m.sup.3]) Point (KJ/kg) ([degrees]C) 1. 45000 840 9 2. 35000 880 12 S. Pour Kinetic N Point Viscosity ([degrees]C) (at 20 [degrees] C [mm.sup.2]/sec) 1. -5 1.97 2. -2.5 4.48 Table 2: Principal Specification of Test. Make and model Kirloskar Type Water Cooled Four Stroke Vertical Single Cylinder Compression Ignition Engine Stroke 110 mm Bore 87.5 mm Rated output 5 HP, 3.68 KW Rated speed 1500 rpm Fuel injection timing 27[degrees] before T.D.C Compression ratio 16: 1