Development and testing of variable valve actuation (Vva) system in homogeneous charge compression ignition (Hcci) Engine.
Raise in fuel prices drastically raises the demand for reduced fuel consumption and increased efficiency. Due to the increase of greenhouse gases in today's world, it more significant to reduce the exhaust pollutants from engines. Homogeneous Charge Compression Ignition (HCCI) engines stands unique for its efficiency and its less pollutant emitting nature. Initially HCCI combustion was implemented to two-stroke engines with improvement in fuel efficiency and combustion stability. When applying HCCI to four-stroke engine, the fuel efficiency could be improved up to 50 % compared to the SI engine. The auto-ignition in HCCI combustion leads to short burn duration and therefore high combustion induced noise. This limits the possible operating range. The peak pressure rate can be reduced with increased charge dilution.
II. Literature Review:
Author has reviewed on the effects of EGR ratio, engine speed in HCCI combustion and importance of adjusting initial temperature to have the same combustion phase are declared. Author  tested the HCCI combustion process using natural gas-gasoline mixtures on a CFR engine, endowed with two injection systems for the accurate control of both fuel mixture composition and overall air-to-fuels ratio. The performance of HCCI engine operates with different inlet air temperature and fuel injection pressure, and analysis the effect of these variables on HCCI engine performance and emissions has inspected by author .
Author  investigated that apart from adopting higher compression ratios and boost pressures use of high swirl ratios is observed to be contributing to a large extent in enhancing the rates of heat transfer which would lead to significant reduction in in-cylinder temperatures suitable for low NOx emission formation in HCCI mode. The analysis of compressor pressure ratio, ambient temperature, equivalence ratio, engine speed and the compressor isentropic efficiency on the performance of the HCCI engine have been examined by author at reference .Author [6,7] investigated the different strategies of controlled auto-ignition by HCCI combustion.
III. Variable Valve Actuation:
In internal ignition engines, variable valve timing is the process of changing the timing of a valve lift event inside the cylinder, and it is used to improve performance, fuel consumption or emissions. It is gradually being used in combination with variable valve timing lift systems and control the flow of the intake and exhaust gases. The timing, period and lift of these valve actions have a major impact on engine performance. Deprived of variable valve timing or variable valve lift, the valve timing necessity is the similar for all engine speeds and conditions, therefore negotiations are necessary. An engine armed with variable valve actuation method is unfettered from this constraint, permitting performance to be better over the engine operating range.
Piston engines usually use valves which are determined by camshafts. The cams open the valves lift for a certain amount of period throughout every intake and exhaust cycle. The control of the valve opening and closing is moreover significant. The camshaft is driven by using the crankshaft to control timing belts, chains.
An engine needs large amounts of air when functioning at high speeds. However, the inlet valves may close before sufficient air has arrived each combustion chamber and dropping performance of the engine. Otherwise, if the camshaft recalls the valves open for longer periods of time, as with a racing cam, problems jerk to occur at the lower engine speeds. This will cause unburnt fuel to exit the engine since the valves are still open. This leads to decreasing engine performance and increased emissions.
IV. Development Of Cam Profile:
Table 1: Development of cam profile Description Inlet cam Angle Existing cam data Inlet valve opening 44.63[degrees] Dwell 14.63[degrees] Inlet valve closing 45.36[degrees] Modified cam data Inlet valve opening 44.63[degrees] Dwell 14.63[degrees] Inlet valve closing 45.36[degrees] Description Exhaust Cam Angle Existing cam data Exhaust valve opening 43.9[degrees] Dwell 20.48[degrees] Exhaust valve closing 42.43[degrees] Modified cam data Exhaust valve opening 43.9[degrees] Dwell 20.48[degrees] Exhaust valve closing 21.21[degrees]
4.1 Design of Exhaust Cam:
The exhaust cam profile is slightly modified from the existing Cam. The forward stroke of cam is uniform velocity and return stroke motion of the cam profile can be modified by acceleration and retardation. The stroke of the follower is 8mm; base circle of the cam is 32mm.
4.2 Design Calculation:
Speed of cam, N = 3000rpm Angular velocity, [??] = 2[pi]N/60 rad = (2 x [pi] x 3000) / 60 = 314.15 rad/s
4.3 Modified exhaust cam:
Outstroke angle, [[THETA].sub.0] = (43.90 x [pi]) / 180 = 0.766 rad
Return stroke angle, [[THETA].sub.R] = (21.21 x [pi]) / 180 = 0.740 rad
Outstroke velocity, [V.sub.0] = [pi][??] / 2[[THETA].sub.0] = ([pi] x 314.15 x 0.008) / (2 x 0.766)
= 5.1536 m/s
Outstroke acceleration, [a.sub.0] = [[pi].sup.2] [??] / [[THETA].sub.0.sup.2] = ([[pi].sup.2] x 314.15) / (2 x [0.766.sup.2])
= 6640.12 m/s2
Return stroke velocity, [V.sub.R] = 2[??]S/2[[THETA].sub.R.sup.2] = (2 x 314.15 x 0.008) / (2 x 0.370)
= 13.58 m/s
Return stroke acceleration, [a.sub.R] = 4[[??].sup.2]S/[[THETA].sub.R.sup.2] = (4 x 314.[15.sup.2] x 0.008) / [0.370.sup.2] = 23068.56 m/[s.sup.2]
4.4 Displacement diagram of existing cam:
[FIGURE 1 OMITTED]
4.5 Velocity Diagram of existing cam:
[FIGURE 2 OMITTED]
4.6 Acceleration Diagram of existing cam profile:
[FIGURE 3 OMITTED]
4.7 Displacement diagram of Modified cam:
[FIGURE 4 OMITTED]
4.8 Velocity Diagram of Modified cam:
[FIGURE 5 OMITTED]
4.9 Acceleration Diagram of Modified cam:
[FIGURE 6 OMITTED]
4.10 Valve Timing Diagram:
[FIGURE 7 OMITTED]
4.11 Modeling of Cam profile:
[FIGURE 8 OMITTED]
4.12 Cad- Modeling of Cam Shaft:
[FIGURE 9 OMITTED]
4.13 Manufactured Cam Shaft:
[FIGURE 10 OMITTED]
V. Experimental Analysis:
Kirloskar engine is a 4-stroke, single cylinder, vertical diesel engine. The performance of the engine is calculated through the ratio of input (fuel) to the output (energy at shaft). The input and output of the engine could be measured by means of a fuel controlling arrangement, stopwatch and absorption type dynamometer.
The brake drum of the dynamometer is controlled by using a wire rope- wound around the drum with one end attached to a hanger and dead weights and the other end to a spring balance. The friction between the drum and rope could be altered by changing the net tension (difference between the weight and the spring balance reading), by tightening the spring balance end and by adding more dead weights. Due to friction heat is produced which is to be removed by circulating cooling water through the groove inside the drum. Finally by adding dead weights and tightening the spring balance end of the wire rope through the fixture arrangement, the load could be varied.
VI. Specification Of Ic Engine:
[FIGURE 11 OMITTED]
Table 2: Specification of IC engine Engine Kirloskar AVI Engine Type Single cylinder, vertical, four stroke, water cooled, Diesel engine Cubic Capacity 0.553 Ltr Bore 80 mm Stroke 110 mm Max power 3.7 Kw Compression ratio 16.5:1 Injection timing 23[degrees] before TDC Injection pressure 215.82 bar Speed 1500 rpm BHP 5 Specific fuel capacity 185+5%gm/hp-hr
RESULTS AND DISCUSSION
The emission test value can be measured from existing cam design and modified cam design. The exhaust stroke cam profile has changed for required position of the follower under acceleration and retardation motion. Thus the exhaust gas of emission was measured and compared for the two cases of the cam.
6.1 Carbon monoxide:
The Co level is decreased in modified cam engine as compared to the existing cam engine. The existing cam engine co level is 0.37% and the modified cam engine Co level is 0.35%.
6.2 Hydro Carbon:
The HC level is decreased in modified cam engine as compared to the existing cam engine. The existing cam engine HC level is 228 ppm and the modified cam engine HC level is 155 ppm.
The [Co.sub.2] level is increased in modified cam engine as compared to the existing cam engine. As a general rule, the higher the carbon dioxide reading, the more efficient the engine is operating. The existing cam engine [Co.sub.2] level is 2.5% and the modified cam engine [Co.sub.2] level is 2.7%.
The [O.sub.2] level is decreased in modified cam engine as compared to the existing cam engine. The existing cam engine [O.sub.2] level is 17.32% and the modified cam engine [O.sub.2] level is 16.73%.
The Lambdalevel is decreased in modified cam engine as compared to the existing cam engine. The existing cam engine Lambdalevel is 6.653% and the modified cam engine Lambdalevel is 6.237%.
6.6 Nitrogen Oxide:
The NoXlevel is decreased in modified cam engine as compared to the existing cam engine. The existing cam engine NoX level is 27 ppm and the modified cam engine NoX level is 21 ppm.
HCCI engine have shown great promise to reduce NOX emission while increasing efficiency the combustion process in an interesting alternative to the conventional spark ignition and compression ignition process. The work outlined in this project, the valve timing cam model was designed and generated by changing the existing cam profile to re-induct the exhaust gas partially in the cylinder since the level of NOX and CO was slightly decreased and fuel consumption can be controlled.
[1.] Mina Nishi, Masato and Norimasa Iida, 2016. "Assessment for innovative combustion on HCCI engine by controlling EGR ratio and engine speed" Published In Applied Thermal Engineering, 99(25): 42-60.
[2.] Emiliano and Giuseppe, 2016. K"NOX reduction and efficiency improvements by means of the Double Fuel HCCI combustion of natural gas-gasoline mixtures", Applied Thermal Engineering, 102(5): 1001-1010.
[3.] Gowthaman, S. and A.P. Sathiyagnanam, 2016. "Effects of charge temperature and fuel injection pressure on HCCI engine", Alexandria Engineering Journal, 55(1): 119-125.
[4.] Ming Asad and Jianxin Wang, 2015. "Investigation of butanol-fuelled HCCI combustion on a high efficiency diesel engine", Energy Conservation And Management, 98(1): 215-224.
[5.] Karthikeya Sharma, T., G. Amba Prasad Rao and K. Madhu Murthy, 2015. "Effective reduction of NOx emissions of a HCCI (Homogeneous charge compression ignition) engine by enhanced rate of heat transfer under varying conditions of operation", Energy, 93(2): 2102-2115.
[6.] Mohamed Djermouni and Ahmed Ouadha, 2014. "Thermodynamic analysis of an HCCI engine based system running on natural gas " Energy Conservation And Management, 88: 723-731.
[7.] Harisankar Benduand, S., Murugan, 2014. "Homogeneous charge compression ignition (HCCI) combustion: Mixture preparation and control strategies in diesel engines ", Renewable And Sustainable Energy Reviews, 38: 732-746.
(1) Selvakumar A, (2) Senthil M, (3) Prabhakaran V, (4) Pavithran S, (5) RakulprasathS, (6) Keshav S
(1) Assistant Professor, Department of Mechanical Engineering, knowledge institute of Technology, Salem, Tamilnadu, India.
(2) Associate Professor, Department of Mechanical Engineering, knowledge institute of Technology, Salem, Tamilnadu, India.
(3) UG Scholar, Department of Mechanical Engineering, knowledge institute of Technology, Salem, Tamilnadu, India.
(4) UG Scholar, Department of Mechanical Engineering, knowledge institute of Technology, Salem, Tamilnadu,India.
(5) UG Scholar, Department of Mechanical Engineering, knowledge institute of Technology, Salem, Tamilnadu, India.
(6) UG Scholar, Department of Mechanical Engineering, knowledge institute of Technology, Salem, Tamilnadu, India.
Received 25 April 2016; Accepted 28 May 2016; Available 5 June 2016
Address For Correspondence:
Selvakumar A, Assistant Professor, Department of Mechanical Engineering, knowledge institute of Technology, Salem, Tamilnadu, India.
Fig. 12: Co Level Co level Existing, 0.37 Modified, 0.35 Note: Table made from bar graph. Fig. 13: HC Level HC level Existing, 228 Modified, 155 Note: Table made from bar graph. Fig. 14: C[O.sub.2] Level C[O.sub.2] level Existing, 2.7 Modified 2.5 Note: Table made from bar graph. Fig. 15: [O.sub.2] Level C[O.sub.2] level Existing, 17.32 Modified 16.73 Note: Table made from bar graph. Fig. 16: Lambda Level Lambda Level Existing, 6.653 Modified 6.237 Note: Table made from bar graph. Fig. 17: Nox Level Existing, 27 Modified, 21 Note: Table made from bar graph.