Experimental Study On The Effects Of Performance Of A Atkinson Cyclegasoline Engine

The Atkinson cycle which using Late Intake Valve Closing(LIVC) strategy through VVT(variable valve timing) mechanism was achieved in a1.6L gasoline engine by replacing thepiston of higher geometry compression ratio and the intake camshaft of longer intake duration.Comparativing analysis of external characteristic and universal characteristic have been madebetween Otto cycle and Atkinson cycle. Then we have studied the effects of the external EGR(Exhaust Gas Recirculation) on Atkinson cycle engine which includs fuel consumption,combustion characteristic in the cylinder and emission characteristics. We have also exploredthe strategy of the Atkinson cycle which can further reduce the fuel consumption through usingexternal EGR. Finally, we have provided the data support of supercharging miniaturizationthrough studying the effects of the simulated supercharging on Atkinson cycle engine, whichincluds dynamic performance, fuel consumption and combustion characteristic in the cylinder.At full loads points, Atkinson cycle engine has better fuel economy but excellent dynamicperformance which is almost as the same as the Otto cycle engine through more intake valvetiming advance. The BSFC (Brake Specific Fuel Consumption) of Atkinson cycle engine islower than the Otto cycle engine at all operating points,especially in the regions of the low loadat medium speed, medium to high load at medium to high speed and high speed, which havebeen improved obviously. The area covered by250g/(kW h) contour line of Atkinson cycleengine is almost twice bigger than the Otto cycle engine. The main reasons why Atkinson cycleengine has better fuel economy is that the higher effective compression ratio and effectiveexpansion ratio which improve the thermal efficiency.A moderate amount of EGR can improve the fuel economy of Atkinson cycle engine.Three loads (0.2MPa,0.4MPa,0.6MPa; BMEP) at the speed of2200rpm have been selected.The optimal EGR ratios of these three operating points are5%,10%,15%and the BSFCdeclines0.94%,1.34%and2.17%. When the circumstance of adopting MBT(Minimum sparkadvance for Best Torque),and the load increases, the tolerance for EGR of Atkinson cycleengine gradually have been enhanced. A higher EGR ratio results in a higher maximumcylinder pressure, but the peak of heat release ratio declines. The corresponding crank angle ofthe maximum cylinder pressure and the peak of heat release ratio in advance as the EGR ratiohas been increased. The ignition delay and combustion duration have extended because ofintroducing the EGR, but the corresponding crank angle of CA50at different EGR ratios havelittle changes. The introduction of EGR shows different effects on emissions, NOx emissionsdrop significantly and HC emissions increaseswhen the EGR ratio has been increased, but COemissions have been seen some fluctuation. The torque and power of Atkinson cycle engine’s external characteristic have increasedsignificantly because of the increasing air inflow by supercharging. At the same timeit hasturned the pumping work to be positive and has improvedthe combustion characteristics bysupercharging, the fuel economy of Atkinson cycle engine’s external characteristic has beenimproved. Meanwhile the load characteristic at the speed of3000r/min has beenimprovedthough the air inflow has been reduced slightly. The largest declines of BFSC is1.65%and2%at30kpa and40kpa when the load is0.6MPa.