Study On The Working Process Optimization And Fuel Economy Performance Of An Otto-Atkinson Cycle Engine

Energy and environment crisis have led to more strict emissions legislation andfleet CO2targets demand for vehicle engines. Gasoline direct-injection and lean burn,gasoline engine downsizing, hybrid electric vehicle and many other technologies arebeing developed for higher engine fuel economy. Atkinson cycle is widely usedcombined with other technologies by different degree, for owning a higher thermalefficiency compare to Otto cycle.This paper investigated the working process optimization and engine performanceof an Otto-Atkinson cycle engine base on variable valve timing (VVT) and highcompression ratio technologies using a1.6L gasoline engine. The objective is toimprove the fuel economy in part load condition with the Atkinson cycle whilemaintain the full load torque with the Otto cycle.First, a simulation of effects on Otto-Atkinson cycle engine by parameters wasdone using a one-dimensional model set-up with GT-power. The main parametersunder simulating include intake-valve closing timing, intake duration and geometrycompression ratio. Base on the simulation result, an Otto-Atkinson cycle engine wasachieved by replacing the piston and intake camshaft of the baseline Otto cycle engine.Several experiments of full load and part load conditions by both engines have beendone. A set of conclusions can be made by comparing experiment results of thebaseline Otto cycle engine and the reformed Otto-Atkinson cycle engine. Compare tothe baseline Otto cycle engine, the full load torque of the Otto-Atkinson cycle engineis nearly the same except for a decrease of2%-5%in low speed under2000r/min.however the average fuel economy improvement is about5%at full load condition.Fuel economy improvement in part load condition area is about4%-10%except forvery low load condition. And the improvement is most significant in low and mediumload conditions which are used commonly in a passenger car. The improvement ofthese conditions are larger than8%. More deeply conclusions can be made with theanalysis of the combustion characteristics in the cylinder. By using the late intakevalve closure strategy，the Otto-Atkinson cycle engine significantly reduced pumpingloss, thus improve the fuel economy. By increasing the expansion ratio andoptimizing the effective compression ratio, the Otto-Atkinson cycle engine improves the combustion characteristics and reduces energy loss in the exhaust gas. The intakevalve closing timing can be more delay to achieve low pumping loss in low andmedium load condition. But it is recommended for more intake valve timing advanceto achieve enough air-intake in high load condition and avoid worsen the combustioncharacteristics in very low load condition.