Experimental And Numerical Study On CAI Combustion Based On Dual Exhaust Valve Opening Strategy

Controlled auto-ignition (CAI) is a combustion mode of engine, That is a greatconcern in the world now, Controlled auto-ignition has a better thermal efficiency thantraditional diesel. It can greatly reduce emission of CO、NOx and Particle. There aremany of methods to achieve, it has become the mainstream of the development ofengine combustion, it is very promising. This article is based on simulation andexperimental study of the second exhaust valve event.Simulation study: We mainly use the one-dimensional simulation softwareGT-Power, large chemical kinetics simulation software the AURORA module inCHEMKIN, and MATLAB software, these software set up the computer simulationplatform for the CAI engine, GT-Power and CHEMKIN software are introduced, theparameters in the GT-Power is setting according to the modified ZS1105engine. Theengine is fitted with electro-hydraulic cam-less valve train, it is used to achieve variableengine valve phasing and valve lift. Simulation method and simulation process are alsointroduced, we use two variables of intake valve opening angle and the second exhaustvalve opening angle. The engine speed is1000r/min, λ=1, changing two variables ofintake valve opening angle and the second exhaust valve opening angle are obtainedby EGR（Exhaust Gas Recirculation）, IMEP and the related simulation parameters.The result of simulation, the first exhaust valve opening angle (EVO) is223°CABTDC(Before Top Dead Center), the first exhaust valve closing angle(EVC) is21°CABTDC. Double exhaust valve open is from18°CA ATDC to40°CA ATDC, Doubleexhaust valve close is182°CA ATDC (After Top Dead Center). Intake valve openingangle is from26°to61°CA ATDC, Intake valve closing angle is205°CA ATDC. Thisrange can be stabilized combustion. EGR rate is from37.7%to61.8%.Experimental study: experimental engine is modified from ZS1105single-cylinderengine, in order to CAI combustion, we do the following modification,1reducing thecompression ratio of the engine,2we put the supply system of diesel engine into thesupply system of gasoline engine,3changing the cooling system,4removing the valvetrain of the engine, installing electro-hydraulic cam-less valve train. The experimentalresults, the first exhaust valve opening angle (EVO) is223°CA BTDC(Before Top DeadCenter), the first exhaust valve closing angle(EVC) is21°CA BTDC. Double exhaustvalve open is from18°CA ATDC to40°CA ATDC, Double exhaust valve close is182°CA ATDC (After Top Dead Center). Intake valve opening angle is from26°to61°CA ATDC, Intake valve closing angle is205°CA ATDC. EGR rate is from38.5%to 57.7%.The conclusion of the experiment and simulation are as follows. The mainparameters of CAI combustion change within the prescribed limits. But in experimentthe conditions of effective combustion is very complex. In the simulation model we cannot do it. So the range of CAI combustion in the experiment is wader than in thesimulation. In the experiment exhaust valve opening angle is from18°to43°CA ATDC.In the simulation exhaust valve opening angle is from18°to40°CA ATDC. It is adifference of3angles. In the experiment the maximum of EGR is57.7%and theminimum of EGR is38.5%. In the simulation the maximum of EGR is61.8%and theminimum of EGR is37.7%. The difference does not affect the experimental results.The parameter variation of CAI engine stability combustion is following: thetemperature of the exhaust increase (or lower). Directly affect EGR lower (orincrease).The air of mixture gas in cylinder increase (or lower). IMEP (Indicated MeanEffective Pressure) increase (or lower).Maximum press in cylinder increase (or lower).Combustion starts advance (or delay).Burn duration shorter (or longer). Combustion incylinder intense (or moderate).