The Research On The Characteristic Of Charge-Temperature Distribution With Residual Gas Recompression Strategy

The HCCI combustion(also named CAI combustion)is widely researched because it could improve the fuel economy and reduce the NOX at the same time.The CAI/HCCI combustion is achieved by the fully variable valve event and the valve parameter is one of the most important control methods to the CAI/HCCI combustion which could adjust the charge composition,temperature and the distribution.The controllability of the valve parameter on the charge composition(the residual gas and the fresh charge)is applied to the engine.But the effects of the charge and temperature distribution on the CAI/HCCI combustion are also important.Therefore,the article has researched the in-cylinder charge and temperature distribution and its effect on the combustion process with different valve parameter and injection strategy.The charge and temperature distribution and their effects on the combustion are more complex and harder to measure.The research has been done on the optical engine platform and the laser measurement technology is used as the main approach combined with the simulation and engine test.The article has studied the in-cylinder flow field with the residual gas recompression strategy and the effects of valve parameters on the in-cylinder flow;the fuel stratification at the end of the compression stroke with different fuel injection method and their effects on the combustion;developing the single-line dual tracer temperature measurement technology to measure the temperature distribution.The results show that the large-scale tumble motion in the intake process with the residual gas recompression strategy is located at the exhaust valve side.After the intake valve is closed,the tumble motion is broken down.The tumble motion is the key parameter to the imhomogeneity of the fuel distribution at the PFI condition.The effect of intake valve parameter on the tumble ratio is decided by two factors: the intake valve peak phase(IVP)and the intake valve lift.Earlier IVP and higher intake valve lift are benefit to get higher tumble ratio which would result in getting homogeneous fuel distribution.The charge imhomogeneity could advance the ignition time and prolong the combustion duration.The effect is obvious at the low load with PFI condition.At the late injection strategy of the direct injection,the in-cylinder flow plays theguidance role on the fuel distribution.The imhomogeneity of fuel distribution is decided by the mixing time and spray structure.The injection time can effectively control the combustion phase by the fuel stratification but the later injection time would bring higher cycle-variation.The valve parameters could be adjusted to alter the backpressure which could adjust the imhomogeneity and cycle-variation of the fuel distribution.The single-line two tracers PLIF temperature measurement is developed which is used to measure the temperature distribution of the residual gas recompression strategy.The result shows that the temperature distribution is inhomogeneous and the front backflow can't change the temperature distribution at the end of the compression stroke.