Onediemensional Simulation And Experimental Study On The Knock Characteristics Of A Direct Injection SI Engine

The detection and suppression of knock is an important issue to be solved for all gasoline engines.As the knock indexes used in present knock detection are different and the determination of knock threshold value is with great randomness.So in this paper,different knock indexes arecompared and a more complete knock evaluation method is proposed.In addition,the three-dimensional model is the main method for the simulation of knock.But considering the calculation time and flexibility of the simulation model,it should be also paid enough attention to one-dimensional knock simulation.So the main work of this paper is from two aspects:develop the research on detection of knock based on a GDI engine;and the main control parameters,including equivalence ratio,compression ratio and intake temperature,of GDI engine were tested by both experiments and simulations.In experiment study,this article did some analysis to quantify the engine knock based on a modified single cylinder GDI engine,After filtering the in-cylinder pressure signal with band pass of 4-25kHz and setting the knock window of-20-60?A,This paper chose six common knock evaluation indexes for comparison,which include MAPO,IMPO,IMPG,average energy,DKI,maximum pressure rise rate of pressure oscillations.The change regulation with spark timing of different knock indexes and the distribution of knock indexes with different cycles were investigated.Results showed that except for DKI and maximum pressure rise rate of pressure oscillations,the other knock indexes can effectively distinguished the occurrence of knock;the distribution of IMPO and IMPG has a greater similarity,and cannot well distinguish the knock and non-knock cycles at the knock limit spark timing.And this paper also put up with the method to find knock threshold for single cycle,which utilized the distribution probability density of critical knock and non-knock conditions;and compared two knock evaluation methods:average value method and knock cycle proportion method,and found that the knock cycle proportion of MAPO has both small computational quantities and high accuracy to distinguish knock.In simulation study,the knock limit spark advance(KLSA)is simulated by GT-Power 1-D software in this article.After verifying the model,the influence of compression ratio,temperature and equivalence ratio on KLSA is simulated.Results revealed that with the increase of compression ratio and temperature,the knock tendency increases.When equivalence ratio is in 0.95-1.0,it has the highest tendency of knock.The result of the simulation is accord to the results of experiment and can be referenced somehow.Therefore,if the position of auto-ignition in end-gas region and the oscillation of in cylinder pressure are not necessary,1-D simulation is proper to carry out to predict the KLSA,which reduces the time period and calculation cost of knock prediction.