The Study On Simulation Of Knock Tendency On Gasoline Engine

In the background of energy shortage and environmental degradation, fuel economy has become a constraint to further development of gasoline engine which has been the primary power for passenger cars. In essence, the fuel economy is mainly limited by the compression ratio on gasoline engine, while knock limit the increase of compression ratio. Knock is an abnormal phenomenon of combustion which attracts a lot of attention during the operation of gasoline engine. Flame front becomes very irregular and flame speed increases rapidly during combustion when it occurs. It just causes some engine noise when it is not very serious, but serious problems happen such as head temperature rises and cooling system overheat and so on when it is very serious. This shows that the study on the suppression of knock is necessary and important.The author study the influence of various factors on knocking using CFD methods based on experimental measurements which was built on a gasoline engine. Firstly, a test system for the detection of knock was established to obtain the cylinder pressure signal of gasoline engine under different operation conditions and the characteristic of knock originates from the proceeding process of cylinder pressure signal. The cylinder pressure signal of the operation condition of WOT was chose for the contrast of knock tendency. Secondly, the model of flow field during the period of compression and combustion was built as well as the three-dimensional mesh of it. The comparison between the results of knock tendency from engine test and simulation for different spark-advanced angles and excess air ratios worked after the calibration for related parameters shows the validation for the simulation of knock tendency with the CFD methods. Finally, this paper studied the effect on knock tendency for different parameters such as intake pressure, intake air temperature, intake tumble ratio, ignition capability, duration of ignition and combustion chamber wall temperature and so on with the three-dimensional combustion model after calibration. According to the simulation results, intake pressure, intake air temperature, intake tumble ratio and ignition capability had greater impact on knock tendency, and duration of ignition and combustion chamber wall temperature on the knocking tendency is relatively weaker. In practical applications, cold air intake, lower intake tumble intensity, multipoint ignition system with proper duration of ignition, the cooling effect of moderate strengthening of the liner wall and other techniques can help to reduce the knock tendency on gasoline engine.