A Study On Knocking Combustion In A Rectangular Constant Volume Bomb

It is extremely difficult to explore the effect of single-factor on knocking due to the complexity of knocking phenomenon on the engine.This paper conducts investigations on knocking phenomenon using a 3-D Computational Fluid Dynamics(CFD)model based on a rectangular constant volume bomb.The model uses a G-equation combustion model and is coupled with simplified chemical kinetics.The purpose of this study is to to examine the influence of independent variable on the knock occurrence boundaries,the knocking intensity and the end gas self-ignition model for premixed n-heptane/air.The initial pressure,the initial mixture temperature and the end wall temperature was set as the independent variable.The results are as follows.1)The initial temperature and the initial pressure are key parameters for the occurrence of knocking,however,the influence of the end wall temperature is relatively weak.If the initial pressure lower than 0.25 MPa knocking does not happen when the initial temperature and the end wall temperature vary from 300 to 700 K.Similarly,knocking does not happen with the initial pressure varying from 0.2 to 0.5 MPa and the end wall temperature varies from 300 to 700 K if the initial temperature lower than 450 K.2)With the increase of the initial pressure and the initial temperature,the knock occurrence advances and the knock intensity rises.On the knocking condition,the maximum pressure amplitude stable at a value when the end wall temperature vary from 550 to 700 K,the maximum pressure amplitude will be decreased and the knock intensity will be reduced when the temperature is increased to 1000 K.3)The end wall temperature is the key parameter influencing the end gas self-ignition model,the influence of the initial pressure and the initial temperature is relatively weak.4)The results imply that the maximum amplitude of pressure oscillation during knocking can be used as an indicator to judge knocking occurrence,the appropriate value of which is 0.02 MPa in this work.Finally,the effects of initial pressure as independent variable on the flame front characteristics are studied base on the rectangular constant volume bomb experimental system by high-speed camera.It also verify the validity of the simulation results with the flame front.