Numerical Simulation Of Knock Combustion In Gasoline Compression Ignition Engines

Under the pressure of severe ecological and energy problems,it’ necessary to develop clean and efficient combustion models.Recent studies shown that through certain auxiliary means and corresponding injection strategies,gasoline compression ignition can be achieved.The gasoline Partial Premixed Compression Ignition(PPCI)has the lower SOOT emission under the higher thermal efficiency.In this paper,the gasoline compression ignition knock was simulated by using CONVERGE.First,based on the experiment of gasoline compression ignition in a naturally aspirated diesel engine,established a 3D CFD model.The KI(Knock index)was used to characterize the knock intensity,and the KI threshold for the engine knocking was given in the simulation according to the experimental knocking boundary.Discussed the relationship between the formation and consumption of OH and HCO and combustion process and knock intensity.The analysis of knock intensity under different injection quantity and injection advance angle is as follows.With the increase of injection advance angle,the normal combustion state is gradually changed into knock combustion state,and the knock intensity is also increased.At a lower fuel injection volume,the knock intensity shows greater tolerance for the increase of injection advance angle.When the injection advance angle is small,the equivalence ratio in the concentrated region is greatly affected by the injection quantity,and the knock intensity changes greatly.When the injection advance angle is too large,the proportion of premixed gas increases,and the change of injection quantity has little effect on the equivalence ratio of premixed gas with wide distribution,and the change of detonation intensity with the increase of injection quantity is small.These shows that the proportion and equivalence ratio of premixed combustion part and diffusive combustion part have an important relationship with the occurrence and intensity of knock.Then,this paper studied the influence of intake air temperature and fuel injection strategy on knock intensity.The result show that at higher loads,lower intake air temperature can effectively reduce the in-cylinder knock intensity,but will significantly delay ignition time and reduce IMEP.Then adjust the fuel beam angle and the fuel injection advance angle under a single injection.When the fuel beam angle is 150 °,it has a lower knock intensity and higher IMEP,reduce the fuel injection advance angle can effectively reduce the knock intensity,but will delay ignition time.While two injection can optimize the problem of ignition difficulty in gasoline compression ignition,IMEP has increased,but its knock intensity also increased.Finally,this paper explored the realization of gasoline compression ignition on supercharged engine.The results show that under the intake pressure boost,the problem of ignition difficulty of gasoline compression ignition is properly resolved,and the in-cylinder water injection strategy makes the knock intensity significantly reduced.With the increasing development of engine control technology,the control of gasoline compression ignition and the realization of efficient and low emission combustion are also become easier.