Numerical Simulation Study On Combustion Characteristics Of CNG-ID Engine

As a substitute fuel for automobile engine,natural gas provides a new direction to solve the problems of shortage of traditional fuel and environmental deterioration in the development of internal combustion engine industry because of its rich resources and clean combustion.The engine technology of natural gas has also been developed rapidly,but as a gas fuel,the shortcomings such as poor power performance of natural gas engine need to be solved thoroughly.Based on Visual study on Combustion process of CNG-ID Optical prototype and basic parameters of 2.0TCI DI Diesel engine in Prophase,a three-dimensional numerical simulation model of CNG-ID engine is established.In-depth study on the variation of in-cylinder flow field,Concentration field,pressure field,flame propagation,temperature field and NO production rate on double-ignition CNG-ID engine,when Change the relative position of double ignition and double ignition timing,and analysis of the effects of different double ignition modes on engine combustion process and emissions.then study on the trend of combustion process and NO emission of CNG-ID engine under different rotation speeds when using double ignition.To provide an effective way to enhance the combustion performance and improve the emission of CNG engine.The results show that:The combustion time of mixture can be shortened obviously by double ignition.However,the process of mixture combustion is different by different ways of double ignition.The effect on the mixture combustion process and NO emission is different.(1)Increasing the relative position of double ignition could accelerate the flame propagation in the combustion chamber,which then strengthen the combustion heat release and the increase rate of the average pressure in the cylinder,but the final NO emission increases with longer the duration of high temperature region.(2)the earlier of the first ignition timing the earlier mixture combustion,but the change of heat release law and average pressure rise rate in cylinder is not obvious,and the final NO emissions are almost unchanged because of the duration of the high temperature zone is constant.However,the overall flame propagation rate decreases,which make the heat release law center of gravity and the maximum burst pressure lags behind when the ignition time is delayed,and the time lag of the establishment of high temperature field results in a significant decrease in the final NO emission due to the shortening of NO generation duration.(3)With the increase of rotating speed,the flow field distribution of the mixture develops unevenly,which is not conducive to the stable flame propagation.However,the combustion time of the mixture is very short when the dual ignition mode is adopted,so the change of the rotational speed has little effect on the combustion stability of the CNG engine.However,the shortening of absolute duration of the temperature field and concentration field to meet the NO production reduce the final NO emission by a large margin with the increase of rotational speed.(4)NO production mainly depends on the range of concentration field and temperature field.When the temperature is fixed,the rate of NO production increases with the equivalent ratio closing to 0.93~0.97,and the rate of NO formation increases with the increase of temperature when the concentration is fixed firstly,then is less affected by the change of temperature when the temperature is higher than 2700 K.