| The particulate emission of automobile has always been the core concern of the industry.Compared with particles with larger particle size and quality,the number of particles with smaller mass and particle size is larger,which is more harmful to the environment and human body.The post injection strategy is a common technical means to reduce the particulate emissions of diesel engines,but the effect of the post injection strategy on the number of particles and the distribution of particle size is not clear.Therefore,this paper will focus on the evolution and variation rule of particle size and particle size distribution in post injection mode by means of bench test and numerical simulation.First,based on the experimental prototype of a four cylinder,the effects of the post injection quantity and different injection pressure on the emission characteristics of the engine particles are studied under two conditions of early and late post-injection.The test results show that: Keep the injection pressure constant,when the post-injection is early,the less post-injection fuel can make the particle quantity and mass concentration lower.And when the post-injection is lately,more post-injection fuel can make the particle quantity and the mass concentration lower.When the quantity of post-injection fuel is small,the particle number concentration and mass concentration is lower under earlier injection timing.When the quantity of post-injection fuel is large,it is lower under later injection timing.Under early post-injection timing and high injection pressure,the peak of particle number concentration curve appeared in the nuclear particle region.The peak of aggregation particles first increase and then decrease as the post injection quantity and injection pressure increasing.Secondly,based on the carbon smoke generation model of the detailed carbon smoke moment equation,an internal combustion engine simulation platform for particle simulation is set up,and the construction and calibration method of the simulation platform is proposed.Finally,using the simulation platform,single injection mode,post-injection mode and different post injection strategy were researched.The simulation results show that: the curve of total particles number shows double peaks under post-injection mode,while it has only one peak under single injection mode.Under post-injection mode,nuclear particle mass of the main-injection fuel is less than that under single injection mode,the nucleate particles of two injection are separated in space,the peak value of the aggregation particles is lower and the decrease is more rapid.When the post-injection fuel is large,the number of particles of main-injection is less while the number of particles of post-injection is more,surface growth and oxidation of soot are enhanced,the nucleation and condensation process are divided into two stages.When the injection pressure is high,no aggregation particle was observed during the process of particle form,the particle number peaks of main-injection and post-injection are both bigger than that under low injection pressure,the soot nucleation was enhanced.While the injection pressure is low,surface growth and oxidation reaction is dominant. |
