The Simulation Of Phenomenological Soot Model Based On Marine Engine

The problem of engine emission is the focus of industry,the emission regulations all over the world are becoming more and more stringent.Marine low speed two stroke diesel are now the main propulsion system of large vessels.In the Tier III emission regulations implemented by IMO in 2016,the emission of marine diesel has been limited.The particles matter as the main emission of diesel engine has received wide attention,and more and more soot models are build for describe the process of soot formation and oxidation.But the fuel used in the marine engine is mainly the high sulfur fuel oil which has complex physical and chemical properties,and the experiment of marine diesel need high cost compare to the numerical simulation method,which has high accuracy and low cost.According to this,this paper will study the soot emission of marine diesel by CONVERGE.With the complex physical and chemical properties and high sulfur content of diesel used in marine,which leading to there are no suitable mechanism for the marine diesel.And there are many research indicated that PAHs is the main species for soot formation.According to this,this paper will build a n-Heptane-PAH mechanism to describe the process of soot formation,and this mechanism will compare with the LLNL mechanism and the experiment data.After building the new mechanism,this paper couple the mechanism with the software CONVERGE to simulate the soot formation.In this step,this paper use three types soot models including empirical soot model,phenomenon soot model and detailed soot model.And the results of the simulation shows the curve of soot mass and number density is different,while the trend of the curves are similar.The results of soot mass shows that empirical soot model provide the smallest data and the phenomenon soot model provide the maximum data.But the results of detailed is the most reliable.And the empirical soot model results are only related to the in-cylinder pressure and temperature.Then this paper study the effect of soot emission with different properties of the fuel and SOI.And the results show that the soot mass and number density will increase when the properties of fuel change to DIESEL.And the results of PSM model shows that the soot size distribution is like Gaussian distribution,and the diameter of soot is almost under 20nm,while the average soot diameter is increase.With SOI increase,the in-cylinder pressure,temperature,indicted power,the emission of HC and NO_X are decrease,while the ISFC,the emission of CO₂,soot mass and number density are increase.And this paper study the UDF in the final,we modified the phenomenon soot model in UDF,and simulated the new model.After that,we compare the simulate results with the original soot model,which found there only some different in the soot precursor species and the soot mass and number density are decrease.In conclusion,this paper study the different soot model based on the marine diesel and study the UDF,which laid the foundation of build the mechanism for soot formation and oxidation of marine diesel and provide a theoretical basis for optimizing the soot emission.