Numerical Simulation Research On Combustion And Emission Characteristics Of Diesel-Natural Gas Dual Fuel Engine

At present,most transport power equipments are powered by internal combustion engines,and it is everywhere.On the one hand,the world's oil resources increasingly depleted,on the other hand,some countries take more and more obvious containment policy to our country,our country's oil lifeline increasingly tense.The development of clean energy which can replace oil can not only reduce pollution and protect the environment,but also has important strategic significance to our country.As a hot spot of alternative energy resource,natural gas is not only a less polluting product,but also a rich resource.In this paper,the CONVERGE is used to simulate the working process of diesel-natural gas dual fuel engine.The effects of different natural gas substitution rates and different injection strategies on combustion and emission characteristics of engine were compared and analyzed.And the optimization scheme is obtained.Simulation modeling for TBD620 diesel engine,including geometric modeling,grid division,calculation of parameter configuration.And combined with the experimental data under a certain condition,completed the calibration of the simulation results and the analysis of the mesh independence.The validity of the model is verified.At the same time,the multi physical fields such as cylinder pressure,temperature,flow field and fuel concentration distribution were analyzed and summarized.The causes and emission of main pollutants such as SOOT,NO_x,HC,CO,CO₂ were also analyzed and summarized.Using the validated model.Base on equivalent calorific value,replace part diesel oil with natural gas,and the simulation of working process of diesel dual fuel engine was carried out.According to the calculation results and the combustion condition of the pure diesel mode,the combustion characteristics of dual fuel engine in cylinder pressure,temperature,heat release rate and fuel concentration distribution were analyzed when the natural gas substitution rates were 50%,60%,70%,80%and 90%,respectively.Emission aspects,combined with pure diesel mode,the formation and emission of NOx,HC,CO and CO2 emissions from dual fuel engines with different natural gas replacement rates were compared and analyzed.Combine the present situation of diesel engine fuel supply system,based on the working condition of natural gas substitution rate of 60%.Study on the effect of different multi injection strategies on engine performance,with the pre injection timing,the main injection timing and the pre injection mass proportion of the twice fuel injection strategy,the triple injection strategy and the post injection mass proportion of the triple injection strategy as variables,research effect of these variables on combustion and emission characteristics of engine.In the end,a practical conclusion of optimization is obtained by combining the multiple injection strategy with different natural gas substitution rate.Research shows that with the increase of natural gas replacement rate,the combustion efficiency will be deterioration following improvement,and the replacement rate threshold will be changed under different fuel injection strategies.According to the results of this study and comprehensive consideration.When the natural gas replacement rate is 80%under the twice fuel injection strategy,it can not only substantial replace the diesel,but also maintain the power level similar to that of the original engine.At the same time,the emissions acceptable.