Modeling And Simulation Research On DOC Of Diesel Engine Aftertreatment System With Hydrocarbon Dosing

With the tightening of diesel engine emission regulations,diesel engine exhaust after-treatment systems have been continuously upgraded.The DOC+DPF+SCR technical route has become the standard configuration of the after-treatment system.When this technical route is applied,exhaust thermal management is required to increase the exhaust temperature.Diesel Particulate Filter(Diesel Particulate Filter,hereinafter referred to as DPF)regeneration and maintaining the catalyst activity of the entire system.Hydrocarbon tailpipe injection technology is an important exhaust heat management technology.It injects diesel in front of the diesel catalytic oxidizer(Diesel Oxidation Catalyst,hereinafter referred to as DOC),so that the diesel is catalyzed and oxidized in the DOC to release heat to improve exhaust temperature.The research and study of the DOC model using hydrocarbon tailpipe injection technology can not only provide a simulation platform for the development of subsequent temperature control strategies,but also can use model simulation to study the reaction characteristics of DOC during hydrocarbon tailpipe injection,which is a good example of temperature control strategies.The development provides a basis and evaluates the influence of hydrocarbon tailpipe injection on the conversion rate of NOx and CO in DOC.The model study is carried out in two steps.The first is to study the reaction kinetics model of C3H6,CO and NO by establishing a sample DOC catalyst model,and conduct sensitivity analysis of the model,eliminate the items in the model that have no effect on the reaction rate,and reduce the model And use the simulated gas flow experimental data to identify the parameters in the model and verify the model.Then build a full-scale DOC catalyst model based on the sample DOC catalyst model,simplifying the evaporation and pyrolysis process of diesel into two steps.The first step is to vaporize and pyrolyze the small molecule hydrocarbon C3H6,and the second step is to vaporize heat.Solve the macromolecular hydrocarbons DF1 and DF2,establish the oxidation model of macromolecular hydrocarbons,and use the engine bench test data to identify the model parameters and verify the model.When verifying the two models,it is found that the maximum transient error is below 8%,indicating that the obtained DOC model has high accuracy.Using the obtained full-scale DOC model to simulate the reaction characteristics of DOC during hydrocarbon tailpipe injection,the following conclusions are drawn.The results of studying the exhaust gas temperature to the HC conversion rate show that when the exhaust gas mass flow rate is 200kg/h,when the exhaust gas temperature is lower than 250℃,the HC conversion rate is very small;when the exhaust gas temperature is in the range of 250-330℃When the temperature increases,the HC conversion rate begins to rise with the increase in temperature,and the rising speed is very fast;when the exhaust temperature is higher than330℃,the HC conversion rate remains above 90%,close to 100%;study the effect of exhaust flow on HC conversion The results show that: the exhaust flow rate has a relatively large impact on the HC conversion rate.With the increase of the exhaust flow rate,the HC conversion rate drops sharply;the results of studying the effect of HC concentration on the temperature rise rate of the DOC outlet show that: There is a linear relationship between the amplitude and the HC injection amount.Exhaust temperature and HC injection volume have a greater impact on the DOC outlet temperature rise rate.With the increase of HC injection volume and exhaust temperature,the DOC outlet temperature rise rate increases.When the exhaust temperature reaches 350℃ or higher,the DOC The peak temperature rise rate of the outlet reaches the maximum value and remains constant;the results of studying the NO2 generation rate of DOC outlet by HC injection show that: HC injection has a greater impact on the NO2 generation rate of DOC outlet.With the increase of HC injection volume,DOC The NO2 generation rate at the outlet decreases;the results of studying the conversion rate of HC injection to CO at the outlet of DOC show that: when HC injection is not performed,DOC has a higher conversion rate to CO.With the increase of HC injection,the conversion rate of DOC to CO Gradually decreases.