Experiment And Simulation Research On VOCs During DPF Regeneration Of Diesel Engine

Volatile organic compounds(VOCs)have serious hazards to the environment and the human body,many of which are classified as toxic and harmful air pollutants and carcinogens.Motor vehicles have become one of the main sources of VOCs in the urban environment.Compared with gasoline engine,the emission of VOCs from diesel engine with oxygen enriched combustion in cylinder is not taken seriously.The contribution of diesel vehicle to VOCs is not taken into account when formulating "The Technical Guide for Compiling Air Pollutant Emission Inventory of road Vehicles".Studies have shown that the VOCs in diesel engine exhaust increase significantly in DPF regeneration stage.With the implementation of the China VI standard for diesel vehicles,DPF has become one of the necessary post-processing technologies for diesel vehicles,and the DPF of diesel vehicles needs to be regenerated 1-2 times a day,lasting 0.5-1 hour on average.Therefore the emission of VOCs in DPF regeneration stage can not be ignored.This paper takes the VOCs generated in the DPF regeneration stage of a China VI diesel engine as the main research object,the main research contents completed are as follows:(1)The emission characteristics of VOCs in DPF regeneration stage of China VI diesel engine were analyzed.Based on the engine test bench,the emission characteristics of VOCs in DPF regeneration stage were studied,and it was found that the VOCs in the exhaust gas of the DPF regeneration stage increased significantly,the total emission of VOCs was 4 times of that in the non-regeneration stage,and the emission of toxic components(formaldehyde,acetaldehyde,benzene,toluene,ethylbenzene,xylene,styrene)was 2 times of that in the non-regeneration phase.Using VOCs emission factors and air pollutant generation potential to quantify the VOCs emitted in DPF regeneration stage,it was found that although the above seven VOCs accounted for only 22.3% of the total VOCs emissions,their contribution rates to ozone and secondary organic aerosol generation potential were 60% and 28.6%,respectively.(2)The simulation model of VOCs toxic components was constructed.The "DOC +DPF + SCR" exhaust after-treatment model was built by AVL BOOST simulation software,and seven VOCs toxic components generation paths based on n-heptane oxidation model were coupled to build VOCs toxic components generation simulation model.The parameters in the chemical reaction kinetic equation were identified by bench test results,and the relative error of VOCs toxic components generation was controlled within ± 15%.(3)Study on the influencing factors of toxic components of VOCs.The DOE method is used to design the simulation test.Based on the simulation test data,the influence of six factors such as exhaust gas temperature and exhaust gas flow rate on VOCs toxic components was explored.It was found that exhaust gas temperature,exhaust gas flow rate and regeneration fuel injection rate were the main influencing factors of VOCs toxic components in DPF regeneration stage.In addition,the emission of aldehydes is more sensitive to the exhaust gas temperature,and the emission of benzene series is more sensitive to the amount of regeneration fuel injection.Finally,the optimization suggestions for DPF regeneration control strategy are put forward according to regeneration time and injection quantity.In this paper,bench test,theoretical analysis and numerical simulation were used to analyze the emission characteristics of VOCs in DPF regeneration stage,and quantified the pollution degree of VOCs in DPF regeneration stage;a simulation model of VOCs toxic components generation was established;based on the model,the influence rules and main influencing factors of seven VOCs toxic components were explored,and then some optimal suggestions for DPF regeneration control strategy were put forward.