Simulation On NO_x Emission Characteristics Of Catalyzed Diesel Particulate Filter

Diesel engines are becoming increasingly popular due to their excellent fueleconomy and efficiency. Motor vehicle pollution prevention in2013annual report byChina ministry of environment protection shows that the emissions of CO, HC, NOX, PMfrom diesel engine in2012are421.2million tons,93.9million tons,397.0million tons,and59.2million tons respectively in China, and these emissions are above14.7%,27.2%,68.1%and99%respectively in total of all vehicel emissions. Thus it can be seen that NOXand PM emissions from diesel vehicel which is only16.1proportion of car ownership arethe main source of pollutant. With the increasingly stringent emission regulations in China,more and more attention is paid on the diesel emissions and the atmospheric environment,it is becoming a hot research topic in recent years at home and abroad. The lots researchesshows that, the NOXand PM are the main pollutant in the diesel engine emissions. NO2ismuch more poisonous than NO in the NOX. The diesel engine install with catalyzed dieselparticulate filter (CDPF) due to the NO2/NOXemission is much more higher.Researching the formation and influence of the NO2/NOXemission for reduce theNO2/NOXemission from CDPF is a new subject. In this paper, the bench test of thecharacteristics on high pressure common rail diesel engine emission with CDPF is beenresearched, and a simulation model of CDPF is established and has been validated througha series of experimental comparison. Then the NO2/NOXemission formation has beenresearched. At last, the model of diesel engine has been established which combine withthe3D CDPF model.First, select10torque points from7speed from diesel engine bench test, there aretotally70operation points which to test the universal characteristic experiment. Throughthe emission test equipment, the emission from before and after CDPF are tested, and theresults are analyzed. The results show that, with the increase of loading, the NO2/NOXfrom engine exhaust is decreasing first and then increasing. The precentage of NO2/NOXfrom CDPF outside is significantly increased.Then, the validity of the model was proved by compared with the experiments. Thecontinuity regeneration process is simulated, the factors of oxygen concentration, exhausttemperature, space velocity, proportion of NO2/NOXand the soot mass fraction influencedthe exhaust NO2concentration from CDPF are studied. The results shows that the higheroxygen concentration might cause an increase in NO2/NOX; the NO2/NOXwillsignificantly increase when exhaust temperature at about350℃; space velocity might lead to higher NO2/NOXin a certain degree; this paper indicate that the increasing proportion ofthe NO2/NOXand the soot mass fraction in the exhaust will not significantly influence theNO2/NOXin the final exhaust, than assume that dynamic equilibrium relationship in CDPF.Finally, in order to better research and analysis the characteristics of mechanism onthe NO2/NOXemission from high pressure common rail diesel engine with thepost-processor CDPF, establish one dimensional simulation model of entire diesel engine,the simulation model is accuracy verified by power and exhaust temperature, then couplingwith the3D CDPF simulation model that has established before, the1D-3D jointsimulation model is bulited. Modify the model initial conditions such as different air inflow,fuel injection quantity and air-fuel, the ratio of NO2/NOXfrom before and after CDPF areresearched. The results are as follows: with the air inflow increasing, the oxygen content atthe combustion process in cylinder and engine exhaust are increased, due to the increase ofspace velocity, before and after the CDPF of NO2/NOXemissions are increasing. Althoughthe increase of fuel injection quantity lead to rich mixture, but relatively low oxygencontent, inhibits the generation of NO and exhaust temperature is higher, so the NO2/NOXemissions before and after the CDPF are falling. Increasing the air-fuel ratio in thesimulation, the combustion and exhaust oxygen levels are rising, and the filter elementairspeed to rise, make the NO2/NOXemission before and after the CDPF are increased.