Applied Research On The PM After-treatment Devices For In-use Diesel Vehicle

This paper draw on the successful experience of the diesel emission control project.The different after-treatment devices were installed in5light-duty diesel vehicle.In order to assess the adaptability and the reliability of the devices,the actual operation program of the vehicles was drew up.The gravimetric method and instantaneous concentration method were put forward to test and analyse the performance of the after-treatment devices.In order to study the reduction effect of different after-treatment devices to the diesel PM (particulate matter) emissions, the suitable diesel particulate filter(DPF) were installed on three Chinese3and one National4light-duty diesel vehicles while a POC(particle oxidation catalyst) was installed on a National4vehicle.Each vehicles completed approximately20000km mileage road running.At the10000km,the vehicles use the50ppm sulfur content fuel,then use the350ppm sulfur content fuel at the rest of the road haul.The emission factor and the concentration of PM2.5were tested when the vehicles finished5000km road haul.The emission factor(EF) of the diesel vehicle before and after the installation of the after-treatment devices by the existing regulation test. The result shows that, when the vehicles using50ppm sulfur content fuel the DPF filter efficiencies can over80%for PM,but the POC filter efficiencies can only get to30%.But when the vehicles use the350ppm sulfur content fuel,the PM will increase50%instead of being reducedjust only the filter efficiencies of some DPF can reach to20%.By the instantaneous concentration method, both number concentration and mass concentration of the PM are tested.The result shows that, the DPF filter efficiencies can reach to90%.Through the above research, we can get that the low sulfur content oil is necessary in the retrofitting to the PM emission of diesel vehicles.The number of the PM should be test when testing the PM emission of diesel vehicles with the after-treatment devices.The filtration efficiencies for the PM are researched after comparing the size distribution of both number concentration and mass concentration of the PM2.5 before and after the devices. Before the devices,the range of the PM number concentration of National3vehicles is about4.0×106to7.0×106per cubic centimeter,and the value of National4vehicle is about1.0X107/cm3.The PM2.5mass concentration have a large difference between the Chinese3vehicles,and it is larger than the value of National4vehicles which is about110mg/m3.After the DPF,the number concentration of PM is decreased by2to3orders of magnitude,and the mass concentration of the PM2.5of some vehicles is close to the level in the ambient air of the laboratory. The DPF filter efficiencies can reach to90%,and the filter efficiencies of POC will not more than50%. The number of the PM should be test when testing the PM emission of diesel vehicles with the after-treatment devices.In this paper,the test cycle was divided in to several intervals according to the speed and the acceleration of the vehicles.Then the PM25characteristics and the effect of driving conditions to the fliters efficiencies are researched. Under the medium speed and the medium acceleration,the fluctuation of the concentration of PM is small.Otherwise,the number of the PM will increase significantly under the high speed and the abrupt deceleration. The driving conditions have a significant impact to the conversion efficiency of POC,which is very low under the low speed and the abrupt deceleration.