Bench test of regeneration characteristics of catalyzed diesel particulate filter based on fuel injection combustion system

Abstract: In order to provide technical references for upgrading emissions of existing vehicles, to meet the four-stage emission limitation requirements of non-road mobile machineries, based on the self-developed fuel injection combustion active regeneration system, the external characteristic tests of diesel engine with diesel particulate filter(DPF) and the active regeneration combustion tests were carried out in this paper. The results showed that the catalyzed diesel particulate filter (CDPF) with 530 g/m3 catalysts loading, name as CDPF1, has little effect on the power and economy performances of the engine under external characteristic conditions. At 3 000 r/min, the volume fraction of NO2 is 81×10-6 at front end of CDPF1, while it is increased by 33×10-6 at rear end of that. This indicates that with the action of Pt and Pd bimetallic catalysts, the binding rate of NO to exhaust O2 is higher than the rate of active oxygen dissociated from NO2 binding to the soot active sites. Adequate NO2 content promotes regeneration efficient of soot in the CDPF, therefore the maximum exhaust pressure difference of CDPF1 was 8.8 kPa which lower than that of DPF. On the basis of external characteristic tests, the active regeneration tests of fuel injection combustion was further carried out. The first part of the regeneration tests were carried on the combustion test bench, the combustion temperatures were controlled by dosing control unit (DCU) to be 550, 600 and 630 ℃, respectively. In order to prevent the peak temperature and thermal stress in the carrier from being too high during regeneration, secondary gas supply was carried out after fuel injection. Based on the principle that the amount of the secondary gas supply matches with displacement of the test engine, 4 different secondary gas supply schemes were adopted. The experimental results showed that when the regeneration temperature was 630 ℃, the regeneration efficiency of CDPF1 reached 96.4% in the absence of secondary gas supply, however, the regeneration efficiency of DPF was only 84.3%. In addition, the maximum temperature of CDPF1 carrier was also lower than that of DPF during regeneration, and the highest temperature of CDPF1 was about 31 ℃ which lower than that of DPF at 630 ℃. It can be seen that CDPF1 could not only improve the regeneration efficiency, but also reduce the maximum temperature in the carrier. When regeneration temperature was 600 ℃, the secondary gas supply scheme 4 was adopted, i.e. the secondary gas supply rate was 1.25 L/s for 180 s, then the gas supply rate was 0.625 L/s for 420 s, and the regeneration efficiency of CDPF1 was 83.2%, the maximum temperature was reduced by about 64 ℃ compared to the absence of secondary gas supply. The second part of regeneration tests were carried out on engine test bench, and the regeneration temperature was still 600 ℃. The regeneration characteristics of DPF, CDPF1, CDPF2 and the CDPF2 with 636 g/m3 catalysts loading were tested under engine stop and idle speed regeneration conditions. The test results showed that CDPF1 had a good regeneration performance, with regeneration efficiency was 76.4% for engine stop regeneration, the idle regeneration efficiency was increased to 88.5%. This was because that the secondary air into the combustion chamber was cold for engine stop regeneration, and the engine exhaust with higher temperature was introduced into the burner for the idle regeneration, the secondary air was combined to improve the burning rate of the fuel in the burner, at the same time, high temperature gas would burn more soot at a faster rate, and the combustion efficiency of the idle condition regeneration was improved. The pressure difference of DPF, CDPF1 and CDPF2 was tesed under 3 000 r/min speed and 100% load conditions. Since the amount of residual soot in the carrier was less after the idle regeneration, the pressure difference of DPF, CDPF1 and CDPF2 after idle regeneration were lower than that of engine stop regeneration. The pressure difference of CDPF1 was about 27 kPa after engine stop regeneration, and the final pressure difference was reduced to 25 kPa after idle regeneration. This study showed that the combination of active and passive regeneration of catalytic CDPF can integrate the advantages of the both, in future research, the active regeneration strategy based on catalytic conditions can be formed by further optimizing the catalytic load and regeneration timing, combining with exhaust heat management technology, and provide a reference for the upgrading and transformation of exhaust emissions of vehicles in use and the realization of the fourth stage emission standards of non-road mobile machinery.