The application of diesel methanol dual fuel (DMDF) technology to diesel engines reduces nitrogen oxides (NOX) and particulate matter (PM) emissions, but increases hydrocarbons (HC), carbon monoxide (CO) and nitrogen dioxide (NO2) emissions in exhaust gas. The traditional diesel oxidation catalyst (DOC) under DMDF mode has the function to simultaneously reduce HC and CO, as well as to make NO2 be converted to nitrogen monoxide (NO). The modified DOC in this study is used to achieve high NO2 emission, which is favor for oxidation of carbon deposited on diesel particulate filter (DPF), and to improve its activity at low temperatures. All the tests were carried out on the DMDF engine bench. The effect of the property of DOC, the methanol substitution ratio (MSR), the DOC inlet temperature and the methanol dosing on the various emissions and temperature in cs16exhaust gas was studied. Results show that the addition of CeO2-ZrO2-La2O3-Pr2O3 promoters to DOC facilitates the formation of NO2 and improves its lowtemperature activity. The NO2 emission and the NO2/NOX increase as the MSR increases with the DOC inlet temperature from 170°C to 280°C. Compared to pure diesel mode, the high NO2/PM ratio after the DOC at DMDF mode means that the performance of passive regeneration for DPF can be improved. Meantime, the high exhaust temperature downstream of the DOC at DMDF mode is beneficial for the passive regeneration. But the temperature-rise of exhaust at DMDF mode is limited at high loads. The DMDF mode at low loads can improve the fuel economy caused by the active regeneration.
Keywords diesel methanol dual fuel engine, diesel oxidation catalysts, nitrogen dioxide, exhaust temperature