Experimental Study On DMCC Engine For Conforming Euro Iv Emission Standard And Its Road Running Test

Under both pressures of the increasing oil security and environmental pollution, governments around the world formulate the increasingly stringent emission regulations. Currently, there are still some difficult in using SCR or DPF to meet EuroⅣ emission standard in China. Due to its high oxygen content, single-carbon structure, and smokeless combustion, methanol is a kind of clean alternative diesel fuel. Previous research showed that diesel/methanol compound combustion(DMCC) could greatly reduce the diesel consumption and improve the smoke and NOX emissions, which are far-reaching significance to energy-saving and emission reduction. But most of previous works were based on naturally aspirated mechanical pump diesel engines, and whether diesel/methanol dual fuel(DMDF) engine can reach EuroⅣ standard has not been sudied.In this study, the effects of different methanol substitution ratios, injection parameters, inlet temperatures and exhaust backpressures on combustion and emission characteristics were experimentally studied on the modified electronic-controlled turbocharged intercooled diesel engine, and the potential ultra-low emissions of DMDF engine was also investigated. Furthermore, road test of DMCC vehicle was also carried out in this study, which could provide the theoretical foundation for the actual promotion. The main conclusions are obtained as follows:Firstly, combustion characteristics of DMDF engine were investigated according to the variation of substitution ratios, injection parameters, inlet temperatures and exhaust backpressures. Results showed that the ignition delay and COVIMEP increased, the position of peak cylinder pressure moved away from top dead center(TDC) with the increase of substitution ratio(SR). The increase of inlet temperature shortened the ignition delay period, advanced the ignition time, and improved the brake thermal efficiency(BTE), and the increase of exhaust backpressure advanced the start of DMDF combustion, decreased the peak cylinder pressure and BTE. The high inlet temperature or exhaust backpressure could lead to the methanol auto-ignition before diesel injection at high load, which could weaken the combustion, soot emission and BTE. As the injection timing advanced and injection pressure increased, the ignition time advanced, the amount of premixed combustion, the peak cylinder pressure and heat release rate, and BTE increased, and combustion duration decreased.Secondly, emission characteristics of DMDF engine were studied according to the variation of substitution ratios, injection parameters, inlet temperatures and exhaust backpressures. Results showed that DMDF could simultaneously reduce NOX and soot for diesel engines, while HC, CO, NO2 and formaldehyde increased. The total number and mass concentrations and geometric mean diameter(GMD) of DMDF particulate decreased as SR increased. With the increase of inlet temperature, NOX and soot increased, NO2/NOX and formaldehyde decreased. As the exhaust backpressure increased, NOX, NO2 and HC decreased, while soot, CO and formaldehyde increased. As the injection timing advanced and injection pressure increased, CO, HC and soot decreased, but NO2 and NOX increased. A flat trade-off curve between NOX and soot was presented for DMDF engine, which meaned that NOX could be decreased by changing injection parameters without increasing soot sharply. Both double DOC and DOC coupled with a POC(DOC+POC) could efficiently oxidize the increased HC, CO, and formaldehyde emissions of DMDF, but DOC+POC could more efficiently convert NO2 and soot emissions.Thirdly, The results of DMCC engine with emission standard test showed that, with the optimized injection strategy and methanol ratio, DMCC engine coupled with DOC+POC could achieve EuroⅣ emission standard. The formaldehyde emission was 24.2mg/(kW·h), and OBD strategy of DMCC was also proposed. DMCC engine coupled with EGR and combined with DOC+POC could reach EuroⅤlevel. A new method was opened up to achieve EuroⅣ and EuroⅤ emission standard without SCR and DPF.Fourthly, the DMCC engine, which could meet the EuroⅣ standard, was mounted on a truck to do road tests. Results showed that DMCC vehicle could run smoothly under transient condition and mode switching process. Compared with the original vehicle, under DMDF mode the speed acceleration increased, the average substitute ratio was 33.28%, the volumetric replacement ratio was about 1.44, the fuel economy was increased by 11.89%, and the smoke was decreased by 46.3% at free acceleration. The inlet temperature and exhaust temperature were decreased by 19.6℃ and 17.6℃, respectively.