An Experimental Study On The Combustion And Exhaust Emissions Of Engine Fueled With DME/Methanol Blended Fuel

With the development of social and economic,the phenomenon of oil shortage become serious, coupled with increasingly stringent emissions regulations, people pay more and more attention to the research of efficient and clean alternative fuel internal combustion engine. As China has abundant coal resources, the research and use of methanol and dimethyl ether (DME) which can take by the coal conversion to fuel, has great strategic significance to solve the energy shortage in China. Both of these fuels are oxygenated fuel, easy to complete combustion and have a good emissions performance, are ideal for clean alternative fuel internal combustion engine, and have the effect of solving energy and environmental issues.The test beds of DME / methanol mixture fuel DI and HCCI engines were modified and established on a ZS195 prototype diesel engine. For DI combustion, by changing the fuel mix ratio and injection timing, the experimental study on engine's performance of combustion and exhaust emissions were carried out. For HCCI combustion, by changing the CO₂ addition in intake air, the experimental study on engine's performance of combustion and exhaust emissions were carried out. And a MATLAB program was using to calculate the heat release rate. With the use of Gas Chromatography and Fourier Transform Infrared Spectrometry, some unregulated emissions such as methanol, formaldehyde, methyl formate and formic acid are analyzed.The result shows that, for DI combustion, high concentrations of methanol in the blended fuel reduce the engine's performance and economy. With the lower concentration of methanol fuel, the emissions of NOX, HC, CO, CO₂ decrease, while the emission of formic acid increase. And there is a good mix ratio, which have a lower emission of methanol and formaldehyde. In the condition of different injection timing, the fuel supply advance angle hysteresis makes combustion lag; the appropriate fuel supply advance angle hysteresis can decrease engine's brake specific energy consumption. With the fuel supply advance angle hysteresis, emissions of NOX, CO₂, methanol and formaldehyde reduce. With the injection timing advance, emissions of HC and methyl formate decrease, and after the fuel supply advance angle change, emission of CO increase, while emission of formic acid decrease. Compare HCCI combustion with direct injection combustion ,DME/methanol blended fuel HCCI combustion's emission of NOX, methyl formate are lower than direct-injection combustion's, while emission of CO, CO₂ and formaldehyde are higher. With CO₂ addition in intake air, as the rate of EGR raise, combustion delay, the engine's maximum effective power increase, and the emission of HC, CO, CO₂, methyl formate increase, while emission of NOX decrease.