An Experimental Study On The Combustion And Exhaust Emissions Of An HCCI Engine Operated With DME/Methanol Dual Fuels

With ever growing concerns on energy crises and environmental issues, people pay more attention to seek non-petroleum based alternative fuels. As clean and oxygen-containing fuels, both DME (dimethyl ether) and methanol have been considered to be the most promising alternative fuels due to the broad resources of its feed stocks and excellent performance of economics and emissions.Compared with conventional combustion mode, Homogeneous charge compression ignition (HCCI) combustion enables lower NO_X emissions and higher thermal efficiency. However, the operating range in the HCCI engine is limited to low load because of misfiring and knocking, and it is hard to control the ignition timing. Adjusting the proportion of two fuels with different ignition properties is an effective technique for controlling ignition timing in HCCI combustion. In this paper, a method to control the ignition timing and expand the operating range of HCCI engine by fueling with dimethyl ether (DME) and methanol dual fuel has been proposed.The test bed of DME/methanol dual fueled HCCI engine is modified and established on a ZS195 prototype diesel engine. By adjusting the amount of DME/methanol supply and the intake temperature, the experimental study on engine's performance of combustion and exhaust emissions were carried out. With the use of Gas Chromatography (GC) and Fourier Transform Infrared Spectrometry (FTIR), some unregulated emissions such as formaldehyde, acetaldehyde, methanol, methyl formate from the DME/methanol duel fueled HCCI engine are specially analyzed.The result shows that the operating region of HCCI engine can be extended effectively with DME/methanol dual fueled mode. With the increase of methanol, the peak power output of the engine, the formaldehyde, acetaldehyde, methanol, methyl formate and DME emissions and the HC and CO emissions are increased, while the NO_X emissions are reduced. And with the increase of engine load, the acetaldehyde, methanol and DME emissions and the HC and CO emissions are reduced while the NO_X emissions are increased slightly, the methyl formate emissions are declined first and then climbed up. When the intake air temperature is increased, emissions of the acetaldehyde, methanol, methyl formate, DME, HC and CO are reduced. However, the NO_X emissions and formaldehyde emissions are increased.