Emissions of dimethyl ether(DME) fuelled engines were investigated by orthogonal experiments on a ZS195 diesel engine.The study mainly focused on the tiny pollutant emissions of formaldehyde(CH2O),methyl formate(CH3OCHO) and formic acid(HCOOH).The presence of CH2O,CH3OCHO and HCOOH are proved in the exhaust by gas chromatograph and Fourier transform infrared spectroscopy.The analysis of variance results indicate that the fuel delivery advance angle is the most important factor for CH2O emission.The fuel delivery advance angle and the interaction of injection pressure and nozzle diameter are considerable factors for unburned hydrocarbon(UHC) emission.The mechanism forming tiny pollutants,primarily through CH2O formation,is suggested to be similar to the mechanism forming UHC by DME partial oxidation existing in crevices and boundary zones,and is verified via DME combustion simulation of a multizone chemical kinetic model.
