This study investigated the effects of high exhaust gas recirculation (EGR) rates\r\non dimethyl ether (DME) fuel combustion performance, exhaust emissions and particle\r\nemission characteristics in a small direct injection diesel engine under various injection\r\ntimings. To examine the effect of EGR and injection timings, the experiment was performed\r\nunder high EGR rates (0%, 30%, 50%) and injection timings were varied from 40�° before\r\ntop dead center (BTDC) to top dead center (TDC) of the crank angle to examine the effects\r\nof early injection of DME fuel. The combustion pressures and heat release rates for\r\ndifferent EGR rates followed similar trends. As the injection timing was advanced, the\r\nindicated mean effective pressure (IMEP) differed little in response to EGR rate in the\r\nrange from TDC to 25�° BTDC, and more for crank angles beyond 25�° BTDC. DME\r\ncombustion exhibited very little soot emission, but soot emission increased slightly with\r\nEGR rate. The use of high EGR during combustion produced very low NOx concentrations\r\nbut increased HC and CO emissions for advanced injection timings from 25�° BTDC to 40�°\r\nBTDC. The use of EGR increased both the emissions of total particle number and particle\r\nvolume over the whole range of the injection timings; for all cases, total particle volume\r\ndecreased as injection timing was advanced.
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