چکیده انگلیسی:
By development of industries, excessive consumption of the fossil fuels is becoming the worldwide crisis in the years ahead. Besides the proper thermal and power performance, the compression ignition engines make lower greenhouse-gas emissions compared to the spark-ignition engines. Using dimethyl-ether (DME) as an environmentally friendly fuel in a diesel engine can improve its advantages. In the present paper, the effects of the piston bowl geometry in a DME-burning direct injection (DI) engine have been numerically evaluated. In order to enhance combustion and emission characteristics, various piston bowls with different bowl volumes are designed and examined. Furthermore, the influences of engine speed and compression ratio are further investigated. The results showed that lower bowl volume led to more air-fuel mixing. Reduction of the bowl volume size from 6.446e-005 m3 to 1.5282e-005 m3 caused reduction in emissions of the soot, NO and CO by 91%, 9.3%, and 99%, respectively (the exhaust CO2 concentration was almost identical for each piston bowls). in addition, lower compression ratio caused reduction in temperature and NO emissions. It is determined that amount of exhaust emissions is affected by increasing the engine speed, and mean pressure of the engine cylinder reduced, dramatically. It is found that taking advantage of DME fuel in the ISM 370 diesel engine caused reduction in the NO, soot, CO and CO2 by 75%, 20%, 8%, and 44.43%, respectively, under 1200 rpm engine speed.
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