Effect of Pilot Injection Parameters on Combustion and Emission Characteristics of Ethanol/Diesel Dual-Fuel Engine
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为了改善乙醇/柴油双燃料发动机工作特性,对一台高压共轨柴油机进气系统改造实现了乙醇/柴油双燃料燃烧模式,并开展了预喷参数(预喷正时、预喷油量和预-主喷间隔)对双燃料发动机燃烧过程和排放特性影响的试验研究.结果表明:提前预喷正时使得双燃料燃烧相位提前,放热率峰值也随之增加;但预喷正时为上止点前(BTDC)22～25° CA时,会导致放热率曲线由双峰分布转变为三峰分布,CO、HC、Soot、甲醛、乙醛和乙烯排放量均降低,而NOx排放量呈现增高趋势,有效热效率(BTE)逐渐降低.在预喷正时为19° CA BTDC时,当预喷油量由2.5 mg/cyc逐渐增加至4.5 mg/cyc时,CO和HC排放量逐渐降低,而NOx排放量逐渐增加,BTE呈先增加后降低的趋势,Soot排放量在预喷油量3.0 mg/cyc下达到最低值0.07 FSN.在预喷策略下,提前主喷正时能够使双燃料发动机主喷燃烧相位逐渐提前并靠近上止点,最大缸内压力增加,CO、HC、Soot、甲醛、乙醛和乙烯排放量显著降低,同时发动机的燃油经济性得到改善;在平均有效压力(BMEP)为1.05 MPa和主喷正时11° CA BTDC的工况下,乙醇/柴油双燃料发动机的BTE达到最高值40.31％.
To improve the operating characteristics of ethanol/diesel dual-fuel engine,an experiment was carried out to investigate the effect of pilot injection timing,pilot injection quantity and pilot-main injection interval on combustion and emissions characteristics of the high pressure common rail engine with a modified intake system to achieve ethanol/diesel dual-fuel combustion mode.Results show that the earlier pilot injection timing can advance the dual-fuel combustion phase and increase the peak heat release rate;however,when the pilot injection timing is 22° CA to 25° CA before top dead center(BTDC),the heat release rate curve to change from a bimodal to a trimodal distribution,and reduce CO,HC,Soot,formaldehyde,acetaldehyde and ethylene emissions,but NOx emissions shows the increase trend and the brake thermal efficiency(BTE)gradually decreases.When the pilot injection timing is at 19° CA BTDC and the pilot injection quantity increase gradually from 2.5 mg/cyc to 4.5 mg/cyc,CO and HC emissions will gradually decrease,while NOx emissions gradually increase;BTE shows a trend of increasing before decreasing,and Soot emissions reach a minimum value of 0.07 FSN at pilot injection quantity of 3.0 mg/cyc.Under the pilot injection condition,advancing the main injection timing can gradually advance the main injection combustion phase of the dual-fuel engine to approach top dead center(TDC).The maximum in-cylinder pressure increases,CO,HC,Soot,formaldehyde,acetaldehyde and ethylene emissions are significantly reduced,and the fuel economy of engine has been improved.At the brake mean effective pressure(BMEP)of 1.05 MPa and the main injection timing of 11° CA BTDC,the ethanol/diesel dual-fuel engine can reach a maximum BTE of 40.31％.
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