| Reducing diesel engine emission especially particulate emission is an important research area under the topic of energy saving and environmental protection.Investigation on the influence of fuels and diesel engine control parameters on diesel particle emission is an important research direction.Polyoxymethylene dimethyl ether(PODE)is a new type of alternative diesel fuel and has been considered to be potential for reducing diesel emissions for its high cetane number,high oxygen content and no C-C bond characteristics.This paper first investigated the influence of PODE on diesel engine combustion and gas emission on a light-duty high speed turbo-charged diesel engine.Then,based on a specific PODE/diesel blending ratio,we focused on the influence of fuel supply parameters on engine combustion and particulate emission performance,and compared with diesel engine performance under same control parameters.Fueled with neat diesel and 3 blends with different PODE/diesel ratio,the test indicated that except for the low-speed&heavy-duty(HD)engine mode,the blend of PODE decreased the heat release rate of the pilot injection fuel,increased the active ingredients in combustion chamber before the main fuel injection,increased the in-cylinder gas mean temperature(GMT),the main fuel combustion duration was shorten.With the increasing of PODE blending ratio,higher peak in-cylinder pressure(IP),shorter combustion duration and higher combustion temperature was obtained.At the same time,with the mixed PODE,NO_x emission increased,HC emission slightly decreased,CO emission showed no obvious change.Besides,the fuel economy and engine thermal efficiency was improved by adding PODE.The study on the influence of engine modes and fuel supply parameters showed that more particles emitted at high speed mode than low speed mode,nucleation mode particle(NMP)reduced under heavy load.With the increasing common rail pressure(CRP),the heat release rate of the pilot injection fuel decreased,the main fuel heat release advanced and its peak increased.The peak in-cylinder pressure and gas mean temperature increased,the combustion duration was shortened.Compared with other fuel supply parameters,the increase of CRP had the most obvious effect on accumulation mode particle(AMP)and total particle number concentration decreasing,but it caused NMP number concentration increasing under light-duty(LD)mode.The advance of pilot injection timing would lower the pilot fuel heat releasing,effectively reduce the AMP number concentration,but cause obvious NMP number increase.The increasing of pilot injection quantity sharply increased the pilot fuel heat release,partly reduced main fuel heat release,but had different effects on particle emission under different engine condition.The advancing of main injection timing directly shifted the main fuel heat release rate and the peak IP to early crank angle and enhanced their values,causing higher peak GMT under low-speed condition.Except for high-speed LD mode,much lower AMP number concentration obtained with earlier main injection timing,but NMP emission increased under low speed LD mode.Detailed investigated reducing diesel particle emission by the use of PODE,the results showed that the blend of PODE could significantly reduce AMP and total particle number concentration under different engine modes,especially for the heavy load.With the change of fuel supply parameters,the particle reducing effect was not weakened with the reducing number concentration,sometimes even strengthened.Besides,the blended fuel had stronger ability to suppress NMP emissions than neat diesel.The low fuel/air ratio mixture during pilot injection was closely related to NMP formation and premixed combustion ratio and combustion temperature had strong influence on both NMP and AMP number concentration.The high volatility of PODE suppressed particle formation better under low CRP.The presence of oxygen can significantly reduce particle formation and its suppressing ability strengthened with higher temperature and longer oxidation time.The research results suggested that PODE had remarkable effect on reducing diesel engine particulate emission under different condition and fuel supply parameter,may be considered as excellent alternative diesel fuel. |
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