| Particle emission from motor vehicle is a major source of atmosphere particulate matter pollution.Investigation on the influence of fuels and engine control parameters on particle emission is an important research direction.Biodiesel and polyoxymethylene dimethyl ether(PODE)are typical alternative fuels which have potential to reduce particle emission for its high cetane number,high oxygen content.Besides,they are liquid states under atmosphere temperature and can be dissolved in diesel at any scales.This paper investigated the influence of PODE and biodiesel on the combustion,gas emission,particles'oxidation characteristics and PAHs emission on a light-duty turbo-charged diesel engine.Then,based on a specific PODE/diesel blending ratio,the influences of fuel supply parameters on engine combustion and particulate emission performance were studied.Finally,the injection parameters of mixed fuel engine based on particle emission under a certain condition were optimized.Fueled with neat diesel and 3 blends with different PODE/diesel(PD)and biodiesel/diesel(BD)ratio,the test indicated that the blend of PODE decreased the heat release rate of pilot injection fuel,advanced combustion of main injection,increased the peak in-cylinder pressure and heat release,shortened ignition delay and combustion duration.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 were improved by adding PODE.The results fueled with biodiesel was almost the same,and the only difference was that the introduction of biodiesel decreased the peak in-cylinder pressure,delayed combustion of main injection under high-speed,heavy-load mode.Effects of fuel oxygen content on emission were investigated.The results showed that increased the oxygen of fuel can reduce the emission of HC and CO obviously,and oxygenated fuel increased NO_x emissions from the engine,but there was no monotonic relationship.Fueled with PD oil,the reduction of accumulate mode particle emission was obvious under various engine modes,but the nuclear mode particle emission increased at low speed.While,fueled with BD oil,the reduction of particle emission was not obvious under low speed mode,the reducing effect improved under high speed mode.The order of particle oxidation reactives for different fuels is PD oil>BD oil>diesel under same engine mode and blending ratio.With the blends of PODE and biodiesel,particle-phases PAHs emission of engine was obviously decreased,the reducing effect of PD oil was better than BD oil.Based on a high PODE/diesel blending ratio,the influence of fuel supply parameters on engine combustion and particulate emission at low speed were studied.The results showed that concentration of particle increased firstly,and then decreased with the advancing of pilot injection timing,the increasing of pilot injection quantity and the increasing of post injection quantity.Under a little-rate range(10 percent of injection quantity per cycle),with the increasing of pilot injection quantity,the concentration of particle decreased gradually.Through comparison analysis,the multi-stage injection strategy of PD oil engine was optimized,which could effectively decreased the emission of nuclear mode particle at low speed. |
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