| In recent years,researchers all over the world are actively developing renewable and environmentally friendly alternative fuels for diesel engines.Because of its extensive and renewable sources,vegetable oil has been widely regarded as the preferred alternative fuel for diesel engines in the future.Although there are many kinds of vegetable oils,they have a lot of problems such as excessive viscosity,which limits the application of vegetable oils in diesel engines.Alcohols,which are common in the study of alternative fuels,also have the advantages of renewable and relatively low viscosity.Therefore,the method of making up for the excessive viscosity of vegetable oils by alcohols has been paid more and more attention by researchers in recent years.According to the physical and chemical properties of different raw materials,four groups of castor oil / diesel / alcohol mixed fuels were prepared according to different volume ratios.According to the volume fraction of various raw materials,they were named as B20E20,B10E10,B20,B40,respectively.After measuring the physical and chemical properties of the mixed fuels,the engine bench tests were carried out on a high pressure common rail six cylinder direct injection diesel engine to study the combustion characteristics,economy and emission characteristics of the mixed fuels,and to compare them with diesel fuel.The feasibility of mixing fuel as an alternative fuel for diesel fuel was studied.The basic conclusions of this paper are as follows:(1)With the increase of castor oil mixing ratio,the viscosity and density of the mixed fuel increased,and the density,viscosity and calorific value of the mixed fuel decreased with the increase of the proportion of alcohols,so the viscosity of the mixed fuel was basically the same as that of diesel fuel.It is a little higher than diesel at room temperature and can meet the requirements of diesel engine application.(2)The combustion characteristics of high pressure common rail diesel engine were studied by two-stage injection at medium and small load.The longer the proportion of alcohols was,the longer the ignition delay of mixed fuel was.In the pre-injection phase,the peak exothermic rate of mixed fuel has a backward trend relative to diesel fuel,and the peak value is slightly lower than that of diesel fuel.In the main injection phase,the peakexothermic rate of mixed fuel is obviously higher than that of diesel fuel.And with the increase of the proportion of alcohols,the trend is more obvious,and the larger the ratio of alcohol to alcohol is,the more obvious the trend is.(3)Compared with diesel fuel,the consumption rate of mixed fuel is higher than that of diesel fuel in general,especially at low speed and low load.When the speed increases and the load increases,the gap will gradually decrease,in the medium and small load range.The effective thermal efficiency of the mixed fuel is slightly lower than that of diesel fuel.(4)Compared with diesel fuel,under different loads and speeds,the emission of NOX increases,the emission of HC is almost the same as that of diesel oil,the emission of CO and soot decreases obviously,and the total number of particulate matter decreases obviously.However,the size of ultra-fine particles smaller than 50 nm increased compared with diesel oil. |
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