Experimental Study On Combustion And Emission Of Waste Cooking Oil Biodiesel/Diesel Blend

Global warming,the depletion of traditional fossil resources,the rise in the price of petroleum products and the implementation of energy conservation and emission reduction policies make ester oxygenated fuels become a research hotspot of sustainable alternative fuels.Biodiesel has similar physical characteristics to diesel,with the characteristics of degradability,high oxygen content and low sulfur content,so it is considered to be a non-toxic and environmental friendly clean fuel.Waste cooking oil biodiesel takes gutter oil as the main raw material.Compared with other biodiesel raw materials,waste cooking oil biodiesel has low production cost and provides a solution for the treatment of domestic waste cooking oil.At present,waste cooking oil is one of the main raw materials of biodiesel.Based on waste cooking oil biodiesel,the combustion process and emission performance of diesel engine fueled with biodiesel blended fuel through experiments were studied in this paper.Under the working conditions of maximum torque speed(1540 r·min^-1)and three loads（25%,50%and 75%）,the influence trend of waste cooking oil biodiesel volume content and injection time on diesel engine combustion process,conventional emission and unconventional emission were investigated.The main contents are as follows:（1）Firstly,B0,B10（10%volume ratio of waste cooking oil biodiesel）,B20 and B30 test fuels were prepared,and then their components and some physical properties were analyzed.The results show that waste cooking oil biodiesel includes seven main components,among which methyl palmitate and methyl linoleate account for a large proportion,and the sum of their mass fractions is more than 60%;Waste oil biodiesel and 0#diesel oil have good mutual solubility;With the increase of biodiesel volume content,the density,oxygen content and surface tension of mixed fuel gradually increase,and the low calorific value gradually decreases.（2）Taking B0,B10,B20 and B30 as test fuels,the effect of biodiesel content of waste cooking oil on the combustion characteristics of diesel engine was studied.The results show that with the increase of biodiesel volume content,CA10 and CA50 are advanced,the ignition delay period is shortened and the combustion duration is prolonged.At the same time,blending biodiesel improves the peak value of in-cylinder pressure,in-cylinder temperature,cumulative heat release and pressure rise rate under each load,and reduces the peak value of heat release rate.Compared with B0,under 25%,50%and 75%load,the peak pressure increase of B30cylinder is 3.9%,2.6%and 0.6%respectively,and the decrease of heat release rate is 8.8%,4.6%and 7.7%respectively.In addition,with the increase of biodiesel volume content,the peak phase of heat release rate of mixed fuel is advanced.（3）Taking B0,B10,B20 and B30 as test fuels,the effect of the volume content of waste cooking oil biodiesel on the emission characteristics of diesel engine was studied.The results showed that with the increase of the volume content of waste cooking oil biodiesel,the specific emissions of soot,CO and THC decreased.At 25%,50%and 75%load,B30 had the lowest specific emissions of soot,which were 71.1%,41.3%and 68.3%lower than that of pure diesel B0,respectively.With the increase of the volume content of waste cooking oil biodiesel,the increase of temperature and oxygen content promoted the formation of NOx emission,and the specific emission of NOx increased;The specific emissions of NO and NO₂ of nitrogen oxides increased;The specific emissions of hydrocarbon methane,n-octane,ethylene and propylene are reduced;The specific emissions of carbonyl compounds（formaldehyde,acetaldehyde）,SO₂,formic acid and isocyanate are reduced.（4）Taking B30 as the test fuel,the influence of injection time（-2,-4,-6,-8,-10,-12°CA ATDC）on the emission characteristics of diesel engine was studied.The results show that with the advance of injection time,the ignition delay period is prolonged,the combustion duration is shortened,and the peak values of in-cylinder pressure,heat release rate,in-cylinder temperature,cumulative heat release and pressure rise rate are increased.With the advance of injection time from-2°CA to-12°CA ATDC,the peak increases of in-cylinder pressure under 25%,50%and 75%load are 47.2%,36.6%and 40.6%respectively,and the increases of heat release rate are 22%,33.3%and 13.7%respectively.（5）Taking B30 as the test fuel,the effect of injection time（-2,-4,-6,-8,-10,-12°CA ATDC）on the emission characteristics of diesel engine was investigated.With the advance of fuel injection time from-2°CA to-12°CA ATDC,the specific emissions of soot,CO and THC under various loads are reduced,and the specific emissions of soot under 25%,50%and 75%loads are reduced by 64.9%,69.7%and 65.3%respectively;The specific emission of NOx increases;Under 25%,50%and 75%load,the specific emission of NOx increases by 140.4%,64.5%and 98.5%respectively;The specific emissions of NO and NO₂ increase under all loads;The specific emissions of methane,n-octane,ethylene,propylene,formaldehyde,acetaldehyde,formic acid and isocyanate are all reduced,while the specific emissions of SO₂ are increased.