| In the context of environmental pollution and the energy crisis,it is extremely important to find one or more renewable clean energy sources.N-butanol is a biomass fuel that can be prepared by fermentation,because the oxygen in n-butanol molecules can promote combustion and can replace gasoline as a car fuel.In addition,exhaust gas recirculation(EGR)technology is a purification method that can effectively reduce NOx emissions.Therefore,this thesis will study the effects of gasoline and n-butanol on combustion and emissions under different EGR conditions.The test is divided into two parts:the first part explores the pre-mixed and direct injection of n-butanol gasoline in the EGR atmosphere(mixed fuel direct injection GNDI mode,and the fuel is mixed by volume ratio);the second part explores the compound injection of n-butanol gasoline mode(gasoline inlet injection,n-butanol direct injection G-NXDI and gasoline direct injection,n-butanol inlet injection N-GXDI,using energy ratio for fuel mixing),the variable that will be involved in the test process is EGR rate,doped alcohol ratio or direct injection ratio(NBr or DIr),ignition advance angle,the research work is summarized as follows:The first part studies the GNDI mode.Pre-mix n-butanol and gasoline according to the volume ratio,and then perform direct injection combustion in the cylinder.During the combustion process,the EGR rate was changed by adjusting the EGR valve,and then a series of studies were performed on the combustion and emission characteristics of the direct injection engine under different EGR rates,alcohol blend ratios,and ignition advance angles.1)At the same EGR rate,with the increase of the alcohol-doped ratio,the total theoretical heat release per cycle continues to decrease,and the NDI mode is the lowest,which is 0.83%lower than the GDI mode;with the increase of the alcohol-doped ratio,the cylinder temperature and cylinder pressures tend to increase first and then decrease.When the alcohol content is 25%,the maximum cylinder temperature and cylinder pressure are obtained.With the increase of the EGR rate,the cylinder temperature and cylinder pressure tend to rise first and then decrease,and the maximum cylinder temperature and cylinder pressure are obtained when the EGR rate is 5%.The IMEP value has a maximum when the blending ratio is 50%and the EGR rate is 5%.2)Under the same alcohol doping ratio,with the increase of the EGR rate,CO shows a trend of decreasing first and then increasing.At 15%,it can decrease to the lowest value,THC keeps rising,and NOx continues to decrease.In addition,at the same EGR rate,as the proportion of alcohol added increases,CO emissions continue to decrease,THC first decreases and then rises to a minimum at 25%,and NOx emissions also continue to decrease.3)At the same alcohol doping ratio,the particle number decreases with the increase of the EGR rate,and the particle size and concentration decrease.At the same EGR rate,the total number of particles decreases first and then increases with the increase of the blending ratio.When the blending ratio is 25%to 50%,the total number of particles has the lowest concentration,and there is an optimal blending ratio.The second part studies the dual-fuel dual-injection mode in the EGR atmosphere.The two fuels are switched for different fuel injection ratios for experimental research.Control the direct injection fuel injection ratio according to the energy ratio,and then analyze the combustion and emission characteristics of the engine under different EGR rates,different injection modes,and different injection ratios.The following conclusions were reached:1)In the dual injection mode,the maximum deviation of the total heat release per cycle of the two injection modes is 0.845%,which is within an acceptable range.With the increase of the direct injection ratio DIr,the cylinder temperature,cylinder pressure,and IMEP value all increased first and then decreased,and the maximum was reached when the direct injection ratio was 25%.When the direct injection ratio increases from 50%to 75%,IMEP decreases sharply,so the optimal direct injection ratio should be between 0%and 50%.In addition,at a 50%direct injection ratio,as the EGR rate increases,the cylinder temperature,cylinder pressure,and IMEP tend to increase first and then decrease,reaching a maximum at 5%,so when the EGR rate is5%fuel burns more fully.2)With the same direct injection ratio in the dual injection mode,with the increase of EGR,CO decreases first and then rises,THC emissions gradually increase,and NO_X emissions rise first and then decrease.At the same EGR rate,with G-NXDI mode,as the direct injection ratio increases,CO decreases slightly,THC emissions first decrease and then rise to a minimum of about 25%,and NO_X emissions continue to decline.In the N-GXDI mode,CO continues to rise,THC emissions continue to rise,and NO_X emissions rise first and then decrease.3)Under the same EGR rate,the total particle concentration in the dual injection mode first decreases and then increases with the increase of the direct injection ratio.When the direct injection ratio is 50%,the total particle concentration is the lowest.In the EGR atmosphere,the three injection modes are compared comprehensively.Under the same NBr or DIr,compared with the dual injection mode,the GDNI mode has the lowest IMEP value,and the G-NXDI mode has the highest.According to the analysis of combustion and emissions,the dual injection mode has better combustion and emission characteristics.The dual injection mode has better combustion and emission characteristics when the EGR rate=5%and DIr=50%.Among them,G-NXDI mode has better advantages in terms of combustion and emissions,and N-GXDI mode has better particulate emission characteristics. |
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