Study On Injection And Combustion Of Diesel-Biodiesel-Ethanol Blended Fuel

As the environmental problems become more and more serious,it is very important to find efficient and clean alternative energy sources for engines.Biodiesel and ethanol are the focus of many alternative fuels,and their own oxygen enrichment helps to reduce emissions.Diesel-Biodiesel-ethanol blended fuel is a good blended fuel.At present,many researches focus on the combustion and emission of the blended fuel,but few researches have been done on its injection process.Therefore,in combination with the diesel-biodiesel-ethanol blended fuel injection experiment,it is of great significance to study its combustion process.Based on high pressure common rail injection test system,the injection rate the fuel injection quantity and the pressure fluctuation of the fuel injection process were investigated by changing the energizing time and the common rail pressure to analyze the influence of injection parameters and fuel properties on fuel injection firstly.Further,the fuel injection process was simulated to analyze the influence of fuel physical parameters,fuel injection parameters and injector structure parameters on fuel injection using AMESim.At last,according to the results of fuel injection test and simulation,the combustion process of fuel at different fuel injection quantity was simulated by KIVA numerical simulation to analyze the influence of fuel injection and fuel blending ratio on combustion.The research on fuel injection under different energizing times and rail pressures showed that energizing time mainly affects the duration of injection while rail pressure mainly changes the maximum fuel injection rate.With the increase of rail pressure and energizing time,the difference of fuel injection characteristics between different fuels decreases.After the addition of ethanol,the injection volume increases,and injection end point is significantly delayed compared with other fuels.The volume injection rate of biodiesel is smallest,but quality injection rate is highest.With the increase of the energizing time,the pressure variation caused by the needle valve seating is more obvious,and the pressure fluctuation difference between the different fuels also becomes larger.The simulation results of injection showed that the fuel density has significant effect on the injection rate and injection quantity of the injection process.The effect of the viscosity and bulk modulus on the fuel injection rate is small,which has certain influence on the injection end time.The influence of spray hole diamater,number and flow coefficient on the injection characteristics are large and almost the same.The fuel injection rate and the injection quantity increase with the pore diameter increasing.With the increase of fuel injection quantity,the average temperature and maximum pressure in the combustion process increase,in addition,the ignition period,combustion phase and combustion duration all show an increasing trend.The average temperature of biodiesel is lower than that of diesel,while its ignition delay is longer;with smaller fuel injection quantity,the addition of ethanol reduces the average temperature and prolongs the ignition delay.From the distribution of the in-cylinder emissions,the incylinder NO_x concentrations of biodiesel are higher than those of diesel,while the CO and HC concentrations are lower.After adding ethanol,the in-cylinder NO_x concentrations increase,but the CO and HC concentrations decrease.From the total emissions,with the increase of injection volume,NO_x emissions increase,HC emissions decrease,CO emission first decreases and then increases.Among them,biodiesel has the lowest NO_x emission;with the addition of ethanol,diesel-biodiesel blends have lower NO_x emissions and higher CO and HC emissions.