| Vehicles powered by internal combustion engines are now facing stringent regulations,so it is urgent to improve engine thermal efficiency and reduce harmful emissions.At present,spark ignition engines are equipped with advanced technologies,such as combined injection technology and so on,to meet the requirements of regulations.At the same time,alcohol fuels have attracted wide attention because of their good renewability and do not need to change the structure too much.In view of this,through constant volume chamber and engine test bench experiments,this thesis explores the spray characteristics of ABE and gasoline and the potential of ABE/gasoline dual fuel to optimize engine combustion and emissions under combined injection mode,in order to clarify the optimal combined injection mode and injection strategy of ABE applied in spark ignition engine.In order to clarify the spray characteristics of ABE in spark ignition engine and the difference between ABE and gasoline spray characteristics,the constant volume testing system was used to shoot ABE and gasoline spray images.The spray characteristics of ABE and gasoline were compared under different injection pressure,environmental pressure and injection pulse width.The results show that the spray development of ABE is slower than that of gasoline,and the transverse width of the first half of gasoline spray is larger than that of ABE,which indicates that the diffusivity of gasoline is greater than that of ABE.Increasing injection pressure can improve the effect of fuel atomization and evaporation.With the increase of fuel injection pressure,the spray penetration distance of gasoline and ABE increases continuously and the growth rate of penetration distance increases,and the effect of increasing injection pressure on increasing penetration distance is more obvious for ABE.The spray penetration distance of gasoline is larger than that of ABE when the injection pressure is5 and 7MPa,but when the injection pressure continues to increase to 9,11 and 13MPa,the penetration distance of ABE is larger than that of gasoline.With the increase of injection pressure,the time when the spray cone angle reaches the peak value is advanced.When the spray cone angle is stable,the ABE and gasoline spray cone angle increase with the increase of injection pressure.The spray cone angle of ABE is larger than that of gasoline at different injection pressures.With the increase of environmental pressure,the spray penetration distance decreases,and the effect of fuel evaporation and diffusion becomes worse.In addition,whether it is ABE or gasoline,the spray cone angle increases with the increase of environmental pressure.When the injection pressure and environmental pressure are constant,the shape of the spray is similar under different injection pulse width during fuel injection process.When the fuel injection process is completed,with the increase of injection pulse width,the amount of fuel injection increases at the same time,which leads to higher fuel concentration and incomplete evaporation and diffusion.In addition,the spray penetration distance increases with the increase of injection pulse width,but the spray penetration curves under different injection pulse width basically coincide.The effect of increasing the fuel injection pulse width to increase the penetration distance is more obvious for the ABE.In the process of fuel injection,the value of spray cone angle is similar under different injection pulse width.On the whole,when the injection pressure and environmental pressure are low,the penetration distance of gasoline is larger than ABE,while when the injection pressure and environmental pressure is higher,the penetration distance of ABE is larger than that of gasoline.Under different injection pressure,environmental pressure and injection pulse width,the spray cone angle of ABE is larger than that of gasoline.In order to determine the optimal injection mode of ABE/gasoline in combined injection engine,the experimental optimization scheme of"injection ratio and alcohol/gasoline ratio unified method"was designed.Based on this scheme,the combustion characteristics,gaseous emissions and particle emissions of ABE port injection plus gasoline direct injection(A+G)and gasoline port injection plus ABE direct injection(G+A)under different direct injection pressure,direct injection timing,speed,load and excess air ratio(?)were compared,and the gasoline combined injection mode(G+G)was introduced as the reference.The results show that the torque of G+A mode is always the highest.The direct injection pressure corresponding to the maximum torque of the G+A mode is higher than that of the A+G and G+G modes.When the engine is under low load,that is,the intake manifold absolute pressure(MAP)=30,40,50k Pa,the torque of G+G mode is higher than that of A+G mode,while at high load(MAP=60,70k Pa),the torque of G+G mode is lower than that of A+G mode.The total combustion duration(CA0-90)of G+A and A+G is basically the same,which is lower than that of G+G.When?=0.9-1.3,the brake thermal efficiency(BTE)of G+A mode is 0.2%,0.4%,0.02%,0.05%and 0.6%higher than that of G+G mode,respectively.The nitrogen oxides(NO_x),hydrocarbon(HC)and total particle number of G+A mode are the lowest among the three modes.When?=0.9,the NO_x and HC emissions of A+G mode is higher than that of G+G mode.But when?=1.2 and 1.3,NO_x and HC emissions of A+G mode is lower than that of G+G mode.According to the combustion and emission characteristics,gasoline port injection plus ABE direct injection has better power performance and lower emissions under different operating conditions,which is the optimal combined injection mode of ABE/gasoline dual fuel.In order to clarify the optimal strategy for gasoline port injection/ABE direct injection mode,the engine performance under different direct injection strategies,speed and loads was investigated through engine test bench experiment.The results show that under the 11MPa direct injection pressure,the indicated mean effective pressure(IMEP)of different ABE direct injection ratio is higher,the HC and carbon monoxide(CO)emissions are lower,and the NO_xemissions are not deteriorated,which can be regarded as the direct injection pressure with better power performance and gaseous emissions.However,at the early direct injection timing,choosing the direct injection pressure of 9MPa can obtain the lowest particle number concentration.At different direct injection pressure,the 300°CA BTDC direct injection timing combined with large ABE direct injection ratio can greatly improve the power performance and reduce the particle number.Considering that the current emission regulations have high requirements on the particle number,the better direct injection strategy is 9MPa of direct injection pressure plus 300°CA BTDC of direct injection timing combined with large ABE direct injection ratio.At low speed and low load,the power performance of ABE80 is the best.With the increase of engine speed and loads,pure ABE has an advantage in improving power performance.At different engine speed and loads,60%or 80%ABE direct injection ratio corresponds to lower HC and NO_x emissions,while 100%ABE direct injection ratio corresponds to lower CO emissions,but the increase of CO emissions of 80%ABE direct injection ratio is smaller.When using the fuel with 60%-100%ABE direct injection ratio,the particle number concentration is very low,and the change of working conditions has little influence on the particle number concentration.In summary,the combustion and emission performance of 80%ABE direct injection ratio is the best at low speed and low load.With the increase of engine speed and loads,pure ABE is the best for better power performance,otherwise 80%ABE direct injection ratio can be selected to take into account the gaseous emissions.In order to further expand the application potential of butanol-based alternative fuel in combined injection engine,the combustion and emission characteristics of gasoline/ABE,gasoline/IBE(Isopropanol-Butanol-Ethanol)and gasoline/butanol were compared based on gasoline port injection/alcohol direct injection mode.The results show that gasoline/IBE is better than gasoline/ABE in power performanc,and gasoline/ABE is better than gasoline/butanol in power performance.In terms of gaseous emissions,the trends of the three fuels are similar with the change of direct injection ratio.When the direct injection ratio is low,the gaseous emission of gasoline/ABE is dominant,while when the direct injection ratio is large,the gaseous emission of gasoline/butanol is dominant.In terms of particle emissions,the particle emissions of gasoline/ABE mode are always the lowest,but when the direct injection timing is earlier and the direct injection ratio is larger,the particle number concentrations of the three fuels are all at a very low level.Generally speaking,as alternative fuels,ABE and IBE have more advantages than butanol in terms of combustion and emission performance as well as cost. |
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