Study On Effects Of EGR On Combustion And Emissions Of Ethanol-Gasoline Hybrid Injection Engine

With the continuous increase of car ownership in recent years,while bringing convenience to people,car emissions have also made humans face more and more serious environmental problems.The Ministry of Environmental Protection has also promulgated the"most stringent"emission standards（the"China VI"vehicle emission standards）in history to curb environmental problems.On the other hand,huge automobile production and holdings have caused the country’s crude oil imports to continue to increase,and energy dependence to continue to rise.At the same time as automobile development,environmental pollution and sustainable energy development issues need to be addressed urgently.Ethanol has similar physical and chemical properties to gasoline.Nowadays,ethanol has become the alcohol substitute fuel（E10）widely used throughout the country,and exhaust gas recirculation technology（EGR）has become the basic configuration of automobiles,which can effectively and significantly reduce NO_X emissions.It is of great significance to study the combined effects of ethanol and exhaust gas recirculation technology on the improvement of engine performance.In order to achieve the research purpose of this thesis,the construction and commissioning of the third-generation inline four-cylinder engine was completed to achieve the injection of gasoline in the intake port and direct injection of ethanol in the cylinder,the establishment of an exhaust gas recirculation system,and the installation and commissioning of test equipment including CA160 dynamometer and control system,lambad tester,AVL DICOM 4000 five gas analyzer,DF-2420 fuel consumption meter,DEWEsoft combustion analyzer and Cambustion DMS500 particle analyzer.The Dspace electronic control system is used to control the excess air coefficient（λ）,ignition advance angle,direct injection ethanol ratio,EGR rate and other parameters.First,the ratio of direct injection ethanol to the engine under different excess air coefficient（0.9,1.0,1.1）was studied.The effects of combustion and emissions were studied.Second,the effects of ethanol on engine combustion and emissions characteristics at different EGR rates were studied.The main conclusions of this study are as follows:（1）When the EGR rate is 0%and the excess air coefficient are 0.9,1.0,and 1.1,direct injection of a certain percentage of ethanol can increase the average indicated pressure by1.83%,1.75%,and 1.11%,respectively;improve fuel economy and reduce the fuel consumption rate;the addition of ethanol shortens the flame retardation period of the combustion,reducing it to the original 90.52%,90.60%,87.15%;when the excess air coefficient is 0.9 and 1,direct injection of ethanol makes the rapid combustion period slightly increase.Direct injection of appropriate amount of ethanol can improve the stability of engine operation,reduce the average indicated pressure change rate(COV_IMEP)and the maximum burst pressure change rate(cov_pmax),especially when the mixture is lean（λ=1.1）,which has a greater impact on the combustion stability of the engine.（2）When the EGR rate is 0%and the the excess air coefficient is 0.9,1.0,1.1,as the proportion of direct injection ethanol increases,NOx shows a gradual decline trend.It can be seen that the latent heat of ethanol vaporization is larger and larger.It can reduce the nitrogen oxide content to a large extent;whenλ=0.9,HC shows a slight upward trend after decreasing with the increase of the direct injection ethanol ratio,and atλ=1.0 and 1.1,it shows a constant downward trend;the effect of CO content is different under different excess air coefficients.Ethanol has a significant effect on reducing particulate emissions,which can eliminate 80-90%of the particulates.（3）When the EGR rate is different（0%,6%,12%,18%,24%）,the change law of the average in-cylinder pressure IMEP with the increase of the direct injection ratio R_Ethanol is a trend of first increase and then decrease.Together with the reduction of throttling loss,IMEP can increase by up to about 10%;at the same EGR rate,the highest burst pressure is affected by the change in the proportion of ethanol,which first increases and then decreases.In different EGR rates,when EGR=12%,the maximum burst pressure is higher than other EGR rates;the addition of ethanol can shorten the flame retardation period,and the effect on the rapid ignition period is shortened first and then extended。（4）Under different EGR rates,the direct injection of ethanol can reduce fuel consumption rate and improve the economy of the engine;the appropriate direct injection ethanol ratio can effectively reduce the average indicated pressure change rate(COV_IMEP)and the maximum burst pressure change rate(COV_Pmax),which improves the stability of the engine.When the proportion of ethanol is high（60%）,the COV increases due to the effect of evaporation and atomization time.（5）Affected by many factors such as the large latent heat of ethanol vaporization,the dilution of the oxidant after the introduction of the exhaust gas,and the increase in the specific heat capacity of the mixed gas,the combustion temperature in the cylinder decreases,resulting in a significant reduction in NOx content;the addition of ethanol promotes the combustion of the mixed gas in the cylinder,making the combustion of the mixed gas more complete and the HC content reduced;70-85%of the particles in the emissions are nuclear membrane state particles,the distribution of most particles appears as a single-peak distribution,with the combined effect of ethanol and EGR,the number of particles in emissions can be greatly reduced.In summary,the addition of ethanol can accelerate the flame propagation speed,make the mixture burn more completely,and improve the efficiency of the engine.The exhaust gas recirculation technology can effectively reduce the nitrogen oxide content,reduce the throttling loss,and increase the output power of the engine.The advantages of ethanol addition and EGR can improve engine combustion and emissions characteristics.