| Ethanol can be easily blended with gasoline,contains oxygen,has high latent heat of vaporization,and it is the most widely used clean alternative fuel.Combustion of ethanol and gasoline can not only improve knock resistance of gasoline engine,but also improve the combustion efficiency and reduce emissions.However,it is difficult to preserve anhydrous ethanol because of its strong hydrophilicity.Moreover,anhydrous ethanol production is complex and prohibitively expensive.Therefore,increasing attention has been given to hydrous ethanol-gasoline blends in spark-ignition engines.In addition,water injection for gasoline engines is a promising field of study.While water injection technology has not been widely used owing to the complex effects of water vapor on gasoline combustion process.Thus,it is of great improtance to study the fundamental combustion characteristics of ethanol-gasoline blends under different water vapor concentrations.But,the studies that were available focused on the engine bench test,and there is still a lack of research on its basic laminar burning characteristics.Based on this,the laminar burning characteristics of ethanol/iso-octane/water were studied experimentally and theoretically.The laminar burning characteristics of iso-octane/water/air were studied:The laminar burning velocity rises first and then falls as equivalence ratio rises,falls linearly with increasing water dilution ratio,and rises exponentially as initial temperature rises;The Markstein length decreases as equivalence ratio rises,rises as water dilution ratio rises,and changes little with increasing initial temperature.The different effects of water vapor always inhibit the laminar burning velocity.The dilution effect is dominant,the thermodynamic effect is the second,and the direct-reaction effect is the least.With the increase of water vapor concentration,the sensitivity coefficients and net reaction rates of H+O2=O+OH,H2+OH=H2O+H and HCO+M=CO+H+M rise,and become more important at a high water dilution ratio.In addition,water addition has little effect on the reaction path of iso-octane/water/air,and the change of path consumption components is not obvious.The laminar burning characteristics of ethanol/iso-octane/water/air were studied:The laminar burning velocity rises exponentially as the ethanol content rises,changes with water vapor and initial temperature are similar to that of iso-octane water mixing;As the water vapor dilution ratio increases,the Markstein lengths of E10W,E20W,E50W first increase and then tend to be flat.For E100W,the Markstein length first increases and then decreases.The free radical changes of mixed fuels at different ethanol concentrations are analogous.The direct-reaction and three-body effects of water vapor increase linearly with increasing water dilution ratio.The direct-reaction effect affects the laminar burning velocity by inhibiting the elementary reactions H+O2=O+OH,H2+OH=H2O+H and HCO+M=CO+H+M.The three-body effect of water vapor reduces the laminar burning velocity by increasing the three-body reaction H+O2（+M）=HO2（+M）and H+CH3（+M）=CH4（+M）.In addition,the different chemical effects of water have little effect on the reaction path of E20W,and water has little effect on the chemical reaction process of ethanol/iso-octane mixed fuel. |
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