Numerical Study On The Control Of Combustion Process Of HCCI Engine By Changing Chemical Properties Of Fuels

Homogeneous Charge Compression Ignition?HCCI?,a promising cleancombustion technology,makes it possible for fuels to combustion in low temperature and lean condition with higher thermal efficiency,lower NO X emission and desirable fuel adaptability.However,the control of combustion process is a hard technical difficulty for HCCI engines due to the fact that the combustion progress of HCCI engines is mainly governed by chemical kinetics of the fuels.Therefore,HCCI engines are restricted within a narrow load range.In this work,the combustion process of DME/Ethanol fueled HCCI engine a nd the impact of ozone on natural gas fueled HCCI engine were investigated numerically.The inhibitory effect of ethanol on the HCCI combustion process was investigated.The results show that ethanol can efficiently reduce the rapid reaction rate and confine the knocking when HCCI runs in high load condition.Suitable increase in ethanol can improve the IMEP,low concentration of ethanol has little impact on CO and HC emissions,but with the increase in ethanol concentration the CO and HC emissions increase rapidly.Increase in the ratio of ethanol can improve the output power without knocking when HCCI engine runs in higher equivalence ratio.Ethanol restricts the reactions which can generate OH in LTR.In addition,the oxidizing of ethanol occurs later than that of DME,a portion of OH radicals generated by DME react with ethanol,and therefore the dehydrogenation between DME and OH radicals is inhibited.The impact of ozone on natural gas fueled HCCI engine was investigated.The result indicated that low concentration of ozone can advance the combustion phase,reduce autoignition temperature of natural gas and make it easier to ignite in low load and cold startup conditions.Through adjusting the concentration of ozone,the combustion phase can be controlled.However,the combustion assisted effect of ozone is restricted by concentration,with the incre ase in concentration of ozone,the combustion assisted effect become weaken.At high tempera ture,ozone is unstable and decomposes easily though the reaction O₃ + M ? O₂ + O + M,generating O,so the fuels can rapid dehydrogenize with O,which dehydrogenation rate is much faster than that with O₂,the concentration of active radicals,such as OH,HO₂ and H,are increased,and therefore the entire combustion process are promoted.