Study Of Incomplete Oxidation Products From EGR On Ethanol/n-heptane Dual-fuel Ignition Characteristics

RCCI（Reactivity controlled compression ignition）merges as a new combustion pattern,and it is known for high combustion efficiency and low emission.However,excessive heat release rate and engine knocking tend to occur under medium or high loads.Therefore,exhaust gas re-circulation（i.e.EGR）is employed under such occasions in order to solve these problems.In this paper,the chemical effects of oxygen,incomplete oxidation products（i.e.IOP）and individual species from EGR are investigated based on a shock tube facility in our lab.Moreover,a detail NO_X/n-heptane has been developed.The comparison between physical effects of CO₂/N₂ and chemical effects of O₂/IOP has been conducted in this paper.Moreover,chemical effects of O2/IOP under different temperature,pressure（10/18atm）,equivalence ratio（0.5/1.0/1.5）and EGR ratio（0%/30%/50%）have been investigated.Results show that the chemical effect of O₂ has been strengthened as the equivalence ratio/EGR ratio increase,and it remains unchanged as pressure increase from 10 atm to 18 atm.As for the chemical effect of IOP,it has been weakened as the equivalence increases,and it is more obvious in a higher EGR ratio.Also,the chemical effect of IOP is not sensitive to the pressure.Moreover,detailed reaction kinetic analysis of O₂ chemical effects has been conducted.A new NO_X/n-heptane reaction mechanism has been developed and validated under different experimental conditions.Results suggest that good agreement has been achieved between current mechanism and experimental data from literature.Thus,current mechanism can be employed to study the chemical effect of individual species.The chemical effect of individual species has been investigated using current mechanism,and results show that the addition of acetaldehyde promote the fuel ignition through R333:CH₃CHO+O₂（?）CH₃CO+HO₂ and R337:CH₃CHO+HO₂（?）CH₃CO+H₂O₂;the chemical effect of ethylene can be ignored under current experimental conditions;the addition of nitric oxide promote the ignition through R5534:CH₃+NO₂（?）CH₃O+NO and R5404:NO+HO₂（?）NO₂+OH,these two reactions produce the OH radical to increase the overall reaction activity.