The influence of intermediate species on the combustion process of n-dodecane flame

Abstract

Split-injection strategy is of great potential to reduce the pollutant emissions without deterioration of engine performance. The combustion of the previously injected fuel has great influence on the ignition of the subsequent second injection. In this study, the main influence of species formed in the first injection on the ignition of the second injection is analysed in detail. Different species are added into the fuel/air mixture to study the influence of the species formed in the first injection on the combustion process of the second injection. Results show that the influence of species addition on the ignition delay is dependent on the initial temperature and oxygen concentration. The presence of acetylene (C2H2) and methane (CH4) prolongs the ignition delay regardless of initial temperatures or oxygen concentrations. However, ethylene (C2H4), hydrogen peroxide (H2O2), hydrogen (H2) and formaldehyde (CH2O) shorten the ignition delay at high temperatures. The temperature increase ahead of the second spray plays a more important role in promoting the overall ignition process regardless of the initial oxygen concentration. Moreover, the effect of species addition on the first- and second-stage ignition processes is also analysed in detail. Different from the results with other species addition, the presence of H2O2 and CH2O in the initial gas leads to the monotonical decrease with the increase in the initial gas temperature, T0.