The quantitative characterization of the ignition process for a lean staged injector: Influence of the air split between pilot swirlers

The ignition of a lean staged injector aimed at aeronautical application is a transient and complex phenomenon, which involves fluid dynamics, turbulent mixing, chemical kinetics, as well as their mutual interactions. In the present research, a staged injector, designed based on stratified partially premixed combustion concept, is introduced. The ignition performance of stratified partially premixed injectors with different air split ratios between pilot swirlers are experimentally acquired, which exhibits apparent distinctions. In order to make quantitative analyses, the classical physical ignition model is improved, in which the flame propagation process is further divided into the axial and radial propagation sub-processes. Nonreacting flow field and discrete phase simulations, validated by experiment results, are utilized to obtain the velocity and spray distributions. Physical parameters characterizing the ignition sub-processes are defined and calculated based on the numerical simulation results. Conclusions are made by comparing the physical parameters of the ignition sub-processes. The radial propagation of the ignition kernel is responsible for the ignition performance difference between the two injectors with different pilot air split ratios (PASR) in that the average equivalence ratio along the radial propagation route of PASR = 7:3 is one order richer than that of PASR = 2:8. The present ignition analysis and model can be further extended and developed for the optimization of ignition performance of lean staged injector.