Characteristics of combustion in stratified mixture

Combustion characteristics of the stratified mixture were investingated by the experiments on the combustion of the transient fuel jet and the numerical simulations of counterflow premixed flames. In the experiments, some characteristic features such as "secondary flame" and "bulk quenching" were observed. The secondary flame came out in the burned region after the primary flame had propagated within the fuel jet. The bulk quenching was found to occur in the periphery of the jet due to the low fuel concentration. Then the "flame inertia" was found in the investigation of the flame propagation into the lean region. The experiment was accomplished by the injection of propane into the lean premixed propane-air mixture charge, whose equivalence ratio was less than the lower flammability limit of the premixed mixture. The flame generated in the fuel jet propagated into the lean premixed mixture charge as if it had an "inertia". Then it was quenched in the premixed mixture charge before it would reach the chamber wall. The flame seems to be supported by the burned region from its back until the decay of this support. These combustion characteristics such as the secondary flame and the flame inertia seem to be due to the interactions of the rich flame and the lean mixture. In order to investigate them, numerical simulations of the counterflow premixed flames were examined next. Rich mixtures, hot nitrogen and burned gas were opposed to the lean mixture. In this study, the secondary flame was considered the diffusion flame in the triple flame configuration. The flame propagating into the over lean region was considered the "supported flame". The results showed the "supported flame" were quite different from the "self-sustaining" flame.