Combustion characteristics of the transient gas fuel jet were investigated in this study. Stratified mixture was formed in the constant volume bomb by the injection of gaseous propane into the quiescent air in the bomb. The amount of the injected fuel was set to 0.07 in overall equivalence ratio. It was ignited by the electric spark. The ignition timing had large influences on the combustion pressure and the amount of the unburned fuel. The amount of the unburned fuel in the burned gas was larger as the ignition timing was later regardless of the ignition positions. Flame did not propagate to the lean region in the cases of late ignition timings. Fuel in this lean region remained unburned. Bulk quenching in the over lean region seems to be the main cause of the unburned fuel because the over lean region will increase as ignition timing is late. The flame propagation in the case of the ignition during the fuel injection was quite different from those in the cases of the ignition after the end of the fuel injection. Secondary flame came out in the burned region after the initial flame had propagated through the fuel jet only in this condition. Its shape was quite different from the initial one in the early stage of the combustion process. And it was luminous and showed red. This secondary flame remained there over 80ms. It seemed that the rich region surrounded by the burned gas and the fuel injected after ignition burned gradually mixing with air entrained into this region after the initial flame propagated throughout the fuel jet. The limit of flame propagation to the lean region was investigated next as the main cause of the unburned fuel was bulk quenching in the over lean region. In order to examine at what fuel concentration flame quenching occurred, lean fuel-air mixture below the flammability limit was supplied as the charge instead of air. Fuel was injected into this mixture and ignited. Though the mixture charge itself was too lean to ignite by the spark ignition, flame initiated in the fuel jet propagated to the large area compared to the case of no fuel addition to the charge. More propane than the amount of the main injection was burned when the equivalence ratio of the charge before fuel injection, φ_c was 0.40 or more. The amount of the burned fuel normalized by the amount of the main fuel injection, N_B increased considerably in the range of φ_c=0.40 to 0.54. The limit of flame propagation to the lean region seemed to be around this range.
|Journal||The Proceedings of the International symposium on diagnostics and modeling of combustion in internal combustion engines|
|Publication status||Published - 2001|