Analysis of Flammable Mixture Formation in a Methane Unsteady Jet

Abstract

Flow and mixture formation processes of a high-speed unsteady methane-jet are calculated using a large eddy simulation in order to investigate the distribution of flammable mixture in a jet. The calculations were performed for wide range of injection pressure, from low pressure injection to super-critical cases and for an impinging jet on a circular obstacle. Based on the calculation result, formation of flammable mixture was discussed and compared with the previous experimental results of spark-ignition combustion of a natural gas jet. A flammable region is formed from 40 to 80 times nozzle diameter downstream on a jet axis and stable combustion starts by spark-ignition in this region for the case of lower injection pressure. On the other hand for high pressure injection case, a flammable region forms farther downstream and a thin flammable region is distorted by turbulence, therefore, spark-ignited combustion was not observed in the experiments. For the impinging jet case, a flammable region spread quickly and widely behind the obstacle, even if for the high pressure injection case, so that stable combustion was achieved in the experiments.