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Combustion characteristics of the transient methane jet were investigated using a constant volume bomb. The amount of unburned fuel increased as the ignition timing was delayed. Bulk quenching was found to occur in the trailing part of the jet due to the low fuel concentration. Then the characteristics of the flame propagation into the lean region was investigated. This is accomplished by the injection of methane into the lean methane-air mixture charge, whose equivalence ratio was less than the lower flammability limit of the premixed methane-air mixture. The effects of methane concentration of the charge on the flame propagation was examined. The flame generated in the fuel jet propagated into the lean mixture charge. Though the flame propagated in the lean mixture charge for a longer duration with the increase of its methane concentration, it was quenched in the charge before it reached the chamber wall.

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”.

The present study is performed to examine experimentally the turbulent burning velocity characteristics of lean hydrogen mixtures with attention to the local burning velocity. The special mixtures, having nearly the same laminar burning velocity with different equivalence ratios Ф=0.3~0.9, are prepared. The measured turbulent burning velocities at the same turbulence intensity show to large increase as Ф decreases until about 0.5. Those, however, do not show such large increase when Ф becomes lower than about 0.5. This phenomenon is discussed by the estimated mean local burning velocity taking account of preferential diffusion, tomograms of turbulent flames and estimated Markstein number.