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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.

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.

In order to study alternate methods of Air Fuel ratio (A/F) perturbation for maximizing three-way catalyst conversion efficiency, two methods for measuring the Oxygen Storage Capacity (OSC) of Catalyst were developed on an engine test bench. The first is to measure just the break-through Perturbing Oxygen Quantity (POQ, which is defined as the product of A/F amplitude, perturbation period and gas flow), and the second is to measure the response delay of the rear A/F sensor, which has been improved to be very similar to the former. Then, the OSC values of many catalysts were investigated with different perturbation parameters. The results show that OSC would not be affected by amplitude, period of perturbation and gas flow, and that the best conversion efficiency is obtained when the value of POQ is about 1/2 of the value for OSC. These results suggest that the best way to control perturbation is to keep POQ at 1/2 of OSC by setting perturbation parameters.

The purpose of this paper is to study the feasibility to utilize methane, which is the main component of natural gas and biogas, as a fuel for lean-burn engines. To realize this, however, there are mainly two problems to solve; the substantial decrease in the burning velocity and the large increase in the misfire probability in the lean mixture region. It has been shown that such problems can be solved by adding hydrogen to the lean methane mixture. By adding only a small amount of hydrogen to the lean methane mixture, the turbulent burning velocity is substantially increased and the lean limit is greatly extended, at the same time. Furthermore the condition at which hydrogen addition most effectively improve the turbulent combustion performance is identified. Finally these improving mechanisms are discussed.

Conventionally, turbulent burning velocity models are compared by showing the model-predicted ST/SL0 ratios in an ST/SL0 - u′/SL0 plane, where ST and SL0 are the turbulent and laminar burning velocities, respectively, with u′ being the turbulence intensity. Such a method applies to only those models which take u′ or u′/SL0 as the only variable of ST or of ST/SL0. In order to analyze and compare most recent models in which turbulence and flame spatial scales (or length scales) are also taken into account because of their importance in combustion, this paper showed the model-predicted ST/SL0 ratios as contours in three planes (Re-Da, ηκ/η0 - u′/SL0 and L/η0 - u′/SL0, where Re, Da, L, ηκ and η0 are the Reynolds number, Damköhler number, turbulence integral scale, Kolmogorov scale and laminar flame preheat zone thickness, respectively); these planes are usually used in discussing the flame structure.