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A Catalytic Hot Wire Probe (CHWP) technique has been developed to estimate local fuel concentration near the spark plug of a 4-valves Spark Ignition Engine. Various levels of gasoline concentrations, stratification and tumble levels have been achieved by modifying the injection and intake valve configurations. To validate this CHWP technique, local fuel concentration was also measured by using an optical diagnostic technique: Planar Laser Fluorescence (PLIF). Comparative results show good agreements, capabilities as well as limitations of both techniques. It can be concluded that CHWP is a minimised intrusive, inexpensive and easy technique which allows the evaluation of cylinder mixture preparation near the spark of an SI engine. This is a promising technique which could be used, in the future, to evaluate the mixture stratification in direct injection engines.

In previous studies, we have shown that even if local conditions and coil charge seem remaining constant, electrical energy deposit by a spark plug was never the same. In fact, its mean and variations depend on local conditions in the vicinity of the plug, and may be linked to phenomena during the breakdown. In this paper, we will focus on spark plug temperature effects, both on the electrical energy deposit and on the early flame kernel development for propane-air lean mixtures in closed vessel.

Combined Catalytic Hot Wires Probe (CHWP) and Fuel Air Ratio Laser Induced Exciplex Fluorescence (FARLIEF) techniques have been applied to a Gasoline Direct Injection Engine to characterize temporal and spatial evolution of the fuel/air ratio in the vicinity of the spark plug. The engine ran below stoichiometric with early injection (homogenous case taken as a reference) or late injection timing with a global equivalence ratio as low as 0.3. Under lean and late injection conditions, the temporal CHWP signal indicates that a rich vapor cloud is carried to the vicinity of the spark plug. CHWP and FARLIEF techniques show that the maximum equivalence ratio in the fuel cloud reaching the spark does not depend on the injection duration. Instead, the duration appeared to affect the size of this rich vapor pocket.