Clean High-speed Combustion with Two-phase Stratification into Rich and Lean Mixtures

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A direct injection stratified charge engine with two-stage fuel injection determined by the piston phase was proposed, and combustion and exhaust gas emissions are discussed in this research. The formation of two-phase stratification of rich and lean mixtures was realized with the two-stage fuel injection into a double cavity in the piston top at suitable timings : the first-stage injected into an outer cavity for the lean mixture and the second-stage into an inner cavity for the rich mixture. An premium gasoline for automobiles was used as the tested fuel. A multi-dimensional CED engine simulation code "FIRE" was used to analyze the mixture formation process in the combustion chamber before the experiments in the engine. The simulation showed that the rich mixture was formed in a part of the inner cavity while the mixture almost in the entire combustion chamber is heterogeneous and leaner than the mixture strength expected from the injected amounts. The simulation predicted that the mixture was very lean near the spark plug at the cylinder head, and the position of the plug gap was changed to near the bottom of the cavity with extended electrodes in the experiment and the stability of combustion was significantly improved. The injection timing in the inner cavity should be during the compression stroke rather than the intake stroke to prevent the diffusion of fuel out of the inner cavity. The injection timing in the outer cavity should be during the intake stroke to insure a homogeneous mixture in the entire combustion chamber.