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Detailed reaction path analyses of DME (dimethyl ether, CH3OCH3) and n-heptane (n-C7H16) were performed computationally with the “contribution matrix” showing the contribution ratios of important elementary reactions to formation or removal of every species or heat release at transient temperatures. It was found that the “H2O2 reaction loop” defined by the authors plays an important role in the initiation of thermal ignition. This is a reaction loop composed of four reactions, H2O2 + M → 2OH + M, OH + CH2O → HCO + H2O, HCO + O2 → HO2 + CO and 2HO2 → H2O2 + O2. The overall reaction is 2CH2O + O2 → 2H2O + 2CO + 473 kJ. This loop begins to be active, when the OH formation by H2O2 + M → 2OH + M becomes dominant against those by cool-flame reactions with NTC's (negative temperature coefficient) at about 950 K. The loop releases a significant amount of heat without consuming H2O2.

The gasoline direct injection engine starts significantly faster than a conventional engine. Fuel can be injected into the cylinder during the compression stroke at the same time of cranking start. When the spark plug ignites the mixture at the end of compression stroke, the engine has its first combustion, that is, the first combustion occurs within 0.2 sec after the start of cranking. This unique characteristic of quick startability has realized a idle stop system, which enables drivers to operate the vehicle in a natural manner.

Gasoline includes various kinds of chemical species. Thus, the reaction model of gasoline components that includes the low-temperature oxidation and ignition reaction is necessary to investigate the method to control the combustion process of the gasoline engine. In this study, a gasoline combustion reaction model including n-paraffin, iso-paraffin, olefin, naphthene, alcohol, ether, and aromatic compound was developed. KUCRS (Knowledge-basing Utilities for Complex Reaction Systems) [1] was modified to produce paraffin, olefin, naphthene, alcohol automatically. Also, the toluene reactions of gasoline surrogate model developed by Sakai et al. [2] including toluene, PRF (Primary Reference Fuel), ethanol, and ETBE (Ethyl-tert-butyl-ether) were modified. The universal rule of the reaction mechanisms and rate constants were clarified by using quantum chemical calculation.

The Mitsubishi GDI engine has adopted a pair of upright intake ports, to induce a rotating in-cylinder flow, reverse tumble, and control air fuel mixing with this flow. The port design of the GDI engine was optimized for achieving a high intensity of the reverse tumble while maintaining a high charge coefficient, by means of modeling of in-cylinder flow and experiment with a steady flow rig. First of all, the ideal design of the upright ports was discussed. It was found that for enhancing the reverse tumble, it is more effective to arrange a pair of the ports parallel, than to arrange them convergent. The parallel arrangement leads to the smoother flows passing through the intake sides of the intake valves, and then descending on the cylinder liner, that is turning toward the rotation direction of the reverse tumble, because of less impingement of the flows through a pair of the valves.