Active control of high speed compression pre-mixture with suppression effect of radical consumers on low temperature oxidation

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High ignitability fuel, which exhibits two-stage ignition, was induced from the intake manifold and water or a low ignitability fuel, which does not exhibit low temperature oxidation, was directly injected early in the compression stroke for ignition suppression in an HCCI engine. Their quantitative balance was flexibly controlled to optimize ignition timing according to operating condition. Ultra-low NOx and smokeless combustion without knocking or misfiring was realized over a wide operating range with water or alcohol injection. The water injection significantly reduced the low temperature oxidation, which suppressed the increase in charge temperature and the rapid combustion caused by the high temperature oxidation. Rapid combustion was suppressed by reductions in the maximum in-cylinder gas temperature due to water injection while the combustion efficiency suffered. Therefore, the maximum charge temperature needs to be controlled within an extremely limited range to maintain a satisfactory compromise between mild combustion and high combustion efficiency. Alcohols inhibit low temperature oxidation more strongly than other oxygenated or unoxygenated hydrocarbons, water, and hydrogen. Chemical kinetic modeling with methanol showed a reduction of OH radical before the onset of low temperature oxidation, and this may be the main mechanism by which alcohols inhibit low temperature oxidation. A combination of lower compression ratio and lower octane number fuel with direct methanol injection can expand the operating load range envelope as low temperature oxidation can be flexibly controlled with methanol injection according to operating condition. The ignition suppression effect of methanol in HCCI combustion is much stronger than those of other fuels with similar octane number.