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

在HCCI发动机中，通过进气歧管和水诱导的高可燃性燃料或不发生低温氧化的低可燃性燃料在压缩冲程早期直接注入以抑制点火。灵活控制其数量平衡，根据工况优化点火时间。在较宽的工作范围内，通过水或酒精喷射，实现了超低NOx和无爆燃、无失火的无烟燃烧。注水显著降低了低温氧化，抑制了装药温度的升高和高温氧化引起的快速燃烧。注水降低了缸内气体最高温度，抑制了快速燃烧，降低了燃烧效率。因此，需要将最高装药温度控制在一个极其有限的范围内，以保持温和燃烧和高燃烧效率之间令人满意的折衷。醇比其他含氧或无氧碳氢化合物、水和氢更能抑制低温氧化。用甲醇建立的化学动力学模型表明，OH自由基在低温氧化开始前就已还原，这可能是醇类抑制低温氧化的主要机制。低压缩比、低辛烷值燃油与直喷甲醇相结合，可根据工况灵活控制低温氧化，扩大了运行负荷范围。甲醇在HCCI燃烧中的抑燃效果要比其他辛烷值相近的燃料强得多。

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.