Ignition Control on Rapidly Compressed Dimethylether Mixtures with Reaction Suppression Effect of Methanol

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Direct injection of an ignition suppressor was attempted to control the ignition timing, suppression of rapid combustion, and expansion of the operating range in an HCCI engine with induced DME. The effect of the ignition suppressors was analyzed with a chemical kinetics, which simulated the engine-like transient gas conditions as well as with experiments in an HCCI engine. The reaction suppressors reduced the low-temperature oxidation reactions and delayed the start of high-temperature oxidation reactions. The chemical kinetic analysis showed a reduction of OH, O, and H radical concentrations in the premixed charge when injecting the suppressors without lowering the temperature. Among the ignition suppressors tested here alcohols had a greater effect for the radical reduction resulting in stronger ignition suppression than water, hydrogen and methane, and methanol had the strongest effects among alcohols. While water had a greater effect on lowering the temperature, methanol had a much stronger chemical effect on the radical reduction. The reduction of low-temperature oxidation suppressed the temperature increase after the reaction and this temperature drop delayed the start of high-temperature oxidation. There was no effect when suppressor injection timing was set after the appearance of the low oxidation, and the reaction suppression effect increased with advanced suppressor injection timings. The control of ignition timing, suppression of rapid combustion, and expansion of the operating range to loads comparable to ordinary diesel operation were achieved with direct injection of the ignition suppressors, and smokeless, ultra low NOx combustion was simultaneously realized over a wide operating range.