Experimental Study On Quick Start Characteristics Of Methanolgasoline Engine Under Warm Condition

Quick start-stop technology can avoid the fuel consumption of vehicle under idle condition, but it also causes engine to start frequently, which will deteriorate emission seriously if controlled improperly. Focusing on the problems during quick start and combining the advantage of methanol in combustion speed, this paper constructed the experimental system for methanol-gasoline engine quick start based on cycle by cycle control. The characteristics of methanol-gasoline engine quick start under warm condition were investigated with the minimum fluctuation of engine speed during start process.First of all, the performance of methanol-gasoline engine were studied under idle condition, and the influences of methanol proportion, ignition advance angle and excess air coefficient on combustion and emission characteristics were analyzed. Experimental results show that methanol has improved the indicated thermal efficiency of engine, and accelerated the combustion in cylinder. In addition, the coefficient of variation of indicated mean effective pressure(IMEP) and regular emissions were reduced. Compared with gasoline, methanol has realized slightly larger optimum ignition advance angle, and it has better combustion and emission performance under lean mixture condition.The combustion characteristics of first cycle during quick start of methanolgasoline engine were studied. It is found that, with the increase of engine start speed, hydrocarbon(HC) emissions and the fuel enrichment of first cycle at which in-cylinder mixture can be ignited are reduced, but the improvement became not obvious when engine start speed exceed 1200 RPM. The combustion characteristics of first cycle change little when methanol proportion is below 50%, however, HC emissions and the fuel enrichment of first cycle at which in-cylinder mixture can be ignited are decreased obviously when the methanol proportion exceed 50%. Under each methanol proportion, the most suitable ignition advance angle of first cycle is 15oCA BTDC, which achieves the highest IMEP and relatively low HC emissions.The subsequent cycles during quick start of methanol-gasoline engine was analyzed. It is found that the effect of first cycle fuel injection enrichment for subsequent cycles decreased with cycle number. The IMEP of 2~10 cycle fluctuated obviously, but with the increase of methanol proportion, the fluctuations are reduced significantly. The fuel injection coefficients of 2~10 cycle were corrected according to the change of intake manifold absolute pressure(MAP). Experimental results show that the IMEP fluctuation of 2~10 cycle after fuel correction has decreased, but HC emissions increased. In correspondence with the test results before fuel correction, with the increase of methanol proportion, the combustion stability of the mixture in cylinder and HC emissions are improved significantly.