Experimental Study On Mixed Combustion Of Dissociated Methanol In Si Engine

With the rapid development of the automotive industry, the growing dependence on oil resources has caused serious environmental pollution problems. It has become an urgent problem for the automotive industry to improve the thermal efficiency of the engine and to search for clean and renewable alternative fuels. Methanol as a source of a wide range of engine alternative fuels, which is an effective way to solve the problem of increasing shortage of vehicle fuel in China. When methanol dissociated gas is transported into cylinder and burned, engine fuel consumption can decrease. At the same time a hydrogen rich methanol dissociated gas can optimize the in-cylinder mixture combustion process, improve the thermal efficiency of combustion and reduce the engine emissions.In order to realize the combustion of gasoline-dissociated methanol mixture, the methanol dissociated system which was connected to the exhaust pipe in series was designed in this study. The methanol dissociated system could recover the waste heat from the engine exhaust to dissociate methanol. The dissociated methanol-blended engine experiments were conducted in a inlet multi-point PFI gasoline engine, and studied the engine economy, power, in-cylinder combustion process and emission characteristics on stoichiometric and lean buen mixture conditions.The test results show that mixed combustion of dissociated methanol can reduce the engine torque and improve effective thermal efficiency on stoichiometric conditions. Under the same load condition, when mixed combustion of dossociated methanol, the peak combustion pressure and peak pressure rise rate are elevated and the time point of peak presssure become earlier, the heat release rate is higher and combustion process is obviously ahead of the gasoline engine. With the increase of methanol substitution ratio, CO emission first decreases and then increases, HC emission decreases, and NOx emission increases.In lean burn conditions, the break thermal efficiency of gasoline engine and dissociated methanol-blended engine both increase with the increase of excess air coefficient. Under the same excess air coefficient conditions, dissociated methanol-blended engine is more efficient than gasoline engine. When inlet pressure is constant, with dissociated methanol addition, the peak combustion pressure, peak pressure rise rate and peak combustion heat release rate are slightly lower on stoichiometric condition; the peak combustion pressure, peak pressure rise rate and peak combustion heat release rate are higner on lean burn conditions, and this trend is more obvious with the increase of excess air coefficient. With the excess air coefficient increasing, CO and HC emissions markedly decrease, NOx emission is increased first and then decreased. Under the same condition of excess air coefficient, CO and HC emissions are lower and NOx emission is higher for dissociated methanol-blended engine.