Study Of Effects Of Dissociated Methanol On Performance Of SI Electronic Controlled Engine

With the reduction of petroleum resources and the increasingly stringent emission regulation, it is of great significance to search for available alternative fuels, of which methanol is one of the most promising alternative fuels.Owing to the problems of low fuel efficiency and high emissions when engine fueled with pure methanol, Pefley R.K, a researcher from American,put forward the method that methanol was dissociated into hydrogen and monoxide carbon as engines'fuel using exhaust energy. Although many researches on dissociated methanol engines have been done by scholars at home and abroad, they are all based on carburetor engine fueled with the mixture of dissociated methanol and gasoline and the dissociated system is complicated.With the progress of the engine technology, the fuel injection systems of modern engines are all electronic-controlled, instead of using traditional carburetor. In order to apply the dissociated methanol to EFI engine,a control strategy was raised:Engine is started by gasoline, when the exhaust energy is enough to produce dissociated methanol to run the engine, the electric control unit will switch the engine from gasoline fuel to methanol fuel. The bench test and vehicle road test of the dissociated methanol engine were conducted and better results were attained.In the engine bench test, the performance of the engine fueled with dissociated methanol reached to that of the original engine and the problem of the frequent damage of methanol nozzles mounted on the dissociator has been solved. Meanwhile,the control strategy of smooth switching between gasoline mode and dissociated methanol mode and of the automatic operation under dissociated methanol mode are achieved successfully. To provide the basis for the dissociated methanol engine with high efficiency , dissociated methanol components were detected using gas chromatograph, and the results show that besides hydrogen and monoxide carbon, certain amount of methanol steam was found in dissociated methanol and they account for 23.3-46% , 11.6-23% and 31-65%, respectively. Since the wide flammability limits of dissociated methanol allow the engine operate at very lean mixture conditions,an experimental research on the emission characteristic, economy and power performance were performed in this paper. The results show that,there is an order of magnitude reduction of NOX and CO compared with the original engine with NOX reduced by 90% and CO almost close to zero emission level,while the HC emission is equivalent to gasoline, when excess air ratio is more than 1.4. The results also show that the CO and HCHO decreased,while NOX and HC increased when using three-way catalytic converter. In addition,the fuel economy of the engine at lean mixture is improved with the minimum substitution ratio of 1.43, which means 1.43L methanol can substitute 1L gasoline,while its power is slightly reduced compared with original engine. In order to deeply understand the combustion characteristics of dissociated methanol,the cylinder combustion pressure was measured , according which the pressure rising rate, maximum combustion temperature and maximum heat release rate were calculated and the results show that they all increased with the dissociation rate of methanol.After all, the vehicle road test with methanol dissociating system was performed without three-way catalytic converter. The results show that the vehicle fueled with dissociated methanol can attain to 140 kilometers per hour,and strong power, smooth switching and stable running can be assured.