| Problems of energy crisis and exhaust pollution have attracted more and more attention in the past decades. Methanol, especially methanol gasoline blended fuel, has been one of the most potential alternative fuels in China, for its lower emissions and higher production. Sinece advantages of reducing emissions and enhancing combustion efficiency are obvious when methanol gasoline are used in SI engines, there still exists problems such as the rise of unregulated emissions and higher fuel consumption. In order to solve these problems and exploit the advantages of the blended fuel, series of theoretical and experimental researches are carried out in this study.First of all, bench tests on a PFI (Port Fuel Injection) SI(Spark Ignition) engine, directly burning methanol gasoline blends, were carried out. Based on the MR479q engine test bench and the advanced test equipments including FTIR (Fourier Transform infrared spectroscopy) and CA (combustion analyzer), emissions under different engine conditions were measured. The result shows that emissions of carbon monoxide, nitrogen oxides and unburned hydrocarbons decrease with the adding conponent of methanol. However, it also results in the increase of several unregulated emissions. When the engine is fueled with M70, CO, NOx and HC emissions are respectively reduced by 66%-71%,29%-54% and 71%-80%. Meanwhile, formaldehyde emission is 183%-255% more than fueled with pure gasoline while unburned methanol tens of times higher. As well as the emission characteristics of methanol gasoline blends, the characteristics of engine power and fuel consumption were obtained through the test.Secondly, researches on the chemical kinetic models for the oxidation of methanol and gasoline surrogate were carried out. A reduced oxidation mechanism for methanol gasoline blends were established. Then, the basic characteristics of the mechanism were validated by various experiment data, including shock tube, rapid compression machine, jet-stirred reactor and laminar flame speed. The validation results indicated that the reduced mechanism could accurately predicate the ignition delay times and flame speeds of methanol gasoline blends. Also, the change of species concentration in the oxidation porcess could be calculated.Subsequently, the calculation time sclae of chemical reaction and fluid dynamics was unified by the Kong model. On this basis, a 3D CFD (Computional Fluid Dynamics) simulation platform coupling chemical kinetics was built, where the entity structure of intake/exhaust ports, intake/exhaust valves and chamber were included. Then the model was calibrated and validated by the experimental data. The simulated in-cylinder pressure and heat release curves agreed well with the experiment results. Moreover, the 3D in-cylinder performed well in predicating the emissions. The predicated error of CO emission was within 8.5% while NOx within 32% and formaldehyde 39%.Finally, simulation research of the in-cylinder process of methanol gasoline blends were carried out. The results of intake flow characteristics, in-cylinder combustion and emission formation under different engine conditions were obtained. By analyzing these results, the formation mechanism of some important emissions were investigated. On the other hand, in-cylinder processes with different engine compression ratios were simulated. The results showed that engine power was improved by reasonably enhancing compression ratio. For the fuel of M20, the enhancment of compression ratio results in the rise of NOx emission and the reduce of CO emission. Moreover, a multi-objective model for engine parameter optimization was proposed. With the model and the data from both numerical and experimental researches, the compression ratio was optimiazed and the best ignition advance angle for the methanol gasoline engine was investigated. The results above provide theoretical basis for the further design and development of a methanol-gasoline engine. |
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