| With the rapid development of national economy, there are a lot of automobiles in China. The main power devices of automobiles are internal combustion engines, which faces more challenges, such as energy saving and environmental protection. But these challenges are advantageous to improve automotive technologies and spur a new generation, energy saving and low emission cars to appear.HCCI (Homogeneous Charge Compression Ignition) is a new kind of combustion mode, which is the autoignition of pre-mixtures when their temperature is high enough to self-ignition by compression. This combustion can reduce the emission of NOXand particulate matters, in addition, use many fuel, so HCCI has been a research hot spot in internal combustion engine field.Firstly, this dissertation illustrates the chemical reaction mechanism of methanol, ethanol and hydrocarbon fuel, simulates ethanol on-board reformation and its effects on HCCI combustion. Secondly, it builds up a HCCI testing platform based on alteration of a CT2100 diesel engine. The effects of variable parameters on the combustion characteristics, operating region and emission characteristics of alcohols (methanol and ethanol) and gasoline HCCI were researched. The main innovative results are summarized as follows:(1) Simulation ethanol on-board reformation with IC Engine of Chemkin. The simulation results shows that as the rate of reformation gas is increased, peak pressure is increased, crank angle of peak pressure is advanced and indicated thermal efficiency is improved. The combustion start point of HCCI is delayed, when the phase position of reformation gas entering the cylinder approachs top dead center.(2) OH,CO,H and O play very important roles in methanol and ethanol combustion according to their detail chemical reaction mechanism, which importantly affect the reaction rate and combustion velocity.(3) Build-up a HCCI testing platform, including the design and re-creation of intake and exhaust system, design of fuel system and re-creation of cooling system. Experimental results indicate that it is successful and feasible.(4) The test results show that as the increase of intake temperature, the peak pressure and temperature in cylinder both are increased, combustion timing and CA50 both are advanced, and combustion duration is shortened. The emissions of HC and CO (which are more sensitive to intake temperature for methanol and ethanol.) are decreased. With the increase ofλ, the in-cylinder peak pressure and temperature are decreased, combustion timing and CA50 both are delayed, and combustion duration was prolonged, the emission of NOx is decreased, the emissions of HC and CO are increased. HC emission of methanol is minimum among the test fuels.(5) The test results show that as the increase of coolant temperature, CA50 is significantly advanced, the emissions of HC and CO are decreased, NOx emission of alcohol is slightly increased.(6) The HCCI test results of the three fuels show that the peak pressure of gasoline is maximum, the peak pressure of methanol was minimum, the peak pressure of ethanol is between gasoline and methanol. With the increase of octane number, the peak pressure is decreased and combustion duration is prolonged.(7) HCCI operating region is determined by two parameters, coefficient of cyclic variation and the maximum rate of pressure rise. For ethanol and gasoline, it is commonly determined by both the two parameters, however, for methanol, it is mainly determined by the former.(8) When HCCI operating region is described by rotation speed andλ, it was knowed that the rotating speed region of alcohols is wider than that of gasoline. Ethanol can extend the region to higher speed, and methanol can extend the region to the lower speed. With the increase ofλ, rotation speed region of alcohols within stable HCCI operating region becomes narrow. Rotation speed region of gasoline is wider than that of alcohols within stable HCCI operating region.
|
PDF Full Text Request