Numerical Simulation Study On N-butanol-diesel Blended Fuel In Low Temperature Combustion

As the car ownership increasing, energy crisis and environmental problem become more and more highlight, the requirement on energy conservation and emission reduction of internal combustion engine become higher. Developing new fuel and applying new combustion mode are the important way to realize energy conservation and emission reduction of internal combustion engine. Low temperature combustion mode is known as a new combustion mode which can reduce the diesel NOx and soot emission effectively at the same time. Researches showed that using n-butanol as the oxygenated alternative fuel of engine could remarkably decrease the emissions, and the low temperature combustion properties could be improved by adding appropriate amount of n-butanol into diesel. Therefore, the study on fuel characteristic of n-butanol and its application as alternative fuel in low temperature combustion of diesel engine is significant to energy saving and emission reduction of internal combustion engine.This paper studied the combustion chemical reaction kinetics of n-butanol and the low temperature combustion characteristics of n-butanol-diesel blended fule by using numerical simulation method. Firstly, using n-butanol detailed mechanism with the constant volume combustion chamber model in CHEMKIN, the chemical kinetics analysis on n-butanol combustion characteristics were studied, including oxidation process, reaction path in low and high temperature, ignition characteristics, sensitivity analysis of ignition delay, and influence of oxygen concentration on n-butanol combustion. Results showed that the reaction path and reaction rate of n-butanol under high temperature and low temperature were respectively different, making ignition time different. The reaction path and reaction rate were both influenced by initial temperature while the oxygen concentration only affected the reaction rate of n-butanol and had no effect on the reaction path of n-butanol. The igniton delay time of n-butanol reduced as the increase of initial pressure, the equivalent ratio, the initial temperature and the oxygen concentration, while the initial temperature had the biggest influence on the ignition delay time of n-butanol.Secondly, in order to study the combustion chemical reaction kinetics of n-butanol-diesel blended fuel, the detailed mechanism of n-butanol-n-heptane-toluene and a diesel engine model were built in CHEMKIN. The influence of n-butanol on the blended fuel combustion including the concentration of each components and OH radical were studied. The results showed that OH radical produced by n-heptane was comsumed by n-butanol, which restrained the combustion of blended fuel.Then, this paper built the combustion chamber model of engine by using the FIRE software for simulating the combustion of n-butanol-diesel blended fuel, and used the n-heptane-n-butanol-PAH-toluene reduced mechanism coupled with CHEMKIN to simulate the low temperature combustion process of n-butanol-diesel blended fuel. The model had been proved to be of high accuracy and could precisely simulate the combustion process of n-butanol-diesel blended fuel.Lastly, with the introducing of high EGR rate, the model realized the low temperature combustion. The influence rules of low temperature combustion and emission performance of n-butanol-diesel blended fuel were summarized by studying the parameters of n-butanol proportion, EGR rate, fuel injection timing, inlet pressure and inlet temperature. Results indicated that these parameters mainly affected the combustion and emission through the impacts on the ignition delay, in-cylinder temperature and oxygen concentration. The mass fraction of soot precursors A4that converted to soot could be reduced by adding n-butanol into diesel, and the EGR could reduce the emission of NOx. Studying the n-butanol-diesel blended fule of B10and B20on45%EGR rate, the resules showed that delaying fuel injection would delay the combustion time, reduce the power and economy of engine and the emission of NOx, while the emission of CO would increase. By increasing the inlet pressure, the power and economy of engine could be improved, but the emission of NOx and the mass fraction of soot precursors A4that converted to soot would be increased. By increasing the inlet temperature, the ignition time advanced, the power and economy of engine were improved significantly, CO emission was reduced while NO emission and the mass fraction of soot precursors A4that converted to soot were increased.