Experimental Study On Combustion And Emissions Characteristics Of An HCCI Engine Fueled With N-Heptane/n-Butanol Blends

As the problems of energy shortage and environment pollution are becoming more and more serious, many researchers have currently tried to explore a cleaner and much more efficiency combustion mode of internal combustion engine, one of the principal routes to deal with these problems is Homogeneous Charge Compression Ignition(HCCI). As a new combustion mode with the strongest potential in internal combustion engine and a focus in the field of combustion study in the world, HCCI combustion contains various advantages of traditional gasoline engine and diesel engine combustion mode, not only has high combustion efficiency and good fuel flexibility, but also can reduce the PM and NOx emissions. However HCCI combustion still faces many problems, such as the combustion phase is hard to control, operating range is narrow and so on, which makes it difficult to get commercialization in short time.In this paper, a series of experiments are carried out on a modified CT2100 Q double-cylinder diesel engine fueled with different mixing ratio n-heptane/n-butanol blends(the volume ratio of n-butanol in the blended fuel was defined as the fuel mixing ratio), and the fuels are supplied by an electric controlled port injection system. The influences of fuel mixing ratio, intake temperature, excessive air ratio and engine speed on the combustion characteristics, emission characteristics, engine performance and operating range are investigated.The experimental results indicate that with the increase of n-butanol mixing ratio, heat release amount of low-temperature and high-temperature is both decreased, combustion phase is delayed, combustion duration is extended, the coefficient of cyclic variation of peak in-cylinder pressure as well as the HC and CO emissions are increased. The more dilute the mixture is, the more obvious these effects are. In addition, under different mixture concentrations, there is an optimal mixing ratio which has the highest indicated mean effective pressure and indicated thermal efficiency. Increasing the n-butanol content in the blended fuel can effectively expand the HCCI high load operating range. Increasing the intake temperature can highly improve the performance of HCCI combustion, advances the combustion phase, results in the decrease of HC and CO emissions, improves the indicated mean effective pressure and indicated thermal efficiency, expands the HCCI engine low load operating range. As the excessive air ratio increases, there are a delay of combustion phase and an increase of combustion duration. Meanwhile, the peak in-cylinder pressure, the maximum heat release rate and the maximum in-cylinder temperature are decreased with the increase of excessive air ratio, but the HC and CO emissions are increased. The higher the n-butanol mixing ratio is, the much more obvious these effects of intake temperature and excessive air ratio on the combustion and emission characteristics are. Under low engine speed, the performance of HCCI combustion becomes poor, HC and CO emissions are increased, combustion stability is reduced. With the increase of engine speed, the performance of HCCI combustion is improved at a certain extent,but there are some differences among the combustion and emission characteristics of different mixing ratio n-heptane/n-butanol blended fuels. Overall, engine speed has greater effects on the combustion and emission characteristics of high mixing ratio n-heptane/n-butanol blended fuels.