Effect Of Gasoline/Diesel Blends On Combustion And Emission Characteristics In Compression Ignition Engine

The energy crisis and environmental problems have become increasingly concerned and emission regulations have also become more and more strict, which both need higher requirements for the optimization of combustion process and emission control of engine. Studies show that fuel characteristics have important effects on combustion and emissions of engine. Through the fuel design, improving the physical and chemical properties of fuel is an important way to optimize combustion and reduce the emission. This paper uses the gasoline/diesel blended fuel, and makes full use of their respective advantages to explore the potential of reducing NOx and PM at the same time, increasing the combustion containment, improving combustion efficiency and achieving the efficient and clean combustion.In this study, a test platform based on a high-pressure common-rail turbocharged diesel engine was established, which could adjust fuel injection parameters and EGR rate flexibly and meet the needs of the test. Based on the Ⅳ diesel, by adding different proportions of gasoline, we got the gasoline/diesel blended fuels which had different volatility and ignition capability. We have studied the effect of the gasoline/diesel blended fuel on combustion and emissions in steady and transient operation conditions. Besides, we sdudied the effect of combustion boundary conditions, such as the combustion phase, rail pressure, EGR, the pilot timing and pilot quantity on combustion and emissions of the engine which burned gasoline/diesel blended fuel combustion and explored the potential of controlling the fuel characteristics and combustion boundary conditions simultaneously to realize efficient and clean combustion.The results show that: In steady state conditions, burming gasoline/diesel blended fuel can prolong the ignition delay, shorten the combustion duration, increase the amount of premixed combustion, and reduce smoke significantly without increasing NOx emissions. In transient conditions, CO and HC emissions of different fuels reduce gradually, and all the particles increase with the load increasing, but burming gasoline/diesel blended fuel can reduce the number of accumulation mode particles significantly; CO and HC emissions increase significantly and NOx emissions reduce gradually with EGR in transient conditions, meanwhile, the number of nuclear mode particles reduces slighely and the number of accumulation mode particles increases significantly. As the proportion of gasoline increases, the number of accumulation mode particles decreases, which will help to ease the effect of transient conditions on accumulation mode particles. Reasonable boundary conditions, such as fuel injection parameters and EGR also have a good effect on combustion and emission characteristics for the engine fueled with gasoline/diesel blended fuel. Under the experimental conditions, the engine fueled with different fuels have less smoke, lower NOx emission and better fuel economy when the combustion phase is 12.5° CA ATDC. For the blended fuel added large proportion gasoline with a large EGR rate can reduce NOx emissions significantly without smoke and fuel consumption increasing obviously. A high rail pressure can improve atomization quality, increase the amount of premixed combustion, reduce the smoke and fuel consumption. But in order not to cause NOx and HC emissions increase obviously, the rail pressure should be in a reasonable range. Two-stage injection with an earlier pilot timing and larger pilot quantity can increase the amount of premixed combustion, reduce the smoke and CO emissions and improve the thermal efficiency of blended fuel.