Investigation Of High-efficiency-clean-combustion Based On Coupling Control Of Fuel And Combustion Boundaries

With the increasingly stringent fuel consumption regulations and Environmental protection regulations, energy efficient utilization and sustainable development of the environment has become an predominant trends. In view of the problem of the uneven mixing gas of the traditional diesel engine, the fuel economy improvement and the emission reduction by using the premixed combustion mode are the future development trend. At the same time, to improve the working process of internal combustion engines and to reduce emissions from the perspective of optimizing the fuel characteristics has gradually become a hot research topic in the field of international internal combustion engines. This paper research the influence of fuel ignition and volatile on premixed combustion process of compression ignition engine and emission pollutant generation using the synthesis of coal based F-T fuel, high octane gasoline and high quality diesel fuel as basic fuel, from the point of view of the control of chemical stability and physical stability of the fuel, based on the cooperative control of the fuel chemical kinetics and combustion boundary control parameters, in view of the above hot spots and difficult problems, supported by the National Natural Science Foundation of China. Comprehensive study have been done to research the control method and the corresponding fuel characteristic index to realize new efficient and clean gasoline / Diesel unified premixed compression ignition combustion mode by actively controlling the combustion boundary conditions such as the parameters of the inlet and fuel injection. The effects of fuel physical and chemical properties and combustion boundary conditions on the mixture formation, combustion and emission of pollutants were determined. The differences of combustion and emission of the engine under steady state and transient state were further clarified, and the mechanism of the fuel chemistry and the activation of the thermal environment in the cylinder were revealed.In this research, compression ignition engine combustion test and control system was designed and built to implement the active control and flexible adjustment of combustion boundary conditions of air intake and fuel injection, and Real-time data acquisition and storage system was employed. Based on CAN communication technology, the electronic control EGR system is developed, which meets the need of the experimental research for the state feedback control and precise regulation. According to the measurement and analysis of engine's gas and solid emission from steady and transient process, exhaust particulate dilution sampling system, Two stage dilution system, single cycle exhaust sampling system and exhaust particulate matter composition analysis system were designed and developed, which can achieve accurately qualitative and quantitative analysis of exhaust HC composition and particle composition under steady state and transient state.The results show that, fuel physical and chemical properties and combustion boundary conditions are important factors that influence the combustion process and emission characteristics of exhaust pollutants. Advancing injection timing during premixed combustion process help to achieve constant volume combustion and improve thermal efficiency, but premature injection has a negative effect on the thermal efficiency. By increasing the fuel injection pressure, it is helpful to reduce the number of accumulated particles, while the proportion of nuclear particles is improved. For the premixed combustion process, it is important to select the appropriate CA50 by controlling the injection timing and fit the appropriate intake oxygen concentration conditions to improve the thermal efficiency and reduce the emission by controlling the injection timing.The research on the effect of fuel physical and chemical properties on premixed combustion and emission shows that reducing the cetane number and improve the volatility of fuel can promote the further mixing of oil and gas, increase the amount of premixed combustion and reduce exhaust smoke. At the same time, with the increase of cetane number, the total number of nuclear particles was significantly decreased, and the total number of accumulated particles increased. When burning strongly volatile fuels, it is helpful to accelerate the mixing process of oil and gas, reduce the locally over-rich area in the cylinder and reduce the quantity of the accumulated particles.Fuel composition has a significant impact on combustion and emissions and addition gasoline results in an increase in ignition delay and improvement of fuel volatility,which is beneficial to increase the premixed combustion,reduce the exhaust smoke,and improve the content of combustion.However,large gasoline in blends significantly increases CO and HC emissions and results in a reduction in thermal efficiency under low loads.It is not suitable to use high gasoline components wide distillatoin range fuels from ensuring the thermal efficiency perspective. But under high load conditions, wide distillatoin range fuels with high gasoline components can further reduce exhaust smoke, and does not lead to a significant increase of NOx, which can realize the premixed combustion process in higher load condition and help to expand the load range of premixed combustion. Considering the operation condition of different load range, the proportion of gasoline is suitable for the control of 50% ~ 40%.Exhaust particles tend to be more refined when burning with wide distillatoin range fuels,and the particle geometric mean diameter was significantly lower than diesel. Wide distillatoin range fuels has more advantages in reducing the number of accumulation mode particles under high load condition,for example, when fueled with G50 fuel accumulation mode particle number concentration is more than 70% lower than that of diesel. From the perspective of controling particle formation, the effect of increasing injection pressure on particle emission can be replaced by that of wide distillatoin range fuels under low oxygen concentration condition,namely fueled with wide distillatoin range fuels can improve tolerance to a higher proportion of EGR, at the same time can be reduced for high pressure demand.In the aspect of gaseous and volatile hydrocarbons emission, compared with diesel fuel,fueled with wide distillatoin range fuels results in higher tendency of the generation of small molecule gaseous hydrocarbons,such as methane and ethylene, at the same time, the proportion of SOF in exhaust particles increases.Overall, fueled with wide distillatoin range fuels results a lower fuel economy compared to the traditional diesel fuel, but still better than that of traditional gasoline, and in the case of no significant increase in NOx emissions, the exhaust smoke is significantly improved compared with the traditional compression ignition diesel engine. From the perspective of energy utilization rate, fueled with wide distillatoin range fuels in a compression ignition engine will, in a certain extent, improve the energy efficiency of gasoline components, which has certain advantages in improving the energy conversion efficiency. Therefore, fueled with wide distillatoin range fuels can perform as an effective means to achieve the combustion process of gasoline engine and diesel engine unification.The study in regard to the spray characteristics of wide distillatoin range fuels in the constant volume container show that the fuel penetration distance is shortened, the spray cone angle is increased, and the macro mixing effect of oil and gas is improved obviously. Simulation analysis of wide distillatoin range fuels combustion process shows that mixing diesel with gasoline can change the reaction activity of fuel in the whole, but because of the inherent properties of single component,during actual combustion process diesel which have strong reactivity will have high temperature exothermic reaction in suitable temperature and pressure conditions rising the local temperature and pressure in cylinder,then ignite the gasoline which have low reactive points.Fueled with wide distillatoin range fuels help to improve transient process. In the transient process of the traditional engine, the delay of the turbocharger lead to the partial cycle combustion distortion and echaust smoke rising sharply in the load increasing process.Burning with wide distillatoin range fuels will reduce the demand of turbocharger's high intake response, which can significantly improve the exhaust smoke performance in load increasing transient process and the improvement effect is more obvious during larger loading rate. At the same time, with the gasoline fractions increasing in wide distillatoin range fuels, the number of accumulation mode particles increased more smoothly and when gasoline incorporation ratio reached 50%, the number of accumulation mode particles does not increase obviously, which show that wide distillatoin range fuels can improve quantity of accumulated particulate emissions under transient condition.