Abstract
The similarities and differences in the combustion and emission characteristics of supercritical- and subcritical-state fuel injection conditions of an internal combustion engine was clarified. The effects of fuel state on temperature, pressure, turbulent kinetic energy, heat release rate, NO, and soot in the cylinder during the operation of the internal combustion engine were simulated. Ignition occurred faster, and the peak temperature in the cylinder was achieved in shorter time under the supercritical-state fuel injection condition than under the subcritical condition. The cylinder pressures in both states peaked at the same time, but the value of pressure in the supercritical fuel state was larger than that in the subcritical state. Furthermore, the turbulence in the supercritical fuel state was more intense than that in the subcritical state. The intense turbulence was beneficial to fuel and air mixing. NO emission increased, and soot emission decreased in the supercritical fuel state. The results show that supercritical fuel can be fully mixed with air to reduce the local concentration area in the cylinder, improve the combustion performance of the engine, and greatly reduce pollutant emissions.
Highlights
The global automotive industry has undergone a period of rapid growth due to social development.Data provided by the Automobile Industry Association [1] show that car ownership in China will increase to 500 million by 2030
gasoline direct injection (GDI) technology can improve the thermal efficiency of gasoline engines, the time of fuel and air mixing is shortened, leading to partial uneven mixing and serious particulate matter (PM) emission problems [7]
We have established and verified the supercritical fuel injection model and chose the modified standard k-ε two equation model as the turbulence model to study the supercritical injection process; and to validate the model accuracy of the spray model, the supercritical nitrogen environment was studied by numerical simulation, the results shows relative error of the jet length is less than 5%, whereas that of the divergence angle is less than 8%
Summary
The global automotive industry has undergone a period of rapid growth due to social development. GDI technology can improve the thermal efficiency of gasoline engines, the time of fuel and air mixing is shortened, leading to partial uneven mixing and serious PM emission problems [7]. Fuel can rapidly form a homogeneous mixture with air for combustion and heat release due to the low surface tension, low viscosity, and large diffusion coefficient of supercritical fuel This feature helps reduce the uneven distribution of concentration in the cylinder so that fuel can be completely burned and thermal efficiency can be improved. Supercritical-state fuel can be combined with the latest injection technology to further control the combustion process, thereby reducing the emissions of pollutants and optimizing the combustion performance of engines. Different combustion and diffusion characteristics of supercritical and subcritical fuels were revealed
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