CFD Analysis of Fuel Spray Characteristics Inside a GDI Engine

K, Santhosh Kumar (2013) CFD Analysis of Fuel Spray Characteristics Inside a GDI Engine. Masters thesis, Indian Institute of Technology Hyderabad.

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Abstract

The work produced discusses the analysis of gasoline atomization generated by different fuel injectors operating in a high pressure direct injection system. The simulation results of the influence of the fuel injection pressure and combustion chamber back pressure on the changes of the fuel spray geometrical parameters during the injection characterizing the injection quality such as injection penetration at different flow time have been presented in the paper. This study is based on dynamic mesh refinement and uses spray breakup models to simulate engine spray dynamics. It is known that the Lagrangian discrete particle technique for spray modeling is sensitive to gird resolution. An adequate spatial resolution in the spray region is necessary to account for the momentum and energy coupling between the gas and liquid phases. On the other hand, the accurate prediction of the spray structure and drop vaporization requires accurate physical models to simulate fuel injection and spray breakup. The present primary jet breakup model predicts the initial breakup of the liquid jet due to the surface instability to generate droplets. A secondary breakup model is then responsible for further breakup of these droplets. The secondary breakup model considers the growth of the unstable waves that are formed on the droplet surface due to the aerodynamic force. The simulation results are compared with experimental data obtained from literature (ILASS and ICLASS)in gasoline spray structure and liquid penetration length. Validations are also performed by comparing the liquid length of a vaporizing Gasoline spray and its variations with different parameters including the injection pressure, and ambient gas temperature and density. The model is also applied to simulate a direct-injection gasoline engine with a realistic geometry (with piston bowl , engine specifications such as bore to stroke ,compression ratio and volume of cylinder as standards)where piston is moving and spray injection at different CA (crank angle) location.The equivalence ratio contours are studied for better stratification at the time of spark for complete combustion to happen in turn increasing performance and decreasing engine emission. The present spray model with dynamic mesh refinement is shown to predict the spray structure and liquid penetration accurately with reasonable computational cost

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