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In a diesel engine, the injection phenomenon is vital because it impacts fuel spray characteristics and mixture formation process. Accurate control of operating fuel injection parameters (injection timing, flow rate shaping and fuel in-line pressure) is necessary as it affects mixture formation method of air and fuel. If the energy content of fuel is less, to sustain the desired power output, the injection duration would increase. The increased injection duration would affect the important combustion parameter predominantly the combustion duration. So, the optimization of the injection system is needed for a diesel engine for better performance and emission characteristic. The fuel atomization characteristics, and subsequently spray development compete a crucial part in the progress of better combustion and engine performance, as it affects the mixture formation in the combustion chamber. There are studies and models available for diesel fuel spray with and without swirl. If the bulk modulus of fuel is higher, the fuel inline pressure increases significantly. The bulk modulus implies compressibility of a fuel. The longer fuel spray penetration observed with rise in the fuel inline pressure further it also increases the chances of wall impingement. It is one of the main durability issues of a diesel engine. On the other hand, it is important to note that the rise in pressure of injection is a useful approach to enhance fuel atomization characteristics and to enhance mixing of air and fuel. The higher bulk modulus of fuel results in advanced injection timing which further leads to high NOx emission. Furthermore, the increased spray penetration increases NOx emission which forms generally around periphery of spray. Therefore, it is necessary to evaluate the spray development and fuel atomization characteristics for reduction of exhaust emissions and subsequently, enhance the efficiency of the engine. The current research work is aimed at the extent review of computational/mathematical models of spray characteristics and empirical models of injection and spray process of engine. The challenges for modeling of spray characteristics are also highlighted. Numerous research works have been referred and analyzed for the effect of injection parameters and fuel properties on injection and spray characteristics of the engine.

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