A set of GDI system for ethanol injection is installed on a F188 diesel engine, and the diesel supply system of the original diesel engine is used for diesel injection. The computational fluid dynamics software FIRE is adopted to establish a 3D combustion model of the ethanol -diesel direct injection engine. The total heat energy of the fuel is equivalent to that of the original diesel engine under the same condition. As the diesel injection starting point is 344°CA and there is simultaneous diesel and ethanol injection, the ethanol injection starting points at 344°CA, 338°CA, 332°CA, 326°CA and 320°CA are subject to 3D simulation for fuel injection, mixed gas formation and combustion and pollutant formation process. The results show that, the earlier the ethanol injection is, the steeper the heat release rate curve during the initial combustion period, the higher the peak value, and the shorter the heat release duration are, and the higher the maximum combustion pressure, the headmost phase of the maximum combustion pressure and the more obvious the premixed combustion are. Earlier ethanol injection starting point and quicker rise of the temperature curve of the cylinder bring the headmost phase of the highest average temperature in the cylinder, and higher average temperature in the cylinder brings higher NO concentration. The ethanol injection starting point shall be earlier than the diesel injection starting point injection, for it is the most favorable for reducing soot generation.
The 396 series diesel engine has high performance, reliability and long service life, which has been widely used in many fields including ship, vehicle and industrial power unit. With the improved injection system and dual-injector in each cylinder, two injectors of the diesel can spray diesel at the same time; or one injector sprays ignition diesel and the other injector sprays biodiesel or alcohol fuel. A 3D combustion model of the 396 series diesel engine with flat-top convex basin combustion chamber is established by using the computational fluid dynamics software FIRE, and the combustion process when uniform 5-hole and 8-hole injectors and 4-hole dual-injector are adopted is simulated to compare and analyze the fuel spray, ignition start point, combustion pressure, combustion heat release rate, average temperature in cylinder and NO emission. Compared with the diesel engine adopting 8-hole injector, the diesel engine adopting 4-hole dual-injector has a wide spray space distribution area, high pressure and temperature in cylinder, and high thermal efficiency. The combustion process with injection duration of 26.84°CA, 22°CA and 20°CA for 396 series diesel engine adopting 4-hole dual-injector is simulated respectively, and the simulation result shows that the shorter injection duration can bring the higher maximum pressure and the maximum average temperature in cylinder, the shorter ignition delay period, the advanced ignition start point, the larger peak value of combustion heat release rate, the more concentrated combustion heat release, the higher NO emission. These three cases have almost the same accumulated heat release and the relatively complete fuel utilization. The proper injection duration shall be selected based on comprehensive consideration of the pressure in cylinder, effective power and NO emission. This research result is conductive to improve the combustion process of the 396 series diesel engine with the dual-injector and provides a basis for using biodiesel and alcohol fuel in the diesel engine.
The 396 series diesel engine has been widely used in many fields in China. The combustion process of the 396 series diesel engine with flat-top convex basin combustion chamber is analyzed by using the computational fluid dynamics software FIRE, and a 3D combustion model was established. The fuel spray, ignition start point, combustion pressure, combustion heat release rate, average temperature in cylinder and NO emission were compared and analyzed when the 5-hole, 6-hole and 8-hole uniformly distributed injectors were adopted. When injectors with different injection holes are adopted, the ignition delay period is basically the same and the fire occurs in the same place. The proper number of injector hole shall be selected to enlarge the space area occupied by fuel spray. The 6-hole injector is featured by higher pressure in the combustion cylinder, higher average temperature, better combustion process, higher thermal efficiency and higher NO emission. This research result provides a basis for selecting suitable injector for the 396 series diesel engine with flat-top convex basin combustion chamber.
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