Numerical study on fuel preheating at cold start phase in an ethanol flex fuel engine

The low vapor pressure of ethanol and the high latent heat of vaporization at low temperatures cause the difficulties of cold start in a flex fuel vehicle when it is fueled with pure ethanol. Preheating fuel is one of the effective methods to solve the above cold start problem. Thus, it is crucial to obtain the fuel temperature distribution in the heating system for fuel preheating process. For this purpose, the numerical analysis is adopted here to simulate the fuel preheating process at a cold start phase and explore the change of the fuel temperature field under different influence factors. The results indicate that the starting temperature has obvious impact on the temperature field distribution in the heating chamber and preheating time but has little effect on the volume of cold fuel in the connecting line at the end of heating. When the starting temperature is -5 °C, the preheating time is 8.3 s. When the starting temperature increases up to 15 °C, the preheating time will decrease as 4.9 s. Furthermore, the lower the starting temperature is, the higher the overall temperature of the heating chamber is. The installing angle of injectors has some influence on the temperature field distribution, and the cold fuel ratio reduces slightly when the angle increases from 30 deg to 60 deg. The calculation results indicate that the temperature of fuel at the injector inlet is above 20 °C, and the fuel injected during the first three cycles of the engine operation is hot fuel.