Effect of fuel temperature and properties on flow characteristics of diesel injector under extremely cold conditions

Abstract

Fuel properties such as viscosity and density are changed with different fuel temperature. The variation of some properties is changed rapidly under extremely cold conditions. Therefore, the flow characteristics of fuel in a diesel injector are also affected by the variation, which relates to the ability of cold-start. The objective of this research is to investigate the variation of flow characteristics of diesel fuel and suggest the injection strategies under extremely cold conditions. Injection rate test, which is based on Bosch tube method, was conducted to investigate the effect of fuel temperature and properties on the flow characteristics of fuel in diesel injector. The special diesel injector adapter circulating coolant was designed to simulate real engine head. The temperatures of coolant and fuel tank were varied from 243K to 303K to change the fuel temperature in the diesel injector. The fuel density was increased linearly and the fuel kinematic viscosity was increased rapidly with decreasing fuel temperature. The start of injection was retarded and the end of injection was advanced with decreasing the fuel temperature. The flow characteristics of the diesel fuel were changed greatly under low injection pressure. The increased kinematic viscosity with lowering fuel temperature led to higher friction force in fuel flow. Therefore, the needle is opened later with a lower fuel temperature. The peak injection rate during steady-state period is reduced with a lower fuel temperature. The discharge coefficient was calculated to analyze the flow characteristics of steady-state period quantitatively. The discharge coefficient was reduced with lowering fuel temperature due to a higher kinematic viscosity. Therefore, the injection quantity was reduced rapidly under extremely low fuel temperature. The reduced injection quantity could be compensated with increasing energizing time of injection signal. The injection timing and energizing time should be changed with the variation of fuel temperature, especially, under extremely cold conditions. The modified injection strategy can contribute to solving the ability of cold-start under low ambient conditions.