Effects of diesel fuel temperature on fuel flow and spray characteristics

The cold start issue has been a problem in diesel engines. Thus, in the present research, the diesel fuel flow and macroscopic spray characteristics over a wide fuel temperature range were investigated to provide valuable insights for solving the cold start problem. An injection system including a common-rail and a fuel supplier was designed to control the fuel temperature from 243 K to 313 K. For the fuel flow characteristics, the results showed that the injection quantity decreased by 50% as the fuel temperature decreased from 313 K to 243 K under the same energizing time. It was also confirmed that the real start of injection timing was retarded as the fuel temperature decreased. The reason is that increased fuel viscosity disturbed the injector needle motion and fuel flow in the nozzle. The spray test was performed under the simulated cold start condition using a constant-volume combustion chamber (CVCC). For the macroscopic spray characteristics, the liquid-phase fuel penetration increased and the spray angle decreased with cold fuel due to attenuated fuel evaporation process and interaction with ambient gas. These results could cause poor air-fuel mixing process under the cold starting.