Experimental study on diesel fuel injection characteristics under cold start conditions with single and split injection strategies

Studies on fuel flow characteristics under both room temperature (25 °C) and low temperature (-18 °C) were carried out under a wide range of injection pressures and back pressures using a long tube real-time fuel flow rate measuring instrument. Both single and split injection strategies were employed. Several modified correlations were proposed to analyze fuel injection characteristics. It was found that low fuel temperature caused longer injection delay, shorter injection duration, lower mass flow rate and less injected fuel mass. The injector discharge coefficient was affected more by fuel viscosity changes due to low temperature than by the geometric structure of the injector. Cold start conditions effectively limited the inception of cavitation as seen in the flow rate/pressure dependence and accelerated the transition of flow regime from cavitation to turbulent and laminar flow with the decrease of injection pressure. This contributed to increased chances for the existence of laminar flow and thus to reduction of the discharge coefficient. Besides, low fuel temperature significantly weakened the degree of interaction between individual parts of split injection and split mass flow rate shapes became much less continuous than those under room temperature. These findings are of great importance for engine cold start studies.