Experimental study on the fuel heating at the nozzle of the high pressure common-rail injector

•Developed a mathematical model of integral form to calculate fuel steady state ΔT for orifice.•Experimentally studied the effects of pressure drop on the fuel heating at nozzle orifices.•Analyzed the change law of steady state temperature increase.•Proposed a new Joule-Thomson coefficient fitting formula with injection pulse width. In this study, an experimental and theoretical investigation of the fuel temperature increase at the nozzle of a common rail injector was conducted. The results showed that the temperature of the fuel at the nozzle began to increase rapidly with an increase in the injector working time and then stabilized. In the steady state, the temperature increase of the fuel at the nozzle holes only depended on the injection pressure drop rather than the discharge coefficient for the nozzle holes. The temperature increase of the fuel at the nozzle was not only related to the pressure drop but was also affected by the duty cycle of the injection pulse, which reflected the relative injection duration. The existing thermogenesis model for continuous flow is not suitable for the calculation of the temperature increase in the pulse injection mode of the common rail injector. A correction formula for the Joule–Thomson coefficient that considered the injection pulse and injection duration was proposed. The calculation results were in good agreement with the experimental data, which proved the accuracy of the model. These results and the mathematical model could be used to determine the thermodynamic boundary conditions inside a nozzle when using a three-dimensional method to calculate the thermodynamic state of the injector.