An Investigation on the Fuel Temperature Variations Along a Solenoid Operated Common-Rail Ballistic Injector by Means of an Adiabatic 1D Model

Most studies about common-rail diesel injection consider the fuel flow along the injector as isothermal. This hypothesis is arguable given the small diameter of the orifices along which the fuel flows, together with the expansions that take place across them. These phenomena may provoke variations in the fuel temperature, which in turn modify the fuel properties (i.e. viscosity, density, speed of sound…), thus influencing injector dynamics as well as the fuel atomization and mixing processes. The present investigation accounts for these effects by means of a 1D model for the fuel flow along a common-rail ballistic injector. Local variations of fuel temperature and pressure are considered by the model thanks to the implementation of the adiabatic flow hypothesis. The model, validated against experimental results, allows to estimate the fuel temperature changes along the injector, including the fuel temperature at the injector outlet, as well as the influence of the thermal effects on the injection rate shape. Results show a significant influence of the fuel temperature and its changes on injection rate and duration, especially for low fuel temperatures at the injector inlet, typical of engine cold-start conditions.