Environmental and economical reasons have led to an increased interest in the usage of alternative fuels for combustion engines. To clarify the influence of these so-called future fuels on engine performance and emissions it is mandatory to understand their effect on spray formation. Usually this is done by performing various spray experiments with potential future fuels which are available for research purposes today. Due to the multitude of possible future fuels and therefore the uncertainty of their properties and their influence on spray formation a more general approach was chosen in the present study.
The possible range of physical properties of future fuels for diesel engines was identified and more than twenty different fluids with representative properties, mostly one-component chemicals, were chosen by means of design of experiment (DoE). The influence of these fluids on spray formation was investigated in a high-pressure cell with a standard, 6-hole conical, hydro-ground diesel nozzle at room temperature. The pressure cell was equipped with a piezo-electric force sensor, measuring the transient force in the spray center at different distances from the nozzle. The investigations were carried out over an injection pressure range from 40 to 120MPa and at a back pressure of 2.1MPa.
The integration of the measured force over time yields the momentum on the sensor for a single injection event. This output was evaluated statistically based on DoE and for each injection pressure a model was composed which enables the prediction of the momentum depending on fluid properties and distance from the nozzle. The models show that fluid density, kinematic viscosity and surface tension have an impact on the progress of momentum over distance. The influence of the fluid properties on the spray momentum is depending on the rail pressure. The models are capable of predicting the momentum characteristics of any fuel inside the examined property range, whether actually available or not, based solely on its physical properties.