Numerical characterization of two alternative-to-diesel fuels using a moments spray model 2014-01-1422

The need to evaluate other fuel types for use in internal combustion engines has increased with the concerns related to the limited availability of fossil fuels and the need to reduce emissions.

In this assessment, two alternative-to-diesel fuels, dimethyl ether and biodiesel, are characterized by their spray tip penetration at different axial distances from the nozzle tip and at different ambient pressure values. The sauter mean diameter values at various axial distances from the injector tip are also evaluated. A novel diesel spray model that presents the hydrodynamics features of sprays from the moments derived from a Gamma size distribution and the droplet-size distribution function, rather than from droplet-size classes, is used for the numerical predictions.

The results indicate that the spray tip penetration for both fuels increases rapidly initially but the rate of increase slows at the later stages of the fuel injection. However, with increases in the ambient pressure values the predicted tip penetration decreases for both fuel sprays. Larger spray tip penetration and droplet size values are also predicted for the biodiesel fuel compared to the dimethyl ether fuel. These suggest better atomization at the given conditions for the dimethyl ether fuel spray. The predictions correctly capture the trends from the experimental data. However, there are differences between the predicted and experimental values at the early spray injection times. Thus, specific analytical models for the initial droplet size distribution and droplet break-up regime for the alternative fuel sprays might be required to improve the numerical model.