An evaluation of alternative fuels' spray penetration at various spray cone angles and injection pressures using a simple evaporation model

Spray characteristics and transient behaviour of alternative fuel droplets at different spray cone angles, injection pressures and droplet diameters are presented, using a simple spray evaporation model. The model only considers drag force acting on the droplet. Radiation heat transfer during the evaporation process is neglected. The model incorporates temperature-dependent fuel properties, drag coefficient and Reynolds number for robustness. It is tested for alternative fuels, namely Jatropha Bio-synthetic Paraffinic Kerosen (JSPK), Camelina Bio-synthetic Paraffinic Kerosene (CSPK) and biodiesel, while Jet-A is used for comparison. The transient behaviour of fuel droplets is visualised through a time-history of the normalised squared diameter. Changes in the particles' temperature, mass, density, velocity and heat transfer coefficient over time are observed. Moreover, penetration of the fuels at different spray cone angles, injection pressures and droplet diameters is compared. Among the tested fuels, biodiesel is found to have the farthest penetration due to its high vapour pressure. Notably, increasing spray cone angle reduces penetration length. A similar trend is observed when injection pressure is increased. However, at constant injection pressure, increasing droplet diameter increases spray cone angle and spray penetration. To obtain optimum penetration, therefore, a larger cone angle should be used for fuel with high density and vapour pressure, and vice versa.