1996-02-01

Fuel Atomization by Flashing of a Volatile Liquid in a Liquid Jet 960111

Flash boiling occurs when a liquid which initially is in a subcooled state, rapidly depressurized to a pressure sufficiently below saturation pressure to initiate a rapid boiling process. This phenomenon can be applied to improve fuel atomization in spark-ignition engines. In the present work, the characteristics of the generated spray were investigated experimentally. This is in order to establishing a designer guideline, for this high potential type of fuel injectors.
The following conclusions have been derived: 1. A typical droplets Sauter mean diameter in the range of 20-40μm can easily be achieved with the present simple fuel injection system. 2. The SMD decreases with the increasing in the mole fraction of the propellant; at high pressure however (high propellant content), the SMD is less and less affected. 3. The SMD and the droplets' uniformity are independent of the orifices' size. 4. The SMD increases with the axial distance. 5. Large size droplets may be generated at the periphery of the spray cone due to imperfections at the discharge orifice. 6. A simple and useful analytical expression which is based on energy balance principles demonstrates a good and practical correlation between the spray SMD and the operation conditions, as follows:
where, yβ,i is the mass fraction of the propellant, η, process efficiency, σ, surface tension, ρ, density, R, gas constant, T temperature and P pressure.

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