Diagnostics for fuel sprays as applied to emulsified fuels

Abstract

Measurements of drop-size distributions and vaporized fuel concentrations have been combined with a spray model in the comparative study of the evaporation of sprays of mulsified and non-emulsified (neat) fuels at elevated temperatures and pressures. The fuel spray was generated by a pressure jet atomizer and was polydisperse; the air stream was approximately fully-developed turbulent flow in a constant area duct. Diagnostic techniques have been adapted or developed which allow rapid measurements of overall drop-size distributions in the presence of evaporation in high-temperature high-pressure air, and also the fuel vapor concentration distribution within sprays. It was concluded that even in conditions of turbulence and high Reynolds number for drop motion relative to the air, some emulsified fuel drops apparently undergo microexplosions. Further, it was determined that the initial atomization quality depends on the air conditions, with better atomization at higher air densities. This implies that spray drop-size measurements performed at atmospheric conditions need to be corrected for air density and temperature effects to predict atomization quality for altitude relight or high-pressure combustion. A spray model has been developed which represents the spray being studied and provides data in a form comparable to the experimental diagnostics. Comparisons are provided between the predicted and measured drop-size distribution and fuel-vapor concentrations during the evaporation process. Trends for changes in drop-size distribution (both average size and width of the distribution) with distance from the nozzle are predicted fairly well by the model except close (