EFFECTS OF DROPLET EVAPORATION ON CALIBRATION OF KH-RT BREAK-UP MODEL FOR HIGH-PRESSURE EVAPORATING DIESEL SPRAYS

Abstract

Spray simulations involve much effort in calibrating the empirical constants in the break-up model case-by-case to obtain good predictions for the target experiments. Most calibrations are based on the ideal-gas evaporation model for the evaporating sprays even under high-pressure conditions. The effect of droplet evaporation on the calibration of the break-up model is first evaluated, and an accurate multi-component evaporation model is suggested to reduce the dependency of the break-up constants on the ambient conditions and fuel types. First, a multi-component evaporation model with the real vapor-liquid equilibrium is introduced and implemented into the OpenFOAM-v6. Then, extensive sprays under a wide range of conditions are simulated by the typical ideal- and suggested real-gas frameworks, respectively. Since the ideal-gas evaporation model underestimates the droplet evaporation rate, especially for the multi-component sprays under high pressures, calibrating the breakup constants is needed to compensate the errors induced by the ideal-gas evaporation model. Even though the spray liquid penetration could be well reproduced through calibrating the constants in the KH-RT model, the droplet size is seriously underestimated. In contrast, the real-gas evaporation model can accurately predict the droplet evaporation rate, and the dependency of break-up constants on the ambient conditions is reduced. Finally, the comparison of n-dodecane and multi-component diesel sprays confirmed that the break-up constants for the multi-component spray simulation are more sensitive to the ambient conditions, and an accurate multi-component evaporation model can reduce this sensitivity.