Application of Probability Density Function Model to Diesel Spray Combustion

PDF-equation approach have been extended and assessed for the diesel spray combustion computation. This approach accounts for the effects of gas turbulence and random dynamics of vaporizing liquid droplets on the chemistry. The combustion process including spray dynamics, evaporation, mixing and combustion have been treated using the combined KIVAII-PDF-equation model.

Numerical computations were compared with the experimental data for spray self-ignition and combustion and with calculations using Eddy-Break-Up combustion model. Both the light-duty and heavy-duty diesel conditions have been operated in computations. Besides, the most probable self-ignition zone was computed and compared with experimental observation.

It was showed that the developed here PDF model is abble to describe species concentrations, auto-ignition phenomenon and overall turbulent heat release significantly better than Eddy-Break-Up model. For two different sets of injection conditions taken from experiment the Eddy-Break-Up model leads to a longer ignition delay and to the rate of fuel consumption that differs substantially from experimental one. In contrast, the PDF equation model gives improved combustion calculation: most probable auto-ignition region, ignition delay and contours that define averaged domains occupied by fuel-like particles and by the hot combustion zone are predicted in qualitative agreement with experimental data.