Intra-Parcel Collision Model for Diesel Spray Simulations

Multidimensional models that are used for engine computations must include spray sub-models when the fuel is injected into the cylinder in liquid form. One of these spray sub-models is the droplet interaction model, which is separated into two parts: first, calculation of a collision rate between drops, and second, calculation of the outcome once a collision has occurred. This paper focuses on the problem of calculating the collision rate between drops accurately. Computing the collision rate between drops or particles when they are non-uniformly distributed and sharp gradients are present in their distribution is a challenging task. Traditionally the collisions between parcels of drops have been computed using the same spatial grid as is used for the Eulerian gas-phase calculations. Recently it has been proposed to use a secondary grid for the collision rate calculation that is independent of the gas-phase grid, as is done in the NTC collision algorithm. While this approach removes the constraint of using the relatively large gasphase grid cells for collision rate calculations, it still suffers from numerics sensitivities. A new drop-drop collision model has been developed and implemented in the KIVA code to improve the droplet collision rate prediction. The new Intra-parcel model proposed here has been validated and compared to experimental measurements. The Intra-Parcel model predicts drop size distributions more accurately than the other drop collision models currently avail-able.