The adaptive collision mesh model [39] also uses a pseudo-collision mesh to partition parcels into collision partners, but is more flexible in that the collision mesh adaptively encloses the evolving spray structure during simulation. This is unlike the previous model in which a cylindrical collision mesh is prescribed. It is helpful in modeling collisions when the spray structure is not axisymmetric, in other words, sprays injected from multi-hole injectors with an asymmetric hole arrangement.

The adaptive collision mesh is constructed in every time step prior to the spray collision calculation. It starts with a bounding box enclosing all the spray parcels, and divides the box equally into 8 smaller cells if it contains too many parcels (that is, the number of parcels exceeds a threshold count, taken as 100). All the cells are recursively checked and divided further if needed, until each cell has a parcel count less than the threshold and the construction of the collision mesh is completed. Spray parcels are allowed to collide only if they are stationed in the same collision cell in the current time step. In each time step, the spray parcels’ coordinates are rotated in a random manner in 3D space, constructing the initial collision cell, in order to remove any preference in the direction of the collision mesh.

Spray structures predicted by the adaptive collision mesh model are expected to be similar to those predicted by the ROI collision model (Radius of Influence (ROI) Collision Model) but the latter is computationally more expensive when the parcel number is large (>100,000).