Direct Numerical Simulation of Fuel Droplet Collision in Diesel Engines

Fuel droplet collision plays an important role in the mixture formation mechanism in Internal Combustion Engines (ICE), since this process significantly modifies the droplet sizes and subsequent spray development and combustion. But one of the major problems in the simulation of the droplet collision process is that the criteria employed to determine outcomes of collisions have not been assessed for accuracy under diesel spray conditions.

The numerical simulation of multiphase flows is a challenging subject due to the difficulty in the tracking of interfaces, the mass conservation of each fluid and the treatment of large density ratio and surface tension.

In this paper a fully 3D two-phase Lattice-Boltzmann Method (LBM) is used to perform Direct Numerical Simulation (DNS) of droplet collision at diesel-like conditions. The LBM has great advantages over conventional methods (e.g., VOF) since it does not track interfaces, but can maintain sharp interfaces without any artificial treatment, and is accurate for the mass conservation of each component. The goal of the paper is to demonstrate that the numerical tool developed can provide a detailed picture of the mechanisms that govern the phenomenon, giving information where experimental investigations are difficult. This approach can therefore assist in the development of accurate collision models for practical CFD applications.