Phenomenological combustion modeling with swirl effects of a two-stroke marine engine for digital twins

In a marine two-stroke engine, swirl flow dominates in the cylinder due to its uniflow scavenging process. The fuel spray and its flame are deflected by the swirl and result in different impingement characteristics on the cylinder wall, which may affect thermal stress/loss and engine’s lifetime of lubrication system. To study the influence of spray and swirl on the combustion of marine low-speed diesel engines, a phenomenological spray and combustion model is developed to predict the spray evolution under the swirl effect. The deflection velocity of the spray is calculated using the momentum conservation theory, and the combined velocity of the spray is determined by superimposing the deflection velocity with the initial velocity of the spray. During combustion, the burned fuel is consumed with a premixed stage and a diffusion stage, while the unburned fuel spray continues the deflection. The simulation results of the phenomenological model are validated by experimental results of a Constant Volume Combustion Chamber (CVCC) and a marine two-stroke engine. The wall impingement in different engine conditions predicted by the proposed model is verified by a CFD engine model. Therefore, the phenomenological spray and combustion model can predict the marine engine performance, while providing the impingement timing for thermal load estimation. In the future, this model could be applied in a digital twin system for engine control decisions with restrictions of spray impingement and thermal load, which may reduce the maintenance efforts.