Investigation on cyclic variation of diesel spray and a reconsideration of penetration model

Spray tip penetration is one of the important characteristics for optimizing an engine combustion system. The conventional penetration models proposed so far have not considered cyclic variations of spray. The spray cyclic variation, however, is an inherent feature of a spray injected into turbulent ambient gas at a high speed. In this work, in order to study the effects of cyclic variations in spray structure on spray tip penetration, the liquid phase distributions of diesel sprays were measured 36 times (cycles) for each condition of injection pressure and ambient density at a constant volume chamber with wide optical windows. The experimental results were analyzed through such statistical methods as Probability Presence Image (PPI) and Intersection over Union (IoU). It was found that the spray cyclic variation gradually increased with time after start of injection and became obviously large at the late stage. This cyclic variation in spray structure might cause variation up to ±9% in spray tip penetration. A spray tip penetration model was developed by introducing a factor to consider the effect of spray cyclic variation. The factor of cyclic variation (f) and the presence probability (PP) could be correlated through experiments and expressed by a cubic polynomial function.