Interpretative Review of Diesel Spray Penetration Normalized by Length and Time of Breakup (Similarity Law of Diesel Spray and Its Application)

Tip penetration of diesel spray is one of the most useful parameters to evaluate diesel combustion dynamics. It has strong relationships with ignition delay, premix/diffusion combustion and engine performance, including exhaust emissions. To discuss general combustion physics in various size sprays, non-dimensional expression of spray tip penetration is reviewed. Length and time of injected fuel jet breakup can be considered as characteristic length and timescale of diesel spray. Then, normalized penetration by length and time of breakup was proposed for the scaling of various diesel sprays. Using the proposed scaling method and similarity law, tip penetrations of various size sprays are collapsed into one simple expression. It becomes a base of similarity law of diesel spray. For example, local or average A/F is uniquely expressed by the normalized length and time of breakup. Penetration of a wall impingement spray is also expressed uniquely by this normalization method and physical parameters affecting the wall impingement spray are explained. Injection rate shaping effect at an initial stage of injection is clearly demonstrated by using this scaling. Further, mixing degrees of diesel spray at an ignition timing and in a combustion phase can be reasonably explained by the equivalence ratio change with non-dimensional elapsed time after injection start.