Study of the far field of a pulsed spray from an automotive fuel injector

Pulsed liquid sprays from automotive fuel injectors are inherently complicated and the formation and development of sprays involve multiple physical processes which take place both simultaneously and sequentially. The pulsed spray characteristics far from the injector orifice are affected by complicated mechanisms of primary and secondary break-up at and close to the injector tip. This complexity usually requires researchers to make assumptions about break-up mechanisms. In addition, several droplet collision models have been proposed for sprays, but when used in conjunction with break-up mechanism models, the accuracy and limitation of collision models have been difficult to judge. This study is intended to explore, examine and compare different collision models in a pulsed fuel spray. Since trustworthy laser diffraction measurements of droplet size distribution can be performed far from the injector orifice, these data can be used as accurate initial conditions for simulating downstream spray development. Since the pulsed sprays from automotive fuel injectors are relatively dense ones, this study eliminates the complexity of simulating two-phase flow equations for break-up and instead solves the simpler fluid mechanics problem of the Lagrangian trajectory of spray droplets, together with a droplet collision model. It was found that for the single-hole sprays of this study, when the droplet size distribution is known at some plane downstream of the break-up region, the development of the spray can be modeled accurately by using a simple Lagrangian model which calculates the droplet collision impact parameter analytically at each collision.