Effects of Injection Sequences on Spray Characteristics of an Air-Assisted Atomizer for Two-Stroke Aviation Engines

The air-assisted atomizer used in a two-stroke aviation engine has two separate operation sequences, namely the fuel injection and air injection, in contrast to the synchronous fuel/air injection of conventional effervescent atomizers for continuous combustion engines. This work presents a numerical flow modeling to explore the effects of these two injection sequences on the effervescent spray formation, using the combined methodology of Eulerian-Eulerian multiphase technique and Shear-Stress Transport k-? turbulence model. The transient fuel delivery in the internal fuel passage of the atomizer and the effects of the injection sequences on the developments of the droplet sprays were studied. Three characteristic times T-1, T-2, and T-3 were introduced to specify the fuel injection duration, air injection duration, and the time interval between these two injection sequences, respectively. The results showed that the most important role of T-1 is to meter fuel mass loading, and T-2 plays the dominant role in anchor-shaped spray structure. For the air-injection sequence, there is a critical time, T-3(c), which is defined as the minimum opening time of the air injector, for the complete ejection of the fuel in the atomizer, which shows a linear correlation to T-2, but is weakly related to T-1.