Spray Visualization and Characterization of a Micro-Variable Circular-Orifice (MVCO) Injector Coupled with a Swirl Adapter for Diesel Reformer Applications

This paper focuses on the spray and atomization characteristics of a Micro-Variable Circular-Orifice (MVCO) fuel injector coupled with a unique swirl adapter. Spray characteristics produced from this configuration, such as spray penetration length, spray velocity and the droplet size distribution were evaluated under different injection pressure and air inlet pressure. Diesel injection pressure ranges from 300 bar to 700 bar at a back pressure of 1bar while compressed air at pressures of 2 bar and 4 bar was supplied to the swirl adapter. High speed Mie scattering images were recorded to capture the spray evolution, as seen from both the front view and the bottom view. Phase Doppler Anemometry (PDA) measurements were conducted at different locations in the spray for the acquisition of droplet sizes and velocity distributions. Unlike traditional multi-hole injectors which normally inject six to eight fuel jets, the MVCO fuel injector presented a unique fan spray pattern displaying more than twenty jets in an approximately axi-symmetric fashion. Due to the interaction between the spray jets, the breakup was enhanced compared to conventional injectors, causing shorter spray tip penetration and finer droplet size. Coupling the swirl adapter with the injector caused the fuel spray to become more uniform, and also achieving a higher degree of atomization. PDA results displayed a clear rotational motion indicating a strong tangential velocity component imparted to the fuel spray by the adapter. The above characteristics favor a highly atomized, uniform mixture formation, thereby reducing coke formation and auto-ignition hot-spots, which could potentially increase diesel reformer efficiency.