Numerical investigation of a trapped vortex miniature ramjet combustor

The design of a miniature ramjet combustor using gaseous methane fuel for Mach 2.5 has been conducted. The main challenges stem mainly from the insufficient space for mixing and burning, short residence time, and the flame stabilization. Impossible utilization of relatively large air-blast fuel injectors provides more difficulties for the design. The trapped vortex combustor, as a novel way of flame holding by trapping the pilot flame inside a cavity instead of exposing it to the mainstream, is selected. Three main parts are studied numerically, which include the cold flow field characteristics, the fuel-injection schemes, and the overall combustion performance. The results show that the drag coefficient can help to determine the optimum cavity size for trapping a stable vortex. Injecting all the fuel in the cavity always leads to an overly fuel-rich condition, whereas injecting in front of the cavity with a momentum flux ratio q between 0.61 and 1.0 can successfully achieve stoichiometric mixing in the cavity. However, compared to non reacting fuel mixing, the combustion performance is found to be more sensitive to the value of q. Among the cases studied, the one with a small q of about 0.61 has more intense pilot flames and shorter main combustor flames. The effects of angled injection, upstream injection location, and the combustor length based on the found q are also investigated.