A parametric study using two design methodologies for pressure jet and swirl injectors

One of the most important subsystems in the air-breathing engines is the atomizers, which break the fuel into many droplets. It is well known that atomization quality has a significant influence on combustion characteristics such as stability limits, efficiency, and pollutant emission. Both jet and swirl injectors are applicable in gas turbine engines. The latter have been widely used for combustion chambers and the former are usually employed for fuel injection in the afterburner part. Since experimental and numerical study of atomizers could be complex and costly, a design methodology of atomizers based on empirical relations is still very advantageous and effective in reducing experimental efforts. We describe the design algorithm for both jet and swirl injectors, for which it is inevitable to use empirical relations. Details of the design algorithm are presented to determine the injector dimensions. The final dimensions are also a function of fuel properties and surrounding conditions. For instance, in liquid jet injectors, the type of the inlet and its length to diameter ratio are very important in term of instability aspects. Therefore, the effect of five type of inlets are considered and compared. Loss effects are also taken into account in this study, including loss of energy related to vortices generated due to fluid contraction, loss of energy related to vortices generated due to expansion after contraction and loss of energy due to friction. Using the methodology of design presented here for both types of injectors, the influence of different parameters on atomizer dimensions as well as spray characteristics of both types are finally compared and discussed.