Abstract : The Air Force and its partners are developing and validating an injector design methodology that utilizes both high-pressure cold-flow testing and uni-element hot-fire testing, to create a high performing, long life swirl coaxial injector. Several gas-centered swirl coax injector configurations have been tested under cold- flow and hot-fire test conditions in a single element research engine. The methodology uses computational fluid dynamics (CFD) analyses to provide insight into the flowfield and guide the evolution of injector designs. Both cold-flow and hot-fire analyses were completed, with cold flow results compared with test data. The companion paper will discuss the experimental results.