An experimental program was conducted to select a combustion system design for the 500 shp Model 250-C28 turboshaft/turboprop engine. The primary goals were: 1. Capability of complying with the Environmental Protection Agency (EPA) 1979 Class P2 turboprop engine emission standards. 2. Capability of ingesting a 100 ml slug of water in 1/4 s without flameout. The Model 250-C28 engine is an uprated version of the Model 250 (T63 military designation) production engine. The conventional Model 250 production combustor meets the EPA 1979 turboprop emission standards for NOx and smoke, but unburned hydrocarbons (UHC) and CO exceed the standards. Also, the water ingestion requirement for the Model 250-C28 exceeded the capability of the current technology conventional combustor.The emission and water ingestion goals of the program were met with a prechamber combustor design. Exhaust emissions measured during testing with a current production engine configuration met all of the EPA 1979 Class P2 turboprop engine emission standards. Engine water ingestion tests with the prototype prechamber combustor exceeded the program goal, and a tolerance level about four times that of the production Model 250 engine was demonstrated.The favorable results from this investigation led directly to a Model 250-C28 prechamber combustor design that is currently undergoing development.