Abstract: Indirectly fired gas turbine engine systems which can be operated on alternative or renewable fuels or by waste heat. Fast response time over the entire operating range of the engine, precise control over turbine inlet temperature, and water injection for increased power output are featured as are arrangements for dumping air and thereby preventing mechanical damage when rapid deceleration occurs or the load is lost. Other mechanical innovations facilitate start-up and shut-down of the turbine engine; make preheated process air available; and provide precise control over the thermal energy supplied to the heat exchanger in which compressor discharge air is heated.