Exhaust Gas Turbine

As discussed in Chapter 2, the supercharger (basically, an air compressor) can also be driven by an exhaust gas turbine. In this case, the overall system is referred to as a turbocharger or turbosupercharger (Abgasturbolader in German). The focus in Kollmann’s manuscript is exclusively on radial compressors used as superchargers driven by a gear drive connected to the main engine shaft. This is not so surprising considering that, although significant R&D effort was spent on the turbine design (especially, turbine blade cooling), turbocharged German aircraft engines did not enter service until the end of the war. Even then, the service experience was limited to Junkers Ju 388 (mostly for high altitude reconnaissance) powered by two 1,500-HP BMW 801 J turbocharged engines. Many other designs (e.g., the DB 623) were eventually abandoned. The dilemma facing the German engineers at the time (1940s) was this: whether to develop an aircraft engine from the get-go with a turbocharger or to develop a turbocharger to be fitted into an existing engine (e.g., the DB 603). Since the need for the turbochargers arose during the war by the need for higher flight altitudes (10 to 14 km), e.g., to attack the Allied bomber formations and their fighter escort, the urgency of the situation made the choice for them1. Not surprisingly, they went with the latter option.