the combustion chamber. The combustion chamber contains  the fuel inlet and igniter for combustion. The expanding  air drives a turbine, which is connected by a shaft to the  compressor, sustaining engine operation. The accelerated  exhaust gases from the engine provide thrust. This is a basic  application of compressing air, igniting the fuel-air mixture,  producing power to self-sustain the engine operation, and  exhaust for propulsion.  [Figure 7-23]  Turbojet engines are limited in range and endurance. They  are also slow to respond to throttle applications at slow  compressor speeds. A turboprop engine is a turbine engine that drives a propeller  through a reduction gear. The exhaust gases drive a power  turbine connected by a shaft that drives the reduction gear  assembly. Reduction gearing is necessary in turboprop  engines because optimum propeller performance is achieved  at much slower speeds than the engine’s operating rpm.  Turboprop engines are a compromise between turbojet  engines and reciprocating powerplants. Turboprop engines  are most efficient at speeds between 250 and 400 mph and  altitudes between 18,000 and 30,000 feet. They also perform  well at the slow airspeeds required for takeoff and landing and  are fuel efficient. The minimum specific fuel consumption  The fourth common type of jet engine is the turboshaft.  [Figure 7-26]  It delivers power to a shaft that drives  something other than a propeller. The biggest difference  between a turbojet and turboshaft engine is that on a  The inlet air that passes through a turbofan engine is usually  divided into two separate streams of air. One stream passes  through the engine core, while a second stream bypasses the  engine core. It is this bypass stream of air that is responsible  for the term “bypass engine.” A turbofan’s bypass ratio refers  to the ratio of the mass airflow that passes through the fan  divided by the mass airflow that passes through the engine  core.  [Figure 7-25]  Turbofans were developed to combine some of the best  features of the turbojet and the turboprop. Turbofan engines  are designed to create additional thrust by diverting a  secondary airflow around the combustion chamber. The  turbofan bypass air generates increased thrust, cools the  engine, and aids in exhaust noise suppression. This provides  turbojet-type cruise speed and lower fuel consumption. of the turboprop engine is normally available in the altitude  range of 25,000 feet to the tropopause.  [Figure 7-24]  Turbofan Turboshaft Turboprop Figure 7-23.  Turbojet engine. Figure 7-24.  Turboprop engine. 7-21 Fuel injector Inlet Combustion chamber Compressor Turbine Hot gases Nozzle Combustion chamber Compressor Gear box Exhaust Fuel injector Inlet Prop Turbine