Gas Turbine Engine Turboprop Engines Figure 14-1.  Basic components of a gas turbine engine. 14-2 INTAKE COMPRESSION COMBUSTION EXHAUST Air inlet Compression Cold section Hot section Combustion chambers Turbine Exhaust The turbojet engine excels the reciprocating engine in  top speed and altitude performance. On the other hand,  the turbojet engine has limited takeoff and initial climb  performance as compared to that of a reciprocating engine.  In the matter of takeoff and initial climb performance, the  reciprocating engine is superior to the turbojet engine.  Turbojet engines are most efficient at high speeds and  high altitudes, while propellers are most efficient at slow  and medium speeds (less than 400 miles per hour (mph)).  Propellers also improve takeoff and climb performance.  The development of the turboprop engine was an attempt to  combine in one engine the best characteristics of both the  turbojet and propeller-driven reciprocating engine. High-pressure exhaust gases can be used to provide jet thrust  as in a turbojet engine. Or, the gases can be directed through  an additional turbine to drive a propeller through reduction  gearing, as in a turbopropeller (turboprop) engine. To start the engine, the compressor section is rotated  by an electrical starter on small engines or an air-driven  starter on large engines. As compressor rates per minute  (rpm) accelerates, air is brought in through the inlet  duct, compressed to a high pressure, and delivered to the  combustion section (combustion chambers). Fuel is then  injected by a fuel controller through spray nozzles and ignited  by igniter plugs. (Not all of the compressed air is used to  support combustion. Some of the compressed air bypasses  the burner section and circulates within the engine to provide  internal cooling, enhanced thrust, and noise abatement. In  turbojet engines, by-pass airflow may be augmented by  the action of a fan located at the engine’s intake.) The fuel/ air mixture in the combustion chamber is then burned in a  continuous combustion process and produces a very high  temperature, typically around 4,000° Fahrenheit (F), which  heats the entire air mass to 1,600 – 2,400 °F. The mixture of  hot air and gases expands and is directed to the turbine blades  forcing the turbine section to rotate, which in turn drives the  compressor by means of a direct shaft, a concentric shaft, or  a combination of both. After powering the turbine section,  NOTE: Because compression produces heat, some pneumatic  aircraft systems tap into the source of hot (480 °F) compressed  air from the engine compressor (bleed air) and use it for  engine anti-ice, airfoil anti-ice, aircraft pressurization, and  other ancillary systems after further conditioning its internal  pressure and temperature. Both piston (reciprocating) engines and gas turbine engines  are internal combustion engines. They have a similar  cycle of operation that consists of induction, compression,  combustion, expansion, and exhaust. In a piston engine,  each of these events is a separate distinct occurrence in each  cylinder. Also in a piston engine, an ignition event must occur  during each cycle in each cylinder. Unlike reciprocating  engines, in gas turbine engines these phases of power occur  simultaneously and continuously instead of successively  one cycle at a time. Additionally, ignition occurs during the  starting cycle and is continuous thereafter. The basic gas  turbine engine contains four sections: intake, compression,  combustion, and exhaust.  [Figure 14-1] the high velocity excess exhaust exits the tail pipe or exhaust  section. (The exhaust section of a turbojet engine may also  incorporate a system of moving doors to redirect airflow  for the purpose of slowing an airplane down after landing  or back-powering it away from a gate. They are referred to  as thrust reversers). Once the turbine section is powered by  gases from the burner section, the starter is disengaged, and  the igniters are turned off. Combustion continues until the  engine is shut down by turning off the fuel supply. 