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Computer drawings of gas turbine engine showing three dimensional
 engine and two dimensional schematic. Location of the beginning of
 each component is assigned a number from 1 to 8.

Most modern passenger and military aircraft are powered by gas turbine engines, which are also called jet engines. Jet engines come in a variety of shapes and sizes but all jet engines have certain parts in common.

Jet engines are complicated pieces of machinery with many moving parts. To help understand how the machines work, engineers often draw simplified diagrams, called schematics, of the engine. The schematic is often a flat, two-dimensional drawing of the engine representing the important components. It is not meant to be a "picture" of the engine, but only to indicate the important parts of the engine. On this slide we show a three-dimensional computer model of an afterburning turbojet at the top and the corresponding schematic drawing at the bottom. Various parts on the computer model are labeled and the corresponding parts on the schematic are indicated. When we discuss the fundamentals of turbojet, turbofan, and turboprop operation, we will use similar schematic drawings.

As a further shorthand for propulsion engineers, locations on the engine schematic are assigned station numbers. Free stream conditions are labeled 0 and the entrance to the inlet is station 1. The exit of the inlet, which is the beginning of the compressor, is labeled station 2. The compressor exit and burner entrance is station 3 while the burner exit and turbine entrance is station 4. The exit of the turbine is station 5 and the flow conditions upstream of the afterburner occur at station 6. Station 7 is at the entrance to the nozzle and station 8 is at the nozzle throat. Some nozzles have an additional section downstream of the throat which would be station 9.

Why do engineers assign numbers to the stations? First, it simplifies the language used when describing the operation of a gas turbine engine. With this numbering convention, engineers can refer to the "turbine inlet temperature" as simply "T4", or the "compressor exit pressure" as "P3". It makes technical reports, documents, and conversations much more concise and easy to understand. Second, in a gas turbine engine the stations correspond to the beginning and the end of thermodynamic processes in the engine. The Brayton Cycle describes the thermodynamics of a gas turbine engine and when describing the processes on a p-V or T-s diagram, we denote the end of a process by using the station number. For example, the end of the isentropic compression performed by the compressor is designated with a 3 on a T-s diagram. You can see the location of the engine stations for various engines by using the EngineSim interactive Java applet. If you choose "Graphs" for the output display, the station numbers will appear on the engine drawing and on the corresponding T-s or p-V diagram.


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Editor: Tom Benson
NASA Official: Tom Benson
Last Updated: Jun 12 2014

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