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1.6. SUMMARY

The theory of gas turbine engine operation is based on the laws or principles of physics. The principle of jet propulsion can be illustrated by a toy balloon. When the balloon is inflated and the stem is unsealed the balloon will move in a direction away from the escaping jet of air. If the balloon is converted into a length of pipe, and at the forward end an air compressor is installed to supply air for combustion, and to expand the volume of air, fuel and ignition are introduced and combustion takes place. Then, in the path of the expanding gases a turbine rotor is installed. As the gases pass through the turbine blades, the turbine rotor is rotated at high speed. This turbine rotor is connected to the compressor shaft, and we now have a means to rotate the compressor to replenish the air supply. The remaining gases are discharged to the atmosphere. The reaction of these gases is thrust, or movement of the tube away from the escaping gases. This is a simple turbojet engine.

Power transformed by turbine wheel is fed back to maintain engine cycle - Energy drawn off for purposes other than maintaining engine cycle

In the turbojet engine, approximately 60 percent of the energy is extracted to rotate the compressor, while the remaining 40 percent is used to develop thrust. In the turboshaft engine, the remaining energy is used to drive a turbine rotor attached to a transmission or propeller. On a free-turbine engine, the gas stream passing across the turbines is the only link between the two turbine rotors. One turbine drives the compressor and the other turbine propels the aircraft. The free-turbine engine is used in Army aircraft.

The gas turbine engine differs radically in construction from the reciprocating engine in that the turbine engine has a separate section for each function, while in the reciprocating engine all functions are performed in the same cylinder.

 

David L. Heiserman, Editor

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Revised: June 06, 2015