Jet propulsion

Figure 6.2 shows schematically, the simplest form of gas-turbine propulsion device; the turbo-jet. The engine consists of three basic components.

1 A compressor is used to increase the pressure (and temperature) of the air at inlet.

2 A combustion chamber, in which fuel is injected into the high-pressure air as a fine spray, and burned, thereby heating the air. The fuel is normally a form of paraffin (kerosene). The air pressure remains constant during combustion, but as the temperature rises, each kilogram of hot air needs to occupy a larger volume than it did when cold. It thus rushes out of the exhaust at a higher speed than at entry. The jet normally emerges at a pressure close to the ambient atmospheric value.

Combustion

Compressor 1.8 7" chamber З 7 Turbine 3.7 7

— Outlet

nozzle 0.5 Г

Net thrust 7

Fig. 6.2 A simple turbo-jet engine with axial compressor and turbine stages

Approximate contributions to the net thrust T are shown for a typical engine

3 A turbine which extracts some of the energy available in the exhaust jet in order to drive the compressor.