Page 179 - The Jet Engine

16: Afterburning

Contents Page

Introduction 169
Operation of afterburning 170

Construction 173

Burners
Jet pipe
Propelling nozzle
Control system 173
Thrust increase 175

Fuel consumption 178

2. Afterburning consists of the introduction and
burning of fuel between the engine turbine and the jet
pipe propelling nozzle, utilizing the unburned oxygen
in the exhaust gas to support combustion (fig. 16-1).
The resultant increase in the temperature of the
exhaust gas gives an increased velocity of the jet
INTRODUCTION leaving the propelling nozzle and therefore increases
the engine thrust.
1. Afterburning (or reheat) is a method of
augmenting the basic thrust of an engine to improve 3. As the temperature of the afterburner flame can
the aircraft take-off, climb and (for military aircraft) be in excess of 1,700 deg. C., the burners are usually
combat performance. The increased power could be arranged so that the flame is concentrated around
obtained by the use of a larger engine, but as this the axis of the jet pipe. This allows a proportion of the
would increase the weight, frontal area and overall turbine discharge gas to flow along the wall of the jet
fuel consumption, afterburning provides the best pipe and thus maintain the wall temperature at a safe
method of thrust augmentation for short periods. value.

169