Page 188 - The Jet Engine

22. It is not possible to go on increasing the amount
of fuel that is burnt in the jet pipe so that all the
available oxygen is used, because the jet pipe would
not withstand the high temperatures that would be
incurred and complete combustion cannot be
assured.

FUEL CONSUMPTION
23. Afterburning always incurs an increase in
specific fuel consumption and is, therefore, generally
limited to periods of short duration. Additional fuel
must be added to the gas stream to obtain the
required temperature ratio (para. 19). Since the
temperature rise does not occur at the peak of
compression, the fuel is not burnt as efficiently as in
the engine combustion chamber and a higher
specific fuel consumption must result. For example,
assuming a specific fuel consumption without after-
burning of 1,15 lb./hr./lb. thrust at sea level and a
speed of Mach 0,9 as shown in fig. 16-9. then with
70 per cent afterburning under the same conditions
of flight, the consumption will be increased to Fig. 16-9 Specific fuel consumption
comparison.

Fig. 16-10 Afterburning and its effect on the rate of climb.

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