1
MAE 112
PROPULSION
FINAL EXAM
March 19, 2009
Do all four problems in 120 minutes.
Books, notes and calculators can be used freely.
1. An afterburner has an exhaust temperature of 3000
R into a nozzle and operates at 4.5
atmospheres of pressure. The afterburner is immediately downstream of the turbine in a
turbojet engine. For every mole of liquid octane fuel C
8
H
18
added to the afterburner, the
inflowing mixture of product gases and excess air has 16, 18, 15, and 150.4 moles,
respectively, of CO
2
, H
2
O, O
2
, and N
2
. The liquid fuel is introduced to afterburner at the
initial temperature of 515
R with a heating value Q=19135 Btu/lbm which accounts for
vaporization heat.
Neglect dissociation. Assume the flow through the afterburner has c
p
=
0.33 Btu/lbmR and a ratio of specific heats equal to 1.25, with values of c
p
= 0.30
Btu/lbmR and a ratio of specific heats equal to 1.30 for the turbine. The polytropic
efficiency of the turbine is 0.96 and the afterburner efficiency is 0.99. The temperature
entering the turbine is 2600
o
R.
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 Winter '09
 LaRue
 Thermodynamics, gas generator

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