Analyses for turbojet thrust augmentation with fuel-rich afterburning of hydrogen, diborane, and hydrazine Page: 4 of 22
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(1) Takeoff with an engine-inlet-air temperature of 298 K, an
afterburner pressure of 2 atmospheres, and an exhaust-nozzle pres-
sure ratio of 2 (complete expansion)
(2) Fllight at Mach 2 and an altitude of about 5 n5,0 feet with an
engine-inlet-air temperature of 4000 K, an afterburner pressure
of I atmosphere, and exhaust-nozzle pressure ratios of 2, 6, and
11. The pressure ratio of 11 gives complete expansion.
The calculations were made for fuel-air ratios ranging from stoichio-
metric values to 0.5. For hydrogen and diborane, it was assumed that the
fuel being considered was used in the primary combustors and the after-
burners. However, the low heat of combustion for hydrazine, about 7170
Btu per pound, requires a different approach. Therefore, for hydrazine,
Sit was assumed that hydrogen was burned in the primary combustors and
o the afterburners of turbojet engines for fuel-air ratios up to the
stoichiometric point. Above this point, hydrazine was added; the fuel-
air ratio for hydrazine is given by the over-all fuel-air ratio minus
0.0293. This method gives low fuel flows for normal turbojet operation.
If fuels were heated by sources external to the engine, higher net
thrusts would result. To indicate this effect, net thrusts were computed
for 7000 K hydrogen burned with 4000 K engine-inlet air. A combustion
pressure of 1 atmosphere and an exhaust-nozzle pressure ratio of 11
(complete expansion) were used.
The results for fuel-rich afterburning are compared with net thrusts
for stoichiometric combustion of the turbojet fuel and air augmented with
a 220-second specific-impulse rocket.
Thermodynamic data from references 3, 4(table III), and 5 were used
in the calculations. The combustion products for hydrogen and hydrazine
were assumed to be the following gases in equilibrium at the combustion
temperature: H2, H20, N2, NO, 02, 0H, H, N, and 0. Unpublished data
for hydrogen indicate that at a combustion temperature of 20000 K about
99 percent of the total enthalpy is required for the nondissociated
products. As the combustion temperature decreases, this percentage in-
creases. Therefore, the products for hydrogen and hydrazine at combustion
temperatures below 20000 K were assumed to be H2, H20, and N2 gases.
* For diborane, the following combustion products were assumed to be
in equilibrium for all combustion temperatures: BH, BO, B203, H2, H20,
SI N2, NO, 02, OH, H, N, 0, and B gases and B203 liquid. The products B202
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Morris, J. F. Analyses for turbojet thrust augmentation with fuel-rich afterburning of hydrogen, diborane, and hydrazine, report, June 18, 1957; (digital.library.unt.edu/ark:/67531/metadc53092/m1/4/: accessed November 18, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.