Balloon Assisted High Altitude Rocket - BAHAR

May 25/2000
big KNO3/icing sugar engine test

Download audio of last static test. About 12lbs of fuel were burnt in 2.2 seconds!

engine details:
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nozzle diameter: 3/4"
nozzle area: 0.44"
exit diameter: 3 1/8"
exit area: 7.66"
nozzle expansion ratio: 17.4x (I have learned that this expansion ratio is too large and should be 7 or 8)
fuel cylinder length: 22"
fuel cylinder diameter: 3 1/8"
fuel core diameter: 3/4"
fuel cylinder volume: 187 in^3
initial surface area of fuel 51.7in^2
average surface area of fuel 133in^2
final surface area of fuel 215in^2
weight of fuel: 12 lbs
burn time: 2.2 seconds

Kn = surface area of fuel/nozzle area
Pc(t) = Kn(t) * Isp(s) * density (lb/in^3) * burn rate(in/s)(t)
average thrust(lbs) = weight of fuel(lbs)/burn time(s) * Isp(s)
the initial thrust and final thrust are estimations based on change in Kn and the calculated average thrust
thrust at time t(lbs) = (Kn at time t/Kn average) * average thrust
the initial burn rate and final burn rate are estimations based on change in Kn and the calculated average burn rate
burn rate at time t(inches/sec) = (Kn at time t/Kn average) * average burn rate
Calculating thrust and burn rate at time t assumes that they are both directly proportional to Kn
Isp = Total Impulse(lb-sec) = thrust * burn time
*Isp = Specific Impulse (sec) = Total Impulse / weight of fuel
n Burn rate pressure = 0.323 (theoretical) thanks to Richard Nakka's website for the a,n, density values
a Burnrate constant = 0.0665 (theoretical)
Density of fuel = 1.80 gram/cu.cm. (theoretical)
Isp Specific Impulse 130 sec. (theoretical)
Burn rate @ 1000 psia = 0.602 in/sec (theoretical)

engine calculations:
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Kn initial: 117
Kn average: 302
Kn final: 488
Pc initial: 172 psi
Pc average: 1148
Pc final: 2988
Isp(s) of KNO3/sugar: ~110 (theoretical)
density of fuel (lb/in^3): 0.064lbs/in^3
initial burn rate (in/s) 0.21"/sec
average burn rate (in/s): 0.54"/sec
final burn rate (in/s): 0.87"/sec
initial thrust: 232 lbs
average thrust: 600 lbs
final thrust: 970 lbs

Table of combustion products and reactants for KNO3/icing sugar fuel (from Richard Nakka's website)

C12H22O11 + 6.29 KNO3    ->    3.67 CO2 + 5.18 CO + 7.91 H2O + 3.09 H2 + 3.14 N2 + 3.14 K2CO3


sucrose solidC12H22O11
potassium nitratesolid KNO3
carbon dioxidegasCO2
carbon monoxidegasCO
steam gas H2O
hydrogengas H2
nitrogen gas N2
potassium carbonateliquidK2CO3

Pics from our last static test:







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