← INDEX — FIG. 00 — THROAT 10.3 IN, EXIT 90.7 IN
ε = Ae / A* = 77.5
NOZZLE
HOW ROCKET ENGINES WORK
A rocket engine is a pump, a fire and a funnel.
BEGIN — CHAPTER 01 →CH.01 / 06 — CONVERGE, CHOKE, DIVERGE
Supersonic gas speeds up in a widening pipe
A nozzle converges to a throat, then diverges.
The area ratio sets the exit conditions.
ISENTROPIC NOZZLE FLOW
ε = A/A* = (1/M) [ (2/(γ+1)) (1 + (γ−1)M²/2) ](γ+1)/(2(γ−1)) · p/pc = (1 + (γ−1)M²/2)−γ/(γ−1)
γ ≈ 1.2 for rocket exhaust.
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CH.02 / 06 — ONE NOZZLE CANNOT FIT EVERY ALTITUDE
The air pushes back on the exit
F = ṁve + (pe − pa)Ae.
RS-25: 418,000 lbf at sea level, 512,300 lbf in vacuum.
THRUST COEFFICIENT
CF = √{ (2γ²/(γ−1)) (2/(γ+1))(γ+1)/(γ−1) [1 − (pe/pc)(γ−1)/γ] } + ε (pe − pa)/pc
Chamber pressures from the sources.
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Your nozzle uses the settings above.
CH.03 / 06 — FEEDING THE FIRE
Where does the turbine's exhaust go?
Gas-generator cycle: the turbine exhaust is dumped.
Staged combustion burns everything.
CH.04 / 06 — KEEPING THE NOZZLE SOLID
The fuel cools the bell before it burns
Regenerative cooling.
Turbine exhaust as film cooling on the F-1.
CH.05 / 06 — ENGINES THAT KEPT FLYING
From throwaway giants to reusable engines
Burn, choke, expand.
CH.06 / 06 — REFERENCES