What the cut shows
Nozzle down, injector at the top. The flat face is a diametral section. Kerosene enters the round manifold beside the nozzle exit, runs up the milled channels between the hot wall and the machined jacket, and leaves through the forward manifold into the fuel gallery behind the face. Each near-side channel is one slot from the divergent, across the throat, and up the barrel (24 of 56 face the camera). The short radial marks at each end of those slots are the distribution holes. They stay outboard of the hot wall, through the closeout into the manifold, and do not open into the gas. The unwrapped strip below is every channel and every rib. The lit pair is one unlike doublet, meeting off the face. The fuel hole leaves the gallery; the oxidizer hole leaves the torus in the dome. Eight bolts hold the injector flange. The small boss on the barrel is a chamber-pressure tap; its station is schematic. The center boss is the igniter, with the electrode on the axis. Two O-ring sections sit on the injector joint and the aft joint. The jacket hides the channels until the explode. The head section below is the same galleries, larger, still in proportion.
The center port drawn in the face is a passage for a non-hypergolic igniter. Its diameter is schematic. The barrel is long on purpose. L* is 40 in and the throat is 31.5 mm, so the cylinder is 237 mm on a 63 mm bore, about 3.8 diameters. The cut passes through a channel on one side and a rib on the other. Wall thicknesses on the main view are true size; the detail below is the same stack, magnified, still in proportion.
Dimensions and assumptions
| Item | Value | Where it came from |
|---|---|---|
| Thrust, sea level | 500 lbf (2224 N) | Request. Optimum expansion, Pe = Pa. |
| Chamber pressure | 300 psia | Request. Injector-end stagnation, treated as uniform. |
| Ambient | 14.696 psia | Standard sea level. |
| Propellants | Liquid N2O / kerosene (RP-1 density) | Fuel is the coolant. Not hypergolic. |
| Mixture ratio O/F | 7.0 | Assumption, fuel-rich of a rough N2O/RP-1 stoichiometric estimate near 9. Not a CEA optimum. |
| γ | 1.233 | Taken from the LOX/RP-1 worked example in Huzel and Huang, NASA SP-125 §4.1 (γ = 1.233). Not an N2O equilibrium. |
| c* | 1500 m/s | Assumption, below the SP-125 LOX/RP-1 example c* of 5400 ft/s, because N2O carries nitrogen. Not a CEA result. |
| Divergence factor λ | 0.983 | (1 + cos 15°)/2 applied to the one-dimensional Cf. |
| Cf, sea level | 1.380 | Momentum Cf at Pe = Pa, times λ. Pressure term is zero. |
| Exit Mach | 2.57 | Isentropic, frozen γ. |
| Expansion ratio ε | 3.53 | Solved so Pe = Pa. The SP-125 example's 8:1 is a different engine. |
| Throat diameter | 31.49 mm (1.240 in) | At = F / (Cf Pc). |
| Exit diameter | 59.14 mm | ε and the throat. |
| Chamber diameter | 62.99 mm | Contraction ratio 4. The SP-125 100 klbf example used 1.60 because its throat was already large. |
| L* | 40 in (1016 mm) | Near the SP-125 hypothetical chamber's 38 in (§4.1 item 16), rounded up for a small N2O chamber. |
| Cylindrical length | 237.3 mm | Whatever is left after the throat land and the convergent frustum so that Vc/At = L*. |
| Convergent | 30° half-angle, 27.3 mm | Layout assumption. |
| Divergent | 15° half-angle cone, 51.6 mm | First-pass cone, not a Rao bell. NASA SP-8120 is the nozzle monograph. |
| Throat land | 3 mm | Short cylinder. The throat plane is its downstream end. |
| Hot wall | 0.9 mm copper-alloy liner | Constant in this pass. A real contour thins it where the flux peaks. Square sidewalls, per the milled-channel correction in Gradl's channel-wall notes. |
| Channels | 56 × 1.1 mm wide × 1.6 mm deep | Constant section. Pitch is closed on the throat mid-channel circumference. |
| Rib at the throat | 0.86 mm | Lands stay wide enough to inspect. Ribs grow as the radius grows; channel width stays at the cutter width. |
| Closeout | 2.4 mm machined jacket | Separate body seated on the lands. Electroformed nickel is the TM-X-3499 closeout; this jacket is machined so it can come off. |
| Coolant path | Kerosene, single up-pass | Inlet manifold at the nozzle exit, counterflow through the closeout into the forward manifold, then into the fuel gallery. Distribution holes do not pierce the hot wall. |
| Fuel gallery | Annulus behind the face | Mean radius on the fuel-orifice circle, 3.5 mm behind the face. The 12 fuel holes leave it. The cross-section is a layout assumption, not a manifold drawing. |
| Oxidizer manifold | Torus in the dome | Feeds the N2O orifices. The section shows the torus and one branch to the drawn doublet. Wall thickness around it is a layout assumption. |
| Injector | 12 unlike doublets | Liquid/liquid. SP-8089 element family. SP-125's illustrated LOX injector is like-on-like; this face is unlike. |
| Injector ΔP | 20% of Pc (60 psi) | SP-125 rule of thumb, 15 to 20 percent of nozzle stagnation pressure. Top of that band. |
| Cd | 0.75 | Inside the SP-125 range 0.5 to 0.92. Not a water-flow calibration. |
| Fuel orifice | 0.86 mm dia, 12 holes | ρ = 810 kg/m³. |
| N2O orifice | 2.29 mm dia, 12 holes | ρ = 780 kg/m³, saturated liquid near 20 °C. Colder liquid is denser and the hole shrinks. |
| Impingement | 60° included | Fan meets off the face. The SP-125 example used 40° included on like doublets. |
| Igniter | Center port in the face | SP-125: an ignition device for a non-hypergolic combination, on the injector centerline. |
| Seals | Two static O-rings | Injector-to-chamber and aft manifold. SP-125 seals the injector to the body with an O-ring compatible with the fuel. |
| Injector bolts | 8 on the flange | Layout assumption for a flange of this diameter. SP-125 bolts the injector to the chamber. The count is not from a callout drawing. |
| Chamber pressure tap | One boss on the barrel | SP-125 instruments chamber pressure. The axial station and the port bore on the drawing are schematic. |
| Mass flow | 1074 g/s (fuel 134, N2O 940) | ṁ = Pc At / c*. |
Checks run with the figure
- Pass: cylinder length is positive. 237.3 mm
- Pass: L* closes. integrated volume / At
- Pass: exit pressure is ambient. Pe = Pa by the area-ratio solution
- Pass: rib at throat is a land, not a knife. 0.86 mm
- Pass: channel count matches the throat pitch. 56 channels
- Pass: fuel orifice is a drillable hole. 0.86 mm
- Pass: oxidizer orifice is a drillable hole. 2.29 mm
- Pass: injector is upstream of the face. face at the forward end
- Pass: coolant enters at the exit and leaves at the injector. single up-pass
Sources
- Dieter K. Huzel and David H. Huang, Design of Liquid Propellant Rocket Engines, NASA SP-125 (1967), NTRS 19710019929, local copy
library/nasa-ntrs/19710019929.pdf. Thrust-chamber elements; the LOX/RP-1 worked example in §4.1 (γ = 1.233, L* = 38 in, contraction 1.60, expansion 8:1 — that contraction and expansion belong to the 100,000 lbf example, not to this chamber); injector ΔP of 15 to 20 percent of stagnation pressure; discharge coefficient 0.5 to 0.92; centerline igniter for a non-hypergolic combination; O-ring between injector and chamber. - NASA SP-8087 (1972), NTRS 19730022965. Regenerative channel, manifold, and closeout.
- NASA SP-8089 (1976), NTRS 19760023196. Unlike-doublet liquid/liquid elements. The SP-125 picture is like-on-like; this face is unlike.
- NASA SP-8120 (1976), NTRS 19770009165. Nozzle monograph. The divergent here is a 15° cone with the divergence factor (1+cos α)/2, not a Rao contour taken from the book.
- NASA TM-X-3499, NTRS 19770013219. Zirconium-copper liner and electroformed nickel closeout. This liner is in that copper-alloy family. The closeout is machined, so the explode can take it off; the electroform is the report's closeout, not the one drawn.
- Gradl and co-authors, channel-wall nozzle manufacturing, NTRS 20190033314 and 20205002297. Square sidewalls and lands wide enough to inspect. The closeout is its own body.
A rough stoichiometric O/F for N2O and a kerosene near CH2 is about 9 if each nitrous molecule is counted as one oxygen atom. O/F 7 is fuel-rich of that estimate so the coolant is not a trickle. It is not a CEA optimum. c* is an assumption below the SP-125 LOX/RP-1 example of 5400 ft/s, because nitrous carries nitrogen. NASA SP-273 in the library is the equilibrium code that would replace both numbers.