RocketEngines
Rocket Engine
The general principle may be simple, but there are numerous ways of achieving it. Different features and properties differ between existing rocket engines, and they all have consequences on complexity of manufacturing, complexity of operation, cost and weight for example.
We gather in this table the main properties of existing rocket engines.
| Company | Rocketdyne | NPO Energomash | XCOR | XCOR | Armadillo |
|---|---|---|---|---|---|
| Model | SSME | RD-107 series (Soyuz) | XR-4A3 (EZ-rocket) | XR-5K18 (Lynx) | LOX/methane (no name) |
| Combustion | |||||
| Propellants | LOX & LH2 | LOX & Kerosene | LOX & Alcohol | LOX & Kerosene | LOX & LCH4 |
| Tank pressurization | Yes, with O2 and H2 gases | Yes, with Nitrogen (same pump than propellants) | No | No | Yes, with Helium |
| Fuel pump | Turbopump | Turbopump driven by gaz generator using hydrogen peroxide decomposition (8300rpm) | Piston pump | Piston pump | No |
| Cooling | Regenerative w/ LH2 in three stages | Regenerative w/ kerosene (5 mm deep channels milled in the inner wall) and film of kerosene | Regenerative (w/ Alcohol?) | Regenerative w/ Kerosene | ? |
| Injector | ? | 337 swirling/mixing injectors, ring of kerosene only for film cooling - view cut | ? | ? | ? |
| Chamber metal | Copper or iron? | 6 mm thick chromium bronze alloy inner wall, steel outer wall | Copper | Copper | ? |
| Ignition system | ? | Pyrotechnic, soon hypergolic | ? | ? | ? |
| Actuators | |||||
| Energy | Hydraulic | Electric | |||
| Provided by | Engine's turbopumps | ? | |||
| Actuator | Six hydraulic servoactuators | Static engine, control by vernier engines | None | None | Servo-motor |
| Others | |||||
| Valves | Hydraulically or pneumatically (helium) actuated | ? | ? | ? | ? |
Pumps and tank pressurization
In order to get fuel from the tanks into the combustion chamber, the tanks must be either pressurized or the fuels pumped. In some cases, both techniques are used. The choice for this concern has a large impact on the design of the engine's hardware, and the complexity of manufacturing and operations.
Traditionnaly, only turbo pumps have been able to feed the engine at a large enough rate. Innovative solutions appeared in research projects or private space projects, like the use of piston pumps for LOX or simple pressurization using liquid helium.
Several possibilities exist for tank pressurization:
- vaporization of liquid propellants back into their own tanks
- external vaporization of inert gas like Helium (can Nitrogen be used for that?)
- smoke generator, that basically react fuel and oxidizer and use the resulting smoke for pressurization.
Cooling
Regenerative cooling is most widely used in rocket engines.
Few of them however use other ways, like ablatively cooling carbon fiber composite in SpaceX Merlin 1A engine, or radiative cooling in the Merlin Vacuum nozzle (still regenerative for the chamber).
