Rocket Engines

[nomorecatering]

I'm trying to get my head around how both the Space Shuttle Main Engines and the Saturn's Rocketdyne J2 engines actually work.

Specifically what is a turbo pump, my take on it is it ups the pressure of the propellant prior to injection into the combustion bell.

What is a thrust chamber, is it the apex of the engine bell?

Lastly, does the liquid oxygen get routed through tubes on the outside of the engine bell, to cool it? How do they prevent the LoX from boiling off in the tubes.

[grounded27]

WIKI copy and paste.........

Fuel turbopump

The fuel turbopump, mounted on the thrust chamber, was a turbine-driven, axial flow pumping unit consisting of an inducer, a seven-stage rotor, and a stator assembly. It was a high-speed pump operating at 27,000 rpm, and was designed to increase hydrogen pressure from 210 to 8,450 kPa (30 to 1,225 psi) (absolute) through high-pressure ducting at a flowrate which develops 5,800 kW (7,800 bhp). Power for operating the turbopump was provided by a high-speed, two-stage turbine. Hot gas from the gas generator was routed to the turbine inlet manifold which distributed the gas to the inlet nozzles where it was expanded and directed at a high velocity into the first stage turbine wheel. After passing through the first stage turbine wheel, the gas was redirected through a ring of stator blades and enters the second stage turbine wheel. The gas left the turbine through the exhaust ducting. Three dynamic seals in series prevented the pump fluid and turbine gas from mixing. Power from the turbine was transmitted to the pump by means of a one-piece shaft.[2] (http://en.wikipedia.org/wiki/Rocketdyne_J-2#cite_note-J2fact-2)
Oxidizer turbopump

The oxidizer turbopump was mounted on the thrust chamber diametrically opposite the fuel turbopump. It was a single-stage centrifugal pump (http://en.wikipedia.org/wiki/Centrifugal_pump) with direct turbine drive (http://en.wikipedia.org/wiki/Direct_drive_mechanism). The oxidizer turbopump increases the pressure of the liquid oxygen and pumps it through high-pressure ducts to the thrust chamber. The pump operated at 8,600 rpm at a discharge pressure of 7,400 kPa (1,080 psi) (absolute) and developed 1,600 kW (2,200 bhp). The pump and its two turbine wheels are mounted on a common shaft. Power for operating the oxidizer turbopump was provided by a high-speed, two-stage turbine which was driven by the exhaust gases from the gas generator. The turbines of the oxidizer and fuel turbopumps were connected in a series by exhaust ducting that directed the discharged exhaust gas from the fuel turbopump turbine to the inlet of the oxidizer turbopump turbine manifold. One static and two dynamic seals in series prevented the turbopump oxidizer fluid and turbine gas from mixing.[2] (http://en.wikipedia.org/wiki/Rocketdyne_J-2#cite_note-J2fact-2)
Beginning the turbopump operation, hot gas entered the nozzles and, in turn, the first stage turbine wheel. After passing through the first stage turbine wheel, the gas was redirected by the stator blades and entered the second stage turbine wheel. The gas then left the turbine through exhaust ducting, passed through the heat exchanger, and exhausted into the thrust chamber through a manifold directly above the fuel inlet manifold. Power from the turbine was transmitted by means of a one-piece shaft to the pump. The velocity of the liquid oxygen was increased through the inducer and impeller. As the liquid oxygen entered the outlet volute, velocity was converted to pressure and the liquid oxygen was discharged into the outlet duct at high pressure.[2] (http://en.wikipedia.org/wiki/Rocketdyne_J-2#cite_note-J2fact-2)

[barit1]

1) Turbo pump is as you describe; it pressurizes the fuel and oxidizer (separately) to motivate those fluids to enter the rocket chamber, which is a high-pressure zone. Without pumps, the rocket gases would reverse-flow into the tanks - BAD news!

2) Thrust chamber - this term seems ambiguous to me so I'll pass.

3) Regenerative cooling is nearly universal; in cooling the shell of the engine, the fuel or oxidizer is boiled so it enters the engine combustion zone as a gas.

[pattern_is_full]

In reverse order:

Fuel or Lox cooling may take place in various locations, depending of the engine design. It could be the bell, or it could be the head of the combustion chamber. Wherever heat will be the biggest problem.

Lox (or whichever liquid is used for cooling) doesn't boil off due to the pressure in the system. Not unlike the water in pressurized water nuke plants (when they work right) - the water can reach 2-3x normal boiling temperature and not boil, so long as it is highly pressurized. Or more simply, the way a pressure cooker can operate at above-normal boiling temperature (to cook food faster).

The thrust chamber is basically the whole "obvious" part of a rocket engine - the combustion chamber where the fuel ignites, AND the flared exhaust nozzle (bell). Any part of the engine where combustion creates enough overpressure to provide thrust, or in other words, any part of the engine that has to withstand the massive thrust forces and transmit them to the vehicle without coming apart.

The turbopump is simply a fuel pump that delivers a controllable and precise amount of fuel and fuel pressure (and oxidizer and oxidizer pressure) to the combustion chamber.

While the fuel/oxidizer tanks are pressurized, and fuel will also flow backwards/downwards under acceleration or gravity, their ability to deliver the right amount of fuel/oxidizer is too random for controlled flight. As fuel or oxidizer get used up (tanks get emptier), their "head pressure" will drop - and as fuel weight decreases, the acceleration (and thus the flow of fuel under G forces) will increase.

The turbo pumps eliminate these variables, and deliver a constant "engineered" amount and pressure of fuel/oxidizer, regardless of tank pressure or other influences.

There are - in the J2 - control valves downstream of the turbopumps to provide even more precise "throttling" of the engine output.

[compressor stall]

There's a Saturn V flight manual freely available on the net somewhere. I downloaded it a whole back. Should answer everything.

[megan]

nomorecatering, plough through this and you should be able to build one. This is for the F-1, the J-2 is similar.

http://agentdc.uah.edu/homepages/dcfiles/USSRC/F1EngiFamiTraiManu%20Section%201_072308152849.pdf