# Tag Info

11

Partial answer: This engine from the 1970s vintage Viking Lander is a liquid engine featuring one combustion chamber and many nozzles. (you can ignore the red arrow, it's from another question). The reason for this design was to prevent exhaust plume erosion of the Martian surface below the lander, to prevent degradation of the science results. Source ...

10

HTP will sustain a combustion reaction without a catalyst once ignited, but it's not clear to me if the reaction proceeds quickly and smoothly enough to be a good idea for rocket combustion chambers. As MSalters comments above, hydrogen peroxide "will undergo potentially explosive thermal decomposition" before reaching its theoretical boiling point,...

10

They are provided to help damp out combustion instabilities. The main injector uses cooled baffle elements, developed at Glenn in the 1960s to control pressure waves that could destroy the engine. Pressure waves in the space shuttle main engine combustion chamber are also controlled by acoustic cavities. Testing by Glenn engineers determined the ...

7

Restartable hydrogen-oxygen engines like the RL10 (used on the Delta and Atlas upper stages) and J-2 (used on Saturn) use spark ignition. On the J-2, the spark igniter is positioned above the fuel injector face, in a small chamber above the main combustion chamber. It's apparently uncooled and actually operates continuously during engine firing. Presumably ...

7

You can referthis book Modern Engineering for Design of Liquid-Propellant Rocket Engines chapter 4. It depends the on the number of performance parameters such as $C_f, C^*$ and $I_{sp}$. From which the Throat area is calculated. Throat area is usually used as a starting point to have the thrust chamber dimensions. Characteristic length and Contraction ratio ...

6

Partial answer because based on a simulation doesn't address the secondary question about changes with throttling The paper CFD SIMULATION OF A LIQUID ROCKET PROPELLANT (LH2 /LOx) COMBUSTION CHAMBER shows a "flame front" in the sense that majority of the combustion reactions take place in a relatively small area of the combustion chamber. (zero ...

6

Anton must really love chemistry or pain. NASA's CEA is a robust tool for analyzing combustion thermo-chemistry which was developed by the same Gordon & McBride mentioned in Anton's answer while they were working at NASA. They also make MATLAB wrappers for the thing, but I'm not sure where to find a publicly available option. It will save you a ...

4

'tubes' aren't enough. You want an injector, in order to atomize the fuel and oxidizer and mix them. A simple one is the pintle injector, which has concentric openings for the fuel and oxidizer. Fuel being injected: and oxidizer: Other injectors have lots of openings alternating fuel and oxidizer, like the F-1 engine used in the Saturn V: You also ...

4

The ACES upper stage (in development at the moment) is being designed to do without an external source of pressurizing gas: Fundamentally IVF is a Hydrogen/Oxygen auxiliary power unit, that uses free boiloff hydrogen and oxygen to generate electricity (eliminating main vehicle batteries), provide autogenous tank pressurization (eliminating most or all ...

4

No, the Centaur with its RL-10 engines requires tank pressurization. Helium Supply and Pressurization System - Helium is the main pressurant used for tank pressurization. Typically, four 26-inch diameter high-pressure helium bottles mounted on the aft bulkhead are used for storage. They are made of a graphite/epoxy composite overwrap enveloping a stainless ...

4

For most rocket engines the fuel is used as nozzle and chamber coolant, which heats it up. It may enter the combustion chamber as gas or liquid, depending on design. But the LOX is merely pumped to the engine, and enters at storage temperature of 90K, and very much a liquid. Example: the Space Shuttle SSME: This LOX is sprayed using various techniques to ...

4

From my (probably) similarily rough understanding of L*, it's a minimum size required for propellants to stay long enough in the chamber to mix properly. If the distance is shorter than that, you will experience problems with combustion instability. As such, having a length that's too large is certainly not as bad as too short, although the engine is then ...

4

The ablation of high-purity graphite in oxygen and air atmospheres was studied in the 1000–1400°C temperature range,Very fast ablation rates were observed. The concern is the graphite wouldn't ablate equally overall, running the risk of uneven heating from combustion products. Also, graphite is pretty heavy substance. Paywalled: Ablation of graphite in ...

4

The reason you can't finish your calculations is that you are missing half of the engine. You are going to have to make some decisions about the nozzle in order to get exhaust velocity. I'll make some decisions for you and show you how to work through it. Your engine's design altitude is going to be 11.8 km. This means that your nozzle exit plane pressure is ...

4

To an old timer like me who was one of the pioneers in much of the rocket engine research during the Saturn V F-1 engine development at Princeton University (around 1966 – 71), I’m glad to see renewed public interest in these topics. My feelings are that the private rocket companies now-a-days are doing some good things with their new designs and strategies. ...

3

You will need to write a solver for the incomplete combustion of your propellant. This can be done by hand, but I recommend writing a program to implement it. These days, such calculations are primarily done by solving for the maximum entropic state of the system (the system being the mixture of reactants at the chamber temperature & pressure). The ...

3

There are different numbers on this NASA page about Saturn V: Finally, the fuel squirted through 3 700 orifices into the combustion chamber to mix with the oxidizer, which entered through 2 600 other orifices in the injector face If the hole numbers of the question are correct, (1428 Oxidizer holes and (approximately) 1404 Fuel (RP1) holes) the explanation ...

3

I would note that the RD-170 and RD-180 designs, while they appear to have two nozzles and two combustion chambers in the assembly, are said to perform as one because there is a pipe from one chamber to the next. I was fascinated to learn that Soviet engineers found they could stabilize the pressure among two or more chambers by doing this. This is the ...

3

I'm not going to do this beautiful beast of a paper justice, so by all means, feel free to dig into it yourself. It actually looks pretty readable, although processing all the math and theory would take me about an hour per page. But luckily, the highlights are at the end: For chugging (low frequency instability): "4. The frequency of unstable ...

2

Think of it in terms of providing enough residence time for the propellants to vaporize, mix, and burn to completion. Since most of the flow is axial, the length of the chamber contributes more directly than any other dimension to the amount of time the propellants have to burn. The second most important dimension is the throat diameter which will set your ...

2

This doesn't have a simple answer. From a pure chemistry standpoint you can observe that one CH4 molecule will completely react with two O2 molecules. CH4 has a molecular weight of 16, O2 has a molecular weight of 32. Thus you need 4x as much O2 by weight. However, there are two other factors involved: You can actually end up with more thrust with a bit ...

2

Inconel is chosen because it has a much higher melting point than copper, so the engine can be run at a high temperature.

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