FUBAR Labs Builds A Rocket Engine


[Graham] over at FUBAR labs took it upon himself to build a rocket engine. This isn’t a simple solid-fuel motor, though: [Graham] went all out and built a liquid-fueled engine that is ignited with a spark plug.

The build started off with a very small ‘igniter’ engine meant to shoot sparks into a larger engine. This engine is fueled with ethanol and air – not the best fuel for a rocket engine by a long shot but save and cheap enough to do a few serious experiments with.

To test out this small engine, [Graham] made a test platform out of aluminum extrusion to remotely control the fuel and oxidizer valves. The valves are controlled by an Arduino and XBee for remote operation and a telemetry downlink for measuring the fluid flow into the engine.

After he had some experience with pressure, plumbing, valves, and engines, [Graham] upgraded his fuel and oxidizer to gaseous oxygen and ethanol. With proper safety protocol in place, [Graham] was able to a series of three 3-second burns less than a minute apart as well as a single burn lasting nearly 5 seconds.

Even though [Graham] eschewed the usual stainless steel construction of rocket engines (his engine is milled out of aluminum), he demonstrated it is possible to build a real liquid-fueled rocket engine at home.

27 thoughts on “FUBAR Labs Builds A Rocket Engine

    1. Thank you very much. I’m not nearly as familiar with ramjets but I believe the challenge is getting the airspeed fast enough in order for the engine to perform. Sounds like an interesting project!

    1. Oxygen was chosen due to it’s availability and relevant safety (at least for an oxidizer). Typically a hydrocarbon is used and I eventually decided on ethanol because it cleans parts as it’s used. With such low flow rates cost was not an issue. A lot of newspace companies use this combination as well, albeit with Liquid Oxygen instead of Gaseous. Armadillo Aerospace is probably the best known of these and I believe both Xcor and Masten use this combination as well.

  1. What temperatures do the combustion areas see? Aluminum is flammable at high enough temps, especially in an oxygen-rich atmosphere. Even without igniting, it melts at about 1200F and loses strength below that.

    That’s not an OMGWFTBBQ thing.. just a design issue. Stainless is the usual choice because it was originally developed for good high temperature performance.

    1. Good Question. The engine was calculated to run @ ~ 4000F with a 1:1 fuel:oxidizer ratio. All of the technical parameters are here: http://wiki.fubarlabs.org/fubarwiki/Gaseous-Oxygen-GOX-Ethanol-Igniter-Engine.ashx (see: Engine Detailed Specs). Aluminum is a pretty good conductor stainless steel not so much (http://www.engineeringtoolbox.com/thermal-conductivity-metals-d_858.html), which is one of the reasons why I went with that material. It sucks the heat away from the inner chamber and it can run for a few seconds without melting even at those temps. The engine run-time was always kept short (maximum was 5 seconds) in order to avoid “melty” issues.

      Unfortunately, just about all metals except for really exotic stuff have melting temps way below 4000F (http://www.engineeringtoolbox.com/melting-temperature-metals-d_860.html) and stainless steel will melt around 1500F, which isn’t much better. In order to run for longer periods of time liquid and film cooling becomes necessary and I plan on incorporating these features into my next engine.

    2. Aluminum burning is a serious concern, especially when used with pure oxygen. Remember that powdered aluminum is one of the most common fuels in solid rocket propellants. The only two reasons it’s a relatively safe material to use is air is only 21% oxygen and once pure aluminum is exposed to air a layer of Aluminum Oxide forms on the surface which protects the Aluminum from further exposure.

      When you use gaseous oxygen or liquid oxygen it’s got 5X as many oxygen molecules as air and many items which are normally not flammable will burn (recall the Apollo 1 fire). With suitable catalysts (or contamination) the ignition temperature can cause Aluminum to burn at relatively low temperatures.

      Clearly from Graham’s references he’s done his homework – as should anybody who wants to work with rockets.

      1. Phil is absolutely correct in his analysis of aluminum/oxygen. Safety was a major concern for me and I had to make sure that I could minimize the chance of any accidents. The only comment I’d add is that while aluminum is used in solid fuels these are tiny flakes not a whole block of the stuff. While yes it is technically possible the engine could catch fire the probability of this is pretty low. Thank you for the comment.

  2. For those who aren’t familiar with it, stainless is much, much more difficult to cut, drill, and machine than mild steel. Aluminum is like butter in comparison, and very forgiving of a wide range of feed rates, cutting speeds and limited machine rigidity.

    The first time I made a drill bit glow red was when I tried to drill some 304 and had the feed rate wrong. If you allow the drill bit to skip across the surface of the metal it will quickly “work harden” and become even harder and more difficult to drill.

    1. No they’re not, this is absolutely incorrect. Ion propulsion only has applications in space (generally speaking), and getting from the ground into low earth orbit cheaply is still the hardest engineering and economic problem in space exploration, and the one in which a great deal of money and energy is being focussed.

      1. Yeah so physicists and engineers at government funded space organization wouldn’t be focusing on that apposed to hybrid, liquid, solid, and gelled systems…

        Fuel rockets like RD-180 are only good for planetary take offs and landing guidance. They are garbage for actual travel…

        Speaking as a former simulation engineer who has worked both at Yuzhnoye and NASA..

        1. I hope you enjoyed your time simulating things. You’re not really saying anything I wasn’t, liquid fuelled rockets are only generally used for planetary takeoff and landing as you say and as I said, and indeed that is one of the hardest and most expensive and risky bits of any space mission. That is why there is still plenty of government and private money going into researching new kinds of liquid rocket engine.

          Moreover, direct government funding isn’t much of a metric of importance in this case. Liquid engine development is a very expensive business, and most of it gets funded indirectly in the form of industrial contracts, such as the tens of billions of dollars given to big players like Boeing, LM, SpaceX but the US government every year. There are plenty of ‘real rocket geeks’ in these organisations. It’s analogous to saying that green energy is where it’s at because government spend lots on R&D into it. Infact the amount they spend is just pissing into the wind compared to how much R&D money gets spent by the oil and gas industry on fossil fuel energy. I’m making no value judgement here, just pointing out that your reasoning doesn’t hold.

          There are also promising chemical rocket technologies that could reduce the cost to orbit per kilogram by a factor of almost 100, such as Sabre Engine technology being worked on by Reaction Engines. This would be of far more importance to the space faring future of humans in the next century or so than ion propulsion, excited as I am by the technology and its usefulness especially in long term deeper solar system exploration where you can’t use gravity assists so conveniently. But you overstate the case for it significantly.

          Speaking as a current, not former, rocket propulsion research scientist.

          1. My company has a gelled system currently being bid on by 8 governments and 3 defense contractors with proven field testing. NASA and Russia are using liquid kerosene hybrids and want our patents…

            My work in computer engineering has been in to space 3 times and I’m under 30 and one of my colleagues is a fields metal winner…

            your turn again

          2. Your argument would be an appeal to authority – a kind of logical fallacy. Regardless, I was a researcher at Cambridge University before my present job, so ‘how many nobel prize/fields medal winners do you know’ is not a game you want to play with me, nor is it interesting to anyone else reading this discussion, and most importantly it makes no constructive contribution towards an argument about propulsion. Nor does my age (25), unless we’re talking about mental age, or the number of times ‘my work’ has been into space, which can mean anything, eg once if you’re talking about hardware and several times if you’re talking about helping the design of things like planetary landers.

            I’m still not sure what your point is? Your original assertion was “All the real rocket geeks are working on ion controllers.” and you haven’t really defended it, except by some embarrassing willy waving.

    2. Thank you. There are a lot of interesting areas of research right now: small-scale liquids and ion/electrical propulsion being 2 of them. Ion propulsion is high-efficiency (eg. high ISP) but low thrust and it’s typical application would be outside of orbit. Liquid propulsion is high thrust and relatively lower ISP and would apply more as a booster or reaction-control system. Both are active areas of research and have non-trivial problems that need to be worked out.

    1. I know :)

      Not sure why that picture was posted besides the fact that it looks neat I guess? The original was taken from here http://wiki.fubarlabs.org/fubarwiki/Gaseous-Oxygen-GOX-Ethanol-Igniter-Engine.ashx (see: Testing 2012-09-09). I posted it as an example of what I thought was combustion instability due to a poorly machined convergence throat, which eventually went away after I smoothed it out. A rocket engine should not be generating sparks like that.

  3. The general sawtooth shape of all your pressure data looks like it may be a power supply issue. Try replacing any switching converters in the measurement circuits with linear regulators.

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