Flintlock Igniter

guest blogger john hare

One of the things that I take exception to is people saying there is only one way to do something. From some people I get irritated, from others I enjoy finding some way of proving them wrong. This one actually was a joke at the expense of the Masten team before I realized they were a team. Between sessions at a conference one of the guys said something to the effect that the only reliable ignition system was electrical, or that there were only two total ignition methods, I think. So I spun this one out as a joke after at least 10-15 seconds of design and planning work. My sense of humor becomes more strange than normal when I’m running minus on sleep at a conference.

An hour or so later, I realized that it was actually possible to use something like this, and lost a bit more sleep trying to figure it out. This is just the simplest way to draw the concept, by no means the only way.

flintlock igniter

A small subchamber has a rotating flap that seals to the edges. When gaseous propellants are introduced into the subchamber, they drive the flap which is also a flint holder. The arc that the flint travels is a serrated steel edge roughly opposite to a cigarette lighter. The sparks from the flint and steel ignite the propellants in the subchamber and they in turn ignite the main chamber propellants. The main chamber ignition pushes the flint holder flap back into the subchamber and holds it there unless main chamber pressure drops below that of the subchamber. If the main chamber drops below that of the subchamber, the spring pushes the flap far enough to release the pressure switch releasing propellants into the subchamber to be ignited. Position of the flint holder flap can be used for the safety interlocks of the main propellant.

The possible use for this would be on a system that required multiple starts, and that for some reason didn’t want to depend on hypergolics or an electrical ignition system. Attitude control just might be one such use. Send the propellants and let the flint ignite them instead of a separate electrical system.

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I do construction for a living and aerospace as an occasional hobby. I am an inventor and a bit of an entrepreneur. I've been self employed since the 1980s and working in concrete since the 1970s. When I grow up, I want to work with rockets and spacecraft. I did a stupid rocket trick a few decades back and decided not to try another hot fire without adult supervision. Haven't located much of that as we are all big kids when working with our passions.

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5 Responses to Flintlock Igniter

  1. t.comterneA_M_Swallow says:

    Just make sure a helium flush does not upset the lighter.

    The fuel and oxidizer will have to be introduced simultaneously.

  2. I like it! Just to take it a step beyond, use a spinning flint inset into a tapered gear. A spark with every tooth strike, and as the flint wears down it can be pulled up against the taper.

    Of course, you then need to power it. Turbo-igniter, anyone?

  3. john hare says:

    Turbo-igniter would be easier to do. Use a tiny radial inflow turbine direct to the Bic steel wheel. Use streams of gaseous fuel and oxidizer simultaneously to drive it with the turbine exhaust right on the flint strike zone. Mass will be in grams. You will need different safety interlocks to make sure of ignition brfore main propellant injection.

  4. Well now that we have admitted the need for a power source, that opens up a lot of possibilities! For example, replace the spinning flint and gear with two pieces of wood and you get the Samoan Rocket!

    More seriously:

    1) You can always start the combustion with a laser
    2) Use a microwave to ignite it
    3) Use a heating element
    4) Use sound, as in sonoluminescence
    5) Use a hammer and anvil (shock ignition)
    6) In a pinch, a match!

    My favorites are the microwave and heating element. I’ve always wondered why people don’t just 1) take 0.1% of the fuel flow and heat it to boiling, 2) take 0.1% of the oxygen flow and heat it to boiling (in a glass tube, for example), and 3) inject them in close proximity. It’s not like hypergolic is a fixed definition – everything is hypergolic if hot enough!

    I suppose spark igniters work well enough.

  5. Eric Collins says:

    I have to admit that I had never given flint too much thought as a rocket igniter. So, I had to think a moment on what was the actual ignition source. Striking the flint against the steel causes sparks, but where do the sparks come from, the flint or the steel?

    Well, I turned to our old friend Wiki-pedia which says that the flint actually shaves off a piece of steel which burns in the atmosphere after being ignited by the heat of friction from the strike. (My guess is that is probably due to the energy released when the steel is sheared off.) So, if you plan on using this igniter to restart your engine in vacuum, you will need to make sure that you provide a sufficient amount of gaseous oxygen for the steel to burn. The wiki-pedia article also notes that the material, ferrocerium, is a better choice than steel, since its sparks tend to burn hotter.

    No matter which of these material that you intend to use, the next question is whether or not the igniter will survive an engine cycle. I guess it’s not such a big deal if the engine is only to be used once. However, if it must be restarted, or possibly reused, then the materials will need to survive the environment of the combustion chamber. In particular, the wiki-article indicates that flint tends to explode when heated.

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