US20120103302 shows a spark ignited prechamber combustion system typically used for IC engines. It basically consists of a chamber which has a input of premixed fuel-air mixture and a spark plug to start the fire. This device spews out hot gases and some amount of flame into the chamber. Not posting images due to copyrights issue

NASA Technical Memorandum 106493 Hydrogen-Oxygen Torch Ignitor shows one of NASA’s design for igniter. The main difference is that the design incorporates non-premixed fuel-oxidiser entry into the igniter combustion chamber.

The IC engine spark igniter appears to be more robust and functionally better than that available in NTRS as mixing does not occur close to ignition point.

But many sources on spark ignition system for rocket appears to follow the reference cited. What is the reason? In what way is the two system different? Is the choice for a simpler ignition system in rockets stem from mass point of view(ie to have a lighter igniter)?

  • $\begingroup$ They are not necessarily different. At least on test stands regular spark plugs are sometimes used for igniting small rocket engines. $\endgroup$ Commented Aug 4, 2018 at 3:13
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    $\begingroup$ What is "perch beer"? $\endgroup$ Commented Aug 4, 2018 at 3:44
  • $\begingroup$ @OrganicMarble no idea! Why is this getting mentioned? $\endgroup$ Commented Aug 4, 2018 at 3:45
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    $\begingroup$ @OrganicMarble sorry. Auto correct issues. I'll correct it $\endgroup$ Commented Aug 4, 2018 at 3:48
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    $\begingroup$ A comment on patent images and US copyright: as a fundamental part of US patent law, the “teachings” of a utility patent are free of copyright limitations. That includes the images, and it includes copying and distributing them. People can’t practice the invention, but they can use the text and images for discussion, even for designing around the patent claims. See the “Patent Information” section of uspto.gov/terms-use-uspto-websites and MPEP608.91(v). $\endgroup$ Commented Aug 4, 2018 at 4:41

1 Answer 1


The design shown in the patent application doesn't look typical of common IC engines; I'll guess it was an idea someone had that may or may not be a real improvement. Engines I am familiar with have no such pre-chamber; the spark fires in the "main" combustion chamber, but I don't think that's relevant to the question.

The NASA device looks like it's designed to generate a continuous torch-like flame for whatever that has to continuously ignite (sustained ignition). The IC application is typically required to ignite a series of discrete charges - hundreds of times a second, not start/maintain a continuous flame.

In an internal combustion engine, pre-mixed fuel and air are admitted to the combustion chamber during an intake stroke, the inlet valve is then closed, the mixture is compressed, and then ignited. Combustion can only occur in the combustion chamber - there is no path for combustion to migrate anywhere else.

The NASA device appears to be intended to support combustion of a flow of fuel and oxidizer, rather than combustion of a discrete charge. The flame can therefore propagate back along any path where there is a suitable mixture of fuel and oxidizer, so they would only be mixed at the point combustion is expected/desired to occur.

  • $\begingroup$ There are prechamber combustion devices for relatively large IC engines.doi.org/10.4271/2010-01-2263 $\endgroup$ Commented Aug 4, 2018 at 4:08
  • $\begingroup$ Do a rocket engine require a continuous ignition flame to sustain combustion? $\endgroup$ Commented Aug 4, 2018 at 4:09
  • $\begingroup$ Page 2 and top of page 3 of the NASA report say that it’s not a continuous operation igniter. After a few seconds, it switches to an inert purge for the rest of the engine burn $\endgroup$ Commented Aug 4, 2018 at 4:48
  • $\begingroup$ @BobJacobsen yes. I checked that one. My query was more general. I asked a separate question too - space.stackexchange.com/q/29876/511 $\endgroup$ Commented Aug 4, 2018 at 5:10
  • $\begingroup$ The patent app is just a modernization of the prechamber stratified charge technology that had a good run over 50 years ago, most commonly known as Honda CVCC. But I agree, it's not typical anymore. Modern stratified charge engines do everything in-cylinder, known as direct injection diesels, and gasoline direct injection (a.k.a GDI, SIDI, Ford EcoBoost). $\endgroup$
    – user71659
    Commented Aug 4, 2018 at 5:47

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