The heroicrelics.org page J-2 Rocket Engine Augmented Spark Igniter mentions that

The ASI operates continuously during entire engine firing

Does this how all spark igniters function in rocket engines? Are the fires in engine’s chamber not self-sustaining?

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    $\begingroup$ If/when web sites rearrange their pages, links break. I've just added a few bits to make it easier for future readers to track it down and repair the link if/when it happens. $\endgroup$ – uhoh Aug 4 '18 at 3:18
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    $\begingroup$ @uhoh thanks for introducing me to the new nice habit! $\endgroup$ – karthikeyan Aug 4 '18 at 3:21
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    $\begingroup$ Some people in SE like to think our questions and answers will be immortal and future generations will admire our knowledge and wisdom ;-) $\endgroup$ – uhoh Aug 4 '18 at 3:23
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    $\begingroup$ @uhoh they sure are! $\endgroup$ – karthikeyan Aug 4 '18 at 3:24

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Perhaps there's some confusion in the terminology? At least for the Space Shuttle Main Engine, the Augmented Spark Igniters didn't fire for the whole burn.

The igniters turn off after 4.4 seconds while the ignition flame continues in order to prevent intermittent and possibly damaging blowback from the main combustion area. This also keeps the system simple and reliable.

This means the electrical igniters turn off, but propellants are still supplied to their little combustion chambers, and they continue to burn throughout engine operation. Valving off this small amount of flow would add un-needed complexity, weight, and failure modes.


  • $\begingroup$ Thanks for the answer! In SE, one can always expect @OrganicMarble to help! $\endgroup$ – karthikeyan Aug 4 '18 at 14:17
  • $\begingroup$ I couldn't understand whether the fuel coming into the ASI is in gas phase or liquid phase. There is a mention of both liquid and gas in the source linked. Is there some form of atomisation used? Or is it gas phase fuel? $\endgroup$ – karthikeyan Aug 4 '18 at 15:45
  • $\begingroup$ It may be a supercritical fluid, but the only way I know to find out is to google for information on fluid properties in the right place in the engine (starting point: google.com/…) then look up the properties in a table. $\endgroup$ – Organic Marble Aug 4 '18 at 15:55

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