Quote:
Originally Posted by RustyLugNut
Having a standard spark plug threaded into a heavy external chamber would work.
Injectors from a Direct Injection system that run at several hundred to thousands of PSI can feed the chamber with a side injection and would provide cooling.
Couple this with port injection of a lean mixture and your DIY system might be a possibility.
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Oh you were talking about a side injector, those are always aimed at the piston, and even if they were aimed at the prechamber, the orfices would be too small for fuel to get in. Stratified injection works late in the compression stroke when lots of lean mix has already gone into the prechamber.
I was thinking about an external chamber too. There's not a lot of space to do that, but one way would be to screw a threaded inconel chamber from the inside (the threads don't need to hold much force), and then have the usual spark plug screwed part of the way in to form a bigger chamber. You can use a surface gap plug to make some more space.
One thing this helps with is cooling, heat would conduct to the head to some degree. Stainless steel/inconel aren't the best conductors of heat but it's worth something. If the jets are very close to the surface of the head, then the hottest part would be conducting some heat away to the head.
One more thing working in favor of the passive prechamber is that the residual exhaust in it mitigates detonation (compression stroke is crucial for getting fuel/air mix into the prechamber).
It's possible that the fuel spray coming from the intake ports washes over the hottest part of the prechamber and provides sufficient cooling, but that's maybe not something you want to count on.