[AR] Re: Igniter Popping Sound
- From: Norman Yarvin <yarvin@xxxxxxxxxxxx>
- To: arocket@xxxxxxxxxxxxx
- Date: Sun, 21 Sep 2014 22:01:49 -0400
Looking at the photos, your spark plug is upstream of the two
orifices, in 'dead space'. It also looks like the two orifices are
pointing directly at each other, both at 90 degrees to the igniter
axis, and 180 degrees apart from each other. (I figure this is what
you mean by 'unlike impinging', but of course I can't tell from the
photos whether this is precisely the case.) That's a really good way
to produce nondeterministic flow patterns: which way the splatter will
go depends on how, precisely, the two streams meet: what the mixture
ratio is going to be at the spark plug is anyone's guess, and could
easily oscillate between too rich and too lean.
If I've misinterpreted, and the two flows are set to miss each other
(and it sounds like this is Robert Watzlavick's design), there will be
less nondeterminism, but I still wouldn't like to predict what the
mixture ratio will be at the spark plug. Besides oscillation between
too rich and too lean, that dead space also could get filled with
nonburnable combustion products, which then got cleaned out by eddies
of the flow, followed by a minor explosion and a return to the
nonburnable state; you could have oscillation that way.
A 'popping sound' is, of course, a small explosion. Which is sort of
okay for an igniter, since the whole point of having an igniter is to
make the 'hard starts' small and containable. But of course you want
just one of them, followed by smooth combustion, not a "machine gun"
like sequence of them.
--
Norman Yarvin http://yarchive.net/blog
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