[AR] Re: Igniter Popping Sound
- From: "Graham Sortino" <dmarc-noreply@xxxxxxxxxxxxx> (Redacted sender "gnsortino@xxxxxxxxx" for DMARC)
- To: "arocket@xxxxxxxxxxxxx" <arocket@xxxxxxxxxxxxx>
- Date: Sun, 21 Sep 2014 19:40:49 -0700
Thank you Norman -
In the picture it is a bit hard to see but the spark plug is actually about
7-8mm downstream of the orifices. Your analysis of the orifice positions is
correct. One of my thoughts was moving the plug a bit further downstream to
give the propellants a bit more time to mix.
I understand your point about non-deterministic flow patterns oscillating
between too rich and too lean. Is there a better approach for producing a more
deterministic mixture ratio at the spark plug?
On Sunday, September 21, 2014 10:02 PM, Norman Yarvin <yarvin@xxxxxxxxxxxx>
wrote:
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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