[AR] Igniter Popping Sound
- From: "Graham Sortino" <dmarc-noreply@xxxxxxxxxxxxx> (Redacted sender "gnsortino@xxxxxxxxx" for DMARC)
- To: Arocket List <arocket@xxxxxxxxxxxxx>
- Date: Sun, 21 Sep 2014 12:08:51 -0700
I’ve been having some intermittent issues with my latest
igniter where I get a loud popping noise that sounds something like a car
backfiring or a gun going off (see test 3
http://wiki.fubarlabs.org/fubarwiki/GOX-Ethanol-Igniter-v2.ashx#CABE-AF-BA:_Test_D_Slightly_Less_Poor_Mixture_Ratio_3
or http://youtu.be/y098qOkC7Vk). I had this problem earlier on and I thought I
had fixed it but it seems to be giving me problems again.
I suspect this is due to combustion instability but I’m struggling
figuring out what the root cause of it is. The interesting thing is that
sometimes one test will not have the popping and then without changing any
parameters the next test will have the popping noise. Needless to say I’m
struggling to come up with an explanation
I have a few theories
1. Originally I assumed this was caused by having a
too low O/F (GOX/Ethanol) ratio so I kept upping this to about 1.3 - 1.5. Now
I’m
wondering if increasing the ratio too high causes the popping sound.
2. The impingement arrangement is unlike with 1 Fuel
and Oxidizer orifice impinging perpendicular to the axis of the combustion
chamber. The Oxidizer orifice is directly upstream of the igniter so the gas
velocity is probably pretty high (see:
http://wiki.fubarlabs.org/fubarwiki/GOX-Ethanol-Igniter-v2.ashx#Ports_10).
Perhaps this is not helping mixing and moving it upstream to slow down the
velocity may help.
3. The spark plug igniter is at almost at same
point along the chamber as the Fuel and Oxidizer. This may mean that the
propellants have not yet had enough time to mix. So perhaps moving downstream a
bit would help?
4. The chamber pressure orifice is fed from 1/8”
NPT stainless steel tube, which has about a 0.2” diameter. On my previous
engine I had used a small diameter copper pipe to feed out to the pressure
transducer but I changed to stainless steel tubing because it was more
convenient
for connecting/disconnecting from the engine. Perhaps the larger diameter is
having an effect on the combustion chamber.
I’m planning on rebuilding my igniter as I’m no longer confident
that the current version is working correctly but before I do I wanted to see
if I could get any feedback on what could cause the popping noise.
Thanks as always.
Graham
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