[AR] Re: Igniter Popping Sound
- From: "Graham Sortino" <dmarc-noreply@xxxxxxxxxxxxx> (Redacted sender "gnsortino@xxxxxxxxx" for DMARC)
- To: "arocket@xxxxxxxxxxxxx" <arocket@xxxxxxxxxxxxx>
- Date: Wed, 29 Oct 2014 12:36:37 +0000 (UTC)
Thanks for everyone’s help with this. I finally(hopefully) figured out what the
problem was. Unfortunately, it came down to me making an obviousmistake in
hindsight. The max diameter of my solenoid valves, which control thepropellant
flow to the igniter is 3/64” (~0.047”) but I seemed to have forgottenthat and
was testing with orifice diameters that were slightly larger ~0.06”.So I was
calculating flow rates based on a higher 0.06” orifice diameter but inreality
the maximum diameter is 0.047”. I made another mistake, which was to measure
flow ratesat lower orifice diameters and then just calculate for higher
diametersassuming the CD would be roughly the same. Had I actually measured at
0.06” I probablywould have discovered the mistake sooner. What was frustrating
about this is that I wouldn’t alwaysget the popping sound but I believe what
was happening is that some un-burntfuel would get stuck in the pressure
transducer line. This wouldn’t be aproblem on the first few tests because there
wasn’t enough of it but after afew runs it would build up enough to create a
problem. To help with this Iswitched from using stainless steel braided hose to
much smaller diametercopper tubing. This past Friday I had some really good
tests with both a3D printed (SLS) and my older aluminum igniter. I also had
some pretty good initialtests with my 3D printed (again SLS) main rocket
chamber. I will get this documentedso that folks can see it in the next week or
so. In the mean time I’m posting a link to some of the flowtesting I did with a
few charts that show CD and flow rates at different orificediameters.
http://wiki.fubarlabs.org/FubarWiki/Default.aspx?Page=Propellant-Flow-Testing#More_Flow_Testing_Oct_CABE_5
From my experiences, I’ve found that measuring propellantflow rates has been
the hardest part of building an engine so hopefully thishelps others in similar
situations. Kind Regards,Graham
On Monday, September 22, 2014 2:20 PM, Norman Yarvin <yarvin@xxxxxxxxxxxx>
wrote:
Ah, okay; I misread your earlier comment about moving the GOX port
"upstream", thinking you meant upstream along the igniter axis. Well,
also, the bit about the two jets impinging on the walls made me think
they weren't impinging on each other. With them impinging at 90
degrees, I guess what you're getting is mostly just the fuel jet
punching through the oxygen jet (due to the oxygen being gaseous and
less dense), with the bulk of both jets then going on to hit the
walls. At the 180 degrees of Graham's setup, they have more
opportunity to fight each other.
On Mon, Sep 22, 2014 at 11:05:32AM -0500, Robert Watzlavick wrote:
>They impinge- in this sketch:
>
>http://watzlavick.com/robert/rocket/igniters/drawings/igniter6-nodims.pdf
>
>The two ports shown in the upper left are 90 deg apart and are the GOX and
>fuel ports. They are lined up at the same point longitudinally. The 3rd port
>located a bit downstream is for the pressure tap. The spark plug threads into
>the end. I was worried about the spark plug being upstream and not igniting
>the mixture but it seems to be reliable. Except for the V5 igniter which
>didn't start as previously mentioned, probably because the orifices were
>pointed downstream.
>
>-Bob
>
>> On Sep 22, 2014, at 10:14, "Graham Sortino" <dmarc-noreply@xxxxxxxxxxxxx>
>> (Redacted sender "gnsortino@xxxxxxxxx" for DMARC) wrote:
>>
>> no worries.. Actually, I appreciate the second opinion on my math. Thanks
>> too for the additional details.
>>
>> If you don’t mind me asking... to confirm regarding Norman's observation are
>> your fuel/ox jets deliberately not impinging directly upon each other in the
>> chamber? If so is the GOX line slightly further upstream of the fuel (or
>> vice versa)? I think I had missed that point when I originally read the
>> description of your design.
>>
>>
>>
>> On Sunday, September 21, 2014 10:49 PM, Robert Watzlavick
>> <rocket@xxxxxxxxxxxxxx> wrote:
>>
>>
>> Oops - I made a mistake. I thought your last run was 0.01 lbm/s but it is
>> 0.01 kg/s (0.022 lbm/s) which is right in the ballpark. So forget the last
>> paragraph.
>>
>> -Bob
>>
>>
>>
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