I say "blank" but it was a filter fitting that was damaged so I tore out the filter. But here is the equivalent part which is just a M-F extension:
http://catalog.beswick.com/#WORKFLOW;PRODUCT,MEB-1010,FILTER_FITTINGSI also learned I was running the filters in the wrong direction so I turned the filter and orifice around (threads pointing away from the igniter) and used one of these to couple it to the igniter:
http://catalog.beswick.com/#WORKFLOW;PRODUCT,MN-1010,FILTER_FITTINGS So my latest arrangement is: MCBL-1018-1 (1/8 compression fitting for incoming tubing) MF-1010 (F-F coupler) CFS-303-43 (40 micron filter, needs to be run this direction)) CC-1010-030 (filter) MN-1010 (M-M coupler) (connects to igniter body)In this arrangement, the MN-1010 coupler also acts to slow down the GOX jet in the same way the MEB-1010 did in my earlier tests.
I haven't worked with ethanol as a fuel so I'm not up to speed on typical mixture ratios or other performance values I'm wondering though if your igniter chamber volume is too large to support the mass flow. If I read your web page correctly, your internal volume is ~1.3 in^3 and the throat area (0.046 in) which gives an L* of 28 (reasonable for an igniter where you want combustion to continue in the main chamber). However, it looks like your mass flow is about 0.01 lbm/s which seems low for that size of a chamber. Just as a check, I adjusted my spreadsheet (keep in mind it is GOX/kerosene) to match your mass flow and I get a design chamber volume of about 0.3 inches. I would double-check your throat area calculations. Working backwards, a throat area of 0.046, an assumed Cf=1.15, and p=100 psi gives 5.3 lbf of thrust. Assuming Isp = 200, that means the mass flow should be around 0.026 lbm/s for that size of a throat and chamber. These are quick calculations though and I may have made a mistake.
For comparison my igniter has an internal volume of 0.125 in^3 and a mass flow of around 0.006 lbm/s.
-BobOn 09/21/2014 07:58 PM, Graham Sortino (Redacted sender gnsortino@xxxxxxxxx for DMARC) wrote:
Thanks very much. I read back through the post and Bruno had mentioned that the popping sound is usually uncombusted gasses so perhaps the theory about the pressure lines being too large makes sense. It's very strange that I don't see this on every test.Regarding erosion, if it is happening it's very slight. The wall on the fuel orifice side looks a bit smoother and the edges are slightly more beveled then on the ox side but I'm not sure if it's actual erosion or me just imagining it.Is a "blank" beswick fitting something like this? http://catalog.beswick.com/#WORKFLOW;PRODUCT,MH,FILTER_FITTINGS. Apologies, I wasn't quite clear what blank meant.Regarding the mixture ratios, test 5 looked pretty good but the pressure was only about 40% of design. The color was nice but that was because it was near dusk. On my most recent test last weekend where I heard the popping (I haven't had a chance to post it yet) I'm estimating that I'm running at a 1.5 and 2.0 O/F ratio but I still get the popping periodically. My worry was that I was overcompensating by putting too much GOX in, which caused the popping, however, I see in your original email postings you said that you went up to about 1.8 - 1.9 without any issue. So it doesn't sound like putting too much GOX in would cause a problem.Best, Graham
