Yes, it's beyond imagination that such a thing could have actually occurred...
On 10/28/2013 08:45 AM, Jonathan Goff wrote:
Thomas,That's a dangerous one in case you get an igniter oxidizer leak, say due to debris getting into the igniter ox valve and preventing it from closing properly. Not saying that we learned that one the hard way at Masten, or melted any engines due to an igniter not actually shutting off because of such a failure...~JonOn Mon, Oct 28, 2013 at 9:22 AM, Thomas McNeill <thomas.mcneill@xxxxxxxxx <mailto:thomas.mcneill@xxxxxxxxx>> wrote:Instead of running a purge you can keep the fuel flowing through the igniter to keep it cool. Thomas On Mon, Oct 28, 2013 at 10:59 AM, Lloyd Droppers <lloyd.droppers@xxxxxxxxxxxx <mailto:lloyd.droppers@xxxxxxxxxxxx>> wrote: Ben's got the answer there, but if your running a test stand two additions are -you need to think though the flow rate after main chamber ignition, i.e you will be probably be running the igniter for a second or two after main chamber ignition, so make sure you don't shift into some really hot O/F. If you are on a test stand it is easier to make sure your igniter feed pressures are 50% over PC or greater and you should be fine, on a vehicle you don't always have that luxury. -Also, if you can, running a purge through the igniter after main chamber ignition at about the pressure as PC will save the igniter from torching in the case of leaks and some instability. Probably not worth it on a vehicle, but for injector characterization tests it is very worth it. Unless you really enjoy rebuilding igniters i guess. Lloyd On Sat, Oct 26, 2013 at 5:22 PM, Ben Brockert <wikkit@xxxxxxxxx <mailto:wikkit@xxxxxxxxx>> wrote: 1. Doesn't matter. Igniters are often run heat sink mode, and heating goes up with higher pressures, so running at low pressures is advantageous for minimizing heating. At the same time you do want to run choked so that you can detect go/no go with a pressure transducer. That sets the reasonable minimum around 30psi, so for off-nominal propellant conditions a nominal operating pressure of 60-100 psi is good. If tank pressure is lower than that then you take what you can get. 2. If the igniter is plumed to main feed pressure, by nature you can't get chamber pressure to flow up the igniter lines because there has to be pressure drop across the rocket injector for the rocket to rocket. You can add check valves if you're really worried about it, but I've never bothered. If you hard start the engine or have severe instability the Pc can be higher than propellant pressure, but then you have other problems worse than igniter trouble. A much more realistic concern is making sure that all of the connections on the igniter are absolutely leak-free. Leaks will turn into (likely rapidly enlarging) hot gas leaks when the igniter is off and the engine is on. It's common to have 1/8" tubing feeding small igniters. Use stainless tubing, the weight difference with aluminum is inconsequential. Never use aluminum tubing smaller than 1/4", it can't survive even small fires when pressurized. Ben On Sat, Oct 26, 2013 at 5:57 PM, Graham Sortino <gnsortino@xxxxxxxxx <mailto:gnsortino@xxxxxxxxx>> wrote: > Apologies, in advance as I'm almost positive this question was already > answered but I can't seem to find the responses. > > Re-phrased: > > 1. When designing a (GOX/Ethanol) igniter should the chamber pressure be > higher or lower then the main engine pressure? Also, are there any rules for > choosing an injector pressure relative to the main engine pressure? > 2. If the igniter pressure should be lower than the chamber pressure then > how does one prevent propellants flowing back through the injector orifices? > > Thank you very much. > Graham > > On Thursday, May 19, 2011 10:16 AM, Joel Scotkin > <arocket@xxxxxxxxxxxxxxxxxxxx <mailto:arocket@xxxxxxxxxxxxxxxxxxxx>> wrote: > On 05/18/2011 10:45 PM, Robert Watzlavick wrote: >> I'm going to be working on an augmented spark igniter (ASI) to try and >> improve the starting of my 250 lb LOX/kerosene motor. I was wondering >> about the chamber pressure for the igniter - I would think it needs to >> be >= than the main chamber pressure to keep it from flowing back into >> the igniter. Am I missing something? I've noticed that some designs >> shut the igniter off after a few seconds and in that case, how do you >> keep from the gases from the main chamber from backing up through the >> igniter orifices and into the feed lines? The few igniter pictures >> I've seen show small solenoid valves that typically aren't rated for >> enough pressure to handle the main propellant tank pressures. My >> kerosene tank pressure is ~490 psi (large drop through cooling jacket) >> and the LOX tank pressure is ~340 psi. >> > >> Thanks in advance, >> -Bob >> _______________________________________________ >> aRocket@xxxxxxxxxxxxxx <mailto:aRocket@xxxxxxxxxxxxxx> >> http://exrocketry.net/mailman/listinfo/arocket > > _______________________________________________ > aRocket@xxxxxxxxxxxxxx <mailto:aRocket@xxxxxxxxxxxxxx> > http://exrocketry.net/mailman/listinfo/arocket > >
