[AR] Re: Fw: Igniter questions
- From: Thomas McNeill <thomas.mcneill@xxxxxxxxx>
- To: arocket@xxxxxxxxxxxxx
- Date: Mon, 28 Oct 2013 11:22:47 -0400
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> 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> 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>
>> 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> 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
>> >> http://exrocketry.net/mailman/listinfo/arocket
>> >
>> > _______________________________________________
>> > aRocket@xxxxxxxxxxxxxx
>> > http://exrocketry.net/mailman/listinfo/arocket
>> >
>> >
>>
>>
>
Other related posts:
