Jon,
Any insights about why those engines in particular had issues? I'm not familiar
with the details of the engines at Masten. I'm pretty familiar with what
pintles from SpaceX, Virgin, and Firefly look like, and I'm curious as to how
your layout might be different.
-Richard
________________________________
From: arocket-bounce@xxxxxxxxxxxxx <arocket-bounce@xxxxxxxxxxxxx> on behalf of
Jonathan Goff <jongoff@xxxxxxxxx>
Sent: Monday, January 4, 2016 10:04 PM
To: arocket@xxxxxxxxxxxxx
Subject: [AR] Re: Combustion instability and injector patterns
Richard,
I remember at least a few pintle engine runs that hooted pretty bad. Our
engines were probably way overbuilt though. Our long engine firing we did at
the X-prize cup in 2006 was buzzing bad enough that Doug or Randall commented
afterwards. And IIRC the LEMDE had certain throttle regions that they
intentionally didn't linger in--for stability issues.
Jon
On Jan 4, 2016 10:19 PM, "Richard Garcia"
<GalaxyNGC1672@xxxxxxxxxxx<mailto:GalaxyNGC1672@xxxxxxxxxxx>> wrote:
I've never herd of a pintle engine with instability issues. I'm curious to what
examples you have in mind.
________________________________
From: arocket-bounce@xxxxxxxxxxxxx<mailto:arocket-bounce@xxxxxxxxxxxxx>
<arocket-bounce@xxxxxxxxxxxxx<mailto:arocket-bounce@xxxxxxxxxxxxx>> on behalf
of David Gregory <david.c.gregory@xxxxxxxxx<mailto:david.c.gregory@xxxxxxxxx>>
Sent: Monday, January 4, 2016 7:37 PM
To: arocket@xxxxxxxxxxxxx<mailto:arocket@xxxxxxxxxxxxx>
Subject: [AR] Re: Combustion instability and injector patterns
This is a claim often repeated by TRW and others but is false.
On Jan 4, 2016, at 8:29 AM, William Claybaugh
<wclaybaugh2@xxxxxxxxx<mailto:wclaybaugh2@xxxxxxxxx>> wrote:
Or a pintel injector, which have no history of instability....
On Sunday, January 3, 2016, Anthony Cesaroni
<acesaroni@xxxxxxxxxxx<mailto:acesaroni@xxxxxxxxxxx>> wrote:
There is if you use fluorine as an oxidizer with a solid gas generator. Just
sayin.
Anthony.
Sent from my iPhone
On Jan 3, 2016, at 10:19 PM, Monroe L. King Jr. <monroe@xxxxxxxxxxxxxxxxxx>
wrote:
There is no "free lunch"
-------- Original Message --------
Subject: [AR] Re: Combustion instability and injector patterns
From: Andrew Burns <burns.andrew@xxxxxxxxx>
Date: Sun, January 03, 2016 7:57 pm
To: arocket@xxxxxxxxxxxxx
Henry,
Do you know of many dished injector faces? I think I saw reference to Titan
II engines having dished injectors but I can't remember where I saw that.
Same for modified chamber geometries, most of the combustion
chamber/injector interfaces that I've seen have been straight 'flat plate
in a cylinder' affairs but it would seem to me that different geometries
might have some stability advantage?
I do think that relatively little work has been done on unusual injector
geometries, most likely because there's plenty of work that has been done
on conventional designs and people understandably don't want to stray from
the known. I think with techniques like 3D printing these days though there
may be options out there that will allow you to have your cake (ISP) and
eat it too (stability).
Andrew
On Mon, Jan 4, 2016 at 3:35 PM, Henry Vanderbilt <hvanderbilt@xxxxxxxxxxxxxx
wrote:
On 1/1/2016 9:29 PM, Ian Woollard wrote:
It's a black art, but there are some results:
1. gasify all the propellants first before combining them if you
possibly can
I would tend to think this helps because it can make mixing quality less
sensitive to minor pressure-wave disturbances of the incoming propellant
streams, thus providing less potential amplification of chamber pressure
waves.
2. particular oscillation modes can be killed with Helmholtz resonators
3. test the engine with small charges in the combustion chamber
NASA does like to test stability by setting off a small charge of RDX fast
high explosive inside an operating chamber, then recording the results with
multiple high-bandwidth chamber pressure sensors. The detonation
essentially pulses the chamber across a very wide range of frequencies, and
the data of interest is how fast the ringing then damps out. If it does
damp out, of course. If instead some frequency builds up and runs away,
well, your engine definitely flunked.
If on the other hand it damps out in a few milliseconds, NASA tends to be
quite surprised and triple-check everything before they believe it...
Henry V
