A little engine rich combustion never hurt no one...
On Wed, Dec 9, 2015 at 10:03 PM, Bruno Berger <mailinglists@xxxxxx> wrote:
Yes, but mainly for health monitoring. If you see copper or chromium
spectras in your exhaust then you know there might be a problem...
Bruno
Am 10.12.2015 um 07:13 schrieb Craig Strudwicke:
Is there a chance spectral emissions could me monitored and used for
useful feedback ?
I guess Troy's comments may rule this out.
The sensors exist but are a little pricey.
On Thu, Dec 10, 2015 at 2:02 PM, Troy Prideaux
<GEORDI@xxxxxxxxxxxxxxxx <mailto:GEORDI@xxxxxxxxxxxxxxxx>> wrote:
Another potential problem with measuring the exhaust composition
for closed loop control is chemical equilibrium (particularly for
deep throttling). For a given typical hydrocarbon:oxygen mix
ratio, the chamber composition should stay pretty constant for
varying chamber pressures over a pretty broad range, however, the
exhaust composition (optimally expanded) – particularly in
relation to CO vs CO2 can vary considerably from significantly
different chamber pressures which could potentially provide you
with some subtly misleading data if you were measuring CO or CO2
concentration at the exit over varying chamber pressures and
didn’t take such into account.
Troy.
*From:*arocket-bounce@xxxxxxxxxxxxx
<mailto:arocket-bounce@xxxxxxxxxxxxx>
[mailto:arocket-bounce@xxxxxxxxxxxxx
<mailto:arocket-bounce@xxxxxxxxxxxxx>] *On Behalf Of *Wyatt Rehder
*Sent:* Thursday, 10 December 2015 2:13 PM
*To:* arocket@xxxxxxxxxxxxx <mailto:arocket@xxxxxxxxxxxxx>
*Subject:* [AR] Re: Closing the loop on rocket engines
Most of the advantage for O2 sensors in car engines stems from
your inputs are not well known. Gasoline is a combination of
chemicals that can vary pretty significantly between gas stations
on the same street, not to mention between different states or
countries. Because of this and other reasons your mixture ratio
tends to vary quite a bit. So an O2 sensor on your exhaust tends
to be handy since you can fine-tune the mixture ratio in your car,
by the end results vs. trying to analyze your fuels for composition.
A rocket is a much more controlled system than a car. Your
propellants are very well defined, So you have a pretty good idea
of what will be going into your rocket. A conventional O2 sensor
also would not work on a rocket since they are designed for use in
the exhaust stream, which might see temps up to 1200F, at pretty
low pressures (a few ATM). If you tapped of your combustion
chamber, or your nozzle you could see temperatures in excess of
4000 degrees, and at much high pressures. It would be more
equivalent to measuring the combustion right after top dead center
right after ignition. So an optical measure would be a likely way,
but even then the properties of the plume can vary significantly
between edges and the interior. So your plume could look rich on
the outside but be very lean in the center. This gets worse if you
use film cooling.
So to measure combustion products on a rocket in the same way as
the car you would have to measure up to 100 ft+ or so behind the
rocket. Quite a few engine controllers control off of chamber
pressure, and sometimes injector pressure. As long as you know the
performance of your injector that is going to give you a pretty
accurate idea of mixture ratio. Just going off of pressures is a
pretty solid way to go since it is very reliable and if you need
any finer control than that, you would do it on the test stand.
You can characterize your mixture ratio pretty accurately on the
ground, and have a pretty solid expectation that it is going to be
the same in flight. Main reason this works is again you have a
high level of control over your propellants.
The SSME has a much more sophisticated suite of sensors than that,
I cant remember the exact number of sensors but it is quite a few.
So liquid engines have been doing closed loop control for quite
awhile.
"At that time [1909] the chief engineer was almost always the chief test
pilot as well. That had the fortunate result of eliminating poor
engineering early in aviation" (Igor Sikorsky)
--
Bruno Berger
Swiss Propulsion Laboratory
E-Mail: bruno.berger@xxxxxx (HTML-Mails will be dropped!)
PGP: http://www.spl.ch/contact/Bruno.Berger.asc
WWW: http://www.spl.ch
HAM: HB9RSU