[TheForge] Gas forge burners

[Jerry Frost]

> ----- Original Message -----
> From: <Keporter@aol.com>
> To: <theforge@mailman.qth.net>
> Sent: Friday, April 09, 2004 10:54 AM
> Subject: Re: [TheForge] Gas forge burners
>
>
>
>
>  This is good stuff guys. I would suggest that any burner makers out there
> read it closely and think about the applications. What he is saying is
that a
> little input energy, properly applied at the beginning of the process,
sets up a
> dynamic motion which is better than a machine in its own right. In effect,
> you create a motor which doesn't where out. The motor runs parallel to the
> flame's needs, making adjustment semiautomatic. This promotes a large
extension in
> turndown range. Turndown range is the second biggest problem with burners.
> You're getting a lot of goodies for a little understanding, and you don't
have to
> take your "motor" in for tune-ups to keep on receiving a racing engine's
> performance.
>
> I do hope you are building my burners, Frosty. If anyone is going to "beat
my
> time," it's you.
> Mikey
>
>

Sorry for the slow reply but the paycheck job called and I end up going
through a few hundred messages on my days off.

Thanks Mike.

I haven't picked up a copy of your book yet but it's on my short list as is
a REAL shop. <grin>

A vortex is only one way to improve prop/air mixing but it's probably the
most suitable for what we want.

A more efficient if more irritating method is cavitation. Cavitation is a
very violent action akin to a vacuum on steroids. Cavitation will destroy
some of the toughest materials around, say a SS boat prop in clean water.
The effects on metal look like deep acid etching or sometimes soil erosion.
I don't understand the mechanics of cavitation except to say from what I do
understand it attacks materials on a molecular level.

Anyway, there are a number of ways to induce controlled cavitation in a
burner, some more conducive to good performance in a naturally aspirated
device than others. A physical barrier shaped to create a vacuum behind
without disrupting the general flow it is one.

Picture the gas jet positioned directly in front of a needle pointed bullet
so the propane is forced to flow over it. The gas flows laminarly over the
bullet, according to bernoulli's principles a vacuum interface is formed
between the flow and the curved surface of the bullet and the flow
accelerates. Now it abruptly comes to the trailing edge and is left to it's
own fate. If the "bullet" is the right shape a hard violent vacuum forms
directly behind it. If we were real lucky or had access to design and
developement resources I surely lack, a standing wave(s) would form, kind of
like the fireballs behind a jet fighter on afterburner.

In such an environment it would be impossible for the air and prop to not
intermix most thoroughly, better in fact than swirl strips, vortices, bends,
turns, etc. The serious downside is the noise, it would be an ungodly loud
shrieking not unlike the difference between an F-16 in flight and one on
afterburner. Another downside is the erosion that would occur on any parts
of the burner coming in contact with the cavitation, primarily the rear of
the "bullet". Once the "bullet" becomes eroded the cavitation would become
unstable and degrade rapidly.

A properly designed cavitation zone would enhance the overall draw of a
burner. It'd be tough to pull off though at least with my knowledge and
equipment.

I'll stick to playing with vortices in naturally aspirated burners.

On the other hand if you're using a gun burner (blower driven) cavitation is
your friend. A gun burner doesn't require the initial violence a naturally
aspirated burner does, the air supply is supplied by the blower instead of
relying on the gas jet. So, inside a gun burner things are a lot more
peaceful. The most obvious evidence of this is how much quieter a gun is
over a naturally aspirated burner.

In some ways this is a bad thing, it means there's less energy in the mixing
tube to mix the prop and air. Putting a bend in the tube helps mixing as
well as making burnback less likely. Swirl strips help quite a bit as will
an open coil spring. The open coil spring works well and if the velocity is
high enough will induce cavitation. An easier way to induce cavitation is to
use perforated steel for the swirl strip.

It's likely to whistle though. <sigh> Still, in a gun burner cavitation
doesn't need to be as violent as in a naturally aspirated burner because the
blower won't let the flow stall. This means you can subject the flow to a
series of low level cavitation zones, like a cascade while the blower keeps
it moving. A naturally aspirated burner on the other hand has no additional
power other than the primary gas jet so one violent cavitation zone is what
you get.

My favorite gas mixer in a gun burner however is placing the gas jet at the
blower intake. Do NOT try this if the motor is INSIDE the blower cage! I
have a BIG caveat for this method though: It seems way too obvious a method
for mixing the air/prop to not have been thought of before, so there's
probably a REALLY good reason this isn't done.

Frosty
------------------------
If it ain't forged
it ain't real.
Wrought iron is.
The FrostWorks

Meadow Lakes, AK.