[TheForge] Building a propane forge

[Chuck Robinson]

Just to let you all know, I ordered my copy of "Gas Burners for Forges,
Furnaces, &
 Kilns" today. They are in stock and presently shipping.
Chuck
----- Original Message -----
From: <Keporter@aol.com>
To: <theforge@mailman.qth.net>
Sent: Monday, February 16, 2004 4:56 PM
Subject: Re: [TheForge] Building a propane forge


> In a message dated 2/16/2004 1:28:34 PM Pacific Standard Time,
> schade@acegroup.cc writes:
> What is a "gas accelerator"?
>
> Bob
> ___
>
> Accelerators
> Called by many an injector, the gas accelerator typically consists of a
gas
> tube, and a MIG tip, screwed together and sealed. The gas tube has
standard
> male pipe thread on one end in order to be easily connected to gas
appliance
> fittings. On the "business end" it has internal thread to match the MIG
tip
> chosen. The best tips are Tweco 14T series, because they are full length
(1 1/2"),
> have a tapered funnel at the orifice entrance (threaded end) and an
exterior
> taper for laminar airflow.
>   The job of the accelerator is to trade gas pressure for momentum in the
> escaping gas molecules the long narrow tunnel provides extended time to
> accelerate the gas molecules, which the hole in a plate does not.
Furthermore, just
> like a rifle barrel it improves the "aim" of the accelerated molecules
into a
> coherent high speed gas stream. This is ideal for entraining air molecules
with
> the venturi effect. The ideal stoichometric mixture for propane and air is
> twenty-four parts air to one part gas. Older gas burners barely reach this
level.
> With twenty to one being considered acceptable. An accelerator can so far
> exceed this mixture that the burner must be choked back to the ideal mix.
> However, entrainment is only the beginning of the picture. Straight pipe
> burners do something that the classic old wasp-waist burners hadn't
> considered--they swirl the gas air mixture, promoting better mixing, and
allowing high
> mixture speeds at the nozzle. Swirl and speed are important to remember;
we will
> come back to them.
>    The first requirement of any hydrocarbon burner is to achieve a neutral
> flame. Both reducing (fuel rich) and oxidizing (oxygen rich) flames waste
heat
> potential, and create hazardous amounts of carbon monoxide.
>     But there are other requirements too. The flame has to be great enough
to
> do useful work, and the burner needs a reasonable turndown range. The
> turndown range is the amount that a burner can be backed off from its
highest setting
> without losing the ability to achieve a neutral flame, or even worse,
blowing
> out.
>     Finally, total or near total primary flame combustion of propane has
been
> an unfilled desire but will be considered a requirement from now on.
> Ordinarily, propane combusts as much or more in the secondary flame as in
the primary.
> The primary flame is the one which is considered important to industry, as
is
> demonstrated by the fact that you will find all fuel gas heating charts
list
> the primary flame temperature first, and very few of them list the
secondary
> flame temperature at all. This brings us back to swirl and speed of the
burner
> gases.
>    Propane is a vapor, not a true gas. It forms miniature clumps that must
be
> broken down into individual molecules for proper mixing and combustion.
When
> air is entrained into a straight pipe, it begins to swirl at the intakes
and
> moving down the tube that swirl is increased in direct proportion to the
> mixture's speed, which is ultimately a function of the gas stream speed
and force.
>   A really good accelerator can be combined with other factors to create a
> gas/air speed at the nozzle that is capable of feeding a very fierce
flame. Such
> a fierce flame that you can watch the explosions ripping back and forth
along
> an extended wave front, which is continuously ignited from the center
> outward, which is normal, and at the same time from its periphery inward.
You can see
> the accelerated and superheated oxygen and fuel molecules (that normally
> escape the primary flame, and which then spread out as they mix with air
to form a
> very problematic secondary flame) being caught up with and ignited in an
> expanded and jagged looking primary flame. Result -- total primary flame
ignition.
> Well, it would be more accurate to say you can see their trail as an after
> image on your retina. Your mind then forms a conglomerate image out of the
> collage of incoming data.
>   So, unless you're the mad scientist type, who glories in such a sight
for
> its own sake, what could this mean to you? It means an added temperature
input
> in any ceramic forge capable of turning a zirconia coating incandescent
and
> causing a secondary heat source to recycle the flame heat as infrared
radiation,
> instead of seeing CO rich blue flames exiting your forge. The forgoing has
> been the result of my observations and reading, However, a combustion
engineer
> might very well take exception to my theories (but not the results). No
doubt I
> will receive much scolding during the coming months. That's OK, Larry
Zoeller
> has already forced a modification of my most dearly held belief. He
managed
> to make a gas tube good enough get around my insistence on the full 1 1/2"
MIG
> tip length, at least in the larger burners. It won't work in the 1/2" hand
> torch size.
> Mikey
>
>
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