[TheForge] Building a propane forge

[theforge@mailman.qth.net]

I'm glad I asked. Neat stuff. Thanks Mikey. Looking forward to the book.

Bob
___


On Monday, February 16, 2004, at 04:56 PM, Keporter@aol.com wrote:

> 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