Fire arch design for propane

[Chris Hollands]

Here is a few photos to show the size , the coke can gives a bit of a reference .

[Marty_Knox]

Chris, that firebox is 8 1/4" wide at the bottom, 7 1/2" high in the center.

[NP317]

I remember Al Von Ruden telling me about your burner he built, while working on mine for my Mikado.
They do a good job of replicating a radiant coal fire at gate lever.
Hot and low, accessing all of the side sheets for radiant heat transfer.
RussN

[Bill Shields]

Yes on performance..even with the huge burner...using the arch is very noticable improvement

[Chris Hollands]

Bill with your 4 attempts at the arch what did you change, did you start with the basic coal dimensions and move on from there ?

Marty it does not get much simpler that in the photos , thanks for that .

[Chris Hollands]

Can someone please do the calculation for me , my math's is getting rusty and I'm coming up with some pretty big numbers using Marty's formulae .
I think I'm doing something wrong .

Marty's formulae -

The area over the arch should be 110-120% of the net area through the tubes, with 115% preferred. This is from the Revised Master Mechanics Locomotive Front End Arrangement from 1936. Note that they base it on the net area through the tubes and flues - not the grate area.

What I have -

5/8 copper tubes ID = 13.5mm / 0.532 inches
Number of tubes = 61
Tube length is = 760 mm / 30 inches

Equal Arch area = ?

Thanks for your help .

[Mountaineer]

Very interested in your burner. Any point in doing what Roy Johnson did with his Four Aces NP 4-8-4 and use mesh nimonic (or maybe hasteloy- can’t recall) to hold pea gravel sized firebrick in the flames as a radiant heat intensifier? I recall the stack temp on his northern was very low compared with the other propane burners.

Mountaineer

[Bill Shields]

I ended up with the gap between the top of the arch being maybe 1/4 " and a gap on the sides of 1/8"

I found that this heated a better and helped to protect the burners from being sucked out should the throttle be yanked open too fast when the burners were turned down.

[Marty_Knox]

Can someone please do the calculation for me , my math's is getting rusty and I'm coming up with some pretty big numbers using Marty's formulae .
I think I'm doing something wrong .

Marty's formulae -

The area over the arch should be 110-120% of the net area through the tubes, with 115% preferred. This is from the Revised Master Mechanics Locomotive Front End Arrangement from 1936. Note that they base it on the net area through the tubes and flues - not the grate area.

What I have -

5/8 copper tubes ID = 13.5mm / 0.532 inches
Number of tubes = 61
Tube length is = 760 mm / 30 inches

Equal Arch area = ?

Thanks for your help .

Chris, I assumed you are using 1/2" K. The net area of 1/2" K copper tube 5/8" OD .049" wall is .218 square inches. Times 61 = 13.298 square inches time 1.15 = 15.29 square inches area over the arch.
Length is not a factor.

[Chris Hollands]

Thanks Marty , I was off the planet compared to what you have .
I did some reverse engineering using your photos and dimensions and got something a bit more on the planet .
With what Bill has stated from his experience I will probably do a combination of both and see what happens , make it adjustable in angle and length got a few ideas in my head .

[Bill Shields]

The angle is not so important as long as the majority of the heat flow is pushed back toward the door end of the firebox...on its way out the flues.

cannot say that i played with the angle except as a way to adjust the clearance at the top.

My arch is anchored to the mud ring and 'bendable'...as opposed to sitting on supports as Marty's pictures show.

[Chris Hollands]

My firebox is 12" wide so 15 sq in is only a one piece of 1 1/4" flat bar that seems a little on the small side ?

I'm I missing something , I would of thought it would have to be bigger than that especially when the firebox is 23" long ?

Sorry Marty I'm not trying to be a pain .