Propane Front End Design

[PRR G5s]

There have been many discussions on burner designs, arches, and turbolators for propane fired engines, but nothing in regards to the front end design. I've had a few private messages with a couple people about what they have done, but thought I'd open this topic up to the entire community. So, that being said, what has everyone done for their front end to burn propane:

1. Minimum top of stack ID = x% of "grate area" or other?
2. Minimum bottom of stack ID = x% of "grate area" or other?
3. Blast orifice diameter = 1/7*piston diameter or other?
4. Min. stack ID location relative to blast orifice? ( I know I'm walking the line, but I don't want this to turn into the 1:3/1:6 discussion )
5. Set up like an oil burning engine? If so, how are those parameters different than coal?
6. Set up like a coal burning engine, and if it works, it works!

While I've built a couple of propane fired locomotives, and they run good, the engineer in me is thinking they could be better. Or at least the next one could be better. So I've laid out the parameters, let's see what everyone has done successfully. Thanks in advanced!

Eric L.

[little giant]

I built an Allen design for coal burning, and then changed to propane. The only thing I changed was adding a copper pipe from the blast pipe to about 3/4 up the stack. This helps so the fire doesn’t go out when pulling to throttle to fast.

[Greg_Lewis]

I built an Allen design for coal burning, and then changed to propane. The only thing I changed was adding a copper pipe from the blast pipe to about 3/4 up the stack. This helps so the fire doesn’t go out when pulling to throttle to fast.

Just to clarify.... it's the exhaust running through that copper pipe, not the blower? And do you run it into the side of the blast pipe, or how? Thanks.

[Bill Shields]

The blast pipe extension you describe is about what I did on my Allwn based propane burner.

It still goes up the stack...it just creates less vacuum in the smokebox because of where the tip of the pipe is with respect to the petticoat of the stack.

It just takes some experimentation to find the optimal relationship between the two. I made and cut off about 5 pipes before I was happy with where it sits today.

[Greg_Lewis]

Ah.... so it's just an extension of the existing blast pipe?

[Bill Shields]

Yes...or a longer one piece pipe. If I were doing it again I would have started with an od threaded pipe and screwed an extension up and down until I found the final position.

[Harlock]

I think over the years of looking at this it comes down to two schools of thought. One is to kill the vacuum at the smokebox by shoving the blast pipe up into the petticoat or near it, the other is to open up the auxiliary air intake at the bottom of the firebox to prevent a vacuum from being pulled. I favor the latter method as it doesn't mess up the bark. I have not seen a noticeably difference in firing in terms of heating, although there is theoretically more cool air coming in. So it's a compromise either way, but you can dial it back and forth until it's 'just enough' with both techniques.

[Greg_Lewis]

So do you not use a blower? I would think that there would need to be some vacuum up front.

[Harlock]

So do you not use a blower? I would think that there would need to be some vacuum up front.

I didn't mean killing all the vacuum, just keeping it to a reduced level.

A blower is key to combustion of propane as with everything else. There needs to be some vacuum for propane but not an excess amount as generated by very hard working cylinders. So either intentionally mess up the blast pipe ratio or open up the firebox a bit to dampen the worst of it.

Propane responds to blower or blast strength the same as other fuels, the more blower you have the bigger a fire you can make, except it has upper limits. Unlike oil it will not flame back to re-ignite itself continuously in an effort to stay alive. (the pulsing thumpeta-thumpeta sound of a leaned out fire in a tight firebox). The main difference is it is easier to suck out the fire completely in a high vacuum situation, using propane.

[Greg_Lewis]

Got it. Thanks, Mike.

[Marty_Knox]

I base the size of the stack on the net area through the tubes, not on the grate area. For oil or propane the petticoat should surround the nozzle but have an opening at the top. This is what Baldwin did on oil burners.

[Dave_Johnson]

I went through quite a lot of changes to my 2-6-0 to get it to work. I ended up with a conventional smoke box arrangement. An arch (re-bent more than once to get it right), and no baffle plate on the Locoparts burner is what made it work. Get a infrared thermometer and aim it at the stack to see what the exhaust temperature is.