Turbulators on propane boiler

This forum is dedicated to the Live Steam Hobbyist Community.

Moderators: cbrew, Harold_V

User avatar
Bill Shields
Posts: 10442
Joined: Fri Dec 21, 2007 4:57 am
Location: 39.367, -75.765
Contact:

Re: Turbulators on propane boiler

Post by Bill Shields »

Which is why I ask.

Most superheaters in our locos are really "dryers"....which is very desirable.

Superheated steam to the valves would have to be at a temperature above the steam temp in the boiler...which is rarely attainable in model locos.

From a realistic engineering standpoint, the only way to determine this is with a thermocouple in the valve chest.

A dry stack, which you have attained is always the holy grail of model steamers who like to (and are good at) experimenting.
Too many things going on to bother listing them.
Berkman
Posts: 679
Joined: Wed Aug 16, 2017 7:55 pm

Re: Turbulators on propane boiler

Post by Berkman »

for many larger 7.5 gauge locomotives, pacifics, atlantics, hudsons, mikados etc, a dry stack is rarely hard to achieve unless the pressure is low or just starting out etc.
User avatar
Drprez
Posts: 59
Joined: Tue Apr 02, 2019 3:55 am
Location: Las Vegas

Re: Turbulators on propane boiler

Post by Drprez »

Here are some thermal images of the locomotive during steam up. The temp is on the right.

*note: these are EXTERNAL TEMPS. Meaning it’s giving the temp off the boiler JACKET, off the stack EXTERIOR LINER, etc. The actual internal temps are much other as seen in lower picture.

**note: the temp scale varies in each picture (ie red might be 249 in one and 100 in another) so check the scale on the right for accurate temp.
During steam up before cylinders ran
During steam up before cylinders ran
After cylinders ran for about 2000 feet
After cylinders ran for about 2000 feet

25B042DE-14DC-49F7-8930-8757F0CFAD65.jpeg
83170F28-F0B4-4379-A4C8-A77B2625D257.jpeg
7264E19D-4A20-4F5D-BC49-C19F565E6A9A.jpeg
Different color mode on image
Different color mode on image
Nicholas Kalair
Las Vegas, NV

...the best is yet to come...
User avatar
Drprez
Posts: 59
Joined: Tue Apr 02, 2019 3:55 am
Location: Las Vegas

Re: Turbulators on propane boiler

Post by Drprez »

2246184F-A34C-4D21-B765-9F2923BD1E3A.jpeg
789B41AE-9021-4D13-A5C7-30983B908316.jpeg
A2BBCC16-2B4F-4829-A57A-4E2DC99D8128.jpeg
61F180C1-03A0-46A8-8903-749590F8410C.jpeg
Here are some more in the different color modes. It helps see different areas when it contrast.
Nicholas Kalair
Las Vegas, NV

...the best is yet to come...
User avatar
Bill Shields
Posts: 10442
Joined: Fri Dec 21, 2007 4:57 am
Location: 39.367, -75.765
Contact:

Re: Turbulators on propane boiler

Post by Bill Shields »

That's cool....or hot.
Too many things going on to bother listing them.
daves1459
Posts: 279
Joined: Mon Jun 07, 2010 7:58 pm
Location: Plainfield, Illinois

Re: Turbulators on propane boiler

Post by daves1459 »

This is an interesting thread with a lot of good information. About 6 years ago I bought a Disney loco to Walt's original design and casting in what I would describe as derelict condition. But it had a very nice copper boiler that hydro tested well. It had the original front end design and blast nozzle. In the firebox was a pair of furnace type slotted burners with no baffle plate under them, you could see the railroad ballast through the fire door. I tried steaming the loco. It was poor at best. It would raise boiler pressure at rest readily enough. However once moving steam pressure dropped rapidly.

I took the loco home to my shop and stripped it down to the bare frame and restored it. First thing I discovered was it was way over cylindered at 2 1/8" bore. I sleeved it down to 1 3/4" bore and it has proven powerful enough. During the restoration I put everything into the boiler firing system that I could think of. Having never fooled with a propane burner before I installed a proper exhaust nozzle that I have developed years ago as shown in the first attached photo. It is kinda a knock off of the PRR "chisel" nozzle. It really sucks! I added turbolizers to the boiler tubes as shown in the second photo. I built a burner a la arch module as in photo 3 using 15 burners rated at 3,000 btu at 13 in. h20 propane gas pressure. The burner head to manifold separator plate was solid stainless with shallow "ash pan" underneath drilled on all sides for air entry. In the smoke box I added a baffle modeled after what the prototype locos used to help equalize the heat flow from the top to bottom rows of flues as I have read was a problem with fire boxes with arches.

I took my shinny freshly restored loco to the track and it ran as bad as at first unrestored. It would raise steam from cold to lifting the safeties at 120 psi in 20 minutes. On the track it was a disaster. First thing was with the solid baffle plate open the throttle and the flame was sucked off the burners. Dropped the burner module and replace the solid plate with a perforated plate with lots of 1/16" holes. Back to the track and things were a little better, but still bad as steam pressure would drop when moving on flat and really drop on a grade. I stuck a thermocouple through the fire door into the burner flames and closed the door on it. This is what I measured: (All at 12" h2o gas pressure)

At rest, fire bed temperature was 2,200 deg F
At 3mph on level track the fire bed temperature was 1,700-1,800 deg. F
At 3mph on 1 to 2 % grade the fire bed temperature was 1,400 deg. F
At 3mph on 2 to 3 % grade the fire bead temperature was 1,100 deg. F

Obviously, my supper nozzle was sucking cold air into the fire box and cooling the fire. At this point it became obvious that handling propane is a lot different than coal. After some research I found that unlike coal where you want to bring as much as possible air through the coal to combine oxygen with the carbon for propane the idea is to move the just fast enough heated air through the boiler to get maximum heat transfer. So I attacked the exhaust nozzle.
Attachments
Disney loco 14.jpg
DSC01303.JPG
DSC01314.JPG
daves1459
Posts: 279
Joined: Mon Jun 07, 2010 7:58 pm
Location: Plainfield, Illinois

Re: Turbulators on propane boiler

Post by daves1459 »

Next I removed my super nozzle and replaced it with a tube 2 3/4" long with a single hole in it with the same area. As can be seen in the first picture the new nozzle protruded into the stack petticoat at about the same height as the venturi diameter. I also added a thermocouple to measure smoke box temperature at the flue exit. My smoke box baffle can also be seen in the picture. Brass is good enough for the temperature. I also installed for tests a proper plug for the fire door with a thermocouple that extended into the firebox above the flame so to capture the temperature near the arch. I also added a hook up for an electronic manometer to measure firebox vacuum. For the tests the burners were set at 12" h2o and the blower set just enough to keep the burner flames inside the fire box. At this setting the burners are all blue flamed. Here is what I found:

At rest the firebox temperature was 1,520 deg. F, the smoke box temperature was 309 deg. F, monometer = .13"-.15" h2o
At 3 mph on a 2-3 % grade the fire box temperature was 1,160 deg. F, smoke box 339 deg. f, monometer = .15" h2o

In looking at the readings I don't pay as much attention to the absolute value as the difference. The fire temperature dropped 1,000 deg. F in the first test. With the extended nozzle the air above the fire dropped 360 deg. F. The smoke box temperature during the test stayed pretty much constant. The thermo efficiency of the boiler appears to be around 70%. Monometer vacuum appears to be negligible.

With this nozzle the loco was operatable. But had to be handled carefully to keep pressure up.

I decided to put a longer exhaust nozzle in place and see what happened.
Attachments
DSC01855.JPG
DSC01869.JPG
daves1459
Posts: 279
Joined: Mon Jun 07, 2010 7:58 pm
Location: Plainfield, Illinois

Re: Turbulators on propane boiler

Post by daves1459 »

For the third test I extended the nozzle to 9 3/4" long to the top of the inner stack of the balloon stack. I also added a thermocouple down the exhaust nozzle to measure cylinder exhaust temperature. The thermocouple was pushed as far down as I could get it so to be at the base of the exhaust nozzle stand. Everything else was the same as the second test. Here is what I got:

At rest the fire box temperature was 1,403 deg. F, smoke box temperature was 359 deg F, exhaust temperature was 331 deg. F.
At 3 mph on a 2 -3 % grade the fire box was 1,280 deg. F, the smoke box was 327 deg. F, and the exhaust was 237 deg F.

The monometer remained at .15" h2o.

In this test the fire box temperature dropped by 123 deg. F. Not bad me thinks when compared the 360 deg F drop during the previous test! Recalculating the boiler thermo efficiency it went up to 74.5%. With this nozzle set up the loco steams freely and a joy to operate. Also, with this nozzle set up the exhaust steam is rather much condensed as it leaves the stack and gives some great plums of steam to watch, particularly on a cool day.

The at rest exhaust temperature was with the steam chest valves in full gear and the loco against a stop with just enough steam passing through the cylinders to read the temperature without wheel slip.

During all tests the valve gear was kept at full gear or about 75% cutoff. On the 2 - 3 % grade the exhaust temperature drop 94 deg. F as compared to at rest. At 237 deg F the equivalent gage pressure would be a mere 24 psi. Whether most of the energy in the steam has been extracted or it simple condensed I hesitate to guess. However it appears that adding 100 deg F more super heat to the steam would be of value and not too hard to obtain.

I hope my thesis has not been too boring and that it may help another modeler in setting up his propane boiler system.

Dave
User avatar
Drprez
Posts: 59
Joined: Tue Apr 02, 2019 3:55 am
Location: Las Vegas

Re: Turbulators on propane boiler

Post by Drprez »

Dave

Your experience was similar to mine although I have not had problems with my. Burners or heat loss from the blower as much. Tens stayed consistent when moving as I show above in the various thermal images noted stopped or moving .

Can you post a drawing of your stack design and blower arrangement that you found worked best. Possibly with some measurements.

My latest is to help slow the heat in the fire box is to coil up a stainless turbulators above the fire so not to quench the flames but to aid In greater heat transfer.

I can steam and keep going until my tender runs out of water. I run at about 90psi when I’m motion in the first notch (one closest to center). I have calculated with pretty exact numbers that I use 1.38 pints per minute. I used to consume a lot more until I installed the coiled super heater in the firebox. Before that it was almost 2 ppm.

I have found that with the propane I keep the blower always on. I used to turn it off when moving but found having it on kept the boiler hotter and I could run longer.
Nicholas Kalair
Las Vegas, NV

...the best is yet to come...
User avatar
Bill Shields
Posts: 10442
Joined: Fri Dec 21, 2007 4:57 am
Location: 39.367, -75.765
Contact:

Re: Turbulators on propane boiler

Post by Bill Shields »

as you will find, what works for one person / setup will not necessarily work for another.

A general 'concept' of how to get there and experimentation is the yellow brick road you must follow:

1> no more air into the system than what the burners pull in to support combustion. I have a plate under my burners that is all but totally sealed against ANY AIR except what is induced (enduced?) by the gas / orifice / velocity through the burner.

I think that the holes in the plate are maybe 0.05" larger than the burner (if that)

2> just enough draft to get the combustion products out of the stack -> which usually means that you run with the blower on a little all the time, unless you have the blower mechanically connected to the throttle so that should you slam the throttle shut, the blower starts automagically. I was playing with a linked valve that controlled the blower as a function of throttle setting...but then life got in the way and I found that I could do just a good a job by ear / hand at the track...and abandoned the project.

3> Lifting the blast nozzle up toward the stack is a step in the correct direction -> however my propane loco runs just fine with what looks like a standard blast pipe / petticoat setup - so it can be done (i like how it sounds that way - loud and barky not soft / purr).

4> an arch that directs heat into / around the firebox rather than out the flues is always helpful. Turbolators and your drier will help, but you also need to keep the heat in the firebox. Most every propane (or diesel) setup I have examined has some sort of arch (for a reason).

The arch that I use is VERY RESTRICTIVE - only 1/8" clearance on the sides and top -> this helps to control 'blast pulses' from the otherwise standard blast pipe / stack / petticoat. You can jerk the throttle open / shut all you want and the flames never suck out. It is a RARE occasion when I need to relight out on the track...

running the blower does increase water consumption....but that's life....

it is a balancing act....
Too many things going on to bother listing them.
daves1459
Posts: 279
Joined: Mon Jun 07, 2010 7:58 pm
Location: Plainfield, Illinois

Re: Turbulators on propane boiler

Post by daves1459 »

I can make a sketch of my exhaust nozzle and stack setup. I'll try to get to it next week.

There is almost always more than one way to solve a problem in this hobby. The main points that I was trying to convey were that boiler set up et al is different for propane than for coal and the goal is to move the combustion heated air through the boiler slower and just fast enough to extract as much energy/heat as possible.

While I calculated the 3rd test boiler thermo efficiency as 74.5% by simply using the difference of the firebox and flu exit temperature divided by firebox temperature. My estimate of the overall loco efficiency is somewhere between 4 and 6 %.

Dave
User avatar
Bill Shields
Posts: 10442
Joined: Fri Dec 21, 2007 4:57 am
Location: 39.367, -75.765
Contact:

Re: Turbulators on propane boiler

Post by Bill Shields »

That high? (4-6%)? Giggle....
Too many things going on to bother listing them.
Post Reply