Shay Operation - More Improvements
New Burner
Nelson Riedel Nelson@NelsonsLocomotive.com
Initial: 10/17/06 Last Revised: 10/23/2006

 

The shay is near the end of the third summer and it seems to run pretty well.   The major limitation is the power output of the boiler system.  There is no problem on a relatively flat track.  However on 3% or greater grades with a large load the speed is limited to about 12 scale mph. ( Note that with the prototype, 12 mph was about top speed and on a 3% grade it'd be going half that or less.)   The shay runs at Mill Creek Central which has lots of hills.  There are usually some large steamers as well as diesels running so it's simple courtesy to run fast enough to not hold up the others.  The boiler output is limited by the boiler design.  The challenge is to get the maximum steam from the design. 

Simply put, the goal is to produce the maximum energy.   This goal can be accomplished by burning fuel at the maximum possible rate and at the same time extracting the maximum heat from fire.  After fooling with several burner evolutions it was useful to list what was learned (this is probably obvious to an experience fireman):

  • Fuel - Oxygen Mixture:   If the mixture is too lean (too much oxygen, too little fuel) the fire will likely go out.   If the mixture is too rich (too little oxygen, too much fuel) the fire gives off a heavy black smoke and quickly fills the flues with soot.    If the proper ratio of fuel and oxygen is present, then the fuel will be completely consumed and little or no smoke will be given off and there will be little or no build up of soot in the tubes.
     
  • Draft:  Draft refers to the current of gases that flows into the firebox and then out of the firebox through the flues and up the stack.  If there is insufficient draft, insufficient oxygen will be draw into the firebox and the fire will burn rich (black smoke  & soot in tubes).   If the draft is too great, the fire may go out.  Another  undesirable effect of too great draft is that the gases leave the firebox and flues at too great a rate and too much heat goes up the stack.
     
  • Forced Draft:  The draft is forced by the engine exhaust and the blower.  The blower has the most effect.  The exhaust nozzle is quite large for the exhaust volume.  This is good in that there is little back pressure thus improving engine efficiency.  Because the draft is primarily controlled by the blower, the proper mixture is not effected much by changes in throttle setting.
     
  • Blower Holes:  Ken Schroeder specified 1/32"  blower nozzle holes in the blower ring.  In the earlier operation there was a problem with these holes plugging so they were enlarged to ~0.050".  This increased the amount of steam required for the blower function and reduced efficiency.  The holes were plugged then drilled 1/32" to match the drawings..   This improved the blower function.  There seems to be no problem with the holes plugging if an overly rich fire is avoided.  
     
  • Closing the Fire Pan:  To avoid excess draft and the associated heat loss up the stack we want to limit the air entering the fire box to the minimum required for proper combustion.   This can be achieved by closing all holes in the fire pan except the entry point of air to be mixed with the fuel.
     
  • Mixing Air & Fuel:   Air that supplies the oxygen for combustion must be mixed with the fuel.  This is true for both oil and gas fired burners.  The better this mixing action, the better the burner efficiency.        

 

Sievert 2960 Burner: The photos at right show the large Sievert burner used for silver soldering large pieces.  It has a maximum output of ~ 400K BTU and can be reduced to about 50 K BTU by reducing the gas pressure.     

The lower photo shows the brass fittings at the back of the burner.  The fitting on the right has the gas orifice.  The fitting on the left is the mixing chamber.  The fitting on the right screws into the right end of the mixing chamber with the front of the orifice just to the right of the holes in the side of the mixing chamber.   The gas shoots through the mixing chamber and picks up air along the way.    

Burner Mixing Chamber:  It was a small step to  copy the Sievert 2960 mixing chamber.  The drawing on the right shows the design. The chamber was fabricated from 1" diameter brass rod.  The nozzle (copied from Bob Reedy's design in the May/June 2003 issue of Live Steam )  fits into the 5/8" hole on the right end. The 7/8" diameter left end is silver soldered into a hole in a ~1.5" X ~ 3" X 1/8" brass bar.  The brass bar with mixing chamber is attached to the front of the fire pan with a couple 6-32 stainless screws and nuts.
The photo at right shows the bottom view of the new mixing chamber installed on the shay fire pan.  The nozzle slides into the chamber so the the tip is at about the middle of the air inlet holes. The nozzle is held in position by the 4-40 socket head cap screw in the bottom of the mixing chamber which serves as a set screw.

Burner Operation: The first tests of the burner were made on the test stand.   After fooling with it a while the best operation seemed to be with:

  • Blower set at ~30 psi
     

  • Atomizer regulator set at ~ 5 psi
     

  • Fuel set at point where a little white smoke is seen.

The fire is not very sensitive to the atomizer setting but is very sensitive to the fuel and blower settings.   For example, a slight increase in fuel setting or slight decrease in blower such as back to 25 psi will cause the fire to smoke.   If the fuel is increased very much beyond this setting the fire will smoke even if the blower is increased to over 60 psi indicating that these settings are near or at the maximum possible heating capability of the firebox volume.     

After the boiler had been up to ~110 psi pressure for about 20 minutes the following temperature measurements were taken using an infrared thermometer:

  • The temperature at the top back of the boiler was 345 F.
     

  • The temperature on the side of the smoke box was 310 F.
     

  • The temperature at the base of the smokestack was 345 F.

By contrast, the first fire pan design had large openings around the nozzle which admitted much more air into the firebox.  With that design and similar fuel settings the temperature at the smoke box base measured between 450 F and 500 F.    This burner seems to be much more efficient.

The first test at the track went very well.  The fire went out once when the throttle was opened the first time and a slug of water blew out the exhaust pipe.  It was a very cold day (high 40s) and there was time for only about one hour of operation.  The burner seemed to operate well.   A week later the shay was operated a couple more hours and it continued to perform well.  A first time operator ran it for about an hour with no problem.  The fire did go out for him a couple times.  Both times the fuel valve had to be opened a little further to get the correct fuel input.  The fuel adjustment was probably required because the fuel level in the tank was lower thus reducing the rate of fuel flow.  The igniter relit the fire with no problem.  

The current plan is to use this design in the Heisler.  The mixing chamber might be made slightly larger by using a 1.25"  OD and 1" ID.  The same type nozzle will probably be used.  It would be nice to find a better quality fuel valve. 

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