Early Heisler &
Late Garratt Burners
I'm in the process of designing the Heisler oil burner and fire pan and have been using some recent photos sent by Mike Getscher as well as some photos of Garratt burners so I thought I'd add that data for reference.
The Heisler and Garratt have similar size openings around the burner nozzle for combustion air. (See MRsR91 Burner for photos of that burner). The Heislers have a damper on the combustion air and the Garratts don't. I suspect that the damper permits a greater range of oil feed to the burner.
The later Heisler and the late Garratts have vents in the fire box door with a damper to control the vent opening. The early Heisler appears to have vents with adjustable dampers at the rear of the fire pan.
I tried some vents at the rear of the fire pan on the Shay with little effect (see More Power). I now suspect that on the prototype the rear vents are used to reduce excessive draft which might blow out the fire. This could happen when the exhaust is creating a lot of draft--- possibly when under a very heavy load. I think I'll make a door with a vent and damper for the Heisler and try opening it when the locomotive is under heavy load.