Corwin Oil Burner
Corwin Oil Burner
The Live Steamer, January-February 1951
Oil has many distinct advantages over solid fuel for firing small locomotives. Diesel fuel oil makes a fine oil for this purpose. It is uniform in quality, readily available and very heap. Firing is accurate and positive at all times. Increases or decreases in the fire can be made almost instantly to compensate for the ever changing demands made of the boiler. The fire can be cut down small to a "standing fire" while the crew goes to lunch and when they return, she will still be cooking away at 70 to 80 pounds. When the injector or pumps are put on, the fire can be raised to hold the needle at 100 or 125 pounds. Or if the engine is working hard and needs water, she can be kept hot - to the popping point if desired - simply by turning up the firing valve and balancing the blower and atomizer. There is no shoveling, poking or waiting. The handling of the three valves of course can be done with no trouble on the run. The fireman can hold the stack clean, fire with a gray haze or belch black smoke at will, simply by turning the firing valve. Of course smoke is bad business, as it is astounding how quickly one can soot up the firebox and flues to the point of complete steam failure. Soot inside the flues is a very effective insulator against heat and smoke at the stack therefore should be avoided as much as possible. The fumes and smoke from oil combustion are not irritating to the eyes, nor do they have an objectionable smell. One does not have a volcano of red hot cinders to ride behind either. The soot produced from oil is dry and soft and can readily be swept out of the flues or blown out with compress air. This soot is much different than some produced by some grades of coal which produce a sticky, heavy coal tar along with a lot of soot which makes a real mess inside flues.
Now to the requirements of the burner. First the oil tank - it should be located as high as possible in the tender to get the greatest possible gravity pressure head. The tank should be shallow so there is the least possible change in head between a full and a very low tank of oil. This makes the firing more uniform and much easier to control. Oil tanks under pressure are a definite nuisance, as the pressure is ever changing. Accurate firing is impossible under these conditions and for that reason a shallow gravity tank is the best method of supply.
The firing valve should give easy and accurate control of the oil flow.
The oil burner should fire from front to rear. It can be one of several types, the general type used in big practice and shown in the Locomotive Encyclopedia can be used very nicely if there is good oil pressure from the tank. If it is not possible to get sufficient pressure from the tank, a "fly spray" type burner can be used in which the atomizer steam assists gravity by siphoning oil from the burner oil standpipe. I am now using the "fly spray" burner, shown in the drawing, on my 3/4 inch scale 4-8-4 and it has proven very successful over the last three years.
The steam supply for the atomizer should be superheated so there is no chance of droplets of water to reach the atomizer nozzle. Should that happen, the fire will be irregular and is very apt to be put out. The least amount of steam possible to do the job of atomizing the oil is all we want. Steam in the firebox has a tendency to retard combustion and an excess will smother the fire. It will be noted in the "fly spray" burner the atomizer nozzle is #80 drill.
The atomizer superheater should be of stainless steel if it is run through the firebox, in order that no scale will form in it and eventually clog the #80 nozzle.
The last and most important thing necessary for successful oil burner operation is draft control. As in big practice only a small amount of air, about 15%, should be allowed to enter the firebox around the burner. More air is let in about 1/3 the way back from the sides of fire box and the most at or near the rear of the firebox. These adjustments of draft are a matter of experiment just as in big practice, for they have their problems too. No brick arch or baffle is used. Once the proper draft is established there no need for further adjustment.
The firepan can be made with 3/8 inch holes along each side spaced about 3/8 inch apart. This will provide an excessive amount of air for the fire. Then as many holes as necessary can be closed with wet fireclay plugs poked in the holes. The plugs will bake in tight and stay put. In this way as much draft as needed can be admitted anywhere along the sides of the firepan without building an elaborate adjustable damper system.
See also Firepan For Oil Burner.