Gas Engine Ignition

| May/June 1969

Avery tractor

Courtesy of Ted Worrall, Loma, Montana

Ted Worrall

Atkins, Iowa 52206

With the invention of the gas engine as such, came many problems, one of the greatest being that of a dependable ignition system.

In the earliest gas engines, an electric spark was used to fire the charge. Electricity then being comparatively little understood, the troubles experienced with this mode of ignition led to its being abandoned in favor of first the slide-valve method of ignition, and later of the hot-tube method.

The slide-valve method consisted of a small reciprocating slide valve which had a pocket that was put in communication alternately with the fresh mixture and the cylinder. When this pocket was filled with the fresh mixture, a further movement of the valve brought it into contact with a small external flame which ignited it. As the slide-valve continued its travel it was brought into communication with the cylinder when the gas still burning in the pocket ignited the compressed charge. Engines of this type were known to be in existence as late as 1907 and possibly some may still exist.

1917 model of a 12-25 Avery tractor and Avery 4 bottom plow owned by Ted. Ted. is the Montana Director of Western Steam Fiends Association.

The many obvious problems encountered with the slide-valve type of ignition led to the development of the hot-tube method of ignition. An iron, nickel or platinum tube having its outer end closed was screwed into the combustion chamber, usually in the cylinder head. The open end of this tube was inside the cylinder. A gas burner kept this tube at a red heat. During the exhaust and suction strokes the tube was filled with burned gases, but toward the end of the compression stroke they were forced into the back of the tube and the fresh mixture following was ignited upon striking the incandescent portion of the tube.