Gas Engine Ignition

Avery tractor

Courtesy of Ted Worrall, Loma, Montana

Ted Worrall

Content Tools

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.

Some hot-tube igniters made use of a 'timing-valve', which opened a passageway between the cylinder and the incandescent tube at the proper instant.

With hot-tube ignition, timing was a matter of trial and error. It proved most satisfactory where the engine was under a constant load, and in fact, this type of ignition held its own for many years, even after electric ignition had made its re-entry into gas engine ignition.

Hot-tube ignition principles were also applied to 'oil-engines'. A tube or plug was heated red hot before starting the engine, after which the heat of the explosions was sufficient to keep the tube incandescent. Engines of this type were built for many years.

In general, hot-tube ignition was destined to failure in favor of electric ignite-century took the findings of their predecessors, developed and refined them, and most important reduced their ideas into practical inventions which paved the way for efficient, cheap and reliable electric ignition.

Ironically, one of the main reasons for the demise of the hot-tube system of ignition was not its lack of dependability, but rather its cost of operation. Most hot-tube burners consumed from 4 to 5 cubic feet of gas per hour, and with a small engine this made the operating cost high. Hot-tube ignition with a timing-valve had some to be fairly reliable, although many inherent problems existed which affected operation such as the air-gas ratio, cylinder temperature, tube temperature and length and other difficulties.

All this led to the development of electric ignition, and as well all know, that's when the headaches really started. More on that issue later.

A pair of beautifully restored and running Evenrude engines-all the way from Detroit for exhibition at the Florida Show in February. The water cooling was nicely arranged as can be seen.

A Mc. D. model LA 3-5 Hp. S/NLAB6151, painted gray with red flywheel. The trucks belong to an older model McD. engine.

Bruce Nicolson and Gary Smith, two city boys, learn what Iron Men mean by a day's work at H. Kenneth McDonald's farm in Dresden, Ohio. Picture taken in August of 1966. That's the 32-54 New Huber Separator, manufactured in the late 1930's.

H. Kenneth McDonald's 40-62 Super Four. This is used every year in driving his separator.

H. Kenneth McDonald's John Deere 10-foot PTO binder, hitched behind a 1939 Model L.C. Huber tractor. Both are used regularly.