Hot Tube Ignition

| October/November 1989

  • Connecting Hot Tube

  • Chimney

  • Burner

  • 2 HP Bovaird
    2 HP Bovaird & Co.

  • Connecting Hot Tube
  • Chimney
  • Burner
  • 2 HP Bovaird

115C Audino Lane Rochester, New York 14624

A while back I bought a vertical, tank cooled 2 HP Bovaird engine at an auction. It is a very simple engine, and it was mistaken for an air compressor by many people because it had no apparent means of ignition at all. After a bit of examination in the form of making the whole thing portable enough to fit in the trunk of the car, we (my friend, Grunch, and I) decided that (1) it had hot tube ignition, and (2) the before mentioned ignition system was completely missing from the engine. So I was confronted with the task of rebuilding this system from scratch.

Now, I've been collecting engines for quite some time, and I understand completely the more traditional forms of ignition, e.g. buzz coils, ignitors and the like. Hot tube engines don't find their way up in the woods of the Tug Hill plateau region of New York very often, however, and this relic from the Pennsylvania oil fields was completely unknown to me. So I talked to collectors from that area, and many others from all over, and have rebuilt it. I would like to share some of my discoveries with fellow collectors who may have run across a similar situation. I have since purchased a 4 HP Eclipse (Olean, New York), which also needed some hot tube ignition work.

Hot tube ignition consists of a hollow tube about ?' diameter which is closed at one end, and threaded at the other with standard pipe thread. This is screwed into the combustion chamber of the engine, and surrounded by an asbestos lined chimney, about 1?' to 2' diameter. The chimney is cast iron, and the tube itself was originally made of an alloy of nickel and silver.

The chimney has an opening on the side, very near the bottom, which has pipe threads inside to support a burner. This burner, when lit, plays a very hot flame on the side of the small tube, which makes the tube red hot. When a charge of natural gas is taken in by the engine and compressed, the mixture will soon compress the air/-burnt gasses in the tube. When it reaches the hot spot on the tube, it is ignited. The point at which ignition takes place is adjusted by the height of the flame on the tube: the higher the flame, the later the ignition.

I have found that tubes made of ?' stainless steel, about 6' long and closed with a cap, work quite well. I have used ungalvanized steel pipe, but this doesn't last as long. Ideally, the pipe should be forged closed for a more reliable tube. For the chimney on the Bovaird I used a piece of 1?' pipe about 12' long. I have not found a substitute for asbestos for the lining, but if someone knows of something else, please let me know. Asbestos is dangerous, as we all know, and fiberglass can't handle the high heat generated during an extended run, it melts.

6/10/2014 7:57:41 PM

What have you found is the optimum intake gas pressure for a hot tube ignition engine?


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