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Flame Ignition Basics

Learn the ins and outs of spark plug/high-tension ignition system basics.

| October/November 2014

  • The 1868 Otto-Langen non-compressing engine on display at the Rough & Tumble Engineer’s Historical Assn. in Kinzers, Pa.
    Photo by Beth Beavers

Editor’s note: This is the fourth in a series of articles by Andrew K. Mackey examining antique engine fuel and ignition system basics.

Flame ignition

The flame ignition was an early attempt at producing an internal combustion engine. It is not the same as a flame licker, which uses vacuum to create power.

Flame ignition engines suck a fuel/air mixture into the combustion chamber through a slide-gated port. That port then closes. As the piston recedes, a cam introduces a flame through a second port, which then lights the charge in the cylinder. The ignited charge closes the second port, and then the pressure generated by the ignited charge drives the piston in a power stroke. The burnt gasses are then exhausted. The process is then repeated.

The best known engine with flame ignition is the Otto-Langen non-compressing engine (above). Most of these engines used hydrogen, but a few used acetylene or illuminating gas for fuel. The Paradox model engine also used a flame ignition. There are also several others of this type at the Rough & Tumble Engineer’s Historical Assn. in Kinzers, Pennsylvania.

Flame licker

The flame licker uses a different principle of operation. On flame licker-ignited engines, a flame is introduced into the cylinder on the piston down stroke through a valved slide port near the top of the cylinder. The port closes as the piston nears the end of the intake stroke, and the flame burns all the remaining fuel and air in the cylinder. As the burnt gasses cool, the vacuum created sucks the piston back toward the top of the cylinder, thus restarting the cycle.

The flame licker is very inefficient, only generating about 25 PSI against the piston, and with internal resistance to turning (read: friction), makes very little power for its size. The heat generated often burns off the lubrication, which makes severe wear a liability, too.


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