Functions of Ignition Apparatuses and Engine Systems
An in-depth look at various ignition apparatuses and engine systems, including hot tube ignition, low-tension systems and flame ignition
Sectional disgram showing the construction of a valve-in-head engine.
Paul R. Bell
Editor's Note: This is a reprint from the book Internal Combustion Engines and Tractors, Their Development, Design, Construction, Function and Maintenance. Notes of a series of lectures, delivered by Oliver B. Zimmerman, of the Engineering Staff, International Harvester Company, Chicago, copyrighted 1920, IHC. It was sent to us by Paul R. Bell, 247 Eldora do Avenue, Louisville, Kentucky 40218.
THE IGNITION SYSTEM
The function of the ignition system is to provide a controlled means of firing the charge of fuel and air mixture.
Various means have been used in the past for this purpose, yielding knowledge which, owing to its value in showing development and requirements, is here reviewed.
Must Withstand High Temperature
It is well to realize something of the exacting requirements of an ignition apparatus, especially the spark plugs or igniters. First, the parts within the cylinder are subjected to the intense heats produced during ignition and burning of the charge 2000 to 4000 degrees Fahrenheit, and to sudden changes during each cycle, ranging from this exceedingly high temperature down to the cool temperature of the incoming charge of air.
Must Work Instantaneously
Next, consider the time required to complete this work. Take an engine running 600 rpm, and using spark plug ignition. It makes one revolution in 1-10th of a second. If we ignite the charge 30 degrees ahead of center, there being 360 degrees in each revolution, the time of ignition would be 30-360ths. This allows only 1-12th of the time required for one revolution or 1-120th of a second for the charge to burn and create its pressure within the cylinder a very short time even for an engine of moderate speed. In that time the spark must jump between the points, the flame start and spread throughout the cylinder to all its corners, if best results are to be obtained. If the cylinder has irregular pockets, the flame must follow into them requiring more time than if there were no pockets. This accounts for the fact that L-head and T-head engines act either slower or with less power than the valve-in-head types.
Naked Flame Ignition
The first method of firing was by igniting the mixture with a naked flame. This flame was easily and often blown out, so the engine required constant attention from the operator. The uncertainty of action quickly put this system aside in favor of hot tube ignition. Hot tube ignition consists of a piece of pipe closed at one end and screwed into the cylinder so that the inside of the tube can receive a part of the burnable mixture during compression. This tube was heated by means of a flame from the outside, thus producing the heat necessary to ignite the charge, but without the danger of blowing out the flame except in windy weather. The control had, therefore, been much improved but permanence and close regulation were still lacking.
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