Ignition is discussed in a broad and non-technical way. The definition of the word ignition should be broad enough to include the complete functioning of the ignition apparatus, beginning from the point where mechanical energy is absorbed to generate current and ending with the completion of the working stroke of the engine. The ignition system includes the mechanical drive to the magneto or generator and the task imposed on the system is by no means completed when a spark has passed over the gap of the spark-plug. Ignition means the complete burning of the charge of gas in the cylinder at top dead-center, at the time the working stroke of the piston commences. The means employed to accomplish this result is the ignition system. In the present-day type of gasoline engine a spark produced by high-voltage electricity is almost universally used for ignition. This high-voltage electricity is produced by a transformer. The transformer “steps up” the lower voltage produced from the source of current, which may be permanent magnets or a storage battery. Regardless of the source, the result must be efficient ignition if the maximum power output per gallon of fuel is to be obtained.
The whole program of events in an internal-combustion engine cylinder is then considered as having been slowed down, to assist in grasping the idea of what takes place, and three specific ways to make the charge burn faster are stated. Preignition and detonation are discussed, a statement of the advantages of using two spark-plugs per cylinder and a table showing power results with from one to four spark-plugs being given. Doped fuel is considered and the matter of certain and uncertain ignition is commented upon. Spark-plug tests at McCook Field are described and the mechanical defects in ignition systems enumerated.