The original internal combustion engines were started via a hand crank mechanism. This system was difficult, physically demanding and in many ways a dangerous approach to starting an engine. When the motor started it was possible for the crank to begin to spin along with the crank shaft and potentially it could strike the person starting the engine. It was also possible for the engine to run in reverse if care wasn’t taken to retard the spark.
As engines grew in size and complexity it became clear that continued use of hand cranks was not viable. This was especially true for diesel engines which rely on compression, rather than a spark for fuel ignition. It was clear as early as the late 19th century that an alternative was required. A number of early attempts at designing electric starters were not effective when used outside the laboratory. The first practical electric starter was developed by Charles F Kettering.
Kettering recognised that a small motor operating with a high voltage and current could develop enough power to crank the engine for starting so long at the starting time was limited to prevent the build-up of heat which would cause the motor and associated wiring to burn out.
In industrial large-scale engines, such as those used in ships and power stations, the very high compression ratio required to provide reliable and complete ignition made the use of electric starting systems impractical.
An electrical starter which could provide sufficient power would be very large and hence an alternative system was required.
So two separate systems using compressed air have since been developed. The first, for engines of about 150mm bore size to 300mm bore size, uses an air starter which drives the flywheel. The second system introduces compressed air directly into the combustion chamber via a distributor and is used for engines larger than approximately 300mm bore size. These bore sizes are only a very broad guideline.