REPRINT: How Your Hobby Started Part 3

| January/February 2001

This month we continue reprinting a series that first appeared in GEM in the March-April 1969 issue. Over the coming months, we will retrace engine history as presented by Carelton M. Mull. This segment originally appeared in the July/August 1969 issue of GEM.

Early inventors as Huyghens, Papin, Robert Street, Barnett, Samuel Brown and others, while testing versions of their engines, realized considerable accomplishment when they were able to get an engine to explode the fuel in a proper progression to create enough power to keep a flywheel turning. Under such circumstances, with crude machines, it was hardly possible to classify engines according to a type such as two or four cycle.

From all of these efforts, a light was dawning. In England, an engineer by the name of Dugald Clerk worked on an idea of one intake stroke and one power stroke on his engine by using the travel of the piston to uncover a port in the cylinder to exhaust the burned gases. His engine was built with an auxiliary cylinder used to compress air for scavenging.

When the power piston moved towards the end of the expansion stroke, it uncovered a port through which the exhaust gases pass; thus reducing the pressure in the main cylinder to that of the atmosphere. Pressure from the displacer cylinder was then admitted through a valve in the head, forcing out the burned gases and charging the combustion space for the next power stroke. This series of events within the cylinder is repeated in every revolution of the engine. The auxiliary or displacer cylinder with the intake valve arrangement made this a rather difficult engine to build. It was a definite type, and Dugald Clerk explained his engine as a two-cycle machine, establishing for the first time this fundamental design.

During the next decade, this two-cycle type was improved and simplified. Much experimentation and research has perfected the two-cycle as it is known today; as it is widely used in the smallest and largest gasoline and diesel engines on today's markets.

While Lenoir and Clerk were building engines, another French engineer, M. Beau de Rochas, 1862, was conducting experiments on the theory of the actual operating conditions inside the combustion space of a gas engine and on the matter of the firing sequence. He found a better operating system by utilizing one stroke of the piston to charge the cylinder with the explosive fuel, and the next stroke to compress the fuel mixture and then fire it at near top dead center using the next forward stroke for power, with the return stroke of the piston to exhaust the burned gases. Thus it was Rochas who was the inventor of the four-cycle internal combustion engine.