Thursday 1st August 1872

Dugald Clerk received a British patent for his two stroke engine. The Clerk cycle engine uses a similar valve arrangement to the four stroke cycle diesel engine, with both exhaust and inlet valves in the cylinder head and operated by a camshaft. At the end of the power stroke, both exhaust and inlet valves open, and the cylinder is filled with fresh air supplied by a supercharger, which replaces or scavenges the exhaust gas. As no fuel or lubricant has been added to this inlet air, some loss through the exhaust manifold is not serious. The inlet gas is then compressed in a compression stroke, and the fuel injected approaching top dead centre and ignited as in a four stroke diesel engine. The Clerk cycle was used in large engines powering railway locomotives and ships, and was adopted by General Motors in the United States to form the Detroit Diesel Company. The Clerk cycle was not adapted to gasoline fuel, nor to smaller engines. The gasoline two stroke cycle, and the concept of cylinder ports replacing head valves, were both later invented by Joseph Day. Day’s inventions were subsequently adapted for two-stroke diesels, and modern two-stroke diesels of all sizes either incorporate elements of both designs, with cylinder port inlets and cylinder head exhaust valves, or use cylinder ports for both inlet and exhaust.