Gas engine, horizontal, Dugald Clerk two-stroke, 'Stockport', cast iron/steel, made by J E H Andrew & Co Ltd, Stockport, England, 1882-1892
The Otto Cycle consists of four strokes, only one of which is a power stroke. In some respects this may be regarded as a significant disadvantage, causing a loss of efficiency. In response to this problem, Dugald Clerk developed a two-stroke cycle, which is now sometimes called the Clerk Cycle. Although the Otto Cycle has been favoured in automobile design, the simpler and less costly two-stroke engine has predominated in applications including motorcycles, lawnmowers and chainsaws. The two-stroke principle has also been applied to large marine engines, which have vindicated Clerk's belief in its potential for greater efficiency.
Clerk first exhibited his two-stroke engine, manufactured by Messrs Thomson, Sterne & Co of Glasgow, in 1880. This engine essentially comprised a double cylinder configuration, in which one cylinder was known as the displacer and the other as the power cylinder. Gas and air were drawn into the displacer and slightly compressed before being transferred to the power cylinder. Both pistons drove the same crankshaft, with the displacer crank about 90 degrees in advance of the power cylinder crank.
The Stockport engine was a development from the Clerk engine where the displacer cylinder is opposite, but in line with, the power cylinder, with the crankshaft between them. Although the two-stroke Stockport was a commercial success, its maker, J E H Andrew & Co, began producing a four-stroke Stockport engine once Otto's patent had expired. Very few of the two-stroke Stockport engines remain today, making this engine a valuable exemplar of Clerk's approach to design challenges that are still being addressed by numerous engineers who share his aim of improving engine efficiency.
Debbie Rudder, Curator, and Noel Svensson, Powerhouse Volunteer, 2007
In 1882 Dugald Clerk was awarded Patent No. 4948 for 'Motive Power Engines Worked by Combustible Gas or Vapour' which document describes the engine.
J E H Andrew & Co Ltd of Stockport, near Manchester in England, began the manufacture of the horizontal two-stroke engine in 1882 to meet a growing demand for a more powerful engine than the Bisschop engine the company had been manufacturing. After about nine years, the company changed over to manufacture four-stroke engines following the expiration of the Otto-Langen and Crossley patents. Thus the date of manufacture of this engine is between 1882 and 1892. A trade journal of July 1891 carried an advertisement from J E H Andrew for a two-stroke engine similar in appearance to this engine except for a different nameplate.
In 1907 Henry Barraclough, then lecturer (and later Professor) in mechanical engineering at the University of Sydney, received a letter from Dugald Clerk, introducing him to the National Gas Engine Co Ltd and expressing Clerk's interest in meeting with Barraclough 'to chat about gas engines'. (Reference: University of Sydney Archives, Barraclough papers, series 32). Barraclough would have acquired the Stockport engine on this or another trip that he made for the purpose of equipping the Peter Nicol Russell Laboratory, where it was used for student experiments.
Tests conducted on Clerk engines in 1885 measured the gas consumption as 30 cuft/hp hr (1139 L/kW hr), for an 8 hp engine, and 24 cuft/hp hr (911 L/kW hr), for a 25 hp engine.