This is an early two stroke engine, a type developed to address a perceived problem in the efficiency of the four stroke engine designed by Otto and Crossley. 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 very nicely presented Fawcett engine was a development from the Clerk engine. One innovation is the placement of its displacer cylinder at an angle to the power cylinder, with its axis aligned with that of the crankshaft. This makes it a little more compact than the commercially more successful two-stroke Stockport engine. No other two-stroke Fawcett engine is known to exist today, so this engine is 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, 2013

The engine is similar to the Dugald Clerk engine, a predecessor of the Stockport engine (object number H10108). It was manufactured by Fawcett, Preston & Co of Liverpool, England, in 1890 in accordance with Beechey's patent of June 30 1890. Mr Beechey took out several patents, the first in October 1880.

Fawcett Preston & Co was established as the Phoenix Iron Foundry in Liverpool in 1758. It manufactured cannons and marine steam engines and tried to enter the steam locomotive market. It exported at least six small, low pressure engines to the lower Mississippi area in the 1820s, and by 1838 they were all driving sugar mills. The company made the steam engine that powered the Maitland, which was wrecked off the Bouddi National Park on 5 May 1898.

The engine was used for teaching purposes at Sydney Technical College, which donated it to the Museum in October 1939.

This engine consists of a horizontal power cylinder and, below it, a compression cylinder with two pistons driven from the same crankshaft. The power cylinder piston rod engages with a crank pin attached to an outboard disc whilst the compression cylinder piston rod engages with a pin attached to the power cylinder piston rod. The compression cylinder is angled so that its axis is aligned with the axis of the crankshaft. A horizontal piston valve operated by an eccentric from the crankshaft controls gas and air admission to the engine. The piston valve and power piston cylinder are both surrounded by cooling water jackets. Speed is controlled through a centrifugal governor. Cylinder bore is 130 mm and piston stroke is 280 mm.

In operation, the air and gas mixture is first drawn into the compression cylinder as the compression piston is moving outwards. The mixture flows past the head of the power cylinder, becoming warmer and cooling the power cylinder. At the same time, the power piston is completing its expansion stroke. As the power piston begins its return stroke the exhaust ports are opened by a lever system operated by the piston valve control rod. On the return stroke of the compression piston, which occurs ahead of the power piston movement, the gases are compressed and subsequently delivered past the piston valve and into the power cylinder where they assist in driving out the exhaust gases. As the power piston reaches the end of its inward movement, the gases have been compressed and the piston valve exposes the ignition tube, which detonates the charge in the power cylinder.

In an experiment carried out on a 6 horsepower engine in 1890, at a speed of 150 rpm the gas consumption was found to be 24.74 cubic feet per horsepower-hour (939 L/kWhr).

Made: 1890

On the makerĀ?s plate: THE ''FAWCETT'' PATENT GAS ENGINE / FAWCETT, PRESTON & Co LMT / ENGINEERS LIVERPOOL / SOLE MAKERS / No 3899. 1890

B814

1890

1100 mm

1660 mm

900 mm

680 kg