A stationary engine is an engine that does not move. Usually, a stationary engine is used not to propel a vehicle but to drive a piece of immobile equipment such as a pump or power tools.

However, in Victorian era railway engineering, many attempts were made to replace locomotives by stationary engines, on the grounds that it was inefficient to move something as large and heavy as a steam engine around. These attempts only succeeded where short distances were to be covered, where various kinds of cable railway were successful, particularly for steep inclines (where the inefficiency of moving the engine up and down a hill is particularly significant). A heroic failure was Isambard Kingdom Brunel's attempt to construct an atmospheric railway from Exeter to Plymouth in Devon, England.

Small stationary engines were frequently used on a farm to drive various kinds of power tools and equipment such as circular saws, pumps, and hay elevators. The engine was fitted to a wooden trolley with steel wheels so that it could be moved to where required, it was then coupled to the equipment by means of a flat belt.

The engines were usually powered by gasoline, or in some cases for economy it was possible to switch over to run on paraffin after the engine had warmed up - to achieve this required a part of the inlet tract to be heated by exhaust gases in order to vaporise the less volatile fuel. Very large stationary engines ran on a heavier type of fuel oil, this type of engine was usually too large to be moved, a typical application would be electricity generation or large scale pumping.

Initially such engines mirrored steam engine design in having the piston move horizontally, with the crank and valve gear exposed and employed a drip-feed total loss lubrication system. Later for safety, cleanliness and longevity the design moved towards enclosing the working parts and using sump lubrication.

The four stroke cycle design was by far the most common, but Petter, a British manufacturer developed a successful two-stroke cycle design.

A centrifugal governor system was usually incorporated to regulate the engines speed under varying loads. This is a simple negative feedback control system. The engine speed is sensed by a pair of weights that rotate with the crankshaft, as the speed increases then centrifugal force causes the weights to move outward against the pressure of a retaining spring. This outward movement is used to restrict the engine power to prevent the speed becoming excessive. If the engine slows down the centrifugal force reduces and the weights are pulled inward by spring pressure, this movement is used to increase the engine power to maintain speed under increasing load.

Eventually such engines were rendered obselete by the development of electrically powered tools, and by newer gasoline engines that were small and economical enough to be permanently built in to each piece of equipment.

See also:

• Canterbury and Whitstable Railway.
• Hillclimbing (railway)