Atmospheric engines

Earliest IC engines of the 17th and 18th centuries are classified as atmospheric engines.
These are large engines with a single cylinder which is open on one end. Combustion is initiated at the open cylinder and immediately after combustion, cylinder would be full of hot gases at atmospheric pressure. The cylinder end is closed at this time and trapped gases are allowed to cool. As the gases are cooled, vacuum is created within the cylinder causing pressure differential across the piston (atmospheric pressure on one side and vacuum on the other side). So piston moves due to this pressure difference doing work.

The atmospheric engine was invented by Thomas Newcomen in 1712, often referred to simply as a Newcomen engine. The engine operated by condensing steam drawn into the cylinder, thereby creating a partial vacuum, thereby allowing the atmospheric pressure to push the piston into the cylinder. It was the first practical device to harness steam to produce mechanical work. New comen engines were used throughout Britain and Europe, principally to pump water out of mines. Hundreds were constructed through the 18th century.

James Watt's later engine design was an improved version of the Newcomen engine that roughly doubled fuel efficiency. Many atmospheric engines were converted to the Watt design, for a price based on a fraction of the savings in fuel. As a result, Watt is today better known than Newcomen in relation to the origin of the steam engine.

Prior to Newcomen a number of small steam devices of various sorts had been made, but most were essentially novelties. Around 1600 a number of experimenters used steam to power small fountains working like a coffee percolator. First an airtight container was filled with water, then heated to make it boil; a pipe extending to the bottom of the container and protruded upward from the container. The steam generated pressurized the container, displacing the water within out of the container, so that it spurted out of anozzle on top of the container. These devices would have been limited in their effectiveness and could only serve to demonstrate a principle.

In 1662 Edward Somerset, second Marquess of Worcester, published a book containing several ideas he had been working on.One was for a steam-powered pump to supply water to fountains; the device alternately used a partial vacuum and steam pressure. Two containers were alternately filled with steam, then sprayed with cold water making the steam within condense; this produced a partial vacuum that would draw water through a pipe up from a well to the container. A fresh charge of steam under pressure then drove the water from the container up another pipe to a higher-level header before that steam condensed and the cycle repeated. By working the two containers alternately, the delivery rate to the header tank could be increased.