Hot Air Power

A hot air engine pumps heated air directly from a furnace into a large cylinder to force the piston upwards.   The air is cooled to condense it, and then the atmosphere does the work on the downward stroke, as with the Newcomen steam engine.   As with steam engines, there are compound hot air engines where the exhaust the steam of the high pressure engine is piped to lower pressure engines.   In this way, double, triple and even quadruple engines obtain maximum use of the energy contained in the steam.   They provide only stationary, low power - to 45 hp in the 1920s - so they were not competitors to the steam engine, which provided much greater power.   The advantages of the hot air engine are it is safe, reliable, simple and cheaper than a steam engine.   On the other hand, the engines tended to be heavy and the hot air sometimes cracked the piston.   They were obsoleted by the gasoline engine and were no longer produced by the 1920s. ^{Cummins 15}

To 1790

Henry Wood (1715-93) obtained a British patent in 1759 on a proposal for a hot air engine.   The residual air in the cylinder would remain above atmospheric pressure and drive out the condensed air through a snifting pipe. ^{Cummins 14}

Jonathan Hornblower, a Watt competitor, in 1781 patented a rudimentary form of compound hot air engine, but by using condensers, infringed on Watt's patent. ^{Cummins 15}

1790-1799

1800-1809

In 1807, Sir George Cayley (1773-1857) was the first person to build a working model of Wood's earlier hot air engine proposal.   In 1837, he patented an improved design that was built by the Caloric Engine Company.   It drew a fresh air charge on each cycle into an enclosed, pressurized (by air pump), coal-fired furnace chamber.   The heated air, which was mixed with combustion products, then passed through a cylinder to raise the piston, was cooled, and then exhausted on the working stroke of the piston.   A serious problem was the scouring of the piston and cylinder walls by the ashes and cinders from the furnace.   His engine was produced in the U.S. in the 1860s.   The improved Buckett design was bult in Great Britain in the 1880s.   (Cayley also contributed to airplane design, but no lightweight engine existed in his time to test his theories.) ^{Cummins 15-16}

1810-1819

In 1816, Rev. Robert Stirling (1790-1878) patented a regenerative hot air engine with a closed cycle.   Air was contained in a cylinder closed at one end by a rigid plate and at the other end by a piston having a small clearance from the cylinder wall sealed by a ring of oil.   The cylinder diameter was nearly 2 feet and the length was nearly 10 feet.   As an example of its use, it pumped water from a quarry in Ayrshire, Scotland in 1818 and delivered 2 hp. ^{Cummins 17-20}

1820-1829

John Ericsson (1808-89), prolific inventor who was born in Sweden, resided in England for a period, and then came to the U.S. to invent the famous U.S.S. Monitor and promulgate the screw propeller that was invented by others.   He obtained his first hot air engine patent in Britain in 1826. ^{Cummins 24}

1830-1839

1840-1849

A double-acting Stirling engine rated at 45 hp and 30 rpm was installed in a Dundee foundry and ran for several years.   It was the last Stirling engine made. ^{Cummins 22}

1850-1859

1860-1869

Wilhelm Lehmann produces a modified Stirling engine in the 1860s. ^{Cummins 23}

1870-1879

A type of Stirling engine was patented in 1876 and built by Alexander Rider of Philadelphia.   It was rated of between ¼ and 1 hp. ^{Cummins 23}

1880-1889

1890-1899

1900-1909

1910-1919

1920-1929

1930-1939

1940-1949

1950-1959

In 1951, the first nuclear-powered generator began to produce electricity at the U.S. Reactor Testing Station in Idaho. ^{Carruth 555}

1960-1969

1970-1979

1980-1989

1990-1999