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Engine Efficiency

Steam Engines in the Industrial Revolution

Prior to about 1760 almost everything that was produced was produced by hand. For example ships, granite cobblestones, textiles. Using machines in production increase output, raise the standard of living for individuals and made nations wealthy. Machine production of textiles and international trade made Great Britain a wealthy nation in late 1700’s and early 1800. Use of machines requires harnessing power. Early power sources include water wheels and windmills. In early 1700’s people were thinking about how to use heat through the medium of steam to obtain useful power. After a number of attempts at producing a practical engine, later steam engines were used as power sources. A few key dates in development of steam engines and steam ships in the industrial revolution are:

1712: Newcomen Engine – More of an atmospheric engine than a real steam engine. Very inefficient but able to pump water from mines.
1804: Locomotive steam engine developed by Trevithick in England.
1807: Fulton’s steamboat operates between Albany and New York City.
1818: SS Savannah – Paddlewheel sailing vessel that used a steam engine to get in and out of port. Engine efficiency was low and the ship could not carry sufficient fuel to cross the entire Atlantic. Relied on sail power for most of trip.
1824: Sadi Carnot – published theories of maximum theoretical engine efficiency.
1835: Ship propeller invented, England.
1838: SS Great Western – first regularly scheduled cross Atlantic steam ship service. Paddle wheel steamer.
1894 – 1897: Turbinia, first steam turbine powered steamship.

Trevithick's Locomotive Engine.

Above Left: Model of the Turbinia. Above Right: Model of Fulton's steamboat.

Steam Engine Efficiency

Useful work out of an engine divided by the work that has to be put into the engine to achieve the work out. Always less than one. According to Carnot theories, the maximum efficiency can be expressed mathematically as:

n = (Tin - Tout)/Tin

Where is n the symbol for efficiency and Temperatures are expressed in absolute values.

To improve theoretical efficiency, either inlet temperature has to be increased or outlet temperature has to be decreased. In 1760 James Watt added a condensing chamber to a steam engine exhaust. The condenser, creates a vacuum and lowered the outlet temperature. A condenser typically operates at about 2 pounds per square inch absolute (psia) and 128 degree F. Atmospheric pressure is about 15 psia, so Watt’s engine exhausted to below atmospheric pressure. Early boilers produced steam at low pressure, typically about 200 psia and 600 degree F. Raising inlet temperature to improve efficiency, requires raising steam generator (boiler) pressure which is limited by the materials and construction of the boiler. Innovations occurring in the later half of 1800’s and early 1900’s that allowed higher pressure and efficiencies include improved:

Engine design (compound reciprocating, turbine)
Boiler design (fire tube boilers to water tube boilers)
Metallurgy of both boilers and engines
Boiler water chemistry to prevent corrosion and scale buildup
Thermodynamic cycle – use of superheated steam and extraction steam for air or feed-water heating. (Superheated steam is steam heated to a temperature greater than the saturated steam it came from)

These were high technology issues in early 1900’s.

Increased Power Demand

Steam engines of 1800’s used piston in a cylinder to transmit steams energy. There are various schemes for operating steam inlet valves and those schemes changed throughout the years. Mostly the inlet valve is controlled by mechanical linkage from the output shaft to the valve itself. A reciprocating engine with triple compound cylinders (first cylinder exhausted to second cylinder, second to third and third cylinder exhausted to a condenser) was common. Steam turbines became more prevalent in the 1900’s.

About 1880, Edison developed the incandescent lamp. By early 1900’s most major cities had electrified their cities which created a whole new and large demand for steam engines and the energy to generate the electricity. Steam plants became larger and more efficient and contributed to improved production. For many years coal was the dominant energy source for production of heat and power. Oil production increased rapidly after about 1900. Natural gas and other sources somewhat later.

Shipbuilding

Shipbuilders in the mid 1800’s and early 1900’s tried to capitalize on advancements in steam engines, conversion of wooden sailing ships to steel ships, and paddle wheelers to propeller driven steel steamships. Success of steel hulled USS Monitor and Confederate Steam Ship Virginia (1862) during the civil war mostly stopped construction of new wooden Navy Ships. Along the Delaware River in Camden and Philadelphia three shipyards were trying to take advantage of demand for new steel steam ships: