Steam Engines and Future Trends
Steam Engines and Future Trends in Marine Engines
Steam Engine – The purpose of a steam engine is to convert the heat energy of burning coal or oil (usually) to mechanical energy of a rotating shaft. For a marine steam engine, the rotating shaft drives a paddlewheel or propeller to move the ship. The term steam engine sometimes refers to just the mechanical device that converts steam pressure to reciprocating motion of a piston in a cylinder. At other times the term refers to all the machinery needed from heat input to output shaft including boiler, steam pipe, piston in a cylinder (or alternate mechanism), a mechanical device for converting the reciprocating motion to rotary motion, a condenser for turning the exhaust steam back to water, and a pump(s) for adding water back into the boiler
Work – The output shaft of a steam engine performs work when it moves the ship forward. Work is measured by force times a distance. In international SI units - Work (Joule) = newton - meter
Steam Engines up to about 1873 – Beam Engines - Characteristics of early steam engines were reciprocating piston in a cylinder, low steam operating pressure and large diameter pistons in order to get power out of the machine. The first early practical steam engine was the 1765 James Watt engine. Watt was the first to add a condenser to lower the engine exhaust temperature and pressure for higher efficiency. It had a high beam that connected the steam piston to a gear system that created rotary motion. The high beam also operated the condensate and boiler feedwater pump.
James Watt steam engine 1765, first practical steam engine
1807 Robert Fulton built a paddlewheel steamer for service on the Hudson River between NY City and Albany.
Common features in subsequent engines were some form of a beam or side levers that connected reciprocating movement of a piston in a cylinder to a gear system for rotary movement. Another example is the 1838 paddle wheel ship Great Western. It had two side lever reciprocating engines that operated at about 4 psia to operate paddlewheels. Great Western was the first steamship for regular scheduled service across the Atlantic.
1838 paddlewheel ship Great Western.
1845 A tug of war between a propeller driven ship and paddlewheel ship, won by the propeller ship demonstrated propeller effectiveness.
Steam pressures kept increasing over the years and reached about 60 psi by 1865. The last example is the engines for Training Vessel Emery Rice (1873) (AKA USS Ranger). It had a low profile steam engine that was located below the waterline of the ship for protection from enemy shelling. The steam engine from TV Emery Rice is located in a museum at Kings Point Maritime Academy, New York.
Low profile steam engine in TV Emory Rice.
Steam Engines – late 1800’s – vertical expansion engines - By the late 1800’s, ship steam engine design were mostly reciprocating vertical compound expansion engines. Compound expansion means that steam is expanded in two or more stages. The first stage or high pressure cylinder receives boiler pressure steam, expands the steam and then exhausts the steam to a second larger diameter cylinder to extract more of the steam energy. Typical arrangement is for a triple expansion engine where the second cylinder exhausts to a third cylinder before the third cylinder exhausts to a condenser. Triple expansion and quadruple expansion engines were common. Pistons in the vertical cylinders operated a piston rod that operated a crankshaft to convert reciprocating motion to rotary motion. The crank shaft was connected to the ships propeller shaft.
1893 ship Christopher Columbus and its triple expansion steam engine.
1893 SS Christopher Columbus had 2 triple expansion reciprocating steam engines with cylinders 26, 42 and 70 inches in diameter. Another example is the engine used in the Liberty ships of WWII. By world war II, the steam turbine was more commonly used but Liberty ships used reciprocating engines because they could not get the big reduction gears needed for steam turbines produced in a war time manufacturing environment. The Liberty ships were 440 foot long, 59-foot beam, capable of 11.5 knots speed, had 1 propeller. The steam system operated at 220 psi, 450 degree F, 2500 HP and consumed about 170 barrels of oil per day.
SS Hellas Liberty and a Liberty ship steam engine.
Steam engines after about 1897 – Turbines – Early 1900’s saw a shift from reciprocating steam engines to turbine steam engines. The dominant marine steam engine in the early 1900’s was an oil-fired boiler, steam turbine with a reduction gear driving a propeller
1897 -The ship Turbinia demonstrated an axial flow (along the shaft) steam turbine. The turbine is a series of blades that create a nozzle that directs steam through several stages of steam expansion. The steam turbine is more efficient than a reciprocating engine but it requires a big reduction gear to transform the high-speed turbine to a low speed propeller shaft. Without the reduction gear, propellers rotate too fast creating cavitation. Turbinia found out about the issue of propeller cavitation the hard way. Turbinia use of steam turbine was set back several years until they overcame propeller cavitation. Cavitation is caused by the propeller accelerating liquid and creating a low-pressure area around the propeller. The low pressure allows formation of a vapor bubble. The sudden collapse of the vapor bubble after the propeller moves forward and pressure returns to surrounding pressure causes erosion of propeller surface and loss of efficiency.
1897 Turbinia, 104 foot long, 9 foot beam, 3 shafts, operating on 200 psi steam pressure and capable of 34 knots.
1910 Electric motor propeller shaft drive - The Navy set up three ships with different propulsion mechanisms; reciprocating steam, steam turbine/geared shaft drive and turbine – electric drive. The turbine electric system proved better in many respects.
1918 – Battleship New Mexico, the first Navy Battleship to use a turbine generator – electric motor propulsion drive system proved operational acceptability.
1925 – Shift to oil for fuel - The USS Texas was the last battleship to use coal for propulsion (converted to oil).
Left - USS Texas BB35 built 1914 and converted to oil 1925.
Above - USS New Mexico BB40 1918 turbo-electric drive.
Gas turbines and diesel engines replace steam engines
1950 – Since the 1950’s diesel or gas turbine engines has supplanted steam engines for main propulsion engines except for nuclear powered ships.
Compression ignition or Diesel internal combustion engine – In 1893, Rudolph Diesel published an essay about a compression ignition internal combustion engine. A prototype engine was built and tested about 1897. By about 1912, the ocean going ship Selandia was operating on diesel engines and proving acceptable operation. The diesel engine has proven more fuel efficient than steam turbine systems resulting in rapid adoption of diesels for ship propulsion. The rapid increase in fuel oil price since about 2003 added to the shift to diesel engines. Railroads reported the cost of operating a steam locomotive at 70 cents per mile vs diesel cost of 31 cents per mile.
1984 - The last cruise ship to be built with steam engines was the Atlantic Star (AKA Fairsky).
1987 - The Cunard Line passenger ship QE2, built in 1969 with steam turbines, converted to diesel electric propulsion with a reported 35% savings in operating fuel costs. The ship is 963 feet long, 105 foot beam.
1987 - Gas turbines – GAS turbine propulsion systems are preferred for larger displacement ships, diesel for smaller vessels.
1967 Ship GTS Admiral William Callaghan, gas turbines propulsion.
For environmental reasons there is also a shift to use of natural gas as a fuel, shift to low sulphur (sulfur) fuel oil and improved fuel injection system (common rail fuel injection).