Inside the engines powering life at sea
For more than two centuries we’ve relied on engines to power our exploration, travel and trade on the seas.
With each new generation of engine technologies, we’ve travelled faster and safer with less impact on the environment.
It’s been a long, exciting journey since the early days when the wind carried the First Fleet’s eleven ships to Sydney Cove on January 26, 1788.
To recognise their voyage this Australia Day, and the spirit of adventure behind marine engine development, here is a look at the technologies that helped connect the world.
Sailing by steam
Marine steam engines emerged during the early 19th century and became a popular propulsion method for turning paddle wheels and propulsion screws, or what’s today called the propeller.
These external combustion engines used wood, coal or fuel oil to fire the burners that turned water into steam inside large boilers, or pressurised tanks. The steam was then used to drive pistons moving inside a cylinder, which then turned the drive mechanism.
Andy Munns, an engineer and teacher at Sydney Heritage Fleet, said the primary advantage of steam engines was releasing ships from the limitations of variable wind conditions.
As metallurgy improved, early copper and wrought iron engines were replaced with stronger steel engines. “Cheaper and higher quality steel led to higher quality pressures and more powerful engines,” he explained.
Three piston models known as triple-expansion engines let steam flow through successively smaller cylinders. The steam also cools through each stage before being recycled in the boiler.
The steam engine reached its zenith with triple-expansion engines featuring vertical pistons, an efficient design that’s echoed in the internal combustion engines of today.
As internal combustion engine technology developed through the 19th and 20th centuries, reciprocating diesel engines superseded steam turbines as more efficient and reliable power sources.
The diesel engine, or compression-ignition engine, followed the invention of the gasoline engine in the late 1800s. Both diesel and gasoline engines use a spark or small explosion to convert chemical energy from fuels into mechanical energy that push pistons inside cylinders. Like steam engines, the pistons drive a crankshaft and propeller.
However, unlike gasoline (or petrol) engines that use a spark to ignite the fuel, diesel engines use the heat generated by compressed air to ignite the fuel.
The main advantage of this approach, Mr Munns explained, is they’re about 30 percent energy efficient, compared to the 15 percent efficiency of a marine steam engine, or the 20 percent efficiency of a car engine.
“The energy doesn’t go into boiling steam and throwing it away,” he said. “With diesel, you transfer the energy directly to the piston.”
Diesel engines remain dominant in marine vessels today because of their simplicity, reliability and ability to generate significant amounts of power at slower engine speeds.
The age of gas turbines
Gas turbine engines emerged towards the end of World War II in German aircraft, such as the Messerschmitt.
Early examples were not as efficient as diesel engines, however gas turbines produced significant amounts of power and were very light, making them ideal for aircraft.
In marine applications, the same advantages apply. Mr Munns said gas turbine technology still operates using the four stroke principle found in diesel and gasoline engines. Air is drawn into a cylinder, compressed, injected with fuel, and the resulting exhaust gases drive the propeller.
Today the advances in gas turbines are coupled with developments in the variety and costs of available fuels.
For example, GE’s LM gas turbine engines run on marine gas oil (MGO), bio diesel, bio-synthetic parraffinic kerosene bends and liquid natural gas (LNG). Cleaner fuels such as LNG are good for the environment and reduce maintenance costs. “The developments are all driven by fuel costs,” Mr Munns said.
In the future, technologies such as Dry Low Emissions (DLE) engines will improve emissions through near-optimum fuel-air distribution and reduced NOx and CO outputs.
The use of hybrid diesel, gas turbine and electric propulsion will also continue to shape engine technologies and new marine vessels.
For example, electric propulsion technology is being used to power ships like the world’s largest ocean liner RMS Queen Mary 2