Engine

• 1. Introduction

  ›

  An engine is a machine designed to convert one or more forms of energy into mechanical energy. That single sentence hides an enormous family of machines, from the lever-like club and oar of prehistory to a diesel engine weighing 2,300 tonnes. Some run on the heat of burning fuel. Some run on falling water, compressed air, or a wound spring. Some even live inside muscle, where molecular motors turn chemical energy into the force of motion. So what counts as an engine, and what does not? Why does the word for a catapult also describe a jet? And how did a partial vacuum and a pressure just above the atmosphere reshape the world's factories? The answers run from Ancient Greece to a container ship launched in 2006.

• 2. The Word Itself

  ›

  The word engine derives from Old French, from the Latin ingenium. Long before factories, pre-industrial weapons of war carried the name. Catapults, trebuchets, and battering rams were called siege engines, and the knowledge of how to build them was often treated as a military secret. The word gin, as in cotton gin, is simply short for engine. Most mechanical devices invented during the Industrial Revolution were described as engines. The steam engine is the notable example, though the original steam engines built by Thomas Savery were not mechanical engines at all but pumps. A fire engine, in its original form, was merely a water pump, with the engine transported to the fire by horses. When the internal combustion engine arrived, the term motor came into use to distinguish it from the steam engine, which already powered locomotives and steam rollers. The term motor derives from a Latin noun meaning 'that which moves something.' In standard English, motor and engine are interchangeable. In some engineering jargon they part ways: an engine consumes fuel and changes its chemical composition, while a motor is driven by electricity, air, or hydraulic pressure without altering its energy source. Rocketry breaks even that rule, since a device that plainly burns fuel is still called a rocket motor.

• 3. Ancient Power

  ›

  Simple machines like the club and the oar, both examples of the lever, are prehistoric. More complex engines using human, animal, water, wind, and even steam power date back to antiquity. The capstan, the windlass, and the treadmill focused human effort, transmitting force that was multiplied while the speed was reduced through ropes, pulleys, and block and tackle. Cranes and ships in Ancient Greece relied on them, as did the mines, water pumps, and siege engines of Ancient Rome. Vitruvius, Frontinus, and Pliny the Elder wrote about such engines as commonplace, a sign their invention may be more ancient still. According to Strabo, a water-powered mill was built in Kaberia in the kingdom of Mithridates during the 1st century BC. Water wheels then spread through the Roman Empire, some fed by aqueducts, dams, and sluices, and regulated by wooden and metal gears. The Antikythera Mechanism used complex trains of gears and dials to act as a calendar and predict astronomical events. In the 4th century AD, the poet Ausonius mentioned a stone-cutting saw powered by water. A century earlier, Hero of Alexandria was credited with the Aeolipile and a vending machine, often built for worship in the form of animated altars and self-opening temple doors.

• 4. Medieval Innovation

  ›

  In 1206, al-Jazari employed a crank-conrod system for two of his water-raising machines. Medieval Muslim engineers fitted gears into mills and water-raising devices, and used dams to add power to their watermills, mechanizing industrial tasks that manual labour had always done by hand. A rudimentary steam turbine device was described by Taqi al-Din in 1551 and again by Giovanni Branca in 1629. In the 13th century, the solid rocket motor was invented in China. Driven by gunpowder, this simplest form of internal combustion engine could not deliver sustained power. It served instead to hurl weaponry at high speeds toward enemies and to launch fireworks, and from there the innovation spread throughout Europe.

• 5. Steam And Combustion

  ›

  The Watt steam engine was the first to use steam at a pressure just above atmospheric to drive the piston, helped along by a partial vacuum. It improved on the 1712 Newcomen steam engine and was developed sporadically from 1763 to 1775. James Watt's design became synonymous with steam engines, owing in no small part to his business partner Matthew Boulton, and it enabled efficient semi-automated factories on a scale never seen before, even where waterpower was absent. Internal combustion piston engines came next. They were tested in France in 1807 by de Rivaz and independently by the Niepce brothers, then advanced theoretically by Carnot in 1824. In 1853 to 1857, Eugenio Barsanti and Felice Matteucci invented and patented an engine using the free-piston principle, possibly the first 4-cycle engine. A commercially successful internal combustion engine arrived in 1860, the work of Etienne Lenoir. By 1877, the Otto cycle delivered a far higher power-to-weight ratio than steam and suited cars and aircraft far better, setting the stage for the first commercially successful automobile created by Karl Benz.

• 6. The Automobile Engine

  ›

  In 1897, Karl Benz was granted a patent for the first engine with horizontally opposed pistons. In his design, corresponding pistons move in horizontal cylinders and reach top dead center at the same moment, balancing each other by their own momentum. Their shape and low profile earned them the names 'flat' and 'boxer,' and they powered the Volkswagen Beetle, the Citroen 2CV, some Porsche and Subaru cars, and many BMW and Honda motorcycles. Opposed four- and six-cylinder versions still drive small propeller aircraft. The lightweight gasoline engine running a four-stroke Otto cycle proved best for light automobiles, while the thermally more efficient Diesel engine took over trucks and buses. Diesel engines are 40% more fuel efficient than comparable gasoline engines, though they produce greater particulate pollution. Engines have ranged from 1- to 16-cylinder designs, with four cylinders and ratings from 19 to 120 hp, that is 14 to 90 kW, dominating most models. The higher forces of more powerful engines created vibration and size problems, pushing designers toward stiffer, more compact V and opposed layouts in place of long straight arrangements. The 1970s and 1980s brought a hunger for fuel economy and a return to smaller V-6 and four-cylinder layouts, with as many as five valves per cylinder. The Bugatti Veyron 16.4 runs a W16 engine, two V8 layouts set side by side to share one crankshaft.

• 7. Scale And Emissions

  ›

  The largest internal combustion engine ever built is the Wartsila-Sulzer RTA96-C, a 14-cylinder, 2-stroke turbocharged diesel designed to power the Emma Maersk, the largest container ship in the world when launched in 2006. The engine has a mass of 2,300 tonnes. Running at 102 rpm, or 1.7 Hz, it produces over 80 MW and can burn up to 250 tonnes of fuel per day. Every chemically fueled heat engine emits exhaust, and the cleanest emit only water. By a strict definition, only engines that combust pure hydrogen with pure oxygen reach zero-emission, achieved in practice by some rocket engines. Exhaust gas from a spark ignition engine is mostly nitrogen, at 70 to 75% by volume, with water vapor at 10 to 12% and carbon dioxide at 10 to 13.5%. It also carries carbon monoxide, which is highly toxic and dangerous to let build up in a confined space. Catalytic converters can reduce these toxic emissions but cannot eliminate them. The carbon dioxide from widespread engine use contributes to the global greenhouse effect, a central concern in global warming.

• 8. Beyond Combustion

  ›

  Not every engine burns fuel, and not every motor is a heat engine. An electric motor turns electrical energy into mechanical energy through the interaction of magnetic fields and current-carrying conductors, and reversing the process yields a generator or dynamo. The physical principle behind it was known as early as 1821, though large-scale use had to wait for efficient generators and distribution networks built up across the 19th century. Electric motors are everywhere, from the smallest found in electric wristwatches to the very largest used to propel large ships and drive pipeline compressors at thousands of kilowatts. A well-designed motor can convert over 90% of its input energy into useful power for decades, and even a few percentage points of added efficiency yield enormous savings in kilowatt hours. Pneumatic motors convert compressed air into work and have thrived in hand-held tools, while hydraulic motors draw power from pressurized liquid to move heavy loads. Some engines never combust anything yet still make heat into work. A nuclear power plant uses reaction heat to raise steam, Stirling engines run a closed thermodynamic cycle between a hot and a cold cylinder, and thermoacoustic engines trade between heat differences and high-amplitude sound waves. In biological systems, molecular motors like the myosins in muscle use chemical energy to create force, a chemical engine that is not a heat engine at all.