Engine

An engine or motor is a machine designed to convert one or more forms of energy into mechanical energy. This means that engines take energy from different sources and turn it into movement or work that we can see and use.

Energy sources for engines include potential energy like the energy from Earth's gravitational field used in hydroelectric power generation, heat from geothermal sources, chemical energy, electric potential, and even nuclear energy from nuclear fission or nuclear fusion. Many of these processes create heat, making heat engines very important. Some natural processes, like rising air currents, also turn heat into movement.

Mechanical heat engines change heat into work through different processes. The internal combustion engine is a common example, where heat from burning fuel makes gases expand and push a piston, turning a crankshaft. Other engines, like jet engines, create movement by pushing out mass in the opposite direction, following Newton's third law of motion. Besides heat engines, there are also electric motors that use electricity, pneumatic motors that use compressed air, and even tiny clockwork motors in wind-up toys that use stored elastic energy.

Emission and byproducts

All engines that use chemicals to produce heat release gases into the air. The cleanest engines only release water. True zero-emissions means only water and water vapor are released. This happens only when pure hydrogen and pure oxygen are burned together, though some rocket engines come close. When hydrogen is burned with normal air, a small amount of a substance called NO_x is created because of a reaction between oxygen and nitrogen in the air. If fuels like alcohol or gasoline are burned, carbon dioxide (a greenhouse gas) is released. Hydrogen and oxygen can also create water without releasing NO_x in a device called a fuel cell, but fuel cells are not heat engines; they work in a different way.

Terminology

The word engine comes from old words in Old French and Latin. Long ago, tools used in war like catapults and trebuchets were called siege engines. During the Industrial Revolution, many new machines were called engines, such as the steam engine.

Today, an engine is a device that uses fuel to do work by creating movement. This can be turning something (like in a car) or pushing forward (like in a rocket). Motors are devices that make things move using electricity or other power sources, but engines create their own power by using fuel.

History

Antiquity

Simple machines like clubs and oars, which are examples of levers, have been used since ancient times. More complex engines that used human power, animal power, water power, wind power, and even steam power date back to very old times. Humans used simple engines such as capstans, windlasses, or treadmills, along with ropes, pulleys, and block and tackle arrangements. These were used in cranes and ships in Ancient Greece, and in mines, water pumps, and siege engines in Ancient Rome. Writers from those times treated these engines as normal, so they may have been invented even earlier. By the 1st century AD, cattle and horses were used in mills, driving machines similar to those powered by humans before.

A water-powered mill was built in Kaberia of the kingdom of Mithridates during the 1st century BC. The use of water wheels in mills spread throughout the Roman Empire over the next few centuries. Some were very complex, with aqueducts, dams, and sluices to maintain and channel the water, along with systems of gears, or toothed-wheels made of wood and metal to regulate the speed of rotation. More sophisticated small devices, such as the Antikythera Mechanism, used complex trains of gears and dials to act as calendars or predict astronomical events. In a poem by Ausonius in the 4th century AD, he mentions a stone-cutting saw powered by water. Hero of Alexandria is credited with many such wind and steam powered machines in the 1st century AD, including the Aeolipile and the vending machine, often these machines were associated with worship, such as animated altars and automated temple doors.

Medieval

Medieval Muslim engineers used gears in mills and water-raising machines, and used dams as a source of water power to provide additional power to watermills and water-raising machines. In the medieval Islamic world, such advances made it possible to mechanize many industrial tasks previously carried out by manual labour.

In 1206, al-Jazari employed a crank-conrod system for two of his water-raising machines. A rudimentary steam turbine device was described by Taqi al-Din in 1551 and 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 was unable to deliver sustained power, but was useful for propelling weaponry at high speeds towards enemies in battle and for fireworks. After invention, this innovation spread throughout Europe.

Industrial Revolution

The Watt steam engine was the first type of steam engine to make use of steam at a pressure just above atmospheric to drive the piston helped by a partial vacuum. Improving on the design of the 1712 Newcomen steam engine, the Watt steam engine, developed sporadically from 1763 to 1775, was a great step in the development of the steam engine. Offering a dramatic increase in fuel efficiency, James Watt's design became synonymous with steam engines, due in no small part to his business partner, Matthew Boulton. It enabled rapid development of efficient semi-automated factories on a previously unimaginable scale in places where waterpower was not available. Later development led to steam locomotives and great expansion of railway transportation.

As for internal combustion piston engines, these were tested in France in 1807 by de Rivaz and independently, by the Niépce brothers. They were theoretically advanced by Carnot in 1824. In 1853–57 Eugenio Barsanti and Felice Matteucci invented and patented an engine using the free-piston principle that was possibly the first 4-cycle engine.

The invention of an internal combustion engine which was later commercially successful was made during 1860 by Etienne Lenoir.

In 1877, the Otto cycle was capable of giving a far higher power-to-weight ratio than steam engines and worked much better for many transportation applications such as cars and aircraft.

Automobiles

The first commercially successful automobile, created by Karl Benz, added to the interest in light and powerful engines. The lightweight gasoline internal combustion engine, operating on a four-stroke Otto cycle, has been the most successful for light automobiles, while the thermally more-efficient Diesel engine is used for trucks and buses. However, in recent years, turbocharged Diesel engines have become increasingly popular in automobiles, especially outside of the United States, even for quite small cars.

Horizontally-opposed pistons

In 1897, Karl Benz was granted a patent for his design of the first engine with horizontally opposed pistons. His design created an engine in which the corresponding pistons move in horizontal cylinders and reach top dead center simultaneously, thus automatically balancing each other with respect to their individual momentum. Engines of this design are often referred to as “flat” or “boxer” engines due to their shape and low profile. They were used in the Volkswagen Beetle, the Citroën 2CV, some Porsche and Subaru cars, many BMW and Honda motorcycles. Opposed four- and six-cylinder engines continue to be used as a power source in small, propeller-driven aircraft.

Advancement

The continued use of internal combustion engines in automobiles is partly due to the improvement of engine control systems, such as on-board computers providing engine management processes, and electronically controlled fuel injection. Forced air induction by turbocharging and supercharging have increased the power output of smaller displacement engines that are lighter in weight and more fuel-efficient at normal cruise power. Similar changes have been applied to smaller Diesel engines, giving them almost the same performance characteristics as gasoline engines. This is especially evident with the popularity of smaller diesel engine-propelled cars in Europe. Diesel engines produce lower hydrocarbon and CO₂ emissions, but greater particulate and NO_x pollution, than gasoline engines. Diesel engines are also 40% more fuel efficient than comparable gasoline engines.

Increasing power

In the first half of the 20th century, a trend of increasing engine power occurred, particularly in the U.S. models. Design changes incorporated all known methods of increasing engine capacity, including increasing the pressure in the cylinders to improve efficiency, increasing the size of the engine, and increasing the rate at which the engine produces work. The higher forces and pressures created by these changes created engine vibration and size problems that led to stiffer, more compact engines with V and opposed cylinder layouts replacing longer straight-line arrangements.

Combustion efficiency

Optimal combustion efficiency in passenger vehicles is reached with a coolant temperature of around 110 °C (230 °F).

Engine configuration

Earlier automobile engine development produced a much larger range of engines than is in common use today. Engines have ranged from 1- to 16-cylinder designs with corresponding differences in overall size, weight, engine displacement, and cylinder bores. Four cylinders and power ratings from 19 to 120 hp (14 to 90 kW) were followed in a majority of the models. Several three-cylinder, two-stroke-cycle models were built while most engines had straight or in-line cylinders. There were several V-type models and horizontally opposed two- and four-cylinder makes too. Overhead camshafts were frequently employed. The smaller engines were commonly air-cooled and located at the rear of the vehicle; compression ratios were relatively low. The 1970s and 1980s saw an increased interest in improved fuel economy, which caused a return to smaller V-6 and four-cylinder layouts, with as many as five valves per cylinder to improve efficiency. The Bugatti Veyron 16.4 operates with a W16 engine, meaning that two V8 cylinder layouts are positioned next to each other to create the W shape sharing the same crankshaft.

The largest internal combustion engine ever built is the Wärtsilä-Sulzer RTA96-C, a 14-cylinder, 2-stroke turbocharged diesel engine that was designed to power the Emma Mærsk, the largest container ship in the world when launched in 2006. This engine has a mass of 2,300 tonnes, and when running at 102 rpm (1.7 Hz) produces over 80 MW, and can use up to 250 tonnes of fuel per day.

Types

An engine can be grouped based on two main factors: the type of energy it uses to create motion, and the kind of motion it produces.

Heat engine

Main article: Heat engine

Combustion engine

Combustion engines are heat engines that work by using the heat from burning fuel.

Internal combustion engine

Main article: Internal combustion engine

The internal combustion engine burns fuel, usually oil, with air inside a special chamber. The burning creates hot gases that push parts of the engine, like pistons or blades, which then create movement.

External combustion engine

Main article: External combustion engine

An external combustion engine heats a special fluid by burning fuel outside the main engine part. This heated fluid then moves parts of the engine to create motion. The fluid can be a gas, like in a Stirling engine, or even steam, as in a steam engine.

Air-breathing combustion engines

Air-breathing combustion engines use oxygen from the air to burn fuel. A stream of air flows through the engine, mixes with fuel, gets ignited, and then leaves as exhaust gas. This process helps create movement or thrust.

Examples include:

Non-thermal chemically powered motor

Non-thermal motors are powered by chemical reactions but do not use heat. Examples include:

Molecular motor – motors found in living things
Synthetic molecular motor

Electric motor

Main articles: Electric motor and Electric vehicle

An electric motor uses electricity to create movement, usually by using magnetic fields and electric currents. The reverse process, creating electricity from movement, is done by a generator. Electric motors are used in many things, from small appliances to large industrial machines. They can run on direct current (like from a battery) or alternating current (from a power grid).

Physically powered motor

Some motors use energy from things like moving water, gravity, compressed air, or springs to create movement. For example, old clocks used weights that fall due to gravity, and some tools use compressed air to work.

Pneumatic motor

Main article: Pneumatic motor

A pneumatic motor uses compressed air to create movement. These motors are often used in handheld tools and are being tested for use in vehicles, though they need to become more efficient to be widely used.

Hydraulic motor

Main article: Hydraulic motor

A hydraulic motor uses pressurized liquid to move heavy loads and power machinery.

Hybrid

Some motors can use more than one energy source. For example, a plug-in hybrid electric vehicle can use electricity from a battery or from burning fuel using an internal combustion engine and a generator.

Performance

Engines are judged by how well they work. We look at several important things to understand this.

Speed tells us how fast parts of the engine are turning. We measure this in revolutions per minute, or rpm.

Thrust is the push that helps airplanes and ships move forward. It happens when the engine makes air or water move faster in one direction.

Torque is the twisting force that makes things turn. It depends on how strong the push is and how far away it is from the center of turning.

Power measures how quickly an engine can do work.

Efficiency looks at how much useful energy the engine makes compared to all the energy it uses.

Finally, we think about sound levels. Engines can be noisy, especially at low speeds. Electric motors are usually quieter than other types of engines. Some engines, like those on airplanes, can be very loud because of how they push air out. There are ways to make engines quieter, like using special parts called mufflers or liners inside the engine.

Engines by use

Engines come in many types and are used for different purposes. Some notable kinds include engines for aircraft, automobiles, models, motorcycles, and boats like outboard motors. There are also engines for machinery that isn’t on roads, engines for railway locomotives, engines for spacecraft propulsion such as rocket engines, and engines for traction.