Engine

An engine or motor is a machine that changes energy into movement or work.

Engines can use many types of energy. These include potential energy from Earth's gravitational field, like in hydroelectric power generation. They can also use heat from geothermal sources, chemical energy, electric potential, and even nuclear energy from nuclear fission or nuclear fusion. Many engines create heat. Some natural processes, like rising air, also turn heat into movement.

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

Emission and byproducts

Engines that use chemicals to make heat send gases into the air. The cleanest engines only send out water. True zero-emissions means only water and water vapor come out. This can happen when pure hydrogen and pure oxygen are burned together, though some rocket engines almost do this. When hydrogen is burned with normal air, a small amount of a substance called NO_x is made 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 make water without releasing NO_x in a device called a fuel cell, but fuel cells are not heat engines; they work differently.

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 have been used since ancient times. These are examples of levers. More complex engines used human power, animal power, water power, wind power, and steam power. They date back to very old times. People 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.

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. Some were very complex, with aqueducts, dams, and sluices to maintain and channel the water, along with systems of gears. 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.

Medieval

Medieval Muslim engineers used gears in mills and water-raising machines, and used dams as a source of water power. 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 useful for propelling weaponry at high speeds towards enemies in battle and for fireworks.

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. 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. 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. In 1853–57 Eugenio Barsanti and Felice Matteucci invented and patented an engine using the free-piston principle.

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.

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. Engines of this design are often referred to as “flat” or “boxer” engines. They were used in the Volkswagen Beetle, the Citroën 2CV, some Porsche and Subaru cars, many BMW and Honda motorcycles.

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.

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.

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. The smaller engines were commonly air-cooled and located at the rear of the vehicle. The 1970s and 1980s saw an increased interest in improved fuel economy, which caused a return to smaller V-6 and four-cylinder layouts.

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.

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 loud. 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.