Internal combustion engine

An internal combustion engine (ICE or IC engine) is a type of heat engine. In this engine, fuel burns with an oxidizer (usually air) inside a special space called a combustion chamber. This burning creates hot, high-pressure gases. These gases push parts of the engine, such as pistons or turbine blades. This movement changes the energy in fuel into motion. The motion can power cars, planes, boats, and more.

The first successful internal combustion engines were made in the mid-1800s. A key design, the Otto engine, was created in 1876 by German engineer Nicolaus Otto. Most common internal combustion engines work in steps, like the two-stroke or four-stroke engines found in many vehicles today. Others, like gas turbines and jet engines, work differently but still use the same basic idea.

These engines are mostly used in vehicles such as cars, aircraft, and boats. They usually run on fuels made from hydrocarbons, such as gasoline or diesel fuel. Some engines can also use renewable fuels like biodiesel or bioethanol. Even hydrogen can be used, though it is less common.

History

Main article: History of the internal combustion engine

Many smart people helped create engines that burn fuel. In 1791, John Barber made a gas turbine. In 1794, Robert Street made an engine that used liquid fuel. In 1807, Nicéphore Niépce and Claude Niépce in France ran an early engine. In 1807, a Swiss engineer made a car that used hydrogen. In 1823, Samuel Brown made the first engine for work.

Later, in 1854, two inventors in the UK got a certificate for making power. In 1860, a Belgian engineer made a gas engine. In 1876, inventors in Germany made a better engine. In 1879, another inventor made a simple gasoline engine. In 1886, the first cars with these engines were sold. In 1939, the world’s first jet aircraft flew.

Etymology

Long ago, the word engine meant any kind of machine. This idea is still used in phrases like siege engine. A motor is a machine that makes mechanical power. Usually, electric motors are not called engines, but combustion engines can sometimes be called motors. In boats, engines placed inside the boat are called engines, while those placed on the back are called motors.

Applications

Reciprocating piston engines are the most common power source for land and water vehicles, including automobiles, motorcycles, ships and to a lesser extent, locomotives (some are electrical but most use diesel engines). Rotary engines of the Wankel design are used in some automobiles, aircraft and motorcycles. These are collectively known as internal-combustion-engine vehicles (ICEV).

Where high power-to-weight ratios are required, internal combustion engines appear in the form of combustion turbines, or sometimes Wankel engines. Powered aircraft typically use an ICE which may be a reciprocating engine. Airplanes can instead use jet engines and helicopters can instead employ turboshafts; both of which are types of turbines. In addition to providing propulsion, aircraft may employ a separate ICE as an auxiliary power unit. Wankel engines are fitted to many unmanned aerial vehicles.

ICEs drive large electric generators that power electrical grids. They are found in the form of combustion turbines. Combined cycle power plants use the high temperature exhaust to boil and superheat water steam to run a steam turbine.

In a smaller scale, small engines are a common power source for lawnmowers, string trimmers, chainsaws, leaf blowers, pressure washers, radio-controlled cars, snowmobiles, jet skis, outboard motors, mopeds, and motorcycles.

Classification

There are many ways to group internal combustion engines.

Reciprocating

Engines can be sorted by how many strokes they use:

• Two-stroke engine
• Four-stroke engine (Otto cycle)
• Six-stroke engine

They can also be sorted by how they start burning fuel:

• Compression-ignition engine
• Spark-ignition engine (commonly found as gasoline engines)

Some less common ways to sort them are used in hybrid vehicles and other vehicles made for fuel efficiency:

• Atkinson cycle
• Miller cycle

Rotary

For rotating-crankcase radial-cylindered engines, see Rotary engine.

• Wankel engine
• Pistonless rotary engine

Continuous combustion

• Gas turbine engine
  • Turbojet, through a propelling nozzle
  • Turbofan, through a duct-fan
  • Turboprop, through an unducted propeller, usually with variable pitch
  • Turboshaft, a gas turbine optimized for producing mechanical torque instead of thrust
• Ramjet, similar to a turbojet but uses vehicle speed to compress (ram) the air instead of a compressor.
• Scramjet, a variant of the ramjet that uses supersonic combustion.
• Rocket engine

Reciprocating engines

See also: Diesel engine, Gasoline engine, and Reciprocating engine

Structure

The base of a reciprocating internal combustion engine is the engine block, made of cast iron or aluminum. The engine block holds the cylinders. Engines with more than one cylinder usually have them in 1 row (straight engine) or 2 rows (boxer engine or V engine). Single-cylinder engines are common for motorcycles and small engines. The pistons are short parts that fit inside the cylinders and move up and down while the engine runs.

The cylinder head attaches to the engine block with bolts or studs. It has small passages for air and gases, and valves that open and close. These valves are often poppet valves but can also be rotary valves or sleeve valves. The cylinder head holds the spark plug for spark ignition engines and the injector for some engines. A head gasket stops gases from leaking between the cylinder head and the engine block. The valves are controlled by one or more camshafts and springs.

The bottom of the engine, called the crankcase, has a part called a sump that holds oil. Inside, a crankshaft changes the up-and-down motion of the pistons to spinning motion. The crankshaft stays in place with main bearings. A connecting rod links the piston to the crankshaft through the gudgeon pin, turning the piston's motion into the crankshaft's spin.

The cylinder head has an intake manifold and an exhaust manifold. The intake manifold connects to the air filter or a carburetor, which then connects to the air filter. It sends air to the cylinders. The exhaust manifold starts the exhaust system.

Four-stroke engines

Main article: Four-stroke engine

The top dead center (TDC) of a piston is when it is closest to the valves; bottom dead center (BDC) is the opposite. A stroke is when the piston moves from TDC to BDC or back. In a 4-stroke engine, each piston does two strokes for every turn of the crankshaft:

1. Intake: The intake valve opens, the piston moves down, and air or a mix of air and fuel enters the combustion chamber.
2. Compression: Both valves close, the piston moves up, and the mix is compressed. Near the top, the mix ignites.
3. Power: The burning mix pushes the piston down, making energy.
4. Exhaust: The exhaust valve opens, the piston moves up, and the gases leave. The cycle then starts again.

Two-stroke engines

Main article: Two-stroke engine

In a two-stroke engine, each piston finishes a cycle every turn of the crankshaft. The four steps happen in two strokes:

1. Power: The burning gases push the piston down.
2. Scavenging: The exhaust leaves, and new air or mix enters.
3. Compression: Both valves close, the piston moves up, and the mix is compressed. Near the top, the mix ignites.

Ignition

Internal combustion engines need to ignite the mix, either by spark ignition (SI) or compression ignition (CI).

Spark ignition process

Main article: Spark-ignition engine

The spark-ignition engine improves on early engines. Bosch made the magneto, which creates electricity for the spark plug. The battery gives power to start the engine and runs things when the engine is off. Gasoline engines mix air and gasoline, compress it, and ignite it as the piston moves.

Compression ignition process

Main article: Diesel engine

Diesel engines use high temperature and pressure from compression to ignite the fuel. They take in air and, just before the piston reaches the top, spray in diesel fuel, which ignites right away.

Lubrication

Moving parts need lubrication to stop wear and work better. Engines need lubrication in many places. In some engines, oil is mixed with the air and fuel and burns with the fuel.

Cylinder configuration

Common ways to arrange cylinders are the straight or inline configuration, the V configuration, and the flat or boxer configuration. Engines with many cylinders arrange their parts so pistons are at different points in their cycles.

Diesel cycle

Main article: Diesel cycle

Most diesel engines for trucks and cars use a cycle like a four-stroke cycle, but they ignite the fuel by heating it through compression, not with a separate system.

Otto cycle

The Otto cycle is the most common cycle for cars using gasoline. It has the same steps as the four-stroke engine: Intake, compression, ignition, expansion, and exhaust.

Five-stroke engine

In 1879, Nicolaus Otto made a double expansion engine. In the 21st century Ilmor made and tested a 5-stroke engine with good power and fuel use.

Six-stroke engine

The six-stroke engine was invented in 1883. These engines have a regular piston and fire every three turns of the crankshaft.

Other cycles

The first internal combustion engines did not compress the mix. There are many variations, like the Atkinson and Miller cycles. Split-cycle engines separate the steps into two paired cylinders.

Combustion turbines

Jet engine

Main article: Jet engine

Jet engines use fan blades to squeeze air. This air goes into a special part called a combustor, where it mixes with fuel and catches fire. The hot air then shoots out of the engine, pushing the jet forward. Modern jet engines can be very efficient.

There are six important parts in a jet engine:

• Fan
• Compressor
• Combustor
• Turbine
• Mixer
• Nozzle

Gas turbines

Main article: Gas turbine

A gas turbine squeezes air and uses it to spin a turbine. It’s like a jet engine, but instead of pushing the jet forward, it turns a shaft. Here’s how it works: air gets squeezed, fuel is added and burns, and the hot air spins turbine blades that turn the shaft.

Gas turbines have three main parts: a compressor, a combustion chamber, and a turbine. The air gets very hot after being squeezed, and this heat makes the turbine spin. Most of the spinning power goes back to the compressor, and some of it can be used to do useful work.

Gas turbines are very efficient.

Brayton cycle

Main article: Brayton cycle

A gas turbine works like a spinning machine similar to a steam turbine. It has three main parts: a compressor, a combustion chamber, and a turbine. The air gets squeezed by the compressor, then it gets even hotter when fuel burns in the combustion chamber. This makes the turbine spin, which powers the compressor. The hot air then shoots out to push or provide power.

These engines work by continuously compressing, burning fuel, and expanding air at the same time in different parts of the engine, giving constant power.

Wankel engines

Main article: Wankel engine

Wankel engines, also called rotary engines, work in a different way from engines with pistons. Instead of pistons moving up and down, a rotor spins to move air and fuel through the engine. These engines follow the same basic steps as other engines but do it in a special way. They can make power more often with each spin, which makes them strong for their size. This type of engine was used in cars like the Mazda RX-8 and RX-7, as well as in small flying machines where their small size and strength are useful.

Forced induction

Main article: Forced induction

Forced induction is a way to push more air into an engine to make it stronger. It uses a special gas compressor to squeeze the air before it goes into the engine. Engines without this are called naturally aspirated engines.

People use forced induction in cars and planes to help engines work better. There are two main ways to do this: with a supercharger, which gets power directly from the engine, or with a turbocharger, which uses the engine’s exhaust to power a turbine.

Fuels and oxidizers

All internal combustion engines need a special fuel to work, usually mixed with oxygen from the air. When the fuel burns, it makes heat and energy, which helps the engine run. The temperature of the burning depends on the kind of fuel used.

Fuels

The most common fuels for these engines come from things like petroleum, such as gasoline, diesel, and propane. Some engines can also use biofuels like ethanol or biodiesel, made from crops. There are experiments with fuels like hydrogen gas or wood gas.

Diesel engines are often heavier and stronger at low speeds, used in big vehicles like trucks and ships. Gasoline engines are used in most cars and motorcycles. Some cars in Europe use diesel engines because they can save fuel.

Oxidizers

Usually, the oxygen we breathe in the air is used as the oxidizer in these engines. This makes the engines lighter and stronger. For special uses, like in torpedoes or rockets, other materials such as compressed air or oxygen can be used.

Cooling

Engines need to stay cool to work well. Too much heat can break parts of the engine. There are two main ways to cool engines: using air and using water. Many car engines use both water and air. The water moves to parts with fins or fans to help cool down. Bigger engines that don’t move, like some machines, often just use water. Small engines, like those in tools, usually use air to stay cool. Some engines also have special parts to keep oil cool. In certain engines, fuel can also help cool things down before it is used to make power.

Starting

Main article: Starter motor

Internal combustion engines need to be started to begin working. In engines that move up and down, this is done by turning a shaft. This helps the engine go through its steps of taking in air, squeezing it, burning fuel, and letting out exhaust.

The very first engines were started by spinning a heavy wheel. The first car, the Daimler Reitwagen, used a hand crank. For many years, all cars with these engines were started with hand cranks. Then Charles Kettering created the electric starter, which is now the most common way to start engines.

As diesel engines grew bigger, some use air to start them because electric starters sometimes don’t have enough strength. Air starters work by sending pressed air into the engine’s cylinders to make it turn.

Two-wheeled vehicles can be started in a few different ways:

• By pedaling, like on a bicycle
• By pushing the vehicle and then using the clutch, called “run-and-bump starting”
• By kicking down on a pedal, called “kick starting”
• By using an electric starter, like in cars

Some small engines use a rope that you pull to start them, called “recoil starting”. This rope winds back up after you pull it. This method is often used in small tools like lawn mowers.

Turbine engines are often started using an electric motor or compressed air.

Measures of engine performance

Engines can be measured in different ways, such as how well they use energy, how much fuel they need, and how much power they make compared to their weight.

When fuel burns in an engine, it creates hot gases that have more energy than the original fuel. This energy turns into movement, making the engine work. Any energy not used is lost as heat. Real engines are not perfect and can have trouble working well, like facing air resistance or not working at their best. Most car engines are about 18–20% efficient, but racing engines can be over 50% efficient. Making engines more efficient helps save fuel.

Air and noise pollution

Air pollution

Internal combustion engines can create air pollution because not all the fuel burns completely. This makes gases like carbon dioxide, water, and small bits of soot called particulate matter. Breathing these tiny bits can make people sick.

These engines also make other gases, such as nitrogen oxides, which can harm people and plants. Some fuels can create gases that lead to acid rain. Scientists are working on cleaner fuels and better engine designs to help reduce pollution.

Noise pollution

Internal combustion engines also make a lot of noise. Cars, trucks, airplanes, and rockets all create noise that can be disturbing.

Idling

When cars sit with their engines running but not moving, they still use fuel and create pollution. Some cars now have systems that turn off the engine when the car is stopped and turn it back on when you need to drive again. This helps save fuel and reduce pollution.

Carbon dioxide formation

When fuel like diesel or gasoline burns in an engine, it makes carbon dioxide.

For diesel, burning one litre makes about 2.63 kilograms of carbon dioxide.

For gasoline, burning one litre makes about 2.3 kilograms of carbon dioxide.

Parasitic loss

Some parts of an engine use energy to help the engine work better or to move energy along. These parts are called parasitic loads because they take energy away from the engine.

For example, parts like bearings, oil pumps, piston rings, valve springs, flywheels, transmissions, driveshafts, and differentials all use some of the engine’s energy. Some of these parts are needed for the engine to work, like the oil pump that keeps everything moving smoothly. Others help move power from the engine to the wheels, like the transmission.

Engineers try to reduce these energy losses to make engines more efficient and powerful. They might choose different parts or systems, like using an electric fan instead of one driven directly by the engine, to save energy.