Internal combustion engine

An internal combustion engine (ICE or IC engine) is a type of heat engine where fuel burns with an oxidizer (usually air) inside a special space called a combustion chamber. This burning creates hot, high-pressure gases that push parts of the engine, such as pistons or turbine blades. This movement changes stored energy in fuel into motion that 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 that used dust explosions to power a boat. Also in 1807, a Swiss engineer made a car that used hydrogen and a spark to go. In 1823, Samuel Brown made the first engine used for work.

Later, in 1854, two inventors in the UK got a certificate for making power by exploding gases. In 1860, a Belgian engineer made a gas engine. In 1876, some inventors in Germany made a better engine with four steps. 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 still exists in phrases like siege engine. A motor is a machine that makes mechanical power. Usually, electric motors are not called engines, but combustion engines sometimes are 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 with a typical electrical output in the range of some 100 MW. Combined cycle power plants use the high temperature exhaust to boil and superheat water steam to run a steam turbine. Thus, the efficiency is higher because more energy is extracted from the fuel than what could be extracted by the combustion engine alone. Combined cycle power plants achieve efficiencies in the range of 50–60%. In a smaller scale, stationary engines like gas engines or diesel generators are used for backup or for providing electrical power to areas not connected to an electric grid.

Small engines (usually 2‐stroke single cylinder gasoline/petrol 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, which is typically made of cast iron or aluminum. The engine block contains the cylinders. In engines with more than one cylinder they are usually arranged either in 1 row (straight engine) or 2 rows (boxer engine or V engine). Single-cylinder engines are common for motorcycles and other small engines. The pistons are short cylindrical parts which seal one end of the cylinder and slide continuously within it while the engine is in operation.

The cylinder head is attached to the engine block by numerous bolts or studs. It contains short ducts for intake and exhaust and the associated intake and exhaust valves. The valves are often poppet valves but they can also be rotary valves or sleeve valves. The cylinder head also holds the spark plug in the case of spark ignition engines and the injector for engines that use direct injection. A head gasket prevents the gas from leaking between the cylinder head and the engine block. The opening and closing of the valves is controlled by one or several camshafts and springs.

The crankcase is sealed at the bottom with a sump that collects oil during normal operation. The cavity created between the cylinder block and the sump houses a crankshaft that converts the reciprocating motion of the pistons to rotational motion. The crankshaft is held in place relative to the engine block by main bearings. A connecting rod is connected to offset sections of the crankshaft in one end and to the piston in the other end through the gudgeon pin and thus transfers the force and translates the reciprocating motion of the pistons to the circular motion of the crankshaft.

The cylinder head has an intake manifold and an exhaust manifold attached to the corresponding ports. The intake manifold connects to the air filter directly, or to a carburetor when one is present, which is then connected to the air filter. It distributes the air incoming from these devices to the individual cylinders. The exhaust manifold is the first component in the exhaust system.

Four-stroke engines

Main article: Four-stroke engine

The top dead center (TDC) of a piston is the position where it is nearest to the valves; bottom dead center (BDC) is the opposite position where it is furthest from them. A stroke is the movement of a piston from TDC to BDC or vice versa, together with the associated process. In a 4-stroke ICE, each piston experiences 2 strokes per crankshaft revolution in the following order. Starting the description at TDC, these are:

1. Intake: The intake valves are open as a result of the cam lobe pressing down on the valve stem. The piston moves downward increasing the volume of the combustion chamber and allowing air to enter in the case of a CI engine or an air-fuel mix in the case of SI engines.
2. Compression: In this stroke, both valves are closed and the piston moves upward reducing the combustion chamber volume. Just before the piston reaches TDC, ignition begins. In the case of a SI engine, the spark plug ignites the charge. In the case of a CI engine, the fuel injector quickly injects fuel into the combustion chamber as a spray; the fuel ignites due to the high temperature.
3. Power or working stroke: The pressure of the combustion gases pushes the piston downward, generating more kinetic energy than is required to compress the charge. When the piston is near to BDC the exhaust valve opens.
4. Exhaust: The exhaust valve remains open while the piston moves upward expelling the combustion gases. At the end of this stroke, the exhaust valve closes, the intake valve opens, and the sequence repeats in the next cycle.

Two-stroke engines

Main article: Two-stroke engine

The defining characteristic of this kind of engine is that each piston completes a cycle every crankshaft revolution. The 4 processes of intake, compression, power and exhaust take place in only 2 strokes. Starting at TDC the cycle consists of:

1. Power: While the piston is descending the combustion gases perform work on it.
2. Scavenging: Around 75° of crankshaft rotation before BDC the exhaust valve or port opens, and blowdown occurs. Shortly thereafter the intake valve or transfer port opens. The incoming charge displaces the remaining combustion gases to the exhaust system. The piston reaches BDC and reverses direction. After the piston has traveled a short distance upwards into the cylinder the exhaust valve or port closes; shortly the intake valve or transfer port closes as well.
3. Compression: With both intake and exhaust closed the piston continues moving upwards compressing the charge and performing work on it. As in the case of a 4-stroke engine, ignition starts just before the piston reaches TDC.

Ignition

Internal combustion engines require ignition of the mixture, either by spark ignition (SI) or compression ignition (CI).

Spark ignition process

Main article: Spark-ignition engine

The spark-ignition engine was a refinement of the early engines which used Hot Tube ignition. When Bosch developed the magneto it became the primary system for producing electricity to energize a spark plug. The battery supplies electrical power for starting when the engine has a starting motor system, and supplies electrical power when the engine is off. Gasoline engines take in a mixture of air and gasoline and compress it by the movement of the piston. The fuel mixture is ignited at different progressions of the piston in the cylinder.

Compression ignition process

Main article: Diesel engine

For ignition, diesel engines rely solely on the high temperature and pressure created by the engine in its compression process. Diesel engines take in air only, and shortly before peak compression, spray a small quantity of diesel fuel into the cylinder via a fuel injector that allows the fuel to instantly ignite.

Lubrication

Surfaces in contact and relative motion to other surfaces require lubrication to reduce wear and increase efficiency. An engine requires lubrication in several parts. In 2-stroke crankcase scavenged engines, the interior of the crankcase is sprayed by oil in the air-fuel mixture which is then burned along with the fuel.

Cylinder configuration

Common cylinder configurations include the straight or inline configuration, the more compact V configuration, and the wider but smoother flat or boxer configuration. Multiple cylinder engines have their valve train and crankshaft configured so that pistons are at different parts of their cycle.

Diesel cycle

Main article: Diesel cycle

Most truck and automotive diesel engines use a cycle reminiscent of a four-stroke cycle, but with temperature increase by compression causing ignition, rather than needing a separate ignition system.

Otto cycle

The Otto cycle is the most common cycle for most cars' internal combustion engines that use gasoline as a fuel. It consists of the same major steps as described for the four-stroke engine: Intake, compression, ignition, expansion and exhaust.

Five-stroke engine

In 1879, Nicolaus Otto manufactured and sold a double expansion engine. In the 21st century Ilmor designed and successfully tested a 5-stroke double expansion internal combustion engine, with high power output and low SFC (Specific Fuel Consumption).

Six-stroke engine

The six-stroke engine was invented in 1883. Four kinds of six-stroke engines use a regular piston in a regular cylinder, firing every three crankshaft revolutions.

Other cycles

The first internal combustion engines did not compress the mixture. There are a number of variations of these cycles, most notably the Atkinson and Miller cycles. Split-cycle engines separate the four strokes of intake, compression, combustion and exhaust into two separate but 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. Some big power plants using these turbines can be more than 61% 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. The burning happens while the pressure stays the same, unlike other engine types.

Wankel engines

Main article: Wankel engine

Wankel engines, also called rotary engines, work differently 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 common engines but do it in a special way. They can produce power more often in each spin, which makes them stronger 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 helpful.

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, making it thicker and hotter 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, especially in planes that fly high up in the sky. 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 kind of fuel to work, usually mixed with oxygen from the air. When the fuel burns, it creates a lot of heat and energy, which helps the engine run. The temperature of this burning process depends on what kind of fuel is used and other factors.

Fuels

The most common fuels for these engines come from things like petroleum, which includes gasoline, diesel, and propane. Some engines can also use biofuels like ethanol or biodiesel, made from crops. There are even 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. But for special uses, like in torpedoes or rockets, other materials such as compressed air or oxygen can be used to make the engine work better.

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 their cycles. In engines that move up and down, this is done by turning a shaft, which 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, and the first car, the Daimler Reitwagen, used a hand crank. For many years, all cars with these engines were started with hand cranks until Charles Kettering created the electric starter, which is now the most common way to start engines, even in machines that are not cars.

As diesel engines grew bigger and heavier, 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, and 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 many 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 face many challenges that lower their efficiency, like air resistance and operating at less than their best load. Most car engines are about 18–20% efficient, but racing engines can be over 50% efficient. Improving engine efficiency helps save fuel, but often involves balancing many different factors.

Air and noise pollution

Air pollution

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

These engines also produce other gases, such as nitrogen oxides, which can harm both people and plants. Some fuels can create gases that lead to acid rain. To help reduce pollution, scientists are looking at cleaner fuels and better engine designs.

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, which helps save fuel and reduce pollution.

Carbon dioxide formation

When fuel like diesel or gasoline burns in an engine, it creates carbon dioxide. We can figure out about how much carbon dioxide is made when one litre of fuel burns.

For diesel, we can think of it as being made of carbon and hydrogen. By using simple math, we find that burning one litre of diesel makes about 2.63 kilograms of carbon dioxide.

For gasoline, which is another common fuel, burning one litre makes about 2.3 kilograms of carbon dioxide. This shows how much of this gas is created when we use these fuels.

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.