Internal combustion engines come in a wide variety of types, but have certain family resemblances, and thus share many common types of components.
Combustion chambers
Internal combustion engines can contain any number of combustion chambers (cylinders), with numbers between one and twelve being common, though as many as 36 have been used, such as in the Lycoming R-7755.
Engines with a high number of cylinders have two operational benefits: first, the engine has a larger displacement with smaller individual reciprocating masses, that is, the mass of each piston can be less thus making a smoother-running engine since the engine tends to vibrate as a result of the pistons moving up and down. The second benefit is that the number of the same size cylinders will double the torque and power. The downside to having more pistons is that the engine will tend to weigh more and generate more internal friction as the greater number of pistons rub against the inside of their cylinders. This tends to decrease fuel efficiency and robs the engine of some of its power. For high-performance gasoline engines using current materials and technology, such as the engines found in modern automobiles, there seems to be a point around 10 or 12 cylinders after which the addition of cylinders becomes an overall detriment to performance and efficiency. Although, exceptions such as the W16 engine from Volkswagen exist. Most car engines have four to eight cylinders, with some high-performance cars having ten, 12 — or even 16, and some very small cars and trucks having two or three. In previous years, some quite large cars such as the DKW and Saab 92, had two-cylinder or two-stroke engines. Radial aircraft engines had from three to 28 cylinders; examples include the small Kinner B-5 and the large Pratt & Whitney R-4360. Larger examples were built as multiple rows. As each row contains an odd number of cylinders, to give an even firing sequence for a four-stroke engine, an even number indicates a two- or four-row engine. The largest of these was the Lycoming R-7755 with 36 cylinders (four rows of nine cylinders), but it did not enter production. Motorcycles commonly have from one to four cylinders, with a few high-performance models having six; although, some 'novelties' exist with 8, 10, or 12. Snowmobiles Usually have one to four cylinders and can be both 2-stroke or 4-stroke, normally in the in-line configuration; however, there are again some novelties that exist with V-4 engines Small portable appliances such as chainsaws, generators, and domestic lawn mowers most commonly have one cylinder, but two-cylinder chainsaws exist. Large reversible two-cycle marine diesels have a minimum of three to over ten cylinders. Freight diesel locomotives usually have around 12 to 20 cylinders due to space limitations, as larger cylinders take more space (volume) per kwh, due to the limit on average piston speed of less than 30 ft/sec on engines lasting more than 40,000 hours under full power.
Ignition system The ignition system of an internal combustion engines depends on the type of engine and fuel used. Petrol engines are typically ignited by a precisely timed spark, and diesel engines by compression heating. Historically, outside flame and hot-tube systems were used, see hot bulb engine.
Spark
In a spark ignition engine, a mixture is ignited by an electric spark from a spark plug — the timing of which is very precisely controlled. Almost all gasoline engines are of this type. Diesel engines timing is precisely controlled by the pressure pump and injector.
The normal plug distance between the spark plug is 1mm apart, and the voltage is 3000v at normal atmospheric conditions.
Compression Ignition occurs as the temperature of the fuel/air mixture is taken over its autoignition temperature, due to heat generated by the compression of the air during the compression stroke. The vast majority of compression ignition engines are diesels in which the fuel is mixed with the air after the air has reached ignition temperature. In this case, the timing comes from the fuel injection system. Very small model engines for which simplicity and light weight is more important than fuel costs use easily ignited fuels (a mixture of kerosene, ether, and lubricant) and adjustable compression to control ignition timing for starting and running.
Ignition timing
For reciprocating engines, the point in the cycle at which the fuel-oxidizer mixture is ignited has a direct effect on the efficiency and output of the ICE. The thermodynamics of the idealized Carnot heat engine tells us that an ICE is most efficient if most of the burning takes place at a high temperature, resulting from compression — near top dead center. The speed of the flame front is directly affected by the compression ratio, fuel mixture temperature, and octane rating or cetane number of the fuel. Leaner mixtures and lower mixture pressures burn more slowly requiring more advanced ignition timing. It is important to have combustion spread by a thermal flame front (deflagration), not by a shock wave. Combustion propagation by a shock wave is called detonation and, in engines, is also known as knocking or pinging.
So at least in gasoline-burning engines, ignition timing is largely a compromise between a later "retarded" spark — which gives greater efficiency with high octane fuel — and an earlier "advanced" spark that avoids detonation with the fuel used. For this reason, high-performance diesel automobile proponents, such as Gale Banks, believe that
Fuel systems
Fuels burn faster and more efficiently when they present a large surface area to the oxygen in air. Liquid fuels must be atomized to create a fuel-air mixture, traditionally this was done with a carburetor in petrol engines and with fuel injection in diesel engines. Most modern petrol engines now use fuel injection too — though the technology is quite different. While diesel must be injected at an exact point in that engine cycle, no such precision is needed in a petrol engine. However, the lack of lubricity in petrol means that the injectors themselves must be more sophisticated.
Carburetor
Simpler reciprocating engines continue to use a carburetor (carburettor in UK and Commonwealth English) to supply fuel into the cylinder. Although carburetor technology in automobiles reached a very high degree of sophistication and precision, from the mid-1980s it lost out on cost and flexibility to fuel injection. Simple forms of carburetor remain in widespread use in small engines such as lawn mowers and more sophisticated forms are still used in small motorcycles.
Fuel injection
Larger gasoline engines used in automobiles have mostly moved to fuel injection systems (see Gasoline Direct Injection). Diesel engines have always used fuel injection system because the timing of the injection initiates and controls the combustion.
Autogas engines use either fuel injection systems or open- or closed-loop carburetors.
Fuel pump
Most internal combustion engines now require a fuel pump. Diesel engines use an all-mechanical precision pump system that delivers a timed injection direct into the combustion chamber, hence requiring a high delivery pressure to overcome the pressure of the combustion chamber. Petrol fuel injection delivers into the inlet tract at atmospheric pressure (or below) and timing is not involved, these pumps are normally driven electrically. Gas turbine and rocket engines use electrical systems.
Other Other internal combustion engines like jet engines and rocket engines employ various methods of fuel delivery including impinging jets, gas/liquid shear, preburners and others.
Oxidiser-Air inlet system Some engines such as solid rockets have oxidisers already within the combustion chamber but in most cases for combustion to occur, a continuous supply of oxidiser must be supplied to the combustion chamber.
Naturally aspirated engines When air is used with piston engines it can simply suck it in as the piston increases the volume of the chamber. However, this gives a maximum of 1 atmosphere of pressure difference across the inlet valves, and at high engine speeds the resulting airflow can limit potential output.
Superchargers and turbochargers A supercharger is a "forced induction" system which uses a compressor powered by the shaft of the engine which forces air through the valves of the engine to achieve higher flow. When these systems are employed the maximum absolute pressure at the inlet valve is typically around 2 times atmospheric pressure or more.
Turbochargers are another type of forced induction system which has its compressor powered by a gas turbine running off the exhaust gases from the engine.
Turbochargers and superchargers are particularly useful at high altitudes and they are frequently used in aircraft engines.
Duct jet engines use the same basic system, but eschew the piston engine, and replace it with a burner instead.
Liquids In liquid rocket engines, the oxidiser comes in the form of a liquid and needs to be delivered at high pressure (typically 10-230 bar or 1–23 MPa) to the combustion chamber. This is normally achieved by the use of a centrifugal pump powered by a gas turbine — a configuration known as a turbopump, but it can also be pressure fed.
Parts
For a four-stroke engine, key parts of the engine include the crankshaft (purple), connecting rod (orange), one or more camshafts (red and blue), and valves. For a two-stroke engine, there may simply be an exhaust outlet and fuel inlet instead of a valve system. In both types of engines there are one or more cylinders (grey and green), and for each cylinder there is a spark plug (darker-grey, gasoline engines only), a piston (yellow), and a crankpin (purple). A single sweep of the cylinder by the piston in an upward or downward motion is known as a stroke. The downward stroke that occurs directly after the air-fuel mix passes from the carburetor or fuel injector to the cylinder (where it is ignited) is also known as a power stroke.
A Wankel engine has a triangular rotor that orbits in an epitrochoidal (figure 8 shape) chamber around an eccentric shaft. The four phases of operation (intake, compression, power, and exhaust) take place in what is effectively a moving, variable-volume chamber.
Valves
All four-stroke internal combustion engines employ valves to control the admittance of fuel and air into the combustion chamber. Two-stroke engines use ports in the cylinder bore, covered and uncovered by the piston, though there have been variations such as exhaust valves.
Piston engine valves
In piston engines, the valves are grouped into 'inlet valves' which admit the entrance of fuel and air and 'outlet valves' which allow the exhaust gases to escape. Each valve opens once per cycle and the ones that are subject to extreme accelerations are held closed by springs that are typically opened by rods running on a camshaft rotating with the engines' crankshaft.
Control valves Continuous combustion engines—as well as piston engines—usually have valves that open and close to admit the fuel and/or air at the startup and shutdown. Some valves feather to adjust the flow to control power or engine speed as well.
Exhaust systems
Internal combustion engines have to effectively manage the exhaust of the cooled combustion gas from the engine. The exhaust system frequently contains devices to control both chemical and noise pollution. In addition, for cyclic combustion engines the exhaust system is frequently tuned to improve emptying of the combustion chamber. The majority of exhausts also have systems to prevent heat from reaching places which would encounter damage from it such as heat-sensitive components, often referred to as Exhaust Heat Management.