Internal combustion engine
The internal combustion engine is an engine in which the burning of a fuel occurs in a confined space called a combustion chamber. This exothermic reaction of a fuel with an oxidizer creates gases of high temperature and pressure, which are permitted to expand. The defining feature of an internal combustion engine is that useful work is performed by the expanding hot gases acting directly to cause movement, for example by acting on pistons, rotors, or even by pressing on and moving the entire engine itself.This contrasts with external combustion engines, such as steam engines and Stirling engines, which use the combustion process to heat a separate working fluid, which then in turn does work, for example by moving a piston.
The term Internal Combustion Engine (ICE) is almost always used to refer specifically to reciprocating engines, Wankel engines and similar designs in which combustion is intermittent. However, continuous combustion engines, such as Jet engines, most rockets and many gas turbines are also internal combustion engines.
Applications:
Internal combustion engines are most commonly used for mobile propulsion in automobiles, equipment, and other portable machinery. In mobile equipment internal combustion is advantageous, since it can provide high power to weight ratios together with excellent fuel energy-density. These engines have appeared in transport in almost all automobiles, motorcycles, boats, and in a wide variety of aircraft and locomotives, generally using petroleum . Where very high power is required, such as jet aircraft, helicopters and large ships, they appear mostly in the form of turbines.
They are also used for electric generators (i.e. 12 V generators) and by industry.
Nowadays are appearing alternative propulsion engines, that don´t use petroleum or uses other energy source (i.e. electricity).
Operation
All internal combustion engines depend on the exothermic chemical process of combustion: the reaction of a fuel, typically with air, although other oxidisers such as nitrous oxide may be employed. Also see stoichiometry.
The most common modern fuels are made up of hydrocarbons and are derived from mostly petroleum. These include the fuels known as dieselfuel, gasoline and petroleum gas, and the rarer use of propane gas. Most internal combustion engines designed for gasoline can run on natural gas or liquefied petroleum gases without major modifications except for the fuel delivery components. Liquid and gaseous biofuels, such as Ethanol and biodiesel, a form of diesel fuel that is produced from crops that yield triglycerides such as soy bean oil, can also be used. Some can also run on Hydrogen gas.
All internal combustion engines must achieve ignition in their cylinders to create combustion. Typically engines use either an electrical method or a compression ignition system.
Engine cycle
Two-stroke
Engines based on the two-stroke cycle use two strokes (one up, one down) for every power stroke. Since there are no dedicated intake or exhaust strokes, alternative methods must be used to scavenge the cylinders. The most common method in spark-ignition two-strokes is to use the downward motion of the piston to pressurize fresh charge in the crankcase, which is then blown through the cylinder through ports in the cylinder walls.
Spark-ignition two-strokes are small and light (for their power output), and mechanically very simple; they are also generally louder, less efficient, and far more polluting than their four-stroke counterparts, and they do not scale well to larger sizes. However in single cylinder small motor applications cc for cc, a two-stroke engine produces much more power than equivalent 4 strokes due to the enormous advantage of having 1 power stroke for every 360 degrees of crankshaft rotation (compared to 720 degrees in a 4 stroke motor).
Two-stroke engines are less fuel-efficient than other types of engines because unspent fuel being sprayed into the combustion chamber can sometimes escape out of the exhaust duct with the previously spent fuel. Without special exhaust processing this can produce high pollution levels. Whilst two-stroke motors remain popular in Europe and Asia, they are penalised in some American markets such as California for this reason.
Continuing research into two-stroke motors is limited, however there is some experiementation being undertaken regarding improvements for these motors, including fuel injection systems amongst other things. Initial results have produced motors that are much cleaner burning than their traditional counterparts.
Two-stroke engines are widely used in snowmobiles, lawnmowers, weed-whackers, chain saws, jet skis, mopeds, outboard motors and manymotorcycles.
The largest compression-ignition engines are two-strokes, and are used in some locomotives and large ships. These engines use forced induction to scavenge the cylinders. An example of this type of motor is the Wartsila-Sulzer turbocharged 2 stroke diesel as used in large container ships. It is the most efficient and powerful motor in the world, with over 50% thermal efficiancy (the most efficiant 4 stroke motors struggle to hit 30% thermal efficiancy).
Four-stroke
Engines based on the four-stroke cycle or Otto cycle have one power stroke for every four strokes (up-down-up-down) and are used in cars, larger boats and many light aircraft. They are generally quieter, more efficient and larger than their two-stroke counterparts. There are a number of variations of these cycles, most notably the Atkinson and Miller cycles. Most truck and automotive diesel engines use a four-stroke cycle, but with a compression heating ignition system. This variation is called the diesel cycle.
Five-stroke
Engines based on the five-stroke cycle are a variant of the four stroke cycle. Normally the four cycles are intake, compression, combustion and exhaust. The fifth cycle added by Delautour[2] is refrigeration. Engines running on a five-stroke cycle are up to 30 percent more efficient than an equivalent four stroke engine.
Bourke Engine
In this engine, two diametrically opposed cylinders are linked to the crank by the crank pin that goes through the common scottish yoke. The cylinders and pistons are so constructed that there are, as in the usual two stroke cycle, two power strokes per revolution. However, unlike the common two stroke engine, the burnt gases and the incoming fresh air do not mix in the cylinders, contributing to a cleaner, more efficient operation. The scotch yoke mechanism also has low side thrust and thus greatly reduces friction between pistons and cylinder walls. The Bourke engine's combustion phase more closely approximates constant volume combustion than either four stroke or two stroke cycles do. It also uses less moving parts, hence needs to overcome less friction than the other two reciprocating types have to. In addition, its greater expansion ratio also means more of the heat from its combustion phase is utilized than is used by either four stroke or two stroke cycles.
Engine Efficiency
The efficiency of various types of internal combustion engines vary. It is generally accepted that most gasoline fueled internal combustion engines, even when aided with turbochargers and stock efficiency aids, have a mechanical efficiency of about 20%. Most internal combustion engines waste about 36% of the energy in gasoline as heat lost to the cooling system and another 38% through the exhaust. The rest is lost to friction, about 6%. Most engine manufacturers have done little to harness this wasted energy, though there are various add on devices and systems that are known to greatly improve combustion efficiency and recover wasted energy.
Hydrogen Fuel Injection, or HFI, is an engine add on system that is known to improve fuel economy of internal combustion engines by injecting hydrogen as a combustion enhancement into the intake manifold. Fuel economy gains of 15% to 50% can be seen. A small amount of hydrogen added to the intake air-fuel charge increases the octane rating of the combined fuel charge and enhances the flame velocity, thus permitting the engine to operate with more advanced ignition timing, a higher compression ratio, and a leaner air-to-fuel mixture than otherwise possible. The result is lower pollution with more power and increased efficiency. Some HFI systems use an on board electrolyzer to generate the hydrogen used. A small tank of pressurized hydrogen can also be used, but this method necessitates refilling.
There has also been discussion of new types of internal combustion engines, such as the Scuderi Split Cycle Engine, that utilize high compression pressures in excess of 2000 psi and combust after top-dead-center (the highest & most compressed point in a internal combustion piston stroke). The claimed efficiency of this engine, by calculation, is 42%.
