Internal combustion engine

An internal combustion engine is an engine that is powered by the expansion of hot combustion products of fuel directly acting within an engine. A piston internal combustion engine works by burning hydrocarbon or hydrogen fuel that presses on a piston; and a jet engine works as the hot combustion products press on the interior parts of the nozzle and combustion chamber, directly accelerating the engine forwards. The rotary combustion engine uses a rotor instead of reciprocating pistons.

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.

Related Topics:
Exothermic - Combustion - Fuel - Nitrous oxide - Stoichiometry

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

The most common fuels in use today are made up of hydrocarbons and are derived from petroleum. These include the fuels known as diesel, gasoline and liquified petroleum gas. Most internal combustion engines designed for gasoline can run on natural gas or liquified petroleum gases without modifications except for the fuel delivery components. Liquid and gaseous biofuels of adequate formulation can also be used.

Related Topics:
Hydrocarbon - Petroleum - Diesel - Gasoline - Liquified petroleum gas - Natural gas - Biofuel

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Some have theorized that in the future hydrogen might replace such fuels. The advantage of hydrogen is that its combustion produces only water. This is unlike the combustion of hydrocarbons which also produces carbon dioxide, a major cause of global warming, and, as a result of incomplete combustion, carbon monoxide and nitrous oxides (NOx). The big disadvantage of hydrogen in many situations is storage; liquid hydrogen has extremely low density- 14 times lower than water and requires extensive insulation, whilst gaseous hydrogen requires very heavy tankage. Whilst hydrogen is light and therefore has a higher specific energy, the volumetric efficiency is still roughly five times lower than petrol.

Related Topics:
Hydrogen - Replace such fuels - Water - Carbon dioxide - Global warming - Carbon monoxide - Nitrous oxide

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

All internal combustion engines must have a means of ignition to promote combustion. Most engines use either an electrical or a compression heating ignition system. Electrical ignition systems generally rely on a lead-acid battery and an induction coil to provide a high voltage electrical spark to ignite the air-fuel mix in the engine's cylinders. This battery can be recharged during operation using an alternator driven by the engine. Compression heating ignition systems (Diesel engines and HCCI engines) rely on the heat created in the air by compression in the engine's cylinders to ignite the fuel.

Related Topics:
Ignition - Electrical - Compression heating ignition - Lead-acid battery - Induction coil - Alternator - Diesel engine - HCCI

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Once successfully ignited and burnt, the combustion products (hot gases) have more available energy than the original compressed fuel/air mixture (which had higher chemical energy). The available energy is manifested as high temperature and pressure which can be translated into work by the engine. In a reciprocating engine, the high pressure product gases inside the cylinders drive the engine's pistons.

Related Topics:
Gas - Chemical energy - Temperature - Pressure - Work

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Once the available energy has been removed the remaining hot gases are vented (often by opening a valve or exposing the exhaust outlet) and this allows the piston to return to its previous position (Top Dead Center - TDC). The piston can then proceed to the next phase of its cycle (which varies between engines). Any heat not translated into work is a waste product and is removed from the engine either by an air or liquid cooling system.

Related Topics:
Valve - Heat

~ ~ ~ ~ ~ ~ ~ ~ ~ ~