What is "water injection"

n. (context automotive English) A fuel system component which squirts a small amount of water, in the form of a fine spray, into the air/fuel mixture going into the engine. This is designed to reduce detonation or knocking in high performance engines, especially when using a high compression ratio.

In the oil industry, waterflooding or water injection is where water is injected into the oil field, usually to increase pressure and thereby stimulate production. Water injection wells can be found both on- and offshore, to increase oil recovery from an existing reservoir.

Water is injected to support pressure of the reservoir (also known as voidage replacement), and also to sweep or displace oil from the reservoir, and push it towards a well.

Normally only 30% of the oil in a reservoir can be extracted, but water injection increases that percentage (known as the recovery factor) and maintains the production rate of a reservoir over a longer period.

Waterflooding began accidentally in Pithole, Pennsylvania by 1865. Waterflooding became common in Pennsylvania in the 1880s.

The term water injection may refer to:

• Water injection (engines), for increasing efficiency or power of internal combustion engines
• Water injection (oil production), for increasing the amount of petroleum extracted from oil wells
• Water injection well, a type of groundwater well through which water is injected into an aquifer system

In internal combustion engines, water injection, also known as anti-detonant injection (ADI), can spray water into the incoming air or fuel- air mixture, or directly into the cylinder, in order to cool certain parts of the induction system where "hot points" could produce premature ignition. In jet engines it is used to increase the thrust of the engine at low speeds and at takeoff.

Water injection was used historically to increase the power output of military aviation engines for short durations such as dogfights or takeoff, however it has also been used in motor sport and notably in drag racing. In Otto cycle engines the cooling effects of water injection also allow for greater compression ratios by reducing the problem of engine knocking (detonation). Alternately this reduction in engine knocking in Otto cycle engines means that in some applications significant performance gains can be obtained when water injection is used in conjunction with a supercharger, turbocharger and/or other modifications such as a more aggressive ignition timing.

Depending on the engine, improvements in power and fuel efficiency can also be obtained solely by injecting water. Water injection may also be used to reduce NOx or carbon monoxide emissions.

Water injection is also used in some turbine engines and in some turboshaft engines, normally when a momentary high-thrust setting is needed to increase power and fuel efficiency.