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 combustion chamber to cool certain parts of the induction system where "hot points" could produce premature ignition. In jet engines—particularly early turbojets or engines in which it is not practical or desirable to have an afterburner—water injection may be used to increase engine thrust, particularly at low-altitudes and at takeoff.
Water injection was used historically to increase the power output of military aviation engines for short durations, such as during aerial combat or takeoff. However it has also been used in motor sports and notably in drag racing. In Otto cycle engines, the cooling effect of water injection also enables greater compression ratios by reducing engine knocking (detonation). Alternatively, this reduction in engine knocking in Otto cycle engines means that some applications gain significant performance when water injection is used in conjunction with a supercharger, turbocharger, or modifications such as 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. Commonly found on large radial engines with pressure carburetors, it is a mixture of water and alcohol injected into the carburetor at high power settings. When using a rich mixture, the engine runs cooler, but cannot reach maximum power, and a leaner mixture means detonation is likely. With the use of ADI, the injected water and alcohol (which is mixed with the water to prevent it from becoming ice) absorbs the excess heat to prevent detonation while still allowing for a leaner and more powerful mixture.
Early versions of the Boeing 707 fitted with Pratt & Whitney JT3C turbojets used water injection for extra takeoff power, as did Boeing 747-100 and 200 aircraft fitted with Pratt & Whitney JT9D-3AW and -7AW turbofans; this system was not included in later versions fitted with more powerful engines. The BAC One-Eleven airliner also used water injection for its Rolls-Royce Spey turbofan engines. Filling the tanks with jet fuel instead of water led to the Paninternational Flight 112 crash.
In 1978, Olympic Airways Flight 411 had to abort and return to its take-off airport due to a failure of the water injection system or its processes.
Use in automobiles
A limited number of road vehicles with forced induction engines from manufacturers such as Chrysler have included water injection. The 1962 Oldsmobile Jetfire was delivered with the Turbo Jetfire engine.
SAAB
Saab used water injection in the 1978 Saab 99 Turbo S for an extra on its 2-litre engine and in the 1980 Saab 900 Enduro.
BMW
thumb|2016 BMW M4 GTS
thumb|BMW M N55 serial engine|alt=File:2014 Washington Auto Show (12140974934).jpg
In 2015, BMW introduced a version of their high performance coupe, the BMW M4 GTS with the straight-6 2,979 cc turbocharged BMW S55 engine, that combined water injection with intercooling. With the aid of the system, BMW stated that the GTS got a boost, increasing power to and torque to . Three water injectors were used to allow boost pressure to be increased from over the N55 engine that it was based on.
BMW had previously used water injection on its BMW 801 aircraft engine using the MW-50 methanol-water system for low altitude boost with the addition of GM-1 nitrous oxide system for high altitude performance.
The BMW M4 GTS was featured in the 2015 MotoGP season as the official safety car for the series and was released for the commercial market in 2016.
By the mid 2020s, engine development was shifted focus also on improved fuel consumption, due to the pressure on emissions reduction and related regulations.
Bosch WaterBoost technology
Co-developed with BMW, Bosch offers water injection systems named WaterBoost for all manufacturers.
Bosch has a heritage of water injection with BMW as early as 1942. First appeared in the BMW 801D in 1942, it never went into production because the cylinder heads developed micro-cracks when MW50 was used. Instead, the Daimler-Benz DB 605 engined later versions of the Messerschmitt Bf 109 were fitted with an MW 50 injection system, beginning in early 1944. Today Bosch claims up to 5% increase in engine performance, up to 4% decrease in emissions and up to 13% improvement in fuel economy. Similar results
Water Injection and cooled exhaust gas recirculation (EGR) could be seen as competitive technologies. It has been demonstrated that at medium load, a 40-50 % Water-to-Fuel Ratio (WFR) with Port Water Injection (PWI) has the same effect as an EGR-rate of 10%, which is seen as relatively limited, even for petrol engines.
On-Board Water Generation
Surveys asking customers about their willingness to regularly fill up an additional operating fluid have demonstrated that the acceptance level is limited.
Use in diesel
A 2016 study combined water injection with exhaust gas recirculation. Water was injected into the exhaust manifold of a diesel engine and, by opening the exhaust valve during the induction stroke, the injected water and some of the exhaust gas was drawn back into the cylinder. The effect was up to 85% reduction in emissions and also significant reduction in soot emissions.
See also
- Crower six stroke