Water injection (engine)

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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.

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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. [1] Water injection may also be used to reduce NOx or carbon monoxide emissions. [1]

Composition of fluid

Many water injection systems use a mixture of water and alcohol (often close to 50/50), with trace amounts of water-soluble oil. The water provides the primary cooling effect due to its great density and high heat absorption properties. The alcohol is combustible, and also serves as an antifreeze for the water. The main purpose of the oil is to prevent corrosion of water injection and fuel system components. [2]

Use in aircraft

A "wet" takeoff of a KC-135 with J57 engines Boeing KC-135 J57 wet takeoff.jpg
A "wet" takeoff of a KC-135 with J57 engines

Water injection has been used in both reciprocating and turbine aircraft engines.

In a reciprocating engine, the use of water injection, also called anti-detonation injection or ADI, is used to prevent engine knocking also known as "detonation". [3] 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. [3]

When used in a turbine engine, the effects are similar, except that normally preventing detonation is not the primary goal. Water is normally injected either at the compressor inlet or in the diffuser just before the combustion chambers. Adding water increases the mass being accelerated out of the engine, increasing thrust and it also serves to cool the turbines. Since temperature is normally the limiting factor in turbine engine performance at low altitudes, the cooling effect lets the engine run at higher RPM with more fuel injected and more thrust created without overheating. [4]

Prior to the widespread adoption of afterburning engines, some first-generation jet fighters used water injection to provide a moderate boost in performance. For example, the late-model variant of the Lockheed F-80 Shooting Star, the F-80C, used water injection on its Allison J33-A-35 engine. Water injection increased thrust from 20.5 to 24.0 kN (4,600 to 5,400 lbf), a 17% thrust increase (at sea level). [5]

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; [6] 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. [7]

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. [8]

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. [9]

In 2015 BMW has introduced a version of their high performance M4 coupe, the M4 GTS, that combines water injection with intercooling. The car was featured in the 2015 MotoGP season as the official safety car for the series and was released for the commercial market in 2016. [10] As per BMW example, current engine developments featuring water injection seem to concentrate on the effect of “Performance Improvement”. But by the mid 2020s, engine development will shift focus also on improved fuel consumption, due to the pressure on CO2 emissions reduction and related regulations. [11] [12]

Bosch, which co-developed the technology with BMW, offers a water injection system named WaterBoost for other manufacturers. The company claims up to 5% increase in engine performance, up to 4% decrease in CO2 emissions and up to 13% improvement in fuel economy. [13] Similar results were reported in "Water Injection - High Power and High Efficiency combined" [14]

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. [15]

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. [12] Therefore, the need for refilling is considered as one of the main barrier for the mass adoption of Water Injection. A key enabler is the development of on-board water generation system to run in close loop system, especially in order to guarantee consistent low level of emissions (engine CO2 emissions will be raised if the water supply is exhausted). Three major sources can be investigated:

The first two variants are highly dependent on weather ambient conditions with sufficiently high humidity levels or driver habits (no A/C operation wanted). Consequently, an adequate supply of water cannot be ensured. In contrast, condensing of water vapour formed during the combustion of gasoline is a reliable source of water: there is approximately a volume of 1L of water vapour in exhaust per each liter of gasoline fuel consumed. In October 2019, Hanon Systems together with FEV presented an Audi TT Sport demonstrator equipped with water injection operating as a closed system thanks to a Hanon Systems "Water Harvesting System". [16]

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 an 85% reduction in NOx emissions, but at the cost of increased soot emissions. [17]

See also

Related Research Articles

<span class="mw-page-title-main">Diesel engine</span> Type of internal combustion engine

The diesel engine, named after Rudolf Diesel, is an internal combustion engine in which ignition of the fuel is caused by the elevated temperature of the air in the cylinder due to mechanical compression; thus, the diesel engine is called a compression-ignition engine. This contrasts with engines using spark plug-ignition of the air-fuel mixture, such as a petrol engine or a gas engine.

<span class="mw-page-title-main">Ramjet</span> Supersonic atmospheric jet engine

A ramjet is a form of airbreathing jet engine that uses the forward motion of the engine to take in air for combustion that produces jet thrust. Since it produces no thrust when stationary, ramjet-powered vehicles require an assisted take-off like a rocket assist to accelerate it to a speed where it begins to produce thrust. Ramjets work most efficiently at supersonic speeds around Mach 3 and can operate up to speeds of Mach 6.

<span class="mw-page-title-main">Pulsejet</span> Engine where combustion is pulsed instead of continuous

A pulsejet engine is a type of jet engine in which combustion occurs in pulses. A pulsejet engine can be made with few or no moving parts, and is capable of running statically. The best known example may be the Argus As 109-014 used to propel Nazi Germany's V-1 flying bomb.

<span class="mw-page-title-main">Turbofan</span> Airbreathing jet engine designed to provide thrust by driving a fan

The turbofan or fanjet is a type of airbreathing jet engine that is widely used in aircraft propulsion. The word "turbofan" is a combination of the preceding generation engine technology of the turbojet, and a reference to the additional fan stage added. It consists of a gas turbine engine which achieves mechanical energy from combustion, and a ducted fan that uses the mechanical energy from the gas turbine to force air rearwards. Thus, whereas all the air taken in by a turbojet passes through the combustion chamber and turbines, in a turbofan some of that air bypasses these components. A turbofan thus can be thought of as a turbojet being used to drive a ducted fan, with both of these contributing to the thrust.

<span class="mw-page-title-main">Exhaust gas recirculation</span> NOx reduction technique used in gasoline and diesel engines

In internal combustion engines, exhaust gas recirculation (EGR) is a nitrogen oxide (NOx) emissions reduction technique used in petrol/gasoline, diesel engines and some hydrogen engines. EGR works by recirculating a portion of an engine's exhaust gas back to the engine cylinders. The exhaust gas displaces atmospheric air and reduces O2 in the combustion chamber. Reducing the amount of oxygen reduces the amount of fuel that can burn in the cylinder thereby reducing peak in-cylinder temperatures. The actual amount of recirculated exhaust gas varies with the engine operating parameters.

<span class="mw-page-title-main">Four-stroke engine</span> Internal combustion engine type

A four-strokeengine is an internal combustion (IC) engine in which the piston completes four separate strokes while turning the crankshaft. A stroke refers to the full travel of the piston along the cylinder, in either direction. The four separate strokes are termed:

  1. Intake: Also known as induction or suction. This stroke of the piston begins at top dead center (T.D.C.) and ends at bottom dead center (B.D.C.). In this stroke the intake valve must be in the open position while the piston pulls an air-fuel mixture into the cylinder by producing a partial vacuum in the cylinder through its downward motion.
  2. Compression: This stroke begins at B.D.C, or just at the end of the suction stroke, and ends at T.D.C. In this stroke the piston compresses the air-fuel mixture in preparation for ignition during the power stroke (below). Both the intake and exhaust valves are closed during this stage.
  3. Combustion: Also known as power or ignition. This is the start of the second revolution of the four stroke cycle. At this point the crankshaft has completed a full 360 degree revolution. While the piston is at T.D.C. the compressed air-fuel mixture is ignited by a spark plug or by heat generated by high compression, forcefully returning the piston to B.D.C. This stroke produces mechanical work from the engine to turn the crankshaft.
  4. Exhaust: Also known as outlet. During the exhaust stroke, the piston, once again, returns from B.D.C. to T.D.C. while the exhaust valve is open. This action expels the spent air-fuel mixture through the exhaust port.
<span class="mw-page-title-main">Turbojet</span> Airbreathing jet engine which is typically used in aircraft

The turbojet is an airbreathing jet engine which is typically used in aircraft. It consists of a gas turbine with a propelling nozzle. The gas turbine has an air inlet which includes inlet guide vanes, a compressor, a combustion chamber, and a turbine. The compressed air from the compressor is heated by burning fuel in the combustion chamber and then allowed to expand through the turbine. The turbine exhaust is then expanded in the propelling nozzle where it is accelerated to high speed to provide thrust. Two engineers, Frank Whittle in the United Kingdom and Hans von Ohain in Germany, developed the concept independently into practical engines during the late 1930s.

In spark-ignition internal combustion engines, knocking occurs when combustion of some of the air/fuel mixture in the cylinder does not result from propagation of the flame front ignited by the spark plug, but when one or more pockets of air/fuel mixture explode outside the envelope of the normal combustion front. The fuel–air charge is meant to be ignited by the spark plug only, and at a precise point in the piston's stroke. Knock occurs when the peak of the combustion process no longer occurs at the optimum moment for the four-stroke cycle. The shock wave creates the characteristic metallic "pinging" sound, and cylinder pressure increases dramatically. Effects of engine knocking range from inconsequential to completely destructive.

<span class="mw-page-title-main">Brayton cycle</span> Thermodynamic cycle

The Brayton cycle is a thermodynamic cycle that describes the operation of certain heat engines that have air or some other gas as their working fluid. The original Brayton Ready Motor used a piston compressor and piston expander, but modern gas turbine engines and airbreathing jet engines also follow the Brayton cycle. Although the cycle is usually run as an open system, it is conventionally assumed for the purposes of thermodynamic analysis that the exhaust gases are reused in the intake, enabling analysis as a closed system.

A combustion chamber is part of an internal combustion engine in which the fuel/air mix is burned. For steam engines, the term has also been used for an extension of the firebox which is used to allow a more complete combustion process.

<span class="mw-page-title-main">Afterburner</span> Adds additional thrust to an engine at the cost of increased fuel consumption

An afterburner is an additional combustion component used on some jet engines, mostly those on military supersonic aircraft. Its purpose is to increase thrust, usually for supersonic flight, takeoff, and combat. The afterburning process injects additional fuel into a combustor in the jet pipe behind the turbine, "reheating" the exhaust gas. Afterburning significantly increases thrust as an alternative to using a bigger engine with its attendant weight penalty, but at the cost of increased fuel consumption which limits its use to short periods. This aircraft application of "reheat" contrasts with the meaning and implementation of "reheat" applicable to gas turbines driving electrical generators and which reduces fuel consumption.

<span class="mw-page-title-main">Pratt & Whitney J58</span> High-speed jet engine by Pratt & Whitney

The Pratt & Whitney J58 is an American jet engine that powered the Lockheed A-12, and subsequently the YF-12 and the SR-71 aircraft. It was an afterburning turbojet engine with a unique compressor bleed to the afterburner that gave increased thrust at high speeds. Because of the wide speed range of the aircraft, the engine needed two modes of operation to take it from stationary on the ground to 2,000 mph (3,200 km/h) at altitude. It was a conventional afterburning turbojet for take-off and acceleration to Mach 2 and then used permanent compressor bleed to the afterburner above Mach 2. The way the engine worked at cruise led it to be described as "acting like a turboramjet". It has also been described as a turboramjet based on incorrect statements describing the turbomachinery as being completely bypassed.

<span class="mw-page-title-main">General Electric LM6000</span>

The General Electric LM6000 is a turboshaft aeroderivative gas turbine engine. The LM6000 is derived from the CF6-80C2 aircraft turbofan. It has additions and modifications designed to make it more suitable for marine propulsion, industrial power generation, and marine power generation use. These include an expanded turbine section to convert thrust into shaft power, supports and struts for mounting on a steel or concrete deck, and reworked controls packages for power generation. It has found wide use including peaking power plants, fast ferries and high speed cargo ship applications.

A combustor is a component or area of a gas turbine, ramjet, or scramjet engine where combustion takes place. It is also known as a burner, burner can, combustion chamber or flame holder. In a gas turbine engine, the combustor or combustion chamber is fed high-pressure air by the compression system. The combustor then heats this air at constant pressure as the fuel/air mix burns. As it burns the fuel/air mix heats and rapidly expands. The burned mix is exhausted from the combustor through the nozzle guide vanes to the turbine. In the case of a ramjet or scramjet engines, the exhaust is directly fed out through the nozzle.

<span class="mw-page-title-main">Gasoline direct injection</span> Mixture formation system

Gasoline direct injection (GDI), also known as petrol direct injection (PDI), is a mixture formation system for internal combustion engines that run on gasoline (petrol), where fuel is injected into the combustion chamber. This is distinct from manifold injection systems, which inject fuel into the intake manifold.

Homogeneous Charge Compression Ignition (HCCI) is a form of internal combustion in which well-mixed fuel and oxidizer are compressed to the point of auto-ignition. As in other forms of combustion, this exothermic reaction produces heat that can be transformed into work in a heat engine.

The Gluhareff Pressure Jet is a type of jet engine that, like a valveless pulse jet, has no moving parts. It was invented by Eugene Michael Gluhareff, a Russian-American engineer who envisioned it as a power plant for personal helicopters and compact aircraft such as Microlights.

Internal combustion engines come in a wide variety of types, but have certain family resemblances, and thus share many common types of components.

<span class="mw-page-title-main">Internal combustion engine</span> Engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber

An internal combustion engine is a heat engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal combustion engine, the expansion of the high-temperature and high-pressure gases produced by combustion applies direct force to some component of the engine. The force is typically applied to pistons, turbine blades, a rotor, or a nozzle. This force moves the component over a distance, transforming chemical energy into kinetic energy which is used to propel, move or power whatever the engine is attached to.

<span class="mw-page-title-main">Pressure gain combustion</span>

Pressure gain combustion (PGC) is the unsteady state process used in gas turbines in which gas expansion caused by heat release is constrained. First developed in the early 20th century as one of the earliest gas turbine designs, the concept was mostly abandoned following the advent of isobaric jet engines in WWII.

References

  1. 1 2 Wilson, J. Parley (February 2011). Effects of Water Injection and Increased Compression Ratio in a Gasoline Spark Ignition Engine (Thesis). University of Idaho.
  2. ↑ Kroes & Wild 1995, p. 143.
  3. 1 2 A&P Powerplant Textbook (3rd ed.). Jeppeson Company. 2011. ISBN   978-0884873389.
  4. ↑ Kroes & Wild 1995, pp. 285–286.
  5. ↑ Roux, Élodie (2007). Turbofan and Turbojet Engines: Database Handbook. p. 213. ISBN   9782952938013.
  6. ↑ Daggett, D. L.; Ortanderl, S.; Eames, D.; Berton, J. J.; Snyder, C. A. (November 2, 2004). "Revisiting Water Injection for Commercial Aircraft". SAE Mobilus. US. doi:10.4271/2004-01-3108.
  7. ↑ Accident descriptionfor Paninternational crash near Hamburg-Fuhlsbüttel at the Aviation Safety Network
  8. ↑ "Ολυμπιακή Αεροπορία πτήση 411: Οταν κατα την απογείωση το ΑΕΡΟΠΛΑΝΟ εξυσε τις πολυκατοικίες στον Αλιμο" [Olympic Aviation flight 411: When during the take-off the PLANE scraped the apartment buildings in Alimos] (in Greek). December 27, 2020. Retrieved February 17, 2022.
  9. ↑ "Jetfire". Oldsmobile Mail List Server Community. Archived from the original on February 25, 1999.
  10. ↑ "New BMW M water injection system". BMW M Power. BMW. October 7, 2015. Retrieved November 14, 2021.
  11. ↑ Durst, B.; Unterweger, G.; Reulein, C.; Ruppert, C.; Linse, D; Kerkn, W. (2015). "Leistungssteigerung von Ottomotoren durch verschiedene Wassereinspritzungskonzepte". MTZ-Fachtagung Ladungswechsel im Verbrennungsmotor (in German). Germany.
  12. 1 2 PAUER, T.; FROHNMAIER, M.; WALTHER, J.; SCHENK, P.; HETTINGER, A.; KAMPMANN, S., 2016. "Optimierung von Ottomotoren durch Wassereinspritzung." In: 37. Internationales Wiener Motorensymposium.
  13. ↑ Bosch WaterBoost - Bosch Mobility Solutions
  14. ↑ THEWES, M.; BAUMGARTEN, H.; SCHARF, J.; BIRMES, G.; BALAZS, A. et. alt., 2016 "Water Injection - High Power and High Efficiency combined" In: 25. Aachener Kolloquium Fahrzeug- und Motorentechnik
  15. ↑ CONWAY, Graham, 2019. "Injection of Alternative Fluids for Knock Mitigation." In: SAE, International Powertrains, Fuels and Lubricants Meeting. San Antonio, Texas, January 22–24, 2019.
  16. ↑ Hébert, Guillaume; Bazala, Jiří; Fischer, Oliver; Nothbaum, Jürgen; Thewes, Matthias; Voßhall, Tobias; Diehl, Peter (2019). Exhaust Gas Condensate as an Enabler for Self-Contained Water Injection Systems. 28th Aachen Colloquium Automobile and Engine Technology.
  17. ↑ Nour, M; Kosaka, H; Abdel-Rahman, Ali K; Bady, M (2016). "Effect of Water Injection into Exhaust Manifold on Diesel Engine Combustion and Emissions". Energy Procedia. 100: 178–187. doi: 10.1016/j.egypro.2016.10.162 .

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