Water injection

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The water injection is a method of reducing the intake air of internal combustion engines . It can be used to increase performance ( downsizing or tuning ), to reduce emissions or fuel consumption. In order not to exceed the maximum temperature of the catalytic converter at maximum power, water is injected into the intake tract or combustion chamber of a piston engine or a compressor of a gas turbine . A water / alcohol mixture (see also MW-50 ) has a similar effect. The evaporating liquid has a cooling effect and reduces the compression work. Injection during the work cycle to generate steam power and to reduce the exhaust gas temperature and thus to reduce the exhaust back pressure is also used. The process is currently part of a series project and many research activities.

Piston engines

The liquid injected into the air intake tract causes effective charge air cooling through the evaporation heat to be applied and thereby also achieves internal cooling of the engine. In addition to being injected into the air intake tract, the water can also be injected directly into the combustion chamber. Furthermore, the ignition point can be adjusted further in the direction of pre-ignition, since the cooler combustion air has less tendency to knock . Added methanol serves primarily as protection against icing in aircraft engines. Because the mixture is injected in front of the compressor, there would otherwise be a great risk of the intake tract icing up, as the air there has the low ambient temperature at high altitude and a lower static pressure .

history

Donát Bánki , chief engineer at Ganz & Co. in Budapest , received a patent in 1898 for an internal combustion engine with water injection and (for that time) an increased compression ratio.

The Soviet chain tractor SChTS-NATI , manufactured from 1937, had a petroleum engine with water injection installed as standard. Water injection was used in the Second World War and in the 1950s to increase the performance of aircraft engines in aviation . The application is limited to periods of about 5–10 minutes, depending on the type of engine. Therefore it was only used to briefly increase take-off performance or, in the case of military aircraft, to increase flight performance in aerial combat.

The first turbocharged production car, the Saab 99 Turbo, was optionally available with water injection. In the 1980s, when turbo engines were still allowed by FISA , Formula 1 rediscovered the benefits of water injection. In the past, water injection was used in motorsport, for example in the World Rally Championship (WRC).

Water injection was also used in two-stroke engines . By injecting water into the exhaust, the speed of sound was significantly reduced in the lower speed range. As a result, the resonance effect of the exhaust could be shifted to lower speeds, the torque curve and thus the performance characteristics are flatter and the usable speed range is increased. Honda in particular used this technology in racing engines in the 1980s.

System structure

The engine control unit calculates the required amount of water. A pump conveys the requested amount of water from a water tank through a filter into a water rail. Depending on how it is integrated, the water is then added to the fuel or injected into the combustion chamber or the intake stroke using an injection valve. In the case of injection into the combustion chamber, the existing direct injection can be used in order to save costs and installation space. Water can either be mixed with the fuel or injected in layers. The water tank must be refilled by the driver. In order to avoid this as far as possible, different methods of obtaining water while driving are being investigated and applied. In addition to refueling, the condensate from the air conditioning system, the exhaust gas condensate or surface water from the body can be used to obtain additional water. To avoid limescale deposits, distilled water should be used whenever possible.

Petrol engines

Water injection is used in gasoline engines to reduce emissions and fuel consumption or to increase performance. This is done in particular by lowering the temperatures of the air flows. Compared to conventional internal combustion engines, highly charged gasoline engines develop a significantly higher intake air temperature due to the charging process. Due to this strong increase in temperature, the knock limit is reached early at high loads and the ignition point must be set in the late direction. Overall, this leads to a poorer efficiency, as a result of which the exhaust gas temperature rises and the output falls. In order to protect the catalytic converter, the exhaust gas temperature has to be reduced. In conventional engines, this is done, among other things, by enriching the fuel mixture (typically λ = 0.8). The additional fuel evaporates and thus lowers the exhaust gas temperature. As a result of the enrichment, the catalytic converter leaves its working window, which significantly increases emissions. In addition, the rich fuel mixture also increases fuel consumption considerably. The water injection provides a remedy here. When the water is injected into the intake manifold, the intake air temperature is significantly reduced, which in turn has a direct effect on the exhaust gas temperature. BMW mentions a reduction in the intake air temperature of 14 K for a research engine. When the water is mixed with gasoline, this is injected directly into the combustion chamber by direct gasoline injection and can thus also significantly reduce the temperature of the cylinder charge (by 55 K in the research engine mentioned). The low temperatures enable a stoichiometric fuel mixture, which means that the catalytic converter remains in its working range. Fuel consumption is also reduced, as the mixture no longer has to be enriched with excess gasoline. Due to the shifted knock limit, the compression can be increased, whereby an increase in performance and a further reduction in fuel can be achieved. With the lower temperature, if the charge is increased, an increase in performance - for example for downsizing - can be applied.

Diesel engine

The system for reducing emissions in the diesel engine is currently being researched. Nitrogen oxides (NO x ) are formed during diesel combustion, especially at high temperatures. These emissions can be effectively reduced by reducing the firing temperatures. Excessively high exhaust gas temperatures also limit the function of the SCR catalytic converter , as a result of which the NO x emissions increase sharply. To remedy this problem, exhaust gas recirculation systems are used in conventional diesel engines . This has the disadvantage that it reacts rather slowly and significantly increases soot emissions. In contrast, water injection has no negative influence on soot emissions and can be controlled very dynamically.

Aircraft turbines

KC-135 at take-off with water injection and clearly visible plumes of smoke.

Especially after the development of the first jet-powered passenger aircraft, water injection was used to increase the power of the engines for full-load starts. In such cases one spoke of a wet start . For this purpose, distilled water or a water-methanol mixture was injected into the combustion chamber of the engines in order to increase the thrust during take-off. This is due to two factors: On the one hand, the evaporation of the water creates additional volume and thus additional thrust (conversion of thermal energy into volume work ). One liter of water at 25 ° C and 1013 hPa pressure produces 1673 liters of water vapor, which corresponds to an increase in volume of more than a thousand times. Second, the engine is cooled by the enthalpy of vaporization of the water (heat of vaporization at 100 ° C is 2257 kJ / kg), so that more fuel can be injected per air volume without exceeding the permissible operating temperature of the engine. In this operating mode with an over-rich mixture, thick clouds of smoke are generated, i.e. a high amount of pollutants due to unburned fuel and soot formation.

Wet starts are rarely carried out. One reason is that twin-engine aircraft are used to a large extent today . In the event of an engine failure, these must have high power reserves, which is why they are usually powerful enough motorized to be able to start without any problems even without water injection. Another reason is increased material fatigue due to the water injection: When the engine was started, the water was injected into the engines that were already running and therefore hot. Due to the sudden cooling, the engine parts exposed to the high temperatures are exposed to thermomechanical stresses.

Aircraft types with water injection were

In order to increase performance in the start-up phase on individual hot days, water injection has recently been discussed again with the Boeing 777X .

A failed wet start was the cause of the spectacular emergency landing of a BAC 1-11 on the A7 north of Hamburg on September 6, 1971. Instead of demineralized water , a flammable kerosene- water mixture was filled into the corresponding tanks, so that both engines were Failed overheating.

Use in motor vehicles

With the introduction of engine charging in road vehicles, some vehicle manufacturers such as B. Chrysler for the use of water injection. The Oldsmobile F85 model - introduced in 1962 - was equipped with the "Jetfire" engine variant with water injection (marketed as "the world's first turbo-charged road vehicle"; at the same time as the Corvair Spyder model). The water / alcohol mixture was marketed by Oldsmobile as 'Turbo-Rocket Fluid'. In Europe, Saab had an engine with water injection on offer with the Saab 99 Turbo until the mid-1980s. With the spread of the intercooler in supercharged engines, the lowering of the intake air temperature was ensured even without water injection. The technology of water injection basically allows the reduction of nitrogen oxide (NO) and carbon monoxide (CO) emissions in the exhaust gas. However, the focus of this technology is currently on the possibility of lowering the temperature of the cylinder charge and shifting the knock limit. This allows a higher compression, which in turn enables an increase in performance or a reduction in fuel consumption.

In 2015, BMW presented a variant of the high-performance M4 coupe, the M4 GTS. This variant combines water injection with the use of a charge air cooler. The market launch took place in 2016. Other vehicle manufacturers are also currently developing engines with water injection, where the focus is on a possible "increase in performance". However, it is to be expected that there will be a shift towards "improving fuel consumption" in the mid-2020s. This is mainly due to the increasing pressure to reduce CO 2 emissions and the associated regulation of limit values.

Bosch, co-developer of this technology in cooperation with BMW, also offers the water injection system to other vehicle manufacturers under the name "WaterBoost". When using this system, Bosch demands up to 5% more engine power, up to 4% lower CO 2 emissions and up to 13% improvement in fuel consumption. Similar results were published by FEV Europe GmbH. Up to 5.3% improvement in the fuel consumption of a 2.0 L petrol engine is possible. In combination with cooled exhaust gas recirculation - depending on the selected driving cycle - more than 7% improvement in fuel consumption can be achieved.

Water injection and cooled exhaust gas recirculation (EGR) can be viewed as competing technologies. Research results have shown that in the partial load range a 40-50% water / fuel ratio (water injection takes place in the intake tract) shows a comparable effect to a 10% EGR rate. The advantages of water injection lie in the simpler system control, since it is not a closed circuit (as with exhaust gas recirculation). In addition, the time of injection of the water is independent of other parameters such as e.g. B. Exhaust back pressure on the turbocharger, gas exchange effects and possible ignition delay (in contrast to EGR). Furthermore, the injection of water has only a minor influence on the stability of the combustion. The ignition delay (caused by the EGR dilution) and the necessary adaptation of the recirculated exhaust gas mass flow to the turbocharger characteristics are usually the two limiting parameters for the maximum possible EGR rate. Therefore, the use of water injection enables synergy effects to be achieved, especially in the operating areas of the engine in which the recirculation of cooled exhaust gas is typically not possible (full load / high speed).

On-board water extraction systems

Customer surveys on the willingness of vehicle users to continuously fill up additional equipment show only a low level of acceptance. Therefore, the necessity of continuously replenishing the water tank is considered to be the major obstacle to the mass use of water injection. This situation will be greatly improved with the development of a closed water recovery system. Such a system also ensures compliance with low CO 2 emissions (possible increase in the absence of water).

Basically 3 types of water extraction are conceivable:

Condensation off

  • the environment (e.g. condensate from humidity (air conditioning))
  • Rainwater (body)
  • Exhaust gas condensate

The first two variants depend on the weather conditions (sufficient relative humidity) or user habits (no use of the air conditioning). As a result, sufficient availability of condensate cannot be ensured. On the other hand, the condensation of water vapor from the exhaust gas is a reliable source. When 1 liter of Otto fuel is burned, approximately the same volume of water is produced, but still in the form of water vapor. In October 2019, Hanon Systems and FEV Europe GmbH presented a modified series vehicle (Audi TT Sport) that is equipped with a water injection system ("Port Water Injection") in combination with a self-sufficient water recovery system ("Water Harvesting System") from Hanon Systems is equipped. The system integrated in the series vehicle was able to provide sufficient water for water injection even under the most unfavorable operating conditions. In fact, about twice the volume of water required was condensed. The condensate was transparent with no strong odor or color.

See also

Web links

Individual evidence

  1. ↑ water injection. BMW, May 5, 2016, accessed May 5, 2016 .
  2. ^ Graham White: R 2800: Pratt & Whitney's Dependable Masterpiece . 2001, ISBN 0-7680-0272-9 , pp. 215-220, 311-313 .
  3. ↑ Banki, Donat . In: Austrian Biographical Lexicon 1815–1950 . 2nd revised edition (online only).
  4. ↑ Small communications. Various. (...) New petrol engine from Ganz & Comp. . In: Johann Sahulka (Red.): Zeitschrift für Elektrotechnik ( ISSN  1013-5111 ), 18th year 1900, issue 47, p. 570. (bottom left)
  5. ^ Horst Hintersdorf: Typenkompass. Tractors and agricultural machinery GDR imports from the Comecon countries. Motorbuch Verlag, 1st edition 2006, p. 31.
  6. ↑ Bosch water injection. Robert Bosch GmbH, August 31, 2016, accessed July 8, 2018 .
  7. ↑ a b c Martin Böhm, Werner Mährle, Hans-Christian Bartelt and Stephan Rubbert: Functional integration of a water injection in the gasoline engine, in: MTZ 77 (2016), No. 1, pp. 38–43, Springer Vieweg, Wiesbaden
  8. ↑ Martin Böhm, Bodo Durst, Georg Unterweger, Stephan Rubbert: Approaches to Onboard Water Production for Water Injection, in: ATZ 118 (2016), No. 1, pp. 54–59, Springer Vieweg, Wiesbaden
  9. ↑ Robert Plöntzke: The internal combustion engine - a drive with a past and a future . Springer, 2017, ISBN 978-3-658-19291-4 , pp. 347-362 , doi : 10.1007 / 978-3-658-19291-4_19 .
  10. ^ Aviation lexicon: W. luftpiraten.de, October 13, 2010, accessed on August 8, 2009 .
  11. ^ Willy JG Bräunling: aircraft engines . Springer, 2004, ISBN 3-540-40589-5 , pp. 179 ( p.179 in Google Book search). , accessed August 8, 2009
  12. ↑ Flight Global: Emirates boss wants more power from 777x engines. Retrieved November 8, 2013 .
  13. ↑ Olds FAQ - Jetfire
  14. ↑ BMW M Power - Innovative water injection system
  15. ↑ DURST, B .; UNTERWEGER, G .; REULEIN, C. et al., 2015. Increasing the performance of gasoline engines through various water injection concepts. In: MTZ conference gas exchange in combustion engines. 8th
  16. ↑ PAUER, T .; FROHNMAIER, M .; WALTHER, J .; SCHENK, P .; HETTINGER, A .; KAMPMANN, S., 2016. Optimization of gasoline engines through water injection. In: 37th International Vienna Motor Symposium
  17. ↑ Bosch WaterBoost - Bosch Mobility Solutions
  18. ↑ THEWES, M .; BAUMGARTEN, H .; SCHARF, J .; BIRMES, G .; BALAZS, A. et. alt., 2016 Water Injection - High Power and High Efficiency combined in: 25th Aachen Colloquium Vehicle and Engine Technology
  19. ^ 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.
  20. ↑ Exhaust Gas Condensate as an Enabler for Self-Contained Water Injection Systems Ing.Guillaume Hébert, Ing.Jiří Bazala Hanon Systems Autopal Services sro, Hluk, Czech Republic Dipl.-Ing. Oliver Fischer, Dipl.-Ing. Jürgen Nothbaum Hanon Systems Germany GmbH, Kerpen, Germany Dr.-Ing. Matthias Thewes FEV Europe GmbH, Aachen, Germany M. Sc. Tobias Voßhall VKA, RWTH Aachen University, Aachen, Germany Dr.-Ing. Peter Diehl Consultant, Cologne, Germany 28th Aachen Colloquium Automobile and Engine Technology 2019