Water injection (engine)

The water injection is a method to enhance performance of internal combustion engines.

This is injected into the intake of a supercharged piston engine or compressor of a gas turbine, distilled water or a water / alcohol mixture into the combustion air. The evaporating liquid has a cooling effect and reduces the compression work. The method is again in the investigation, as it may reduce emissions, especially nitrogen oxides from jet engines.

Piston engines

The injected fluids into the air - intake tract of the effect by the applied evaporation heat, an effective charge-air cooling, and thus also achieve internal cooling of the engine. Due to the colder and thus higher density of the combustion air results in an increase in performance. Furthermore, the firing angle can be adjusted in the direction of pre-ignition because the cooler combustion air is less prone to knock. Beige -mixed methanol also increases knock resistance enormously and acts as an additional fuel.

Water injection has been used primarily in World War II and in the 1950s to increase the performance of machines in aviation. Also, the first turbocharged production car, the Saab 99 Turbo was optional purchase with water injection. In the 1980s, were as turbo engines by the FIA ​​still allowed discovered the formula 1, the benefits of water injections new. Currently, water injections in motorsport, for example, in the World Rally Championship ( WRC), are used. The technology has been developed and refined since then. Modern water injection systems regulate the injection quantity by means of the data of mass air flow sensor, the applied loading pressure, fuel injection quantity and additionally via the exhaust gas temperature.

Also in two-stroke engines, the injection of water was applied. The sound velocity was reduced significantly in the lower speed range by injecting liquid water in the exhaust. This enabled the resonant effect of the exhaust pipe also move downwards. Characterized the torque curve, and thus the power characteristics much flatter and the useful rpm range has been significantly increased. Especially Honda put this technique in the 1980s, one of the racing world.

The technology is now in the car tuning used. Moreover, the use in the test of influencing the behavior of exhaust gas from diesel engines takes place.

In the field of diesel cogeneration water injection is applied recently.

Gas turbines

Especially after the development of the first jet-propelled passenger aircraft, the water injection was used to increase thrust at launch. They spoke in such cases by 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 their capacity for full-load starting. This thrust increase comes about by two factors: Firstly, the evaporation of water produces extra volume and thus extra boost (conversion of heat energy into volume work). One liter of water occur at 25 ° C and 1013 hPa pressure to 1673 liters of water vapor, which corresponds to an increase in the volume by more than a thousand times. Second, the engine is cooled by the evaporation enthalpy of the water, so that there is more fuel may be injected, without exceeding the permissible operating temperature of the engine. A disadvantage of the method were partially strong smoke that could develop the aircraft engines during wet start when water and fuel supply were not coordinated.

Wet start time are rarely performed for. One reason for this lies in the fact that, nowadays, twin-engine aircraft to be used in a high degree. This must hold for the case of an engine failure high power reserves, which is why they are usually motorized strong enough to start fine without water injection can. Another reason lies in increased strength due to the water injection: At startup, the water was injected into the already ongoing and accordingly, hot engines, due to the sudden cooling of the high temperatures exposed engine parts thermomechanical stresses are exposed. For these reasons, wet -offs have rarely applied.

Major aircraft types where water injection was used, were the Boeing 707, the Douglas DC -9, and the Sud Aviation Caravelle and the famous bomber Boeing B -52 of the U.S. Air Force. Also the Boeing 747, the first series took advantage of this technology, particularly in engines of the type Pratt & Whitney JT9D. The corresponding systems, however, were later removed from most aircraft. To improve performance in the start phase at individual hot days the water injection was also recently back in the Boeing 777 -X in conversation.

An unsuccessful wet start was the cause of the historic landing of a BAC 1-11 on the A7 north of Hamburg on September 6, 1971. Instead of demineralized water a combustible fuel / water mixture into the corresponding tank was filled, so that both engines due to overheating failed.