Introduction:
Engines must of course be cooled. The petrol fuel in a petrol engine also provides cooling. At higher engine loads, the mixture is enriched. There is then an excess of fuel, which among other things ensures that the combustion chamber (the cylinder) is cooled from the inside. This is because the petrol absorbs extra heat during evaporation. This helps prevent detonation, where the fuel ignites uncontrollably due to the high temperature of the engine components.
Injecting water into the cylinder also cools the components in the combustion chamber. If an engine is equipped with water injection, no extra fuel needs to be injected for cooling; this results in lower fuel consumption and in more engine power.
The water in water injection is therefore not used as a fuel, as is the case with hydrogen. These techniques should not be confused with each other!
Operation of water injection:
The water injector can be mounted in the cylinder head or in the intake manifold of a petrol engine. This is possible both when injecting petrol fuel and when injecting hydrogen, in liquid or gaseous form, used as a fuel. The water injector should be located as close as possible to the intake valve.
When additional cooling in the combustion chamber is desired, the water injector is controlled by the ECU. This will happen when power is demanded (such as during acceleration or when driving at high speeds) and there is a risk of knocking. That is why water injection is also called “anti-detonation injection”. In cars where only RON98 may be used, water injection can also be a solution to allow the use of RON95, because the water vapour prevents detonation phenomena.
An external water pump provides the water pressure in the injector line. At the moment the injector is actuated by the ECU, it will open and a water mist will be injected. The water mist is mixed with the incoming air for the combustion chamber in front of the intake valve. The tiny water droplets evaporate immediately and absorb some of the heat present in the combustion chamber.
The resulting water vapour disappears into the exhaust. Because the amount of injected water is minimal, there is no danger of rust or oxidation of the engine components. The water reservoir will need to be periodically filled with distilled water.
In the image below, the water injector is placed in the cylinder head.
Engine power also increases when using water injection. A higher boost pressure of the turbo and earlier ignition are possible without the risk of detonation.
The power of, for example, the BMW M4 GTS increases by no less than 37 kW with water injection. That is a power gain of approximately 10% compared to the “standard M4”. This is accompanied by a fuel saving of up to 13% in situations where a rich mixture is desired; during acceleration and when driving at high speeds.
The engine can also run without water injection without any problems. However, maximum performance cannot be achieved because there is then a lack of cooling. Without the use of water injection, there will therefore be a limitation of engine power.
