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Water injection
© 2017 Mattia Piron. All rights reserved.
DECEMBER 29th, 2018
Introduction top
This system consists in the injection of water (or a water/alcohol mixture) in the intake duct, in mixture with the fuel or directly inside the combustion chamber, in order to cool it and avoid the danger of detonation, thus allowing the use of higher compression ratios and higher ignition timing. Water, having a high latent heat of vaporization, requires a lot of energy to pass from the liquid to the gaseous state. Some of the injected water evaporates immediately, cooling the fuel line walls and inlet air, improving volumetric efficiency. During the compression phase, the water still present in liquid form starts to evaporate due to the increase of temperature in the combustion chamber, cooling it and lowering its pressure, thus allowing a reduction of the compression work and the probability of detonation. During combustion a lot of heat is developed, which is partly absorbed by the water, decreasing the peak cycle temperature and consequently the formation of NOx. In addition, the steam produced helps to generate thrust on the piston, slightly increasing engine power.
Water injection during WWII top
Called MW50, this is a 50% methanol/water mixture used in aviation during World War II. Created to reduce the risk of detonation, it then allowed the boost ratio to be increased. For the same purpose there was also MW30, containing 30% methanol and 70% water, with worse antifreeze properties and for this reason used in low altitude missions, and EW30 and EW50, in which instead of methyl alcohol ethyl alcohol was used. In the aero engines BMW 801 and DB 605 the sole activation of the water injection system allowed an increase in power of about 100 horsepower, however it was possible to simultaneously increase the boost pressure, reaching an increase of 500 horsepower (just under 30% more power).
White diesel top
So called because of its color, it is a mixture 88% diesel, 10% water and 2% stabilizing additive. It is mainly used in urban Diesel buses, the presence of water, in addition to reducing NOx emissions, also reduces particulate matter.
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