Water Injection has been around for a
long time. it was used in some World War II aircraft engines
to prevent pinging/detonation under boost. In times of tight
emission controls, decreasing fuel octane and rising petrol
costs, water injection is one of the best ways of
controlling detonation whislt increasing engines performance
through cooler intake air tempratures, more timing and/or
boost. It is also easy to install.
What is Detonation /
"Pinging"?
Detonation, an effect also known as engine knock or pinging,
occurs when the air/fuel mixture ignites prematurely or
burns incorrectly. In normal engine operation the flame
front travels from the spark plug across the cylinder in a
predefined pattern. Peak chamber pressure occurs at around
12 degrees after TDC and the piston is pushed down the bore.
How the Boost Cooler
works:
Water injection works in three main ways. Firstly,
when the water is injected into the intake system prior to
the cylinder head, the atoms of water absorb heat from the
intake air. Water cools air 4x better than air, it takes 4x
the energy to heat water than it does to cool air. As the
hot air rushes past the mist of water it is forced to cool
to the same temprature as the water.
Next, the small drops of water start to evaporate. Water has
a very high latent heat of evaporation (its change of state
absorbs a lot of heat) and so the intake air charge is
cooled still further.
Finally, when the remaining water droplets and water vapour
reach the combustion chamber, steam is produced. This acts
as an anti-detonant and also keeps the interior of the
engine very clean, so preventing the build-up of carbon "hot
spots".
