The BMW M4 GTS is one of few production cars to use a
water injection system. The M4 GTS sprays water into the intake manifold to
cool down air for its engine.
How in the world does water help make more horsepower?
That's the question Jason Fenske of Engineering Explained answers in this
episode. First, a quick overview of the air intake system for the 3.0-liter
turbo-6 engine.
The M4 GTS takes in air and
it passes through the air filter into the turbo's compressor where it's heated.
The air then makes its way to an air-to-water intercooler where the compressed
air cools down, and then into the intake manifold for the engine. The goal is
to always push cooler, denser air into the engine, which also reduces knock.
While the air-to-water intercooler is effective (BMW says it
can reduce the air temperature from 320 degrees to 158 degrees), higher revs
and more combustion cycles mean more heat will be produced. That's where the
water injection helps.
When two conditions are met, the engine is revving over
5,000 rpm and the driver floors it, the water injection system kicks in. A
water tank in the trunk pumps water to the engine, where injectors in the
intake manifold spray water to create cooler air. The injectors spray water at
about 145 psi. The water reduces in the intake air's temperature by another 77
degrees to 113 degrees.
As the water evaporates, it absorbs energy from around it
and cools down the air. Subaru uses a somewhat similar practice to cool down
the intercooler in the WRX STI S209.
This leads us to how water actually makes more horsepower.
The water itself doesn't create more power, but it lets the engine operate
better. With cooler air, there's less chance for knock, so BMW was able to dial
up the M4 GTS' boost pressure to 21.6 psi, up from 17.2 psi in the M4
Competition. With the extra boost, the M4 GTS makes an extra 49 horsepower.
source; https://www.motorauthority.com/news/1121006_learn-how-bmw-used-water-to-make-more-horsepower-in-the-m4-gts
by Sean Szymkowski
http://www.boscheuropean.com
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