It's a complex process that's made understandable in this six-minute video.

It has been more than three years ago when BMW introduced the M4 GTS – its first Bimmer to be installed with a Bosch water injection system. With this system, the track-focused M4 GTS is able to produce 493 bhp. However, that process, even though it has been used before by Chrysler and Saab, as well as in the aircraft industry, has never been explained quite fully to the point that a common motorhead would be able to understand it. 

Fortunately, Engineering Explained goes back to the whiteboard and took time to explain the seemingly engineering miracle.

In a nutshell, the main purpose of the water injection system is to decrease the temperature before the combustion chamber in order to prevent the possibility of engine knocks or premature ignition. This is done by spraying distilled water onto the intake manifold, which comes from the 50-litre tank at the trunk. But how does that provide an extra 50 bhp boost to the engine?

Apparently, with the air denser and the temperatures lower, BMW was able to increase the boose from the turbocharger from 17.2 to 21.6 PSI. The increased boost should, of course, increase the final output and together with aggressive timing, the M4 GTS could produce 493 bhp – up by 49 bhp from a regular M4.

Another advantage of the water injection system is that it could reduce thermal stress within the engine parts like the pistons, exhaust valves, and catalytic converters since they would be operating in lower temperatures. The turbocharger would also be subjected to less thermal stress. 

As the water injection system would only engage when driving in heavy load (5,000 rpm and wide open throttle), refilling the water tank in the trunk with water won't really be an issue if it's only a regular road drive. And besides, the engine will recognize if the tank doesn't have water, and will automatically adjust the timing, so there's that.

For the record, the water injection system has been used in the aftermarket scene, but this is almost the first time that an OEM manufacturer included the system in a car right out of the showroom. With that, it makes us wonder what would happen if methanol and water would fill the tank. Would it promote a higher boost? Or is it even possible with the Bosch system installed in the M4 GTS? Guess we'll leave that to the aftermarket geniuses.

Source: Engineering Explained via Youtube