Water injection relies on water's naturally high specific heat, which means it requires a lot of heat to change liquid water-to-water vapor (steam). The high specific heat is one of the reasons water is an excellent coolant. When injected into an engine, water does several things. When it is first injected, some of the water vaporizes, absorbing heat from the incoming intake stream. This helps cool the hot intake charge in much the same way N2O injected into the intake of a nitrous-equipped car does. Once inside the combustion chamber, the water is fully vaporized into steam. This vaporization absorbs a tremendous amount of heat from the combustion reaction, helping cool the engine internally to prevent hot spots that can be areas of self-ignition where detonation propagates. The heat absorbed from the water's phase change also acts to buffer the combustion event, slowing it down. Thus the water helps regular pump gas behave much like slow, controlled-burn, high-octane race gas.
The super-heated steam also acts like a powerful steam cleaner inside of the engine, removing compression rising, hot-spot propagating carbon deposits from inside the combustion chamber. As water does absorb power-producing heat, it does not produce quite the same horsepower per lb. of boost as race gas does, but it does allow quite a bit of additional boost. The water also goes a long way to eliminate engine-damaging detonation.
The Aquamist water injection system uses a unique proprietary atomizer nozzle to introduce the water to the intake air stream. The nozzle produces a range of droplet sizes from a fine fog to a coarse mist. This helps the water work more efficiently. The fine water fog vaporizes almost immediately, helping reduce the intake air temperature by about 20 to 30 degrees. The larger droplets don't vaporize until they reach the combustion chamber where they can cool and buffer against combustion. All the droplets are small enough where the even distribution of water throughout the manifold plenum is ensured.
Most modern fuel injected cars have manifolds that are designed to flow dry air only, not a mixture of liquid and air so the maintenance of correct water droplet size is critical for even cylinder-to-cylinder water distribution.
The common, old-school water injection system typically available makes no attempt to atomize the water. As a result, unequal distribution and over injection of water occurs, creating bogging and other driveabilty problems with still poor suppression of detonation.
The Aquamist system works so well the Euro Ford Sierra Cosworth uses this system as original equipment from the factory. The Aquamist system can be tuned using different sizes of jets ranging from 0.40mm to 1.0 mm. Because the SR20 engine has a relatively high (for a turbocharged engine) compression ratio of 9.5:1 stock and is burning 91-octane unleaded pee water, the large 1.0mm orifice jet with a flow rate of 335cc per minute was selected. Since the SE-R has a large windshield washer reservoir, it was tapped with a pick-up for the high-pressure water pump.
To partially offset the power reducing internal cooling produced by the water, it's possible to run a leaner fuel-air mixture and more ignition advance.
Clark Steppler of JWT integrated the water injection to the Engine Control Computer he reprogrammed for us in the last project installation. Using a microprocessor containing a daughter board interfaced to the ECU to control the water injection pump, Clark programmed the daughter board to turn on the injector pump at a mass airflow meter voltage approximating 8 psi of boost whenever the water injection master arm switch was activated.