DISADVANTAGES OF WATER INJECTION

There are some disadvantages to using a water injection system, some of which can be catastrophic! Firstly, a failure in your water injection system would mean a complete lack of detonation suppression, which could quickly lead to engine failure! To prevent such a scenario, you need a failsafe system that will cut engine power when the intake charge temperature downstream from the water injector reaches a certain threshold. Secondly, the minerals in tap water will quickly clog up the water injector and will result in a failure to deliver the correct amount of water.

For this reason you should use distilled water in your water injection system. As with any other system, you need to ensure that only quality hoses and clamps are used in order to ensure the reliability of you water injection system.

Finally, determining the correct amount of water that needs to be injected can be pretty tricky as you do not want high boost pressure with too little detonation suppression! The safest way of reaching the correct amount of water injection for a particular application is to start with a lower boost pressure and slowly increase boost pressure. If detonation occurs, back off immediately and increase the water injection if a greater boost pressure is required.

HOW WATER INJECTION WORKS

Atomized water rather, that vaporized water is injected into the air intake system as water only boils at 212° F at sea level while temperature of the intake charge would be much lower, having already passed through the intercooler. When water is injected into the air intake system it absorbs quite a bit a heat from the intake charge. When the atomized water, together with the intake charge, enters the combustion chamber, the high temperature of the combustion chamber causes the atomized water droplets to vaporize.

During the process of vaporization a large amount of heat energy is absorbed, resulting in anther drop in intake charge temperature! Unfortunately, vaporized water also displaces a large volume that would have been filled with air molecules, but the lowered temperature in the combustion chamber more than makes up for this loss in volume. Indeed, the lowered temperature in the combustion chamber allows us to run higher boost pressures and, consequently, allows us to make more power!

WATER AND METHANOL

Some engine tuners prefer to inject a mixture of water and methanol into the intake system. Usually 50% methanol by weight is used. This provides the desired detonation suppression while also providing maximum horsepower. Methanol is both hygroscopic, which means it absorbs water, and miscible, which means it mixes well with water. It is also much more volatile than water, which means it vaporizes much quicker.

This vaporization further reduces the temperature of the intake charge, but it occurs before the combustion chamber is reached. Once the combustion chamber is reached, the atomized water droplets vaporize so temperatures are still reduced in the combustion chamber. But methanol is also a fuel and thus provides extra horsepower as well.

Water Injection

On turbocharged cars water injection can also be used to cool the intake charge and reduce the possibility of detonation, though some engine tuners to frown upon it. Nonetheless, water has a very high specific heat capacity, which means it can absorb a lot of heat energy without a significant increase in temperature. As a result, water injection systems have been around in one form or the other since 1936 and were used on a variety of aircraft engines during World War II. However, water injection is only required if you're running high boost of more than 12 psi, and should be used in conjunction with a good intercooler.

The water injection system basically consists of a storage tank, a water injector, which is similar to a fuel injector, a high pressure pump, a pressure sensor connected to the intake manifold, and an intake air temperature sensor. Calling it water injection is possibly inaccurate as it can wither be pure water, preferably distilled water, or a mixture of water and methanol. Either way, atomized liquid is usually injected into the intake system when the intake air temperature is exceeding a certain value and the engine is on boost and is usually injected downstream of the intercooler.