Function

• This injection system works very similarly to a fuel injection system. The only difference is that a water injection system injects water, or an alcohol and water solution, instead of fuel. According to rallycars.com, "Water injection is used to lower in-cylinder temperatures and burn the air/fuel mixture more efficiently thus helping avoid detonation." Detonation, which is also known as engine knock, occurs when the air and fuel mixture is ignited prematurely or burned incorrectly.
  
  

Variations

• The three variations of a water injection system depend on the location of their injector. One technique involves injecting water at the entrance of an automobile's intake manifold. Another technique involves the injection of water at the exit pipe of an intercooler. The last technique involves injecting water at the entrance of the intercooler. This last technique is traditionally used in competition vehicles.
  
  

Features

• A water injection system employs three basic elements to function properly. Water injection systems include a water injector that is similar to a fuel injector and an inlet air temperature sensor. A pressure sensor is connected to the automobile's manifold. Water injection systems also include a high pressure pump which is capable of reaching at least three to four bar pressure. A "bar" is a unit of measurement used to gauge pressure. One bar is approximately equal to atmospheric pressure or 101,325 pascals.
  
  

How It Works

• A water injection system engages when the inlet air temperature exceeds a certain value, usually around 40 degrees Celsius. More advanced systems add to the electronic circuitry that provides three-dimensional cartography similar to fuel injection systems. Cartography devices consider many parameters like air to fuel ratios and throttle position.
  
  

Considerations

• Detonations should always be avoided in vehicles. It can be avoided by either lowering inlet temperatures, using a higher octane fuel or by lowering the compression ratio. Water injection systems only benefit normally aspirated engines in cases involving high compression ratios, low octane fuel or too much ignition advance.