Cooling the charge

In a turbo application the intake air charge temperatures increase as you move/compress the air, so to improve the volumetric efficiency and thus improve power, it is good practice to increase intake air charge density through isochoric cooling. The decrease in temperature of the charge air provides a denser intake charge to the engine and therefore allows more air and fuel to be burnt, increasing the power output of the engine. There are three methods of doing this; air-to-air (also known as an intercooler), air-to-liquid (also known as a chargecooler) and water-injection

Air-to-liquid cooling

A chargecooler is essentially a heat exchanger that rejects the heat energy in the intake charge air to an intermediate fluid, which is usually water that then rejects the heat to the air. Chargecooler systems use a remote radiator usually located at the front of the vehicle (much like an intercooler) and are used in applications where space is at a premium. Chargecooling systems are comprised of the following components;

Chargecooler systems are widely available and are normally sold as a system that supports a desirablable power output.

Air-to-air cooling

An intercooler is simply a heat exchanger, it allows the compressed and heated intake charge to pass through it to reduce the charge's temperature (due to heat rejection) and pressure (due to flow restriction of fins). A correctly designed and specified intercooler can result is a net increase in density. A further cooling effect can be provided by spraying fluid on the external surface of the intercooler to further reduce intake charge temperature through evaporative cooling. Intercoolers are designed to be mounted in areas of a vehicle with maximum air flow, normally in front of the radiator and are commonly called 'Front mounted intercoolers' (FMIC). Care has to be taken not to use too large an intercooler, as it can result in the intercooler having very little or no effect. If the pressure drops too much across it, the increase in density can be counteracted by the pressure drop.

Water injection

This can be done as a single solution, but also in conjunction with the two above methods. Water injection adds water to the incoming fuel-air mixture, which allows for greater compression ratios (i.e. turbo or supercharger) and largely eliminates the problem of engine knock. Most water injection systems can be used with a mixture of water and alcohol (normally 50/50). This is partly because the alcohol is itself combustible, whereas water is not (the alcohol also acts as an antifreeze for the water). Therefore in most cases water injection is known as methanol-water injection, due to the fact that the alcohol mixed into the injection solution is often methanol, CH₃OH. Only methanol and isopropanol cna be used as the alcohol, as ethanol is corrosive. Most commonly used is the methanol owing to its higher availability