There are three main types of cleaning fluid.
Water and kerosene, with or without an emulsifier
This is the longest-established fluid. It cleans quite well and is cheap, especially since operators have kerosene available as fuel and sometimes forget the cost of this component.
It is not widely used now, partly because aromatic hydrocarbons (present in the fuel or the emulsifier) are banned in some countries, but mainly because the emulsion can split into water and kerosene. When this happens during a hot wash, the results can be catastrophic in overfuelling the engine and have led to the loss of aircraft in the past. The procedure is prohibited by many operators for this reason.
Usually these contain 50%-70% solvent such as White Spirit with the remainder being water with a detergent present to emulsify the solvent/water. They are diluted with water before use. Generally they are good cleaners, and are in wide use in the USA. However, the trend now is away from solvent-based cleaners. They tend to have an unpleasant smell and may be harmful, and handling is hazardous. Many contain aromatics and are banned in some countries. They are usually flammable and have restrictions on transport or storage. They can attack rubber seals causing swelling and possibly permanent damage to the rubber, and soften the paintwork of aircraft on which they splash. They can also be corrosive to some metals, and need many rinses to completely remove all traces of cleaner after a wash. Many specifications also prohibit the use of cleaners which cause embrittlement of high-strength steel or crazing of acrylic windows.
Although these products may be stored at +10F(-12C) without freezing, when used at low temperature an antifreeze must be added.
Aqueous-based cleaners (e.g. ZOK27® and ZOKmx®)
This is the most recent development in compressor cleaners and is steadily replacing older methods. Aqueous-based cleaners are solutions of detergent in water, sometimes with corrosion inhibitors. Usually diluted 1+4 with water before use, they have little solvent present and are non-flammable
They offer safe transportation and handling and ZOK27® has corrosion- inhibition as a bonus. They tend to freeze around 0C, so for operation at low temperature an antifreeze must be added.