Water injection. RR Dart
Although the Dart is not a modern engine there are still a few around, the injection is a water methonol system for use during take off.
The mixture is water 63 per cent, methonol 37 per cent plus Pyrodine at 0.5 % by weight, ( usually purchased ready mixed)
The system can be a power restoration system, (F27), where by the power is increased to the rated take off power, or boosted (Herald) where the power is inceased from a "dry" torque to a "wet" torque. This is achieved by simple adjustments to the water meth control unit, and these are set during the engine installation process.
The mixture increased the air density and adds more fuel, the aircraft that operated at max take off weight ie freight operators, tended to use water meth every time.
Regards,
om15.