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The BAC 1-11 did not use water/meth, it used de-mineralised water injection.
If water/meth is used it burns out the turbines.
Water injection is used for thrust augmentation and is injected into the combustion chamber to cool the flame temperature which allows more fuel to be added to the fuel/air mix thus giving a power increase.
The BAC 1-11 gained an extra 500lbs. of thrust per engine using water injection.
CC