the water thing is correct... you'd have to TRY to feed the engine enough water to hydraulic it... water injection has been used on turbo/piston airplanes for a LONG time, and it's been used in many automotive applications, including high performance diesels... it's generally used on gas engines to cool the charge and keep detonation at bay, and on diesels to keep EGT's down, but as an added benefit, it basicly "steam cleans" the pistons and cylinder head chambers and valve faces...
so, yes, it can be used to clean the carbon out of a chamber...
Forrest