A cylinder leakage test will confirm a bent valve. We use a boroscope to inspect the interior of the cylinder and piston top when an engine injests something.

I have seen debri imbedded in a piston top that was hitting the head and making noise, like a small screw or washer. When the gods smile upon you, the debri can be removed through a spark plug hole or through a diesel injector hole. Leaving a sharp spot on the piston can cause you grief in a gas or a diesel engine.

Using water and or alcohol injection, even in a turbo charged diesel engine, has little effect. Back in the days before anti-knock sensors the water/alcohol injection systems worked marginally well for hot rod gas engines by slowing the flame spread in the cylinders.