Back in the day, a development project for an un-named gov' t agency resulted in an lightweight aircooled 2 cylinder Diesel engine running on Jet A. Starting it up resulted in it running away and it couldn't be controlled or stopped by throttling. As above, the fuel shutoff was the only way to shut it down. Scary with it running at full chat, and a tribute to it's robust but lightweight construction that it held together for quite a long time as they tried to control it.