Why a governor

I was a originally answering to the OP that asked,why do diesel engines need a governor? My original reply was that a diesel engine has no control to top RPM without a governor.It would just keep increasing RPM until it self destructed.

 

Gasoline engines have a Rev limiter, where the ignition cuts out until RPM's decrease. The air is mixed with fuel in the intake, and the amount of air entering the cylinders is controlled by a butterfly valve in the throttle. Ignition cut-out works because without a spark, there is no combustion.

Diesel engines don't have spark plugs, so the governor cuts the amount of fuel injected into the cylinder. They don't have a butterfly valve, either. They suck in as much air as they can take in with each and every intake stroke, and then the heat from compressing that air ignites the fuel as it is injected directly into the cylinder. As long as there is a fuel supply, the diesel will continue running...so the governor restricts that fuel.

 

Yet you took my response to any of the post as being to only yours.