The MAN M-System, also referred to as M-Process and M combustion process, is a direct injection system for Diesel engines. In M-System engines, the fuel is injected onto the walls of the combustion chamber that is solely located inside the piston, and shaped like a sphere. The M-System was rendered obsolete by modern fuel injection systems for Diesel engines. Due to its particularities, the M-System was only used for stationary applications and commercial vehicle engines, passenger car engines with this design have never been made. The letter M is an abbreviation for the German word Mittenkugelverfahren,[1] meaning centre sphere combustion process.