Max Fiedler developed a lightweight automotive diesel engine with a novel combustion system, presenting initial results in 1939. A unique injection concept incorporated in the engine created a pre-mixed, semi-homogeneous charge using uniformly low injection pressures and advanced injection timing. His evidence showed: extremely smooth combustion and controlled energy release in the early stages of burning; complete elimination of diesel knock; appropriate timing of the onset of combustion; and a combustion event that remained robust through to its conclusion, likely forming a minimum of particulate. Fiedler’s work was largely ignored by other engineers of the day, but there is significant evidence in later work that both explains and confirms his basic claims. The available knowledge relating to Fiedler’s combustion system provides important information about the conditions required to produce smooth heat release in well mixed compression ignition systems.