Photographic Study of Combustion in Compression-Ignition Engine

THIS combustion study was made in a high-speed compression-ignition engine. A high-speed motion-picture camera and an optical indicator were used to take motion pictures of the flame travel and the pressure development during combustion in the N.A.C.A. combustion apparatus. Tests were made in which both the injection-advance angle and the engine-coolant temperature were varied. The results show that, in a compression-ignition engine with a quiescent combustion-chamber, the flame first appears in the spray envelope and from there spreads to other parts of the chamber. The course of the combustion is controlled by the temperature and pressure of the air in the chamber from the time at which the fuel is injected until the time at which combustion starts.

The conclusion is presented that, in a compression-ignition engine, the ignition lag should be decreased to the largest value that can be used without excessive rate of pressure rise. Any further decrease in this lag decreases the combustion efficiency of the engine.