<div class="htmlview paragraph">High-speed cine photography has been used to study the combustion process in a variety of diesel chambers. These chambers, used in engines of 12–1200 cu in. swept volume per cylinder, differ considerably in the level of air utilization achieved within the cylinder at acceptable exhaust color or temperature.</div> <div class="htmlview paragraph">These differences are attributed to the method of fuel/air mixing employed and the influence of fuel injection, air motion, and fuel quality are discussed.</div> <div class="htmlview paragraph">It is concluded that while there is an obvious correlation between air utilization and the level of air swirl or turbulence employed, from other points of view high gas velocities are undesirable. Further development will therefore depend largely on the evolution of the fuel injection equipment toward the achievement of good mixing and combustion control with reduced gas velocities.</div>