This research proposed a new combustion chamber to achieve simultaneous reduction of NOx and smoke from diesel engines. This combustion chamber generates a strong disturbance in the middle and late stages of combustion that enhances smoke oxidation. The initial combustion occurs in a fuel-rich state in the prechamber and the middle and late stages of combustion occur in a lean state mostly in the main chamber; hence, NOx is reduced. The disturbance tends to shorten the combustion duration which compensates for the tendency of the lean combustion to prolong the combustion duration. Performance and emission characteristics of the test engines are examined, and a discussion of the results is presented.