Abstract: A method and system for late cycle injection of oxygen enriched air into the combustion chamber of an internal combustion engine is disclosed. The late cycle oxygen injection system is part of an airflow management system that effectively controls the use of oxygen and nitrogen available in the intake air. The preferred system comprises an intake air separation device adapted for separating a prescribed portion of intake air into a flow of oxygen enriched air and a flow of nitrogen enriched air. The system includes an oxygen enriched air flow circuit extending from the intake air separating device to one or more combustion chambers and a control device adapted for controlling the introduction of the oxygen enriched air into the combustion chambers late in a combustion cycle in response to selected engine operating conditions such as engine speed or engine load or both.