Oxygen-enriched combustion (OEC) is used in industrial combustion applications to increase the adiabatic flame temperature. OEC has also been studied previously as a means to increase the efficiency, power density, and low-quality fuel compatibility of internal combustion engines, including diesels. Although oxygen-enriched air can be produced in a number of ways, membrane air separating is the preferred method. Under this program, a high-flux membrane was experimentally tested for this application. A small-displacement (200 cm3), single-cylinder diesel engine was also modified for OEC. The modifications included development of a custom electronic fuel injection system and changes to the inlet manifold to dynamically change the oxygen concentration in the combustion air. Membrane testing, engine dynamometer testing, and system analysis demonstrated that current air-separation membranes require excessive parasitic losses for improvement of power density and efficiency. However, OEC can enable the use of low ignition-quality fuels. OEC was also observed to decrease carbon monoxide (CO) and smoke emissions, although nitrogen oxide (NOx) emissions were observed to increase. Transient testing was also performed; a membrane-based OEC system was shown to respond to step changes in engine load with an acceptable time response.

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