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The effects of nitrogen-enriched air, supplied by an air separation membrane, on NOx emissions from a 1.9-L turbocharged direct-injection diesel engine were investigated. To enrich combustion air with more nitrogen, prototype air separation membranes were installed between the after-cooler and intake manifold without any additional controls. The effects of nitrogen-enriched combustion air on NOx emissions were compared with and without exhaust gas recirculation (EGR). At sufficient boost pressures (>50 kPag), nitrogen-enriched air from the membrane provided intake oxygen levels that were similar to those of EGR. Compared with EGR, nitrogen-enriched air provided 10-15% NOx reductions during medium to high engine loads and speeds. At part loads, when turbocharger boost pressure was low, the air separation membrane was not effective in enriching air with nitrogen. As a result, NOx reduction was lower, but it was 15-25% better than when EGR was not used.

Exhaust emissions consisting of oxides of nitrogen (collectively known as NOx) from internal combustion engines present a serious environmental problem. Although the problem exists for both gasoline and diesel engines, the problem is more severe for the diesel engine. NOx formation in an engine depends strongly on flame temperature, and flame temperature is dependent upon the composition of the fuel and the intake air. The concept is to develop and test copolymer modules for Nitrogen Enriched Air (NEA) supply to diesel engines. The objective is to minimize NOx production from diesel engine emissions without a significant loss of fuel efficiency or a significant increase in carbon monoxide and smoke related emissions. In the present study, a module using the latest membrane technology was designed, tested and fabricated. The modules were installed in a diesel engine test stand and tests were run. The NOx level from the test engine using standard air was established.