Utilizing Intake-Air Oxygen-Enrichment Technology to Reduce Cold-Phase Emissions

Oxygen-enriched combustion is a proven, seriously considered technique to reduce exhaust hydrocarbons (HC) and carbon monoxide (CO) emissions from automotive gasoline engines. This paper presents the cold-phase emissions reduction results of using oxygen-enriched intake air containing about 23% and 25% oxygen (by volume) in a vehicle powered by a spark-ignition (SI) engine. Both engine-out and converter-out emissions data were collected by following the standard federal test procedure (FTP). Converter-out emissions data were also obtained employing the U.S. Environmental Protection Agency's (EPA's) “Off-Cycle” test. Test results indicate that the engine-out CO emissions during the cold phase (bag 1) were reduced by about 46 and 50%, and HC by about 33 and 43%, using nominal 23 and 25% oxygen enriched air compared to ambient air (21% oxygen by volume), respectively. However, the corresponding oxides of nitrogen (NO_x) emissions were increased by about 56 and 79%, respectively. Time-resolved emissions data indicate that both HC and CO emissions were reduced considerably during the initial 127 s of the cold-phase FTP, without any increase in NO_x emissions in the first 25 s. Hydrocarbon speciation results indicate that all major toxic pollutants, including ozone-forming specific reactivity factors, such as maximum incremental reactivity (MIR) and maximum ozone incremental reactivity (MOIR), were reduced considerably with oxygen-enrichment. Based on these results, it seems that using oxygen enriched intake air during the cold-phase FTP could potentially reduce HC and CO emissions sufficiently to meet future emissions standards. Off-cycle, converter-out, weighted-average emissions results show that both HC and CO emissions were reduced by about 60 to 75% with 23 or 25% oxygen-enrichment, but the accompanying NO_x emissions were much higher than those with the ambient air.