The long time challenge for diesel engine manufacturers has been to reduce both particulate matter (PM) and NOx emissions simultaneously without sacrificing engine performance. One technique for reducing PM has been to inject air or oxygen-enriched air directly into the combustion chamber. Previous studies using the KIVA-3V computational fluid dynamics (CFD) model have shown benefits and the importance of the gas injection’s characteristics on the technique’s effectiveness in reducing emissions. Using a Caterpillar 3401E single cylinder engine, an experimental investigation has been conducted to demonstrate the effectiveness of an oxygen-enriched air injection system and fuel injection timing retard in reducing the NOx and the PM emissions in terms of both the particulate size and concentration. The gaseous emissions were measured using a Pierburg AMA 2000 gaseous emissions bench which included a chemiluminescent analyzer for NOx volumetric measurements, non-dispersive infrared (NDIR) analyzer for CO and CO2 measurements, and a parametric fuel cell for O2 measurements. PM emissions (i.e., soot particle concentration and size distribution) were measured using a TSI Model 3936 Scanning Mobility Particle Sizer (SMPS). The experimental observations regarding the effects of oxygen-enriched air injection on NOx and PM emissions were in accord with the previously reported results for late-cycle gas injection from a KIVA-3V model. The air injection technique additionally provided a low level of oxygen-enrichment during the compression cycle, with results similar to previous intake air oxygen-enrichment studies. A simultaneous reduction of NOx and particulates was demonstrated when the fuel injection timing characteristics were optimized in conjunction with the oxygen-enriched air injection. The experimental PM emissions were analyzed for number and size distributions and also found to be consistent with previously reported trends.

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