CYCLE-TO-CYCLE NO & NOx EMISSIONS FROM A HSDI DIESEL ENGINE

Engine-out NO,, emissions from diesel engines continue to be a major topic of research interest. While substantial understanding has been obtained of engine-out (i.e. before any aftertreatment) NO formation and reduction techniques, not least EGR which is now well established and fitted to production vehicles, much less data are available on cycle resolved NO2, emissions. In this work, crank-angle resolved NO and NO,, measurements have been taken from a high-speed light duty diesel engine at test conditions both with and without EGR. These have been combined with 1D data of exhaust flow and this used to form a mass average of NO and NO,, emissions per cycle. These results have been compared with combustion data and other emissions. The results show that there is a very strong correlation (R-2 > 0.95) between the NO emitted per cycle and the peak cylinder pressure of that cycle. In addition, the crank-angle resolved NO and NO measurements also reveal that there is a difference in NO : NO2 ratio (where NO2 is assumed to be the difference between NO and NON) during the exhaust period, with proportionally more NO2 being emitted during the blowdown period compared to the rest of the exhaust stroke.