Knowledge of the NO:NO~2~ ratio emitted from a diesel engine is particularly important for ensuring the highest performance of SCR NO~x~ aftertreatment systems.  As real driving emissions from vehicles increase in importance, the need to understand the NO:NO~2~ ratio emitted from a diesel engine undergoing transients similarly increases.

Previous work by the authors has identified significant differences in NO:NO~2~ ratio (where NO~2~ is defined as the difference between NO and NO~x~) throughout the exhaust period of a single engine cycle, with proportionally more NO~2~ being emitted during the blowdown period compared to the rest of the exhaust stroke.  At the time it was not known what caused this effect.

In this study, crank-angle resolved NO and NO~x~ measurements using fast response CLD (for NO) and fast LIF (for NO~2~) have been taken from a single cylinder high-speed light duty diesel engine at three different speed and load points.  In addition, crank-angle resolved total hydrocarbon (THC) measurements have been taken simultaneously using a fast FID.  The previous results linking the NO~x~ emitted per cycle and the peak cylinder pressure of that cycle at all test points have been repeated, as has the variation of the NO:NO~2~ ratio through the exhaust stroke.  These previously published findings are extended in the present work which now, for the first time, links the NO:NO~2~ ratio to the THC emissions from an individual engine cycle.  The results show that where there are higher levels of THC emissions in the first part of the exhaust stroke (blowdown), perhaps caused by injector dribble or release from crevices, the proportion of NO~2~ emitted from that cycle is increased.


The Influence of Cycle-to-Cycle Hydrocarbon Emissions on Cyclic NO:NO2 Ratio From a HSDI Diesel Engine

Division / Sponsors: 
Internal Combustion Engine Division (ICED)

Paper Proceedings: https://asmedigitalcollection.asme.org/ICEF/ICEF2020/volume/84034

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