Dependence between Nonvolatile Nucleation Mode Particle and Soot Number Concentrations in an EGR Equipped Heavy-Duty Diesel Engine Exhaust

Abstract

Heavy duty diesel engine exhaust characteristics were studied with direct tailpipe sampling on an engine dynamometer. The exhaust particle size distributions, total particle mass, and gaseous emissions were measured with different load conditions without after-treatment. The measured particle size distributions were bimodal; distinctive accumulation and nucleation modes were detected for both volatile and dry particle samples. The condensing volatile compounds changed the characteristics of the nonvolatile nucleation mode while the soot/accumulation mode characteristics (concentration and diameter) were unchanged. A clear dependence between the soot and the nonvolatile nucleation mode number concentrations was detected. While the concentration of the soot mode decreased, the nonvolatile nucleation mode concentration increased. The soot mode number concentration decrease was related to soot-NOx trade-off; the decrease of the exhaust gas recirculation rate decreased soot emission and increased NOx emission. Simultaneously detected increase of the nonvolatile nucleation mode concentration may be caused by the decrease of the soot mode sink or by changed combustion characteristics. However, the total particle number concentration increased with decreasing soot mode number concentration. The proportion of the particle number concentration between the nonvolatile nucleation and soot mode followed the NO2:NO ratio linearly. While ratio NO2:NO increased the proportion of soot mode number concentration in total number concentration increased. Regardless of the mechanism that causes the balance between the soot mode and the nonvolatile nucleation mode emissions, the changes in the particle number size distribution should be taken into account while the particle mass emissions are controlled with combustion optimization.

Continental anthropogenic primary particle number emissions

“…However, these limits are set only for solid particles larger than 23 nm. In practice, this means that only particles with black carbon core are taken into account, since the secondary particles are not considered as solid (they evaporate when the sample is heated) and the nucleation mode particles with a non-volatile core (Rönkkö et al, 2007;Lähde et al, 2010) have diameters well below 23 nm after evaporation of condensed matter. Thus, the particle number emission limits mentioned above are in principle reached already when older diesel vehicles are equipped with a diesel particle filter (DPF) .…”

“…in new particle formation processes occurring already before the combustion plume is emitted to the atmosphere and thus producing cores for cooling vapours to condense on (e.g. Rönkkö et al, 2007;Lähde et al, 2010). Black carbon, i.e.…”

Nature of Sub-23-nm Particles Downstream of the European Particle Measurement Programme (PMP)-Compliant System: A Real-Time Data Perspective

“…Solid particles in the sub-23-nm size range have been found in heavy-duty diesel vehicle exhaust under different load conditions (Kittelson et al 2006;Herner et al 2007;Rönkkö et al 2007;Filippo and Maricq 2008;Lähde et al 2009;Lähde et al 2010). These findings raise questions as to whether excluding the sub-23-nm particles is appropriate or necessary.…”

Particle Number Emissions of Nonroad Diesel Engines of Various Ages

“…15 illustrates the ratio of the measured brake-specific HC and CO emissions of eight [8] test engines at Modes 1, 3 to 5, and 7. At most Modes, the modem CR 4 V SCR 4 engine emitted clearly the highest HC emissions in relation to the CO emissions, thus, perhaps showing the greatest potential for nucleation.…”

“…There are even indications of a tendency of the number of ultrafine particles of low-emission engines to be on the increase or that a decrease of the soot particle concentration is linked with an increase in the nucleation mode particles. Through the recent few years, the question of the PM number concentration has, thus, become more important and regulations have indeed already been enacted [2,3,[5][6][7][8].…”