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Figure 16. - Measured size distributions with and without particle filter (v = 120 km/h) at a dilution ratio of 1:12 for a passenger car (from Kauffeldt and Schmidt-Ott, 1998) Kruger, Lüders, Luers, Kaufmann, Koch and Kauffeldt (1997) and Lüders (1997): This study also investigated the influence of exhaust gas aftertreatment and measurement conditions on particle size characteristics of exhaust from diesel engines. (This research is described in more detail in Supplemental Report No. 2.) Number weighted size distributions were obtained using a differential mobility particle spectrometer (DMPS). Sampling was done from a dilution tunnel followed by secondary dilution. 10 The authors suggest that their results are largely independent of secondary dilution process, although they said it had some influence. The secondary dilution ratio was usually about 10:1 and was obtained using an ejector diluter. The engines tested were 3 l, indirect injection (IDI), naturally aspirated and 1.9 l DI, turbocharged and intercooled passenger car diesels and a 6.9 l, DI, turbocharged and intercooled truck engine. • When a trap was used, the passenger car with the DI engine showed a significant decrease in particle number for particles > 50 nm, but a significant increase in particle number for particles < 50 nm. • For the truck engine the particle trap again showed an increase in the number of particles < 50 nm, but a decrease in larger particles. The use of an oxidation catalyst also showed an increase in the in number of particles < 50 nm, but this effect was time dependent. To determine the nature of the < 50 nm particles the DMPS was modified so the < 50 nm particles could be analyzed separately. A heating element was integrated into the measurement system so the aerosol could be heated before passage into the DMPS. With this 10 Not reported in the published literature. Based on personal communication with the authors. (Kittelson, 1997) 01/14/99 Page 44
system, volatile particles evaporate and lose their charge, while solid or solid core particles retain their charge. Volatiles that nucleate upon cooling have no charge and are not detected. One potential problem is that some particles may pyrolyze in the heater. This system was used to examine particles emitted from the different control devices. As temperature was increased the number of 6 - 12 nm particles decreased, when the truck engine and fiber coil were used at 2400 rpm, full load. A similar observation was made with the truck engine and oxidation catalyst. As the temperature was increased up to a approximately 175 o C, a decrease in the < 50 nm particles was observed. The authors conclude that the nuclei mode particles observed after the particle filter or oxidation catalyst consist entirely of volatile material that evaporates at 180 o C. The authors suggest that the material primarily consists of sulfuric acid droplets. The condensation effect is strongly dependent on the temperature and the partial pressures of the single components, which are affected by the dilution of the exhaust gas. The effect of the dilution ratio was further characterized. For the truck engine running at rated power without a control device while the dilution ratio was varied from 12 to 32, no effect on the size distribution was observed. However, when the particle filter was installed an increase in the number of < 50 nm was observed at a 12:1 dilution ratio. However, when the ratio was increased to 19 and 32:1 the increase disappeared, as illustrated in figure 17. The dependence of nanoparticle formation on dilution conditions is consistent with findings from Abdul-Khalek, et al., 1998a. The < 50 nm particles appear after the particle trap below a critical dilution ratio. The trap drastically reduces the mass and the number of particles available as condensation adsorption sites. This leads to the process of homogeneous nucleation of the exhaust gases and the creation of a large number of new particles not previously observed in the exhaust stream. The oxidation catalyst does not reduce the quantity of particulate material but can lead to an increase in the concentration of sulfuric acid in the exhaust gas, which leads to the same effect because of the change in the ratio of adsorption sites to condensing matter. Compared to tunnel dilution, ambient dilution ratios may be much higher, therefore the authors question whether the < 50 nm particle increase would be observed under ambient driving conditions. However, it should be noted that dilution conditions found in a city are probably quite different from those encountered on-highway (at high speed) in that combustion particle concentrations are higher and are generated under different driving conditions. A number of measurements on and near roadways show a nuclei mode is present under real atmospheric conditions (Kittelson, et al., 1988, Weingartner, et al., 1997a, Harrison, et al., 1996). 01/14/99 Page 45
Page 1 and 2: REVIEW OF DIESEL PARTICULATE MATTER
Page 3 and 4: ABSTRACT Federal government regulat
Page 5 and 6: INTRODUCTION Federal government reg
Page 7 and 8: • to critically evaluate methods
Page 9 and 10: Table 2. Changes in diesel engine t
Page 11 and 12: AEROSOL SIZE DISTRIBUTION Figure 3
Page 13 and 14: Figure 5. - Schematic illustrating
Page 15 and 16: Heat transfer during sampling and d
Page 17 and 18: • humidity and temperature • ba
Page 19 and 20: Doyle (1961) predicted that homogen
Page 21 and 22: Engine Emission Characteristics Eng
Page 23 and 24: accumulation mode particle diameter
Page 25 and 26: Adverse health effects of respirabl
Page 27 and 28: content of the particle. (Burtscher
Page 29 and 30: Table 7. Instrument summary Miscell
Page 31 and 32: Table 8. Studies Measuring Diesel A
Page 33 and 34: slowly moving diesel trucks, and a
Page 35 and 36: Figure 13. - Volume fraction versus
Page 37 and 38: Table 10. N/VT Ratios (Number of pa
Page 39 and 40: Figure 15. - Relationship between d
Page 41 and 42: Exhaust Constituents The nature of
Page 43: increased number concentrations of
Page 47 and 48: With low carbon emission engines, t
Page 49 and 50: Kreso, et al. (1998a,b) looked at t
Page 51 and 52: • Treatment of sample dilution ai
Page 53 and 54: somewhat larger, 60 - 70 nm. The ma
Page 55 and 56: Bagley, S. T., et al. 1996. Charact
Page 57 and 58: Doyle, G.J. 1961. Self-Nucleation i
Page 59 and 60: Keady, P.B., F. R. Quant, and G. J.
Page 61 and 62: Seminar on Particle Size Distributi
Page 63 and 64: Watson, J. G. et al. 1998. Northern

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