Review of diesel particulate matter sampling - Department of ...

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• to examine the relationship between methods used for laboratory dilution and the actual atmospheric dilution process; • to recommend the best current method(s); • to identify areas requiring further research; • to publish the results in the refereed literature and make it available on the Internet. Three reports were prepared under the EPA grant. The first report describes instruments used to characterize diesel aerosol, summarizes information obtained from engine laboratory visits and present results from a diesel aerosol sampling questionnaire circulated to major engine labs. The second report reviews fundamental aerosol dynamics and non-laboratory studies that have focused on determining the size distribution of diesel aerosol. This report summarizes the findings of the project including recently published information not included in the first two reports, presents general recommendations for diesel aerosol measurement and recommendations for future research. The major findings from the literature review are: • Because conditions vary so greatly in diesel exhaust testing, it is critical to understand how sampling and testing conditions may affect the nature of the diesel particulate matter being measured. • The strongest driving force for gas to particle conversion occurs in the critical dilution ratio range (5 - 50:1), roughly the same range produced by the typical laboratory dilution tunnel system 3 - 20:1. These conditions are not representative of real-world conditions. • The balance between carbonaceous agglomerates and volatiles (hydrocarbons and sulfuric acid) in diesel exhaust is critical to the understanding of particle dynamics. • To correctly interpret diesel aerosol measurements and to correlate roadway and laboratory experiments, the relationships between exhaust aerosol and testing parameters must be well understood. • Selection of aerosol instrumentation should be based on particle size and aerosol characteristics, the goals of the study, and the respective limitations of each instrument. Laboratory techniques that result in diesel aerosol measurements similar to ones obtained under real-world conditions need to be developed and evaluated. This will allow future regulatory decisions to be based on laboratory data that differentiate solid and liquid (hydrocarbon and sulfate) aerosols and dilution conditions that are representative of actual tailpipe and on-highway conditions. 01/14/99 Page 4
INTRODUCTION Federal government regulations limiting emissions from heavy-duty, on-highway diesel engines have driven DPM emissions measured on the Federal Transient Cycle from 0.6 g/bhp-hr in 1988 to less than 0.1 g/bhp-hr in 1994 and 0.05 g/bhp-hr for urban buses in 1996. Diesel engine manufacturers have developed low-emission diesel engines to meet these regulations. Many of the engine modifications that reduce DPM emissions from on-highway engines are also applied to off-road engines. Recently, Michigan Technological University (MTU) conducted a laboratory study to characterize the physical and chemical composition and the mutagenicity of emissions from two heavy-duty diesel engines operated with low-sulfur diesel fuel at a constant speed under two different steady-state load conditions, with and without an exhaust aftertreatment devices. One interesting result reported by Bagley, et al. (1996) was that the newer engine, meeting 1991 emissions levels 1 , significantly reduced emissions, but dramatically increased the number and volume of very small nuclei mode particles 2 when compared to a similar engine meeting 1988 emissions levels 3 . The research was conducted using a prototype 1991 Cummins LTA10 engine, with a high pressure, mechanically controlled, unit fuel injection system and other design features now commonly used in heavy-duty, high-speed, on-highway diesel engines. The particular engine configuration used for this research was a pre-production prototype developed to meet 1991 Federal on-highway emissions limits. Up to 40 % of the volume of particles in the exhaust was found to be present within the nuclei-mode range of particle-size. It is important to note that the MTU data were generated under steady-state conditions. Outside of the laboratory, most DPM is generated under transient operating conditions. Dilution conditions used in the Federal Heavy Duty Test Procedure are quite different from on-highway dilution condition, thus transient particle size measurements based on this test procedure are also not entirely representative of real-world conditions. Therefore there is a need to gather field data representative of real-world conditions to confirm the MTU findings. The large concentration of nuclei mode particles, accounting for a large percentage of the total volume of particles in the exhaust, differs from most past reported laboratory results. Previous research measuring the size distribution of DPM from diesel engines found distributions which were bimodal and lognormal (Abdul-Khalek, et al., 1995, Baumgard, et al., 1985, Kittelson et al., 1991). Typically, the majority of the mass or volume 1 0.25 g/hp-hr particulate matter emissions and 5.0 g/hp-hr NOx emissions. 2 The nuclei mode particles present in diesel exhaust primarily consist of condensed organic compounds, condensed sulfuric acid, and primary soot particles. Nuclei mode particles typically have diameters of approximately 5 nm to 50 nm, with a volume mean diameter of approximately 20 nm. 3 0.60 g/hp-hr particulate matter emissions and 6.0 g/hp-hr NOx emissions. 01/14/99 Page 5
Page 1 and 2: REVIEW OF DIESEL PARTICULATE MATTER
Page 3: ABSTRACT Federal government regulat
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 and 44: increased number concentrations of
Page 45 and 46: system, volatile particles evaporat
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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