The effective density and fractal dimension of particles emitted from a light-duty diesel vehicle with a diesel oxidation catalyst

Olfert, Jason S.; Symonds, Jonathan P. R.; Collings, Nick

doi:10.1016/j.jaerosci.2006.10.002

Cited by 185 publications

(188 citation statements)

References 31 publications

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“…Based on reference SMPS measurements, the distribution is a unimodal with a GMD of 52 nm. This GMD is consistent with previous studies (Harris and Maricq 2001;Zervas and Dorlhene 2006) and suggests that the majority of the particles are accumulation mode soot particles with a mass-mobility scaling exponent of approximately 2.2 (Mariq and Xu 2004; Olfert et al 2007). We expect this condition to represent the relative performance of the size distribution methods when measuring diesel exhaust from engines operating on ULSD without DPF aftertreatment.…”

Section: Resultssupporting

confidence: 92%

Comparison of Vehicle Exhaust Particle Size Distributions Measured by SMPS and EEPS During Steady-State Conditions

Xue

Wang

et al. 2015

Aerosol Science and Technology

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Fast-sizing spectrometers, such as the TSI Engine Exhaust Particle Sizer (EEPS), have been widely used to measure transient particle size distributions of vehicle exhaust. Recently, size distributions measured during different test cycles have begun to be used for calculating suspended particulate mass; however, several recent evaluations have shown some deficiencies in this approach and discrepancies relative to the gravimetric reference method. The EEPS converts electrical charge carried by particles into size distributions based on mobility classification and a specific calibration, and TSI recently released a matrix optimized for vehicle emissions as described by Wang et al. (Submitteda). This study evaluates the performance of the new matrix (soot matrix) relative to the original matrix (default matrix) and reference size distributions measured by a scanning mobility particle sizer (SMPS). Steady-state particle size distributions were generated from the following five sources to evaluate exhaust particulates with various morphologies estimated by mass-mobility scaling exponent: (1) A diesel generator operating on ultralow sulfur diesel, (2) a diesel generator operating on biodiesel, (3) a gasoline direct-injection vehicle operating at two speeds, (4) a conventional port-fuel injection gasoline vehicle, and (4) a light-duty diesel (LDD) vehicle equipped with a diesel particulate filter. Generally, the new soot matrix achieved much better agreement with the SMPS reference for particles smaller than 30 nm and larger than 100 nm, and also broadened the accumulation mode distribution that was previously too narrow using the default matrix. However, EEPS distributions still did not agree with SMPS reference measurements when challenged by a strong nucleation mode during high-load operation of the LDD vehicle. This work quantifies the range of accuracy that can be expected when measuring particle size distribution, number concentration, and integrated particle mass of vehicle emissions when using the new static calibration derived based on the properties of classical diesel soot.

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Section: Resultssupporting

confidence: 92%

Comparison of Vehicle Exhaust Particle Size Distributions Measured by SMPS and EEPS During Steady-State Conditions

Xue

Wang

et al. 2015

Aerosol Science and Technology

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“…The measured mass-mobility exponents for the GDI vehicles in the present study are higher than the reported values for diesel soot Olfert et al 2007) or flame-generated soot with little or no semi-volatile material condensed on the particle (typically 2.2-2.3). This suggests that the GDI particles may have a fundamentally different structure than diesel soot .…”

Section: Effective Density and Volatility Of Gdi Particles Powerscontrasting

confidence: 77%

Effective Density and Volatility of Particles Emitted from Gasoline Direct Injection Vehicles and Implications for Particle Mass Measurement

Momenimovahed

Olfert

2015

Aerosol Science and Technology

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The effective density and volatility of particulate emissions from five gasoline direct injection (GDI) passenger vehicles were measured using a tandem differential mobility analyzer (DMA) and centrifugal particle mass analyzer (CPMA) system. The measurements were conducted on a chassis dynamometer at three steady-state operating conditions. A thermodenuder was employed to find the volatility and mixing state of the particles as well as the effective density of nascent and non-volatile particles (defined as particle phase remaining after denuding at 200 C). The mass-mobility exponent ranged between 2.4 and 2.7 for nascent (or undenuded) particles and between 2.5 and 2.7 for non-volatile particles; higher than typical diesel soot. The effective density function was 4278d m ¡0.438 § 76.3 kg/m 3 (for mobility diameter, d m , in nm) for nascent particles and 3215d m ¡0.395 § 37.9 kg/m 3 for non-volatile particles. The effective density functions of the non-volatile particles were fairly similar for the conditions studied. The uncertainty in using the effective density and mixing state data to determine the mass concentration of the aerosol by integrating mobility size distributions was examined. The uncertainty in mass concentration is minimized when only the non-volatile component is measured. However, the uncertainty in the mass concentration increases substantially if nascent particles are measured due to uncertainties in the particle mixing state and their associated effective densities. Furthermore, transient vehicle operation (cold-starts, accelerations, and decelerations) would likely change the mixing state of the exhaust particles suggesting it is difficult to accurately measure the mass concentration of undenuded GDI exhaust particulate using integrated size distribution methods.

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“…41,92,112,118 -122 Park et al 41 showed that the effective density of diesel exhaust aerosols varies from approximately 1.2 to 0.3 g/cm 3 in the size range of 50 -300 nm. Olfert et al 102 measured slightly higher values and attributed the difference to higher levels of sulfuric acid vapor present in the exhaust because of sulfate oxidation by the oxidation catalyst. Condensation of sulfuric acid on aggregates during dilution leads to higher intrinsic and measured effective densities.…”

Section: Elpi and Smpsmentioning

confidence: 99%

“…96 These particles are collections of aggregated primary particles, the fractal dimension of which ranges from 2.2 to 2.8, with primary particles that range in diameter from 13 to 40 nm. 41,[97][98][99][100][101][102][103] Primary particle size tends to decrease with air-to-fuel ratio and engine speed. 104 These and other variables (e.g., sampling conditions) may contribute to the variability because the measured fractal dimension may depend on the amount of vapors that have condensed on the soot.…”

Section: Application To Dpmmentioning

confidence: 99%

“…104 These and other variables (e.g., sampling conditions) may contribute to the variability because the measured fractal dimension may depend on the amount of vapors that have condensed on the soot. 102,105 Figure 5 is an electron micrograph showing a 200-nm mobilityclassified diesel particle that is made up of 24-nm primary particles. The primary particles are lognormally distributed with a standard deviation of 7 nm.…”

Section: Application To Dpmmentioning

confidence: 99%

See 1 more Smart Citation

Alternatives to the Gravimetric Method for Quantification of Diesel Particulate Matter near the Lower Level of Detection

Swanson

Kittelson

Pui

et al. 2010

Journal of the Air & Waste Management Association

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This paper is part of the Journal of the Air & Waste Management Association's 2010 special issue on combustion aerosol measurements. The issue is a combination of papers that synthesize and evaluate ideas and perspectives that were presented by experts at a series of workshops sponsored by the Coordinating Research Council that aimed to evaluate the current and future status of diesel particulate matter (DPM) measurement. Measurement of DPM is a complex issue with many stakeholders, including air quality management and enforcement agencies, engine manufacturers, health experts, and climatologists. Adoption of the U.S. Environmental Protection Agency 2007 heavy-duty engine DPM standards posed a unique challenge to engine manufacturers. The new standards reduced DPM emissions to the point that improvements to the gravimetric method were required to increase the accuracy and the sensitivity of the measurement. Despite these improvements, the method still has shortcomings. The objectives of this paper are to review the physical and chemical properties of DPM that make gravimetric measurement difficult at very low concentrations and to review alternative metrics and methods that are potentially more accurate, sensitive, and specific. Particle volatility, size, surface area, and number metrics are considered, as well as methods to quantify them. Although the authors believe that an alternative method is required to meet the needs of engine manufacturers, the methods reviewed in the paper are applicable to other areas where the gravimetric method detection limit is approached and greater accuracy and sensitivity are required. The paper concludes by suggesting a method to measure active surface area, combined with a method to separate semi-volatile and solid fractions to further increase the specificity of the measurement, has potential for reducing the lower detection limit of DPM and enabling engine manufacturers to reduce DPM emissions in the future.

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The effective density and fractal dimension of particles emitted from a light-duty diesel vehicle with a diesel oxidation catalyst

Cited by 185 publications

References 31 publications

Comparison of Vehicle Exhaust Particle Size Distributions Measured by SMPS and EEPS During Steady-State Conditions

Comparison of Vehicle Exhaust Particle Size Distributions Measured by SMPS and EEPS During Steady-State Conditions

Effective Density and Volatility of Particles Emitted from Gasoline Direct Injection Vehicles and Implications for Particle Mass Measurement

Alternatives to the Gravimetric Method for Quantification of Diesel Particulate Matter near the Lower Level of Detection

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