Athanasios Mamakos

Measurement of Automotive Nonvolatile Particle Number Emissions within the European Legislative Framework: A Review

In 2011, the European Commission introduced a limit for nonvolatile particle number (PN) emissions >23 nm from light-duty (LD) vehicles and the stated intent is to implement similar legislation for on-road heavy-duty (HD) engines at the next legislative stage. This paper reviews the recent literature regarding the operation-dependent emission of PN from LD vehicles and HD engines, and the measurement procedure used for regulatory purposes. The repeatability of the PN method is of the order of 5% and higher scatter of the results can easily be explained by the effect of the vehicles or the aftertreatment devices on the PN emissions (e.g., the fill state of the diesel particulate filters). Reproducibility remains an issue since it may exceed 30%. These high-variability levels are mainly associated with calibration uncertainties of the PN instruments. Correlation measurements between the full-flow dilution tunnels (constant-volume samplers, CVS) and the proportional partial-flow dilution systems (PFDS) showed agreement within 15% for the PN method down to 1 × 1011 p/kWh. At lower concentrations, the PN background of the CVS and/or the PFDS can result in larger inconsistencies. The filter-based particulate matter (PM) mass and the PN emissions correlate well down to 1–2 mg/km for LD vehicles and to 2–3 mg/kWh for HD applications. The correlation improves when only elemental carbon mass is considered: it is relatively good down to 0.1–0.3 mg/km or mg/kWh. Copyright 2012 American Association for Aerosol Research

Characterization of Combustion Aerosol Produced by a Mini-CAST and Treated in a Catalytic Stripper

We characterized the properties of combustion aerosol produced at different operating conditions of a mini-CAST burner that was treated in a Catalytic Stripper (CS) operating at 300°C. The goal was to establish a methodology for the production of soot particles resembling those emitted from internal combustion engines. Thermo-optical analysis of samples collected on Quartz filters revealed that the particles contained semi-volatile material that survived the CS. The amount of semi-volatile species strongly depended on the operating conditions ranging from less than 10% to as high as 30% of the particle mass. The mini-CAST operating conditions were also found to have a strong effect on the effective particle density (ρe ). The ρe , for example, ranged from as low as 0.3 to 1.05 g/cm3 for mondisperse 80 nm particles, although the mass-mobility exponent remained relatively constant (2.1–2.25). These differences are indicative of differences in the primary particle diameter, which was estimated to range between 8.5 and 34 nm depending on the operating conditions. The different types of particles produced were also found to exhibit different affinities for butanol but also different light absorption per mass of elemental carbon which can, therefore, lead to inconsistencies in aerosol instrumentation calibrations (e.g., condensation and optical particle counters, photoacoustic sensors). The work highlights the importance of establishing a detailed and well-defined method in using the mini-CAST-CS approach for instrument calibration in ways mimicking various engine combustion sources. Copyright 2013 American Association for Aerosol Research

Aerodynamic and Mobility Size Distribution Measurements to Reveal Biodiesel Effects on Diesel Exhaust Aerosol

This article examines the effect of biodiesel blends on the exhaust aerosol from a Euro 3 passenger car. Five different feedstock oils (soybean, palm, sunflower, rapeseed, and used frying oil) were used to produce fuels with 10% vol. content in biodiesel (B10). Use of the B10 blends led to a systematic reduction of PM mass emissions in the range of ∼9% (rapeseed) to 23% (used frying oil) on average. The combination of particle size distributions based on the aerodynamic and the mobility diameters led to the estimation of the fractal dimension (DF) for non-volatile particles. This was found to range from 2.52 for the baseline (fossil) fuel to 2.62 for the palm oil blend, suggesting that biodiesel can affect the particle morphology, even at this low blending ratio. The differences were statistically significant. The increase of the DF is translated to more compact particle structure, which in turn denotes lower specific surface area. The volatile fraction of PM lies within a range of 1–9% when fossil diesel fuel is employed. Use of palm, sunflower and rapeseed B10 blends results to PM that contain up to 28% volatile particulate mass. The higher emissions of volatile components together with the lower specific area of non-volatile particles, promotes the formation of volatile particles, especially at high speed conditions. This increases the total particle population under motorway driving by up to three times over the baseline levels.

Comparability of particle emission measurements between vehicle testing laboratories: a long way to go

The characterization of automotive exhaust aerosol today involves determination not only of the mass emission rate but additional particle properties such as number and surface concentration and size distribution. However, despite the fact that several measurement campaigns are conducted world-wide utilizing various sampling systems and measurement devices, there is no consistent information on the uncertainty range for such measurements. This paper presents the within laboratory and between laboratories variability expected for measurements of exhaust particle properties, processing the data of several instruments and driving cycles collected in a specifically designed interlaboratory study. Results show that within laboratory variability is in the range of 20% of the mean value, excluding outliers. However, between laboratories variability can regularly reach or exceed 50% when small deviations from the sampling protocol occur, bringing significant implications to the comparability of the results. However, continuation of the study demonstrated that it is possible to decrease the between labs uncertainty range below 20% when laboratories get more experienced in the strict application of the measurement protocol. The study concludes that the comparability of exhaust aerosol measurements can only be verified with enforcement and strict application of common sampling, measurement and calibration protocols.

Experimental and Theoretical Investigations of the Effect of the Calibration Aerosol Material on the Counting Efficiencies of TSI 3790 Condensation Particle Counters

The counting efficiencies of two TSI 3790 Condensation Particle Counters (CPCs) were investigated experimentally for graphite, poly-(alpha)-olefin (PAO), tetradecane (C14), and hexadecane (C16) particles at saturator-to-condenser temperature differences spanning from 5.6°C to 11.3°C. The efficiencies determined with PAO, C14, and C16 particles were broadly similar, while tests with graphite particles resulted in systematically lower counting efficiencies. The differences between PAO and graphite particles were reduced at elevated temperature differences, i.e., as the saturation ratios inside the condenser increased. The possibility to predict measured counting efficiencies by heterogeneous nucleation theory was also assessed. The results for PAO, C14, and C16 were representative of perfectly wettable particles, while graphite data could only be reproduced with a contact angle of 6–12°, for all temperatures examined. Line tension fits revealed a linear correlation with the graphite mobility diameter for all operating temperatures (5 × 10−11 N at 15 nm to 4 × 10−10 N at 70 nm). This could actually indicate that the mobility diameter underestimates the contact line for these complex geometry graphite aggregates. An examination of the calculated activation regions inside the condenser indicated that the upper part of the counting efficiency curve (>50%) is very sensitive to flow and temperature nonidealities. This observation is in quantitative agreement with systematic deviations observed between theoretical predictions and experimental data. Numerical calculations for a range of working fluids suggested that for a given affinity of the calibration particle to the examined vapors (i.e., for a finite contact angle), the benefit from shifting to a fluid alternative to butanol is limited. Further investigations on the reduction of the material dependence should focus on the identification of working fluids exhibiting greater affinity for different particle materials (e.g., lower contact angle). Copyright 2012 American Association for Aerosol Research

Methodology to quantify the ratio of multiple-to single-charged fractions acquired in aerosol neutralizers

ABSTRACT A methodology for the quantification of the ratio of multiple- to single-charged fractions acquired in aerosol neutralizers is presented. These quantities are necessary for an accurate monodisperse calibration of aerosol instrumentation. A tandem Differential Mobility Analyzer (DMA) setup is required, with the second DMA scanning the electrical mobility spectra classified in the first DMA. In contrast to previous studies on the quantification of bipolar charge distribution utilizing tandem DMA schemes, the methodology targets at the direct determination of the multiple- to single-charge fractions and does so through the analysis of the raw signal instead of the inverted size distributions, thus circumventing errors associated with the assumptions in the DMA data inversion. The proposed methodology is employed for the characterization of different types of aerosols commonly employed for instrument calibration. Spherical liquid particles (emery oil and dioctyl sebacate) were found to acquire lower multiple charge fractions than those suggested by the commonly employed regression fits of Wiedensohler, which was published in the year 1988 in the Journal of Aerosol Science (vol. 19, pp. 387–389), but still within the range of values reported in the literature. Diffusion flame soot and spark generated graphite particles, produced by a miniCAST 6203C burner and a PALAS DNP 3000, respectively, exhibited higher fraction of multiple charges, in good agreement with previous work on agglomerates. The use of a soft X-ray bipolar charger (TSI 3088) yielded systematically higher multiple fractions of positive charges compared to a 85Kr neutralizer (TSI 3077A), confirming the importance of direct photoionization charging on the former. Copyright