Jacob Swanson

Comparison of strategies for the measurement of mass emissions from diesel engines emitting ultra-low levels of particulate matter

Regulatory methods for the measurement of particulate matter (PM) mass emissions have traditionally been gravimetric. Modern diesel engines equipped with aftertreatment systems, especially Diesel Particulate Filters (DPFs), however, emit much smaller amounts of particulate matter as compared to traditional diesel engines and emit particulate matter with variable compositions. These changes have led to difficulties in measuring PM emissions rates from modern diesel engines using gravimetric methods. Issues associated with diesel PM mass measurement, such as the semi-volatile nature of PM, the interactions with components in the dilution air such as water and ammonia, and the possibility of sampling artifacts, have counteracted a singular focus on mass measurements. These inherent problems may warrant some alternative approaches to characterizing emissions, using methods related to mass and impacts of emissions that can be more accurately defined. The present study provides a comparison and relative precision of several alternative mass measurement methods employed to measure the mass emissions of particulate matter from diesel engines with low and ultra-low levels of emissions. The methods of measurement reviewed in this study include two gravimetrically based methods, a chemically reconstructed mass method, and an integrated particle size distribution (IPSD) method. The mass measurements were consistent at low emission levels but the chemical speciation and IPSD methods achieved closer agreement and were more precise at ultra-low emission levels. Although mass measurement is a NIST-traceable quantity, alternative methods may present a new paradigm that better characterizes engine emissions in an atmospherically relevant manner.

Comparison of methods for online measurement of diesel particulate matter.

Gravimetric analysis is the regulatory method for diesel particulate mass measurement. Because of issues such as adsorption/volatilization artifacts, it faces obstacles in measuring ultra low level emissions from modern diesel engines. Alternative methods of suspended particle mass measurement have been developed that show improvements in time resolution, sensitivity, and accuracy. Three size-resolved methods were considered here. Two methods rely on converting number size distributions obtained using a scanning mobility particle sizer (SMPS). Conversion techniques were based on effective density measurements and the Lall-Friedlander aggregate model. The third method employs the Universal Nanoparticle Analyzer (UNPA) to measure the aggregate size distribution from which mass is calculated. Results were compared with mass concentrations obtained using gravimetric analysis. The effective density conversion resulted in mass concentrations that were highly correlated (R(2) >0.99) with filter mass. The ratios to filter mass concentration were found to be 0.99 ± 0.04, 0.45 ± 0.03, and 0.45 ± 0.19 for the effective density conversion, the Lall-Friedlander conversion, and the UNPA, respectively, for a wide range of engine operating conditions. In addition, the diesel aerosol mass distributions measured by the online techniques are in agreement to within 15-20% with respect to the mass median diameter, while discrepancies were observed in the mass concentration.

Effective density and mass-mobility exponent of aircraft turbine particulate matter

A centrifugal particle mass analyzer and a modified differential mobility spectrometer were used to measure the mass and mobility of particulate matter emitted by CFM56-5B4/2P, CFM56-7B26/3, and PW4000-100 gas turbine engine sources. The mass-mobility exponent of the particulate matter from the CFM56-5B4/2P engine ranged from 2.68 to 2.82, whereas the effective particle densities varied from 600 to 1250  kg/m3, depending on the static engine thrust and sampling methodology used. The effective particle densities from the CFM56-7B26/3 and PW4000-100 engines also fell within this range. The sample was conditioned with or without a catalytic stripper and with or without dilution, which caused the effective density to change, indicating the presence of condensed semivolatile material on the particles. Variability of the determined effective densities across different engine thrusts, based on the scattering about the line of best fit, was lowest for the diluted samples and highest for the undiluted sample without a catalytic stripper. This variability indicates that the relative amount of semivolatile material produced was engine thrust dependent. It was found that the nonvolatile particulate matter, effective particle density (in kilograms per cubic meter) of the CFM56-5B4/2P engine at relative thrusts below 30% could be approximated using the particle mobility diameter (dme in meters) with 11.92d(2.76−3)me.

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

Abstract 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 gravi-metric 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.

Particle Emission Characteristics of a Gas Turbine with a Double Annular Combustor

The total climate, air quality, and health impact of aircraft black carbon (BC) emissions depend on quantity (mass and number concentration) as well as morphology (fractal dimension and surface area) of emitted BC aggregates. This study examines multiple BC emission metrics from a gas turbine with a double annular combustor, CFM56-5B4-2P. As a part of the SAMPLE III.2 campaign, concurrent measurements of particle mobility, particle mass, particle number concentration, and mass concentration, as well as collection of transmission electron microscopy (TEM) samples, allowed for characterization of the BC emissions. Mass- and number-based emission indices were strongly influenced by thrust setting during pilot combustion and ranged from <1 to 208 mg/kg-fuel and 3 ×× 1012 to 3 ×× 1016 particles/kg-fuel, respectively. Mobility measurements indicated that mean diameters ranged from 7 to 44 nm with a strong dependence on thrust during pilot-only combustion. Using aggregation and sintering theory with empirical effective density relationships, a power-law relationship between primary particle diameter and mobility diameter is presented. Mean primary particle diameter ranged from 6 to 19 nm; however, laser-induced incandescence (LII) and mass-mobility-calculated primary particle diameters demonstrated opposite trends with thrust setting. Similarly, mass-mobility-calculated aggregate mass specific surface area and LII-measured surface area were not in agreement, indicating both methods need further development and validation before use as quantitative indicators of primary particle diameter and mass-specific surface area. Copyright 2015 American Association for Aerosol Research

Greenhouse Gas and Noxious Emissions from Dual Fuel Diesel and Natural Gas Heavy Goods Vehicles.

Dual fuel diesel and natural gas heavy goods vehicles (HGVs) operate on a combination of the two fuels simultaneously. By substituting diesel for natural gas, vehicle operators can benefit from reduced fuel costs and as natural gas has a lower CO2 intensity compared to diesel, dual fuel HGVs have the potential to reduce greenhouse gas (GHG) emissions from the freight sector. In this study, energy consumption, greenhouse gas and noxious emissions for five after-market dual fuel configurations of two vehicle platforms are compared relative to their diesel-only baseline values over transient and steady state testing. Over a transient cycle, CO2 emissions are reduced by up to 9%; however, methane (CH4) emissions due to incomplete combustion lead to CO2e emissions that are 50-127% higher than the equivalent diesel vehicle. Oxidation catalysts evaluated on the vehicles at steady state reduced CH4 emissions by at most 15% at exhaust gas temperatures representative of transient conditions. This study highlights that control of CH4 emissions and improved control of in-cylinder CH4 combustion are required to reduce total GHG emissions of dual fuel HGVs relative to diesel vehicles.

A Method to Measure Static Charge on a Filter Used for Gravimetric Analysis

Static charge present on a filter contributes substantial error to low-level mass measurements. The measurement and sources of static charge are not well understood and this article presents a fundamental method of static charge measurement. As predicted by other researchers, triboelectric charging was found to generate significant static charge on a filter when using 2007 Diesel particulate matter (PM) measurement protocols. Measurements made using our method indicate that PM filters are rapidly and effectively neutralized by 210 Polonuim ( 210 Po) sources. The neutralization of charge occurred exponentially with characteristic time constants (the time it takes for the charge on the filter to decay by 63%) of 0.4 and 0.7 s, depending on the strength of the source. The experimental neutralization time constants were consistent with theory. The charge remaining on highly charged 47 mm Teflon and TX40 filters after 5 s of neutralization with year old 210 Po sources biased the true filter mass by <1 μg when the filters were weighed with a 1 μg resolution Cahn microbalance.

Uncertainty in Gravimetric Analysis Required for LEV III Light-Duty Vehicle PM Emission Measurements

Author(s): Swanson, Jacob; Pham, Liem; Xue, Jian; Durbin, Tom; Russell, Robert; Miller, Wayne; Kittelson, David; Jung, Heejung; Johnson, Kent

Size and volatility of particle emissions from an ethanol-fueled HCCI engine

ABSTRACT A scanning mobility particle sizer was used to determine the size, number, and mass concentration of particle emissions from an ethanol-fueled homogeneous charge compression ignition (HCCI) engine. Semi-volatile particle composition was characterized using tandem differential mobility analysis (TDMA). Variable temperature thermal conditioning was used to gain insight into particle volatility and a catalytic stripper was used to determine the solid particle distribution. Four engine conditions were evaluated, including low to moderate range loads and motoring (deceleration, coasting). Results indicated that aerosol from a fully premixed HCCI engine under firing conditions is formed almost entirely via nucleation of semi-volatile material originating from the lubricating oil. TDMA analysis indicated 98% of total particle volume evaporated below 100°C. Results pointed towards homogeneous nucleation of precursors derived from the organic species in the lubricating oil, possibly in combination with a sulfur species. The motoring condition, with no fuel injected, exhibited the highest number and mass concentrations. During motoring, there was poor sealing leading to increased atomization of oil and associated ash emissions. Emissions were lower during firing with better sealing and much less atomization, but evaporation of the most volatile fractions of the lubricating oil still led to significant PM emissions consisting of nearly entirely semi-volatile particles containing very little ash.

Microglial Immune Response to Low Concentrations of Combustion-Generated Nanoparticles: An In Vitro Model of Brain Health

The brain is the central regulator for integration and control of responses to environmental cues. Previous studies suggest that air pollution may directly impact brain health by triggering the onset of chronic neuroinflammation. We hypothesize that nanoparticle components of combustion-generated air pollution may underlie these effects. To test this association, a microglial in vitro biological sensor model was used for testing neuroinflammatory response caused by low-dose nanoparticle exposure. The model was first validated using 20 nm silver nanoparticles (AgNP). Next, neuroinflammatory response was tested after exposure to size-selected 20 nm combustion-generated nanoparticles (CGNP) collected from a modern diesel engine. We show that low concentrations of CGNPs promote low-grade inflammatory response indicated by increased pro-inflammatory cytokine release (tumor necrosis factor-α), similar to that observed after AgNP exposure. We also demonstrate increased production of reactive oxygen species and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) p65 phosphorylation in microglia after CGNP stimulation. Finally, we show conditioned media from CGNP-stimulated microglia significantly reduced hypothalamic neuronal survival in vitro. To our knowledge, this data show for the first time that exposure to AgNP and CGNP elicits microglial neuroinflammatory response through the activation of NF-κB.