Impact of Biofuel Blends on Black Carbon Emissions from a Gas Turbine Engine.

Presented here is an overview of non-volatile particulate matter (nvPM) emissions, i.e. "soot" as assessed by TEM analyses of samples collected after the exhaust of a J-85 turbojet fueled with Jet-A as well as with blends of Jet-A and Camelina biofuel. A unifying explanation is provided to illustrate the combustion dynamics of biofuel and Jet-A fuel. The variation of primary particle size, aggregate size and nanostructure are analyzed as a function of biofuel blend across a range of engine thrust levels. The postulate is based on where fuels start along the soot formation pathway. Increasing biofuel content lowers aromatic concentration while placing increasing dependence upon fuel pyrolysis reactions to form the requisite concentration of aromatics for particle inception and growth. The required "kinetic" time for pyrolysis reactions to produce benzene and multi-ring PAHs allows increased fuel-air mixing by turbulence, diluting the fuel-rich soot-forming regions, effectively lowering their equivalence ratio. With a lower precursor concentration, particle inception is slowed, the resulting concentration of primary particles is lowered and smaller aggregates were measured. The lower equivalence ratio also results in smaller primary particles because of the lower concentration of growth species.

Gravimetric Measurements of Filtering Facepiece Respirators Challenged With Diesel Exhaust.

Elevated concentrations of diesel exhaust have been linked to adverse health effects. Filtering facepiece respirators (FFRs) are widely used as a form of respiratory protection against diesel particulate matter (DPM) in occupational settings. Previous results (Penconek A, Drazyk P, Moskal A. (2013) Penetration of diesel exhaust particles through commercially available dust half masks. Ann Occup Hyg; 57: 360-73.) have suggested that common FFRs are less efficient than would be expected for this purpose based on their certification approvals. The objective of this study was to measure the penetration of DPM through NIOSH-certified R95 and P95 electret respirators to verify this result. Gravimetric-based penetration measurements conducted using polytetrafluoroethylene (PTFE) and polypropylene (PP) filters were compared with penetration measurements made with a Scanning Mobility Particle Sizer (SMPS, TSI Inc.), which measures the particle size distribution. Gravimetric measurements using PP filters were variable compared to SMPS measurements and biased high due to adsorption of gas phase organic material. Relatively inert PTFE filters adsorbed less gas phase organic material resulting in measurements that were more accurate. To attempt to correct for artifacts associated with adsorption of gas phase organic material, primary and secondary filters were used in series upstream and downstream of the FFR. Correcting for adsorption by subtracting the secondary mass from the primary mass improved the result for both PTFE and PP filters but this correction is subject to 'equilibrium' conditions that depend on sampling time and the concentration of particles and gas phase hydrocarbons. Overall, the results demonstrate that the use of filters to determine filtration efficiency of FFRs challenged with diesel exhaust produces erroneous results due to the presence of gas phase hydrocarbons in diesel exhaust and the tendency of filters to adsorb organic material.

Lagrangian Hotspots of In-Use NOX Emissions from Transit Buses.

In-use, spatiotemporal NOX emissions were measured from a conventional powertrain transit bus and a series electric hybrid bus over gradients of route kinetic intensity and ambient temperature. This paper introduces a new method for identifying NOX emissions hotspots along a bus route using high fidelity Lagrangian vehicle data to explore spatial interactions that may influence emissions production. Our study shows that the studied transit buses emit higher than regulated emissions because on-route operation does not accurately represent the range of engine operation tested according to regulatory standards. Using the Lagrangian hotspot detection, we demonstrate that NOX hotspots occurred at bus stops, during cold starts, on inclines, and for accelerations. On the selected routes, bus stops resulted in 3.3 times the route averaged emissions factor in grams/km without significant dependence on bus type or climate. The buses also emitted 2.3 times the route averaged NOX emissions factor at the beginning of each route due to cold selective catalytic reduction aftertreatment temperature. The Lagrangian hotspot detection technique demonstrated here could be employed in future connected vehicles empowered by advances in computational power, data storage capability, and improved sensor technology to optimize emissions as a function of spatial location.

Comparison of particle mass and solid particle number (SPN) emissions from a heavy-duty diesel vehicle under on-road driving conditions and a standard testing cycle.

It is important to understand the differences between emissions from standard laboratory testing cycles and those from actual on-road driving conditions, especially for solid particle number (SPN) emissions now being regulated in Europe. This study compared particle mass and SPN emissions from a heavy-duty diesel vehicle operating over the urban dynamometer driving schedule (UDDS) and actual on-road driving conditions. Particle mass emissions were calculated using the integrated particle size distribution (IPSD) method and called MIPSD. The MIPSD emissions for the UDDS and on-road tests were more than 6 times lower than the U.S. 2007 heavy-duty particulate matter (PM) mass standard. The MIPSD emissions for the UDDS fell between those for the on-road uphill and downhill driving. SPN and MIPSD measurements were dominated by nucleation particles for the UDDS and uphill driving and by accumulation mode particles for cruise and downhill driving. The SPN emissions were ∼ 3 times lower than the Euro 6 heavy-duty SPN limit for the UDDS and downhill driving and ∼ 4-5 times higher than the Euro 6 SPN limit for the more aggressive uphill driving; however, it is likely that most of the "solid" particles measured under these conditions were associated with a combination release of stored sulfates and enhanced sulfate formation associated with high exhaust temperatures, leading to growth of volatile particles into the solid particle counting range above 23 nm. Except for these conditions, a linear relationship was found between SPN and accumulation mode MIPSD. The coefficient of variation (COV) of SPN emissions of particles >23 nm ranged from 8 to 26% for the UDDS and on-road tests.

Carbon nanotubes among diesel exhaust particles: real samples or contaminants?

During three separate studies involving characterization of diesel particulate matter carbon nanotubes (CNTs) were found among diesel exhaust particles sampled onto transmission electron microscopy (TEM) grids. During these studies, samples were collected from three different diesel engines at normal operating conditions with or without an iron catalyst (introduced as ferrocene) in the fuel. This paper is to report the authors' observation of CNTs among diesel exhaust particles, with the intent to stimulate awareness and further discussion regarding the formation mechanisms of CNTs during diesel combustion.

Simultaneous reduction of particulate matter and NO(x) emissions using 4-way catalyzed filtration systems.

The next generation of diesel emission control devices includes 4-way catalyzed filtration systems (4WCFS) consisting of both NOx and diesel particulate matter (DPM) control. A methodology was developed to simultaneously evaluate the NOx and DPM control performance of miniature 4WCFS made from acicular mullite, an advanced ceramic material (ACM), that were challenged with diesel exhaust. The impact of catalyst loading and substrate porosity on catalytic performance of the NOx trap was evaluated. Simultaneously with NOx measurements, the real-time solid particle filtration performance of catalyst-coated standard and high porosity filters was determined for steady-state and regenerative conditions. The use of high porosity ACM 4-way catalyzed filtration systems reduced NOx by 99% and solid and total particulate matter by 95% when averaged over 10 regeneration cycles. A "regeneration cycle" refers to an oxidizing ("lean") exhaust condition followed by a reducing ("rich") exhaust condition resulting in NOx storage and NOx reduction (i.e., trap "regeneration"), respectively. Standard porosity ACM 4-way catalyzed filtration systems reduced NOx by 60-75% and exhibited 99.9% filtration efficiency. The rich/lean cycling used to regenerate the filter had almost no impact on solid particle filtration efficiency but impacted NOx control. Cycling resulted in the formation of very low concentrations of semivolatile nucleation mode particles for some 4WCFS formulations. Overall, 4WCFS show promise for significantly reducing diesel emissions into the atmosphere in a single control device.

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.

Evaluation of a portable photometer for estimating diesel particulate matter concentrations in an underground limestone mine.

A low cost, battery-operated, portable, real-time aerosol analyzer is not available for monitoring diesel particulate matter (DPM) concentrations in underground mines. This study summarizes a field evaluation conducted at an underground limestone mine to evaluate the potential of the TSI AM 510 portable photometer (equipped with a Dorr-Oliver cyclone and 1.0-mum impactor) to qualitatively track time-weighted average mass and elemental, organic, and total carbon (TC) measurements associated with diesel emissions. The calibration factor corrected correlation coefficient (R2) between the underground TC and photometer measurements was 0.93. The main issues holding back the use of a photometer for real-time estimation of DPM in an underground mine are the removal of non-DPM-associated particulate matter from the aerosol stream using devices, such as a cyclone and/or impactor and calibration of the photometer to mine-specific aerosol.

Effect of organometallic fuel additives on nanoparticle emissions from a gasoline passenger car.

Particle size measurements were performed on the exhaust of a car operating on a chassis dynamometer fueled with standard gasoline and gasoline containing low levels of Pb, Fe, and Mn organometallic additives. When additives were present there was a distinct nucleation mode consisting primarily of sub-10 nm nanoparticles. At equal molar dosing Mn and Fe gave similar nanoparticle concentrations at the tailpipe, whereas Pb gave a considerably lower concentration. A catalytic stripper was used to remove the organic component of these particles and revealed that they were mainly solid and, because of their association with inorganic additives, presumably inorganic. Solid nucleation mode nanoparticles of similar size and concentration to those observed here from a gasoline engine with Mn and Fe additives have also been observed from modern heavy-duty diesel engines without aftertreatment at idle, but these solid particles are a small fraction of the primarily volatile nucleation mode particles emitted. The solid nucleation mode particles emitted by the diesel engines are likely derived from metal compounds in the lubrication oil, although carbonaceous particles cannot be ruled out. Significantly, most of these solid nanoparticles emitted by both engine types fall below the 23 nm cutoff of the PMP number regulation.

The effect of federal fuel sulfur regulations on in-use fleets: on-road heavy-duty source apportionment.

From 2002 to 2007 fuel sulfur content in the Minneapolis/St Paul area decreased from about 325 ppm S to <15 ppm S as a result of EPA regulations. We hypothesized that the reduction in fuel sulfur would result in a reduction of fuel specific heavy duty (HD) particle number emissions for the on-road diesel fleet. Fuel specific emissions were estimated by collecting on-road aerosol data, and exploiting the difference in the relative volumes of HD and light duty (LD) traffic on the roadway. Fuel-specific particle number emissions for HD vehicles were measured to be 9.1 +/- 6.6 x 10(15) and 3.2 +/- 2.8 x 10(15) particles/kg of fuel burned, in 2006 and 2007, respectively, a reduction of 65%. In an earlier study in 2002 particle number emissions for the in-use HD fleet were 4.2 +/- 0.6 x 10(15) particles/km compared to the current measurements of 2.8 +/- 2.1 x 10(15) and 9.9 +/- 8.7 x 10(14) particles/km in 2006 and 2007, respectively. The HD particle mass emission standard remained unchanged from 1994 through 2006 and few 2007 HD vehicles were on the road at the time of this study so the decreases in number observed emissions are more likely due to reductions in the sulfur content of the fuel than to changes in engine and aftertreatment design.

Nuclei-mode particulate emissions and their response to fuel sulfur content and primary dilution during transient operations of old and modern diesel engines.

The effects of fuel sulfur content and primary dilution on PM number emissions were investigated during transient operations of an old and a modern diesel engine. Emissions were also studied during steady-state operations in order to confirm consistency with previous findings. Testing methods were concurrent with those implemented by the EPA to regulate PM mass emissions, including the use of the Federal Transient Testing Procedure-Heavy Duty cycle to simulate transient conditions and the use of a Critical Flow Venturi-Constant Volume System to provide primary dilution. Steady-state results were found to be consistent with previous studies in that nuclei-mode particulate emissions were largely reduced when lower-sulfur content fuel was used in the newer engine, while the nuclei-mode PM emissions from the older engine were much less affected by fuel sulfur content. The transient results, however, show that the total number of nuclei-mode PM emissions from both engines increases with fuel sulfur content, although this effect is only seen under the higher primary dilution ratios with the older engine. Transient results further show that higher primary dilution ratios increase total nuclei-mode PM number emissions in both engines.

Characteristics of SME biodiesel-fueled diesel particle emissions and the kinetics of oxidation.

Biodiesel is one of the most promising alternative diesel fuels. As diesel emission regulations have become more stringent, the diesel particulate filter (DPF) has become an essential part of the aftertreatment system. Knowledge of kinetics of exhaust particle oxidation for alternative diesel fuels is useful in estimating the change in regeneration behavior of a DPF with such fuels. This study examines the characteristics of diesel particulate emissions as well as kinetics of particle oxidation using a 1996 John Deere T04045TF250 off-highway engine and 100% soy methyl ester (SME) biodiesel (B100) as fuel. Compared to standard D2 fuel, this B100 reduced particle size, number, and volume in the accumulation mode where most of the particle mass is found. At 75% load, number decreased by 38%, DGN decreased from 80 to 62 nm, and volume decreased by 82%. Part of this decrease is likely associated with the fact that the particles were more easily oxidized. Arrhenius parameters for the biodiesel fuel showed a 2-3times greater frequency factor and approximately 6 times higher oxidation rate compared to regular diesel fuel in the range of 700-825 degrees C. The faster oxidation kinetics should facilitate regeneration when used with a DPF.

Chemical and physical properties of ultrafine diesel exhaust particles sampled downstream of a catalytic trap.

The chemical and physical properties of exhaust particles produced by a Caterpillar 3176 C-12 heavy duty diesel engine equipped with a catalytic trap (CRT) are reported. The engine was operated at 600 Nm and 1500 rpm, using fuels containing 15 and 49 ppm sulfur. A two-stage dilution tunnel designed to simulate the reactions that occur when hot combustion products mix with cooler atmospheric air was used. Particle size distributions were measured using a scanning mobility particle sizer (SMPS) and nano-scanning mobility particle sizer (nano SMPS); a nanomicro-orifice uniform deposit impactor (nano MOUDI) collected size-resolved samples for gravimetric and chemical analysis. A nanometer tandem differential mobility analyzer (nano TDMA) was used to measure the volatility and hygroscopicity of 4-15 nm particles. These measurements confirm that the particles consisted primarily of sulfates.

On-road exposure to highway aerosols. 2. Exposures of aged, compromised rats.

Ambient particulate pollution is associated with adverse health effects in epidemiological studies of the elderly with cardiopulmonary diseases. We hypothesize that ultrafine particles (UFP) contribute to these effects, especially when they are freshly generated and occur at high number concentrations. Studies to determine adverse effects have been performed using laboratory-generated surrogates, diluted exhaust from stationary engines, or concentrated ambient UFPs. Methodological difficulties exist with such experiments, and questions remain about how well these particles model those found in ambient air. Freshly generated UFPs are present at high concentrations on highways and vehicle passengers are directly exposed to them. We wished to expose rats to these UFPs to test their potential to cause effects. Since such exposures have not been done before, one objective of our study was to demonstrate the feasibility of an on-road exposure study. Secondly, we wished to determine if there are significant exposure-related effects in aged, compromised rats. Old rats (21-mo F-344) were exposed directly on highways to either the aerosol (<1 microm)/gas phase, gas phase only, or filtered air using an on-road exposure system. Some rats were pretreated with a low dose of inhaled endotoxin or with instilled influenza virus to induce lung inflammation. The exposures in compartmentalized whole-body chambers consisted of 6-h driving periods on I-90 between Rochester and Buffalo once or 3 days in a row. Endpoints related to lung inflammation, inflammatory cell activation, and acute-phase responses were measured after exposure. The on-road exposure system did not affect measured endpoints in filtered air-exposed rats, indicating that it was well tolerated by them. We observed the expected increases in response (inflammation, inflammatory cell activation) to the priming agents. We also found a significant particle-associated increase in plasma endothelin-2, suggesting alterations in vascular endothelial cell activation. In addition, we observed main effects of particles related to the acute-phase response and inflammatory-cell activation. Interactions between on-road particles and the priming agents were also found. These results suggest that exposures to on-road particle mixtures have effects on the pulmonary and cardiovascular system in compromised, old rats. Furthermore, they demonstrate that on-road exposures are feasible and could be performed in future studies with more continuous particle exposures.

Kinetics of diesel nanoparticle oxidation.

The technique of high-temperature oxidation tandem differential mobility analysis has been applied to the study of diesel nanoparticle oxidation. The oxidation rates in air of diesel nanoparticles sampled directly from the exhaust stream of a medium-duty diesel engine were measured over the temperature range of 800-1140 degrees C using online aerosol techniques. Three particle sizes (40, 90, and 130 nm mobility diameter) generated under engine load conditions of 10, 50, and 75% were investigated. The results show significant differences in the behavior of the 10% load particles as compared to the 50 and 75% load particles. The 10% load particles show greater size decrease at temperatures below 500 degrees C and significant size decrease at temperatures between 500 and 1000 degrees C in a non-oxidative environment, indicating release of adsorbed volatile material or thermally induced rearrangement of the agglomerate structure. Activation energies determined are 114, 109, and 108 kJ mol(-1) for the 10, 50, and 75% load particles, respectively. These activation energies are lower than for flame soot (Higgins et al. J. Phys. Chem. A 2002, 106, 96), but the preexponential factors are lower by 3 orders of magnitude, and the overall oxidation rates are slower by up to a factor of 4 over the temperature range studied. Possible reasons for the differences are discussed in the text.

Relationship between particle mass and mobility for diesel exhaust particles.

We used the aerosol particle mass analyzer (APM) to measure the mass of mobility-classified diesel exhaust particles. This information enabled us to determine the effective density and fractal dimension of diesel particles as a function of engine load. We found that the effective density decreases as particle size increases. TEM images showed that this occurs because particles become more highly agglomerated as size increases. Effective density and fractal dimension increased somewhat as engine load decreased. TEM images suggest that this occurs because these particles contain more condensed fuel and/or lubricating oil. Also, we observed higher effective densities when high-sulfur EPA fuel (approximately 360 ppm S) was used than for Fischer-Tropsch fuel (approximately 0 ppm S). In addition, the effective density provides the relationship between mobility and aerodynamic equivalent diameters. The relationship between these diameters enables us to intercompare, in terms of a common measure of size, mass distributions measured with the scanning mobility particle sizer (SMPS) and a MOUDI impactor without making any assumptions about particle shape or density. We show that mass distributions of diesel particles measured with the SMPS-APM are in good agreement with distributions measured with a MOUDI and a nano-MOUDI for particles larger than approximately 60 nm. However, significantly more mass and greater variation were observed by the nano-MOUDI for particles smaller than 40 nm than by the SMPS-APM.

Size-dependent mixing characteristics of volatile and nonvolatile components in diesel exhaust aerosols.

Mixing characteristics of particles of different volatilities from a diesel engine were studied with two tandem differential mobility analyzers (TDMAs) and an aerosol particle mass analyzer (APM). In both TDMA systems, a heater was located in the aerosol path between the first and second DMAs. Diesel exhaust particles that were size-selected in the first DMA were passed through the heater, and the change in particle size due to loss of volatile components was determined by the second DMA. On the basis of the volatility measurements, the particles could be separated into two overlapping modes that varied in peak diameter and magnitude depending on the engine operating conditions. Particles in the smaller size mode were almost completely volatile, while those in the larger size mode contained a nonvolatile core. The TDMA data inversion technique used here allowed accurate determination of the mixing ratios of the two types of particles. These data were in turn used to validate a simple fitting method that uses two log-normal curves to obtain the mixing ratios. In some experiments, the APM was used downstream of a TDMA to directly measure the particle mass loss due to evaporation. The loss determined bythe TDMA-APM system was significantly greater than that calculated from mobility size changes measured solely with the TDMA. The TDMA-APM results were used to calculate the size-dependent mass concentrations of volatile and nonvolatile components for particles in the size range from 70 to 200 nm.