Imad A. Khalek

Regulated and unregulated emissions from highway heavy-duty diesel engines complying with U.S. Environmental Protection Agency 2007 emissions standards.

ABSTRACT As part of the Advanced Collaborative Emissions Study (ACES), regulated and unregulated exhaust emissions from four different 2007 model year U.S. Environmental Protection Agency (EPA)-compliant heavy-duty highway diesel engines were measured on an engine dynamometer. The engines were equipped with exhaust high-efficiency catalyzed diesel particle filters (C-DPFs) that are actively regenerated or cleaned using the engine control module. Regulated emissions of carbon monoxide, nonmethane hydrocarbons, and particulate matter (PM) were on average 97, 89, and 86% lower than the 2007 EPA standard, respectively, and oxides of nitrogen (NOx) were on average 9% lower. Unregulated exhaust emissions of nitrogen dioxide (NO2) emissions were on average 1.3 and 2.8 times higher than the NO2 emissions reported in previous work using 1998- and 2004-technology engines, respectively. However, compared with other work performed on 1994- to 2004-technology engines, average emission reductions in the range of 71–99% were observed for a very comprehensive list of unregulated engine exhaust pollutants and air toxic contaminants that included metals and other elements, elemental carbon (EC), inorganic ions, and gas- and particle-phase volatile and semi-volatile organic carbon (OC) compounds. The low PM mass emitted from the 2007 technology ACES engines was composed mainly of sulfate (53%) and OC (30%), with a small fraction of EC (13%) and metals and other elements (4%). The fraction of EC is expected to remain small, regardless of engine operation, because of the presence of the high-efficiency C-DPF in the exhaust. This is different from typical PM composition of pre-2007 engines with EC in the range of 10–90%, depending on engine operation. Most of the particles emitted from the 2007 engines were mainly volatile nuclei mode in the sub-30-nm size range. An increase in volatile nanoparticles was observed during C-DPF active regeneration, during which the observed particle number was similar to that observed in emissions of pre-2007 engines. However, on average, when combining engine operation with and without active regeneration events, particle number emissions with the 2007 engines were 90% lower than the particle number emitted from a 2004-technology engine tested in an earlier program. IMPLICATIONS To meet the 2007 EPA heavy-duty highway PM emissions standard, engine manufacturers have elected to equip engine exhaust with a high-efficiency C-DPF. Because of the use of the C-DPF, the PM emissions were 86% below the 2007 standard, and many unregulated gas and particle-phase emissions compounds were substantially lower than those emitted from pre-2007-technology engines. Signifi-cant air quality benefits can be expected as the C-DPF technology, or other equivalent technology, continues to be applied to future highway engines and to other nonroad and stationary diesel engines.

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

Regulated and unregulated emissions from modern 2010 emissions-compliant heavy-duty on-highway diesel engines

The U.S. Environmental Protection Agency (EPA) established strict regulations for highway diesel engine exhaust emissions of particulate matter (PM) and nitrogen oxides (NOx) to aid in meeting the National Ambient Air Quality Standards. The emission standards were phased in with stringent standards for 2007 model year (MY) heavy-duty engines (HDEs), and even more stringent NOX standards for 2010 and later model years. The Health Effects Institute, in cooperation with the Coordinating Research Council, funded by government and the private sector, designed and conducted a research program, the Advanced Collaborative Emission Study (ACES), with multiple objectives, including detailed characterization of the emissions from both 2007- and 2010-compliant engines. The results from emission testing of 2007-compliant engines have already been reported in a previous publication. This paper reports the emissions testing results for three heavy-duty 2010-compliant engines intended for on-highway use. These engines were equipped with an exhaust diesel oxidation catalyst (DOC), high-efficiency catalyzed diesel particle filter (DPF), urea-based selective catalytic reduction catalyst (SCR), and ammonia slip catalyst (AMOX), and were fueled with ultra-low-sulfur diesel fuel (~6.5 ppm sulfur). Average regulated and unregulated emissions of more than 780 chemical species were characterized in engine exhaust under transient engine operation using the Federal Test Procedure cycle and a 16-hr duty cycle representing a wide dynamic range of real-world engine operation. The 2010 engines’ regulated emissions of PM, NOX, nonmethane hydrocarbons, and carbon monoxide were all well below the EPA 2010 emission standards. Moreover, the unregulated emissions of polycyclic aromatic hydrocarbons (PAHs), nitroPAHs, hopanes and steranes, alcohols and organic acids, alkanes, carbonyls, dioxins and furans, inorganic ions, metals and elements, elemental carbon, and particle number were substantially (90 to >99%) lower than pre-2007-technology engine emissions, and also substantially (46 to >99%) lower than the 2007-technology engine emissions characterized in the previous study. Implications: Heavy-duty on-highway diesel engines equipped with DOC/DPF/SCR/AMOX and fueled with ultra-low-sulfur diesel fuel produced lower emissions than the stringent 2010 emission standards established by the U.S. Environmental Protection Agency. They also resulted in significant reductions in a wide range of unregulated toxic emission compounds relative to older technology engines. The increased use of newer technology (2010+) diesel engines in the on-highway sector and the adaptation of such technology by other sectors such as nonroad, displacing older, higher emissions engines, will have a positive impact on ambient levels of PM, NOx, and volatile organic compounds, in addition to many other toxic compounds.

Particle size distribution from a heavy-duty diesel engine: Steady-state and transient emission measurement using two dilution systems and two fuels

Particle size distribution and number concentration were measured in the dilute exhaust of a heavy-duty diesel engine for steady-state and transient engine operation using two different dilution systems that included a full flow CVS that was coupled to an ejector pump (CVS-EP), and a double-ejector micro-dilution tunnel (DEMDT) that was connected to engine exhaust close to turbocharger outlet. Measurements were performed using a scanning mobility particle sizer (SMPS), an electrical low pressure impactor (ELPI), and a parallel flow diffusion battery (PFDB). Fuels with sulfur content of about 385 ppm and 1 ppm were used for this work. The PFDB performed well in measuring nanoparticles in the size range below 56 nm when compared with the SMPS. This was especially valid when a distinct log-normal size distribution in the size range below 56 nm in diameter, the upper size limit of the PFDB, was present. The dilution method and the sulfur content in the fuel influenced the characteristics of the size distributions significantly under both steady-state and the FTP hot-start transient cycle. The CVS-EP resulted in more particle growth and higher number of nanoparticles compared to the DEMDT. Harmonizing the measurement method of total particle number and size emissions from engines by providing a reference condition to variables such as dilution temperature, dilution rate, dilution ratio, relative humidity, dilution and transfer line residence time, will be a key next step in developing a protocol and a standard operating procedure for such measurement. Until then, different researchers will continue to produce different results in measuring total particle size and number, depending on the sampling and dilution system selected.

Particle size distribution and mass emissions from a mining diesel engine equipped with a Dry system technologies emission control system

Particle size distribution, number, and mass emissions from the exhaust of a 92 kW 1999 Isuzu 6BG1 nonroad naturally aspirated diesel engine were measured. The engine exhaust was equipped with a Dry System Technologie® (DST) auxillary emission control device that included an oxidation catalyst, a heat exchanger, and a disposable paper particulate filter. Particle measurement was taken during the ISO 8178 8-mode test for engine out and engine with the DST using a scanning mobility particle sizer (SMPS) in parallel to the standard filter method (SFM), specified in 40 CFR, Part 89. The DST efficiency of removing particles was about 99.9 percent based on particle number, 99.99 percent based on particle mass derived from number and size. However, the efficiency based on mass derived from the SFM was much lower on the order of 90 to 93 percent. This discrepancy in particle mass efficiency between the two methods was mainly due to poor correlation between the mass derived from number and size and the mass measured using the SFM. This poor correlation was obtained for the DST out particulate matter (PM) emission and not for engine out. For DST out PM, the SFM tends to exaggerate the mass emissions of particles due to the condensation/adsorption of gas phase non aerosol volatile compounds on the PalflexT60A20 filters used for particle mass measurement, thus resulting in a lower efficiency of particle removal. If the health effect of particles is due to the mass and number of their physical characteristics, particle measurement using the SFM may need rethinking, particularly if the nature of the measured product is dominated by volatile rather than soot.

CRANKCASE EMISSION CONTRIBUTIONS TO PM FOR TWO TIER 2 LINE-HAUL LOCOMOTIVES

This paper documents the quantification and characterization of particulate matter (PM) emitted from two Tier 2 diesel locomotives, and the impact of crankcase ventilation (CCV) on PM emissions. Emission testing was performed on one General Electric (GE) model ES44DC locomotive, and one Electro-Motive Diesel (EMD) model SD70ACe. A semi-continuous organic carbon/elemental carbon (OC/EC) analytical procedure was used to collect and determine the OC and EC of PM. PM was also measured gravimetrically using Teflon membrane filters. Testing was performed for the locomotives in an unmodified configuration “with CCV”, and then again without the CCV included in the emissions measurements. Without CCV, the two-stroke SD70ACe brake specific filter-based PM and OC/EC PM, over the Line-haul Locomotive Duty Cycle (LHLDC), were reduced by approximately 15% to 16%, respectively, compared to testing with CCV. The 4-stroke ES44DC showed a reduction of 11% for the OC/EC PM which was mainly due to a reduction in OC PM. When crankcase emissions were not included, OC PM was reduced for nearly all throttle notches, and especially under high load conditions, although the differences were not always significant at a 95% confidence interval. With CCV, the relative OC portion of the Line-haul composite PM value for both locomotives was approximately 42–47%. Without CCV, the absolute brake-specific OC PM over the LHLDC was reduced by 30%, thereby reducing the relative OC portion to approximately 34–38%. This work showed that the OC PM fraction is significant for the locomotives tested, and controlling OC can lead to more than 40 percent reduction in PM. Furthermore, almost one-third of the OC PM was contributed by CCV, therefore better control of blow-by PM from both locomotive types can lead to a significant reduction in OC PM.Copyright

Characterization of Particle Size, Number, and Mass Emissions From a Diesel Powered Generator

Total (volatile plus solid) and solid particle size, number, and mass emitted from a 3.8 kW diesel powered generator were characterized using a Scanning Mobility Particle Sizer (SMPS) that measures the size distribution of particles, and a catalytic stripper that facilitates the measurement of solid particles. The engine was operated at a constant speed for six steady-state engine operations ranging from idle to rated power. The solid particle size distributions were mainly monomodal lognormal distributions in nature reflecting a typical soot agglomerate size distribution with a number mean diameter in the size range from 98 nm to 37 nm as the load decreases from high to low. At idle, M6, however, the solid particle distribution was bimodal in nature with a high number of solid nanoparticles in the sub-20 nm size range. It is likely that these solid particles nucleated later in the combustion process from metallic ash typically present in the lube oil. The total particle size distributions exhibited a bimodal structure only at light load, M5, engine operation, where a high number of volatile nanoparticles were observed. The rest of the operating conditions exhibited monomodal distributions although the nature of the particles was vastly different. For the medium load modes, M2, M3, and M4, the particles were mainly solid particles. For the rated power, M1, and idle, M6, modes of engine operation, significant number of volatile particles grew to a size nearing that of soot particles making the distribution monomodal, similar to that of a solid particle distribution. This shows that monomodal distributions are not necessarily solid particle but they can be strongly dominated with volatile particles if significant particle growth takes place like the case at M1, and M6. The total number and mass concentration were extremely high at engine rated power. The number concentration exceeded 1.2 billion particles per cubic centimeter and the mass exceeded 750 milligrams per cubic meter. The number concentration is more than five orders of magnitude higher than a typical ambient level concentration, and the mass concentration is more than four orders of magnitude higher. It is important to indicate, however, that if the engine power rating is lowered by 35 percent from its designated level, both particle mass and number emissions will be reduced by two orders of magnitude. By measuring total and solid particle size and number concentration of particles, one can calculate other metrics such as surface area and mass to provide detail information about particle emissions. Such information can serve as an important database where all metrics of particle emissions are captured.Copyright

Marine outboard and personal watercraft engine gaseous emissions, and particulate emission test procedure development

The U.S. EPA and the California Air Resources Board have adopted standards to reduce emissions from recreational marine vessels. Existing regulations focus on reducing hydrocarbons. There are no regulations on particulate emissions; particulate is expected to be reduced as a side benefit of hydrocarbon control. The goal of this study was to develop a sampling methodology to measure partic late emissions from marine outboard and personal watercraft engines. Eight marine engines of various engine technologies and power output were tested. Emissions measured in this program included hydrocarbons, carbon monoxide, oxides of nitrogen. Particulate emissions will be presented in a follow-up paper.

Particle Free Exhaust Gas Recirculation by Molecular Diffusion: Proof of Concept

This work included design and fabrication of a particle free exhaust gas recirculation element (PF-EGR-E) that included two concentric tubes, one for a clean air stream and the other for a simulated exhaust stream. The inner tube was a perforated tube to allow molecular diffusion between the two streams. The design and dimension of the PF-EGR-E was guided with the help of theoretical prediction of gas and particle diffusion. The goal was to build a PF-EGR-E that retains particles in a dilute exhaust stream while allowing maximum molecular exchange with the air stream. The performance of the PF-EGR-E was investigated using dilute diesel engine exhaust and clean air flowing in parallel at different flow and temperature levels. Measurements of NO x , CO 2 , and particle concentration at inlet and exit of the perforated tube demonstrated that it was possible to achieve high molecular transfer between a dilute exhaust stream and clean air stream while particle transfer was still at minimum level. This work proofed the concept of achieving particle free EGR with a single perforated tube using molecular and particle diffusion principles. The next step will be to demonstrate this concept in a prototype system to be used on a diesel engine.