Environ. Sci. Technol. 2007, 41, 5037-5043
Unregulated Emissions from a Heavy-Duty Diesel Engine with Various Fuels and Emission Control Systems S H I D A T A N G , * ,† B R I A N P . F R A N K , † THOMAS LANNI,† GREG RIDEOUT,‡ NORMAN MEYER,‡ AND CHRIS BEREGSZASZY‡ Bureau of Mobile Sources and Technology Development, Division of Air Resources, New York State Department of Environmental Conservation, 625 Broadway, Albany, New York 12233, and Emissions Research and Measurement Division, Environment Canada, Ottawa, Ontario, Canada K1A 0H3
This study evaluated the effects of various combinations of fuels and emission control technologies on exhaust emissions from a heavy-duty diesel engine tested on an engine dynamometer. Ten fuels were studied in twenty four combinations of fuel and emission control technology configurations. Emission control systems evaluated were diesel oxidation catalyst (DOC), continuously regenerating diesel particulate filter (CRDPF), and the CRDPF coupled with an exhaust gas recirculation system (EGRT). The effects of fuel type and emission control technology on emissions of benzene, toluene, ethylbenzene, xylene (BTEX), and 1,3butadiene, elemental carbon and organic carbon (EC/OC), carbonyls, polycyclic aromatic hydrocarbons (PAHs), and nitro-PAHs (n-PAHs) are presented in this paper. Regulated gaseous criteria pollutants of total hydrocarbons (THC), carbon monoxide (CO), oxides of nitrogen (NOx) and particulate matter (PM) emissions have been reported elsewhere. In general, individual unregulated emission with a CRDPF or an EGRT system is similar (at very low emission level) or much lower than that operating solely with a DOC and choosing a “best” fuel. The water emulsion PuriNOx fuel exhibited higher BTEX, carbonyls and PAHs emissions compared to other ultralow sulfur diesel (ULSD) fuels tested in this study while n-PAH emissions were comparable to that from other ULSD fuels. Naphthalene accounted for greater than 50% of the total PAH emissions in this study and there was no significant increase of n-PAHs with the usage of CRDPF.
Introduction Diesel exhaust has been suggested as a probable human carcinogen by several state, national, and international agencies (1). A growing recognition of the harmful effects of diesel emissions on air quality and human health led the U.S. EPA to propose new heavy-duty engine and vehicle standards (2). This major regulatory initiative addresses the * Corresponding author phone: 518-782-7248; fax: 518-782-7255; e-mail:
[email protected]. † New York State Department of Environmental Conservation. ‡ Environment Canada. 10.1021/es0622249 CCC: $37.00 Published on Web 06/09/2007
2007 American Chemical Society
problem of particulate matter (PM) and oxides of nitrogen (NOx) emissions by setting much stricter standards for emissions and for the sulfur content of diesel fuel. Significant emission reduction has been achieved over the years by progress in engine design and electronic control. Advanced aftertreatment devices, which require ultralow sulfur diesel (ULSD), are also necessary to meet new emission standards. The development of alternative fuels to control automotive emissions and provide energy independence is becoming more important with increased public concern about energy security and environmental pollution. Previous work has shown that the combination of continuously regenerating diesel particulate filter (CRDPF) with ULSD is a very effective approach for diesel PM emission reduction (3, 4). Alternative fuels such as compressed natural gas (CNG) (5, 6), FischerTropsch (F-T) diesel (7, 8), biodiesel blend diesel (9-11), the water emulsion diesel (12), and ethanol blend diesel (13, 14) have been studied for this purpose. Aftertreatment strategies for NOx emission reduction include exhaust gas recirculation (EGR) (15, 16), NOx absorbers (17), and selective catalytic reduction (SCR) systems (18, 19). A variety of fuel and aftertreatment technologies to reduce diesel emissions are now available as retrofit strategies for existing diesel fleets. While many factors are involved in choosing a strategy, achievable emissions reduction is a key consideration. The objective of this study was to evaluate the impact of 10 diesel fuels in conjunction with three commercially available diesel emission control technologies including diesel oxidation catalyst (DOC), CRDPF, and CRDPF coupled with an exhaust gas recirculation system (EGRT). Ten different fuels were studied in twenty four combinations of fuel and aftertreatment configurations. Emissions of the regulated gaseous criteria pollutants carbon monoxide (CO), NOx, total hydrocarbons (THC), PM as well as carbon dioxide (CO2) determined in this study have been reported elsewhere (4). In this paper, we present the results of the effects of the fuel and aftertreatment device on unregulated toxic emissions of benzene, toluene, ethylbenzene, xylene (BTEX), 1,3butadiene, elemental carbon (EC) and organic carbon (OC), carbonyls, polycyclic aromatic hydrocarbons (PAHs), and nitro-PAHs (n-PAHs).
Emission Measurement Diesel Engine and Aftertreatment Devices. The selected engine for this study was a model year 2000, electronically controlled six cylinder International-Navistar DT466 diesel engine with turbocharger. This engine has a displacement of 7.6 L with 237 hp maximum power and 620 ft-lb maximum torque at 2300 and 1400 rpm, respectively. Details of the engine and aftertreatment technologies have been described previously (4). The DOC used in this study was an AZ Purimuffler, a U.S. EPA Voluntary Retrofit Program “verified product”, provided by Engine Control Systems, a division of Lubrizol Canada. The Johnson Matthey CRT filter or CRDPF is a two chamber device that oxidizes a portion of NO emissions to NO2 by the oxidation catalyst in the first chamber and then uses the NO2 to oxidize PM in a wall-flow particulate filter in the second chamber. Detailed descriptions of the CRDPF have been provided in previous studies (3, 20). CRDPF testing was performed only with ULSD (74.8 49.7 50.9 43.4 40.4
1.73 2.39 1.50 1.79 1.72 3.56 2.11 2.20 1.59 1.77
472 410 162 28 27 1.2 21 30 315 242
86.2 86.5 86.6 86.4 85.7 85.1 84.5 80.1 84.0 83.9
13.5 13.2 13.7 13.5 13.7 15.1 13.3 13.5 13.9 13.6
11.4 24.9 6.5 5.6 4.4 0.6 4.2 794 232 287
22.2 30.6 17.8 20.2 20.9 0.8 29.6 21.6 22.1 30.2
1.4 1.2 2.8 3.6 1.5 0.8 3.5 3.4 1.5 1.9
a D1 is Canadian no. 1 diesel; D2 is Canadian no. 2 diesel; LSD is low sulfur diesel; E-ULSD is Equilon ultralow sulfur diesel; T-ULSD is Tosco ultralow sulfur diesel; F-T is Fischer-Tropsch diesel; B20 is E-ULSD blended with 20% biodiesel; PuriNOx - A water/diesel emotion containing 7% water and 93% E-ULSD by weight; ED1 is 7% corn-derived ethanol blended with 93% Canadian no. 1 diesel; ED2 is 7% corn-derived ethanol blended with 93% Canadian no. 2 diesel. b Additional cosolvent and ethanol added prior to test.
TABLE 2. (A) Fuel and Aftertreatment Configurations Evaluated. (B) Emission Characterization Analysis and Sample Collection
EO DOC CRDPF EGRT
D1 x x
D2 x x
compound
LSD x x
E-ULSD x x x x
Part A T-ULSD
F-T
B20
PuriNOx
x x x
x x x
x x x
x x
Part B analysis method
EC/OC
NIOSH 5040 thermal optical transmittance
carbonyl compounds
high performance liquid chromatography (HPLC) gas chromatography-flame ionization detection (GC-FID) high resolution gas chromatography mass spectrometry (HRGC/MS)
volatile organic compounds (VOC) PAHs and n-PAHs
Test Fuels. The 10 different fuels evaluated are listed in Table 1. Analysis of selected physical properties was performed by the Alberta Research Council. The ULSD provided by Equilon (E-ULSD) and Tosco (T-ULSD) are almost identical (Table 1) and commercially available to fleet operators on the east coast of the U.S. The F-T diesel fuel is produced from natural gas using the Fischer-Tropsch method which has a high cetane number and low aromatic content. For PuriNOx, a water emulsion diesel fuel, a proprietary hydrocarbon additive created by Lubrizol Corporation is used to keep water in emulsion. The E-ULSD was chosen for blending with biodiesel and PuriNOx because of the U.S. regulations for the use of ULSD in 2006. Prior to initiating the emissions testing on each different fuel, the engine was thoroughly flushed to ensure there was no contamination from the previous fuel. This included draining all fuel lines and changing fuel filters between test fuels. The engine was run for more than 1 h with each fuel before emission tests for that fuel were started. Test Procedure/Cycle and Emission Measurement. Emission testing was performed on an engine dynamometer with the federal heavy-duty transient cycle or the so-called federal testing procedure (FTP). Pretest engine and dynamometer preparation as well as the engine emission testing were conducted in accordance with the respective sections of the U.S. Code of Federal Regulation (CFR). Emissions were determined over a cold start cycle followed by three hot starts of the FTP testing cycles, with each cycle separated by the required 20-min soak period. The sampling system was preconditioned by operating the engine at the rated-speed and 100% torque for a period 5038
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ED1 x x
ED2 x x
sample collection Pallflex 47 mm quartz filters (ISSUQUARTZ-2500QAT) 2,4-DNPH coated-silica gel cartridges Tedlar bag Pallflex TX40HI20WW filter and polyurethane foam (PUF)
of 20 min. The constant volume sampling (CVS) and secondary dilution system temperatures were verified to establish conformance with CFR. Emission measurements were performed on diluted exhaust from the CVS system, which diluted the engine exhaust during the test with dilution air filtered through a set of filters (bag, activated carbon, and HEPA). Data was gathered over the heavy-duty FTP for twenty four combinations of fuel and aftertreatment configuration as summarized in Table 2A. The FTP is a certification testing cycle composed of both hot and cold starts. As practical considerations prevented cold start data from being obtained for some cases, only hot start results from three repeated hot start tests are presented. Table 2B provides an overview of the unregulated emissions that were characterized during the study. The emissions characterization consisted of per cycle sampling during the hot start test with the exception of PAH/n-PAH which had one sample collected over three cycles. The PM EC/OC was measured using a thermal-optical method (21) on quartz filters collected during the hot start test. To compensate for the contributions of vapor-phase OC in the dilution air and diluted exhaust, two quartz filters were collected simultaneously from parallel filter packs, one with a quartz filter only and the other with a Teflon filter followed by a quartz filter. The quartz filter in the Teflon/quartz pack only collects vapor-phase OC, as the Teflon filter should capture all of the particle phase OC. This vapor-phase OC was then subtracted from the total OC measured from the quartz filter in the quartz only pack to obtain PM phase OC. Elemental carbon was not present in the dilution air as it was HEPA filtered.
TABLE 3. Comparison of BTEX and 1,3-Butadiene Emission Rates (mg/bhp-hr)a D1
D2
LSD
E-ULSD
T-ULSD
B20
PuriNOx
EO
benzene toluene ethylbenzene m,p-xylene o-xylene 1,3 butadiene BTEX
2.55 ( 0.19 1.70 ( 0.18 0.80 ( 0.10 2.04 ( 0.32 1.00 ( 0.05 0.06 ( 0.04 8.09 ( 0.43
3.31 ( 0.08 3.16 ( 0.20 1.67 ( 0.07 4.31 ( 1.06 0.17 ( 0.05 0.96 ( 0.07 0.92 ( 0.06 2.42 ( 0.14 0.57 ( 0.02 1.11 ( 0.05 0.05 ( 0.03 0.05 ( 0.02 6.64 ( 0.14 11.96 ( 1.09
1.82 ( 0.05 0.71 ( 0.03 0.51 ( 0.03 0.76 ( 0.08 0.29 ( 0.03 0.04 ( 0.00 4.09 ( 0.11
benzene toluene ethylbenzene m,p-xylene o-xylene 1,3 butadiene BTEX
0.76 ( 0.00 0.43 ( 0.02 NR 0.44 ( 0.01 0.10 ( 0.00 ND g 1.73
0.68 ( 0.14 0.03 ( 0.05 0.09 ( 0.05 0.02 ( 0.04 0.05 ( 0.05 ND 0.87 ( 0.17
0.51 ( 0.06 0.39 ( 0.03 0.06 ( 0.10 ND 0.10 ( 0.04 NR 0.04 ( 0.06 ND 0.07 ( 0.12 0.10 ( 0.12 ND ND 0.78 ( 0.18 g 0.49
0.51 ( 0.01 0.05 ( 0.05 0.01 ( 0.01 0.04 ( 0.04 0.08 ( 0.11 ND 0.68 ( 0.13
F-T
E-D1
E-D2
3.76 ( 0.07 3.73 ( 0.12 3.26 ( 0.13 1.83 ( 0.49 1.79 ( 0.06 1.17 ( 0.06 5.02 ( 0.22 2.41 ( 0.06 2.56 ( 0.08 1.42 ( 0.06 0.07 ( 0.04 0.05 ( 0.05 16.38 ( 0.29 10.56 ( 0.52
DOC
CRDPF
0.16 ( 0.01 0.08 ( 0.14 0.11 ( 0.05 0.02 ( 0.03 0.20 ( 0.06 ND 0.57 ( 0.17
0.52 ( 0.01 0.03 ( 0.05 ND 0.03 ( 0.04 0.19 ( 0.10 ND 0.76 ( 0.12
4.14 ( 0.08 2.09 ( 0.11 0.22 ( 0.06 1.15 ( 0.08 0.72 ( 0.02 0.07 ( 0.03 8.32 ( 0.17
0.05 ( 0.07 0.01 ( 0.02 0.01 ( 0.02 ND 0.02 ( 0.03 ND 0.09 ( 0.08
0.43 ( 0.06 0.14 ( 0.12 NR 0.99 ( 0.99 0.52 ( 0.13 ND g 2.08
benzene toluene ethylbenzene m,p-xylene o-xylene 1,3 butadiene BTEX
0.05 ( 0.03 0.02 ( 0.03 0.02 ( 0.03 ND 0.01 ( 0.01 ND 0.09 ( 0.05
0.01 ( 0.02 0.03 ( 0.02 0.07 ( 0.10 ND 0.05 ( 0.03 NR NR 0.03 ( 0.05 0.03 ( 0.05 ND ND ND g 0.17 g 0.07
benzene toluene ethylbenzene m,p-xylene o-xylene 1,3 butadiene BTEX
0.07 ( 0.02 ND 0.03 ( 0.00 0.01 ( 0.02 ND ND 0.11 ( 0.03
0.06 ( 0.01 0.01 ( 0.02 ND ND 0.02 ( 0.03 ND 0.09 ( 0.04
EGRT
1.49 ( 0.15 1.10 ( 0.08 0.53 ( 0.04 1.09 ( 0.06 0.48 ( 0.04 ND 4.70 ( 0.19
1.58 ( 0.14 0.80 ( 0.79 0.38 ( 0.35 0.67 ( 1.16 0.32 ( 0.35 ND 3.75 ( 1.49
0.03 ( 0.01 0.03 ( 0.04 0.09 ( 0.15 ND 0.02 ( 0.02 ND 0.01 ( 0.01 ND ND 0.01 ( 0.01 ND ND 0.14 ( 0.15 0.04 ( 0.04
a Values represent means and standard deviations for three hot start tests; NR is not reported due to interference in GC/MS analysis; ND is not detected (below detection limit).
FIGURE 1. Total carbonyl emissions with various fuel and aftertreatment configurations. Error bar represents standard deviation for three separate hot start tests. Quartz filters were precleaned by baking at 550 °C for 12 h and stored in baked aluminum foil prior to deployment. Carbonyls were determined using a previously described method (22) by collecting carbonyl species in diluted exhaust from the CVS on DNPH-coated silicon cartridges. Determination of carbonyl species in the cartridge extracts was achieved using HPLC with UV detection. The collection of both PM-phase and gas-phase PAHs and n-PAHs was achieved with a 70 mm precleaned Pallflex Emfab filter followed by a PUF plug. The filter and PUF plug were treated
as one sample and extracted with a precleaned Soxhlet extraction apparatus. The analyses for PAHs and n-PAHs were performed on the extracts using a high-resolution GC/ MS. Over forty-five PAH/n-PAHs compounds were analyzed.
Results and Discussion BTEX and 1,3-Butadiene. Methane and non-methane hydrocarbons were determined for all fuels in DOC, CRDPF, and EGRT configurations. The complete sets of results are provided in the Supporting Information (Table 1). This section VOL. 41, NO. 14, 2007 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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FIGURE 2. Comparison of organic and elemental carbon emissions with various fuel and aftertreatment configurations (A) and EC/OC ratio with various fuels under EO and DOC configurations (B). Error bar represents standard deviation for three separate hot start tests. discusses the emission rates of benzene, toluene, ethylbenzene, xylene, 1,3-butadiene, and BTEX, the sum of the first four, as listed in Table 3. The engine-out (EO) emissions were tested with E-ULSD, LSD (∼150 ppm S), ethanol diesels and their conventional base fuels. It can be seen from Table 3 that benzene, toluene and m,p-xylene accounted for the majority of the BTEX emissions. E-ULSD had the lowest BTEX emission while increased emissions of all BTEX compounds were observed with ED1 and ED2, which resulted in approximately twice the total BTEX emissions relative to their conventional counterparts. Increased BTEX emissions were also observed with ethanol diesels compared to their counterparts with DOC configuration where the ED2 data exhibited greater uncertainty. Our observation differs from a recent U.S. Department of Energy study where no significant effect on BTEX emissions has been found with the addition of 7.715% ethanol in diesel (14). This may be due to the possible dependence of the BTEX emissions on the engine operation conditions as seen by others for the effect of ethanol on the hydrocarbon (HC) emissions (13). Benzene dominated BTEX emissions for all fuels with the exception of the F-T fuel in the DOC configuration. For D2, LSD, E-ULSD, T-ULSD, and B20 fuels, benzene accounts for approximately 65-80% of BTEX emissions compared to 0.1 mg/bhp-hr. The lower PAH emissions with CRDPF and EGRT configurations compared to that with DOC configuration is in agreement with previous findings on the benefits of employing CRDPF (20, 27). PAH emissions are associated with poor combustion characteristics, and usually tend to increase with water content of a fuel. PuriNOx is a water fuel emulsion and it is not surprising that it experienced the highest PAH emissions of those fuels tested in the DOC and CRDPF configurations. The results of the n-PAH analysis are presented in Figure 3B. The total n-PAH emission rates (µg/bhp-hr) are about 3 orders of magnitude lower than the PAH emission rates observed, with speciated n-PAHs in the ng/bhp-hr range. This is in agreement with results reported by others (5, 34). The EGRT and CRDPF configurations performed similarly to the DOC with regard to total n-PAH emission. The highest EO emissions of n-PAHs were detected for the ethanol diesels (ED1 and ED2) and conventional diesels. The ethanol diesels exhibited similar n-PAH emissions to other fuels with the DOC in place. The fact that there is no significant increase of n-PAHs with the use of CRDPF is in agreement with our previous observations on transit buses (5). The speciated results for the n-PAHs can be also found in the Supporting Information (Table 3). Overall Performance. In summary, some emission reduction can be achieved with the use of DOC. Much higher reduction of both regulated and unregulated emissions can be achieved with a CRDPF (except for NOx) or an EGRT system than by operating solely with a DOC and choosing a “best” fuel. If a DOC is chosen for economic considerations, better emission reduction for PM and EC can still be achieved by the use of cleaner fuels (ULSD, F-T, and PuriNOx) compared to the use of regular diesel. This provides additional justification for the use of ULSD apart from its required use in advanced aftertreatment devices. The PuriNOx is the only fuel that achieved significant NOx emission reduction with DOC, similar to the use of an EGRT with ULSD. However, increased THC, BTEX, carbonyls, and PAH emissions are also 5042
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observed with the use of PuriNOx fuel, a penalty resulting from the associated lower combustion temperature intended to reduce NOx emissions. Unlike the use of ethanol blended diesel fuels (ED1 and ED2), which produce significantly more carbonyls (mostly acetaldehyde) than their conventional diesels, there is no noticeable penalty from using biodiesel (B20). No significant increase of n-PAH emission with the use of CRDPF, potentially due to the presence of excess NO2, was noticed. Various fuel and aftertreatment technologies for reducing diesel emissions are now available to decision and policy makers in addressing vehicle emission concerns when determining the appropriate retrofit strategies for existing vehicle fleets. Although many factors must be involved in any such determination, emissions reductions and any potential increase of toxic emissions must be key considerations. It should be pointed out that both the regulated emissions reported previously (4) and the unregulated toxic emissions presented here are from a single diesel engine. Therefore, caution should be exercised in the interpretation of the results presented.
Acknowledgments We thank the Clean Diesel Vehicle Demonstration Program, which was initiated by the New York City Metropolitan Transit Authority under the supervision of NYSDEC, and the Canadian Program of Energy Research and Development for funding this project. This project could not have been undertaken without additional co-funding from the Canadian Renewable Fuels Association for the ethanol-diesel testing as well as in-kind contributions that were provided by other industrial and governmental partners. Sincere appreciation is extended to the staffs of the Emissions Research and Measurement Division of Environment Canada and Bureau of Mobile Sources and Technology Development of NYSDEC for the work described in this paper. We also wish to acknowledge Engine Control Systems, Johnson Matthey, Corning Inc., and Equilon, LLC for technical support and Robert Whitby, John Higgins, and James Hyde of NYSDEC for helpful comments.
Supporting Information Available Emission of speciated hydrocarbons, carbonyls, PAHs, and n-PAHs with various fuels and emission control systems. This material is available free of charge via the Internet at http://pubs.acs.org.
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Received for review September 18, 2006. Revised manuscript received April 6, 2007. Accepted April 30, 2007. ES0622249
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