REAL-WORLD MEASUREMENT AND EVALUATION OF HEAVY

TRB 12-4674 1 REAL-WORLD MEASUREMENT AND EVALUATION OF HEAVY DUTY TRUCK 2

DUTY CYCLES, FUELS, AND EMISSION CONTROL TECHNOLOGIES 3 4 5

Gurdas S. Sandhu 6 Graduate Research Assistant 7

Department of Civil, Construction, and Environmental Engineering 8 North Carolina State University 9

Raleigh, NC 27695-7908 10 Telephone 919-600-0490, Fax 919-515-7908 11

Email [email protected] 12 13

H. Christopher Frey, Ph.D.* 14 Professor 15

Department of Civil, Construction, and Environmental Engineering 16 North Carolina State University 17

Raleigh, NC 27695-7908 18 Telephone 919-515-1155, Fax 919-515-7908 19

Email [email protected] 20 21 22 * Corresponding author 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40

Submitted for Consideration for Presentation and Publication at the 91st Annual Meeting of the 41 Transportation Research Board 42

43 Submission Date: November 3, 2011 44

45 Text words 6231 plus 1,250 words for 3 Tables and 2 Figures = 7481 Words 46

TRB 2012 Annual Meeting Paper revised from original submittal.

2 Sandhu, Frey

ABSTRACT 1 The purpose of this paper is to assess the robustness of relative comparisons in emission rates 2 between fuels and technologies to differences in real-world duty cycles based on in-use 3 measurements of five heavy duty diesel vehicles (HDDVs). The paper briefly reviews prior 4 comparisons of biodiesel versus ultra low sulfur diesel (ULSD) with respect to emissions, recent 5 changes in emission standards applicable to HDDVs, and typical emission control technologies 6 used in HDDVs. The study methodology includes field measurements with a portable emission 7 measurement system (PEMS) and related instruments and sensors for five selected HDDVs 8 operated in normal service by professional drivers on multiple roundtrip routes within North 9 Carolina. Duty cycles and emission rates are quantified based on manifold absolute pressure 10 (MAP), which is an indicator of engine load. Variability in engine load for each observed 11 roundtrip is quantified based on the cumulative distribution function of normalized MAP. The 12 effect of variability in duty cycles on fuel-based emission rates for NO, CO, hydrocarbons, and 13 particulate matter is evaluated. Comparisons are made for emissions of three trucks operated on 14 each of B20 biodiesel and ULSD. Furthermore, comparisons are made among five trucks with 15 model years ranging from 1999 to 2010 to illustrate the impact of different emission standards 16 and emission control technologies on real world emission rates. A key finding is that relative 17 comparisons pertaining to fuels and technologies are robust to variability in observed duty 18 cycles. 19


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INTRODUCTION 1 2

A third of Nitrogen oxides (NOx) emissions and a quarter of Particulate Matter (PM) 3 emissions from mobile sources are from heavy-duty trucks and buses (1). Ultra low sulfur diesel 4 (ULSD) enables the use of post-combustion controls that would have been poisoned by higher 5 exhaust sulfur levels. Post-combustion emissions control devices reduce PM and NOx emissions 6 from heavy-duty diesel vehicles (HDDVs) by more than 90 percent (2). These emissions 7 reductions are estimated to prevent 8,300 premature deaths, 5,500 cases of chronic bronchitis, 8 and 17,600 cases of acute bronchitis in children annually (2). These reductions translate to 9 annual benefits of over $290 billion with a benefit to cost ratio of 19:1 (3). 10 11 Over the last four years, a unique dataset has been accumulated based on in-use measurements of 12 five combination trucks. These data are based on repeated measurements of these trucks on 13 several study routes, enabling assessment of inter-route variability and its impact on the 14 robustness of relative comparisons between fuels and technologies. For three trucks, 15 measurements were made for both soy-based B20 biodiesel and ULSD. The five trucks 16 represent 1999 to 2010 model years, thereby covering a wide range of emission control 17 technologies. The main research objectives of this paper are to: (1) quantify inter-run variability 18 in emission rates; (2) compare fuels; (3) compare technologies; and (4) assess the robustness of 19 relative comparisons between fuels and technologies taking into account run-to-run variability. 20 21 22 BACKGROUND ON TRUCK FUELS AND EMISSION CONTROL TECHNOLOGIES 23 24 This section provides a brief review of truck emissions for biodiesel versus ULSD, HDDV 25 emissions standards, and the related emission control technologies. 26 27 B20 Biodiesel and Petroleum Diesel (PD) 28 Diesel engines can accommodate biodiesel (BD) without major modifications (4). Neat biodiesel 29 (B100) is typically blended in a 20:80 volume ratio with ULSD to create B20 biodiesel (B20). 30 The U.S. Energy Independence and Security Act of 2007 places emphasis on using biodiesel 31 blends to reduce dependence on foreign oil and improve US energy security. 32 33

Engine dynamometer tests compiled by the U.S. Environmental Protection Agency 34 (EPA) indicate an average 2% increase for NOx emissions, 20% decrease for HC, and 35 approximately10% decrease for CO and PM for B20 (5). These results are comparable to chassis 36 dynamometer test results by National Renewable Energy Laboratory (NREL) (6). However, real-37 world in-use measurements of more than 30 onroad and nonroad HDDV made using a Portable 38 Emissions Measurement System (PEMS) show average reductions in exhaust emissions of NOx, 39 HC, CO, and PM for B20 (7-11). Another study reported about 20% reduction in HC, CO, and 40 PM and about 1% increase in NOx (12). Variations in comparisons could be partly attributable to 41 whether the measurements are based on real world activity. There is a need for additional data 42 for real-world comparisons of B20 and ULSD to further expand the existing database. 43 44


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Emissions Standards 1 EPA has put in place increasingly stringent exhaust emissions standards for HDDV engines (13). 2 Diesel engines emit relatively high uncontrolled levels of NOx and PM compared to other 3 sources. A key research need is for real-world verification of the efficacy of the standards. 4 5 From 1998 to 2003 the NOx standard was 4.0 g/bhp-hr. From 2004 to 2006, NOx and 6 non-methane hydrocarbons (NMHC) were regulated jointly. A typical acceptable NOx emission 7 rate under this standard was approximately 2.0 g/bhp-hr, in combination with a NMHC rate of 8 0.5 g/bhp-hr. During 2007 to 2010, a NOx emission limit of 0.2 g/bhp-hr (0.075 g/MJ) was 9 phased in. From 1998 to 2006 the PM standard was 0.1 g/bhp-hr. From 2007 onwards the PM 10 standard has been 0.01 g/bhp-hr (0.0037 g/MJ) (13). 11 12 Emissions Control Technologies 13 HDDVs have different combinations of emissions control technologies depending on their year 14 of manufacture. Model year 2010 and newer trucks typically have a combination of exhaust gas 15 recirculation (EGR), diesel oxidation catalyst (DOC), diesel particulate filter (DPF), and 16 selective catalytic reduction (SCR). Each is briefly described. 17 18 Exhaust Gas Recirculation 19 EGR is an in-cylinder method to reduce NOx emissions. Mixing the exhaust with intake air 20 lowers the peak flame temperature, thus lowering NOx production. However, there is a penalty of 21 higher PM emissions, decrease in engine power output by 3-5%, and subsequently increase in 22 fuel consumption. To combat the penalty, Cooled EGR technology was introduced in which the 23 exhaust being fed back is first cooled. EGR systems were introduced by heavy duty diesel 24 (HDD) manufacturers in mid-2002 in response to the 1998 Consent Decree with EPA under 25 which the 2004 NOx emissions standards were moved ahead to October 2002 (14-16). 26 27 Diesel Oxidation Catalysts 28 DOC is a post-combustion device that has a porous honeycomb structure coated with catalyst. 29 The catalyst oxidizes CO, HC, and the soluble organic fraction (SOF) of PM. DOCs reduce PM 30 emissions by 20-40 percent, CO by 10-60 percent, and HC by 40-75 percent. DOCs provided 31 adequate PM control to meet emission standards up to 2006; however, 2007 standards for PM 32 required emissions reduction beyond DOC capability (17-19). 33 34 Diesel Particulate Filter 35 DPFs are aftertreatment devices that can trap PM. Periodically, filter regeneration oxidizes 36 trapped PM to ash, carbon dioxide (CO2) and water vapor (H2O). “Active” regeneration relies on 37 fuel burners or catalytic burners and may involve a fuel consumption penalty. All on-road HDD 38 engines use active regeneration technology. According to EPA and California Air Resources 39 Board (CARB), NO2 emissions are allowed to increase by no more than 20% as a result of use of 40 DPFs. DPFs typically remove 85 to 90 percent of the exhaust PM and achieve up to 70 to 90 41 percent reduction in HC and CO emissions (1, 20, 21) 42 43 Selective Catalytic Reduction 44 SCR systems inject Diesel Exhaust Fluid (DEF) into the hot exhaust (800-1000 oF) upstream of a 45 catalyst. DEF is a solution of 32.5% pure urea in 67.5% deinonized water. The DEF decomposes 46


5 Sandhu, Frey

to CO2 and ammonia (NH3) through hydrolysis, which, in the presence of the catalyst, converts 1 NOx to nitrogen (N2) and water vapor. SCR systems are often used downstream of a DOC and/or 2 DPF. SCR is used in response to the 2010 NOx standard. It is typically used in combination with 3 EGR. SCR systems typically achieve 65-75% reduction in NOx emission levels (14, 22, 23). 4 5 METHODOLOGY 6 HDDV emissions measurements are often done using engine dynamometers, chassis 7 dynamometers, tunnel studies, remote sensing, and on-board measurements (24-27). Engine 8 dynamometer measurements are reported in units of g/bhp-hr, which are not directly relevant to 9 in-use emissions estimation. Many engine dynamometer test cycles are steady-state modal 10 profiles that do not capture real world activity patterns. Further, standardized transient test cycles 11 are not likely to be representative of real-world operation of a particular vehicle. 12

Chassis dynamometer tests provide emission factors in grams of pollutant emitted per 13 mile of vehicle travel, which can be multiplied by estimated vehicle miles traveled to arrive at an 14 inventory. However, they may not be representative of real world operation, are relatively 15 expensive, and there are few facilities capable of performing such tests (28, 29). 16

Tunnel studies provide site-specific measurements averaged over many vehicles. They 17 may not be representative of emissions for real-life duty cycles and have limited capability to 18 differentiate between vehicle types (30). Remote sensing measurements are a snap shot of 19 vehicle activity at a particular location, and thus may not characterize an entire duty cycle (31). 20 On-board emission measurements quantify real-world in-use emissions over entire duty cycle. 21 Compared to a chassis dynamometer, on-board systems are easier to setup thus making it 22 possible to test multiple vehicles per day and for each collect several hours of in-use data. The 23 cost of commercially available PEMS is far smaller than that of a chassis dynamometer facility. 24 Commercially available on-board systems first appeared in the late-nineties and have gained 25 more acceptance over the last decade (32-38). On-board measurement is used here. 26 27 Vehicles 28 Measurements were made on combination tractor trailer trucks with model years 1999, 2005, 29 2007, 2009, and 2010. The technical specifications of each truck are given in Table 1. These 30 trucks are owned and operated by the North Carolina Department of Transportation (NCDOT) 31 for the purpose of delivering highway maintenance supplies to field sites at various locations in 32 the state. The trucks were operated by NCDOT drivers on regular routes during the 33 measurements. All trucks pulled 48-foot long trailers. The weight at the start of a run was 34 always more than the weight at the end. The trucks delivered cargo originating from the Raleigh 35 depot. On occasion, back-hauled cargo was transported from a field site to Raleigh depot. The 36 total weight of the trucks varied from 33,300 lbs to 44,800 lbs. The weight at the end of the trip 37 was typically 80% to 90% of the weight at the start of the trip. The Gross Vehicle Weight 38 (GVW) of these trucks ranged from 53,200 lbs to 60,600 lbs. Thus, the loads were relatively 39 small. 40

41 Instrumentation 42 Measurements in 2008 and 2009 used the OEM-2100 Montana portable emissions measurement 43 system (PEMS) from Clean Air Technologies International (CATI, Buffalo, NY) and 44 measurements in 2011 used CATI’s OEM-2100AX Axion PEMS. Both systems are similar with 45 regard to sensors. They differ mainly with respect to software used. 46


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The PEMS have two parallel operation 5-gas analyzers to measure exhaust gas 1 concentrations of HC, CO and CO2 using nondispersive infrared (NDIR), nitric oxide (NO) and 2 O2 using electrochemical sensors, and PM concentrations using light scattering (32, 39, 40). 3 Two point calibration is used for the gas analyzers. While in-use, the gas analyzers are “zeroed” 4 using ambient air as a reference to recalibrate the oxygen sensors to ambient concentration and 5 the CO2, CO, HC, and NO concentrations to baseline values to prevent instrument drift. The 6 levels of the latter in ambient air are negligible compared to tailpipe exhaust. Both benches zero 7 every 10 minutes staggered to provide uninterrupted data recording. Span calibration is done in 8 the lab using a BAR 97 low calibration gas mixture. 9

Battelle (41) compared the CATI PEMS to standard testing equipment using 40 CFR Part 10 86 reference methods. The tests were conducted on a chassis dynamometer and used FTP and 11 US06 test cycles. Linear regression slopes for measurements from the PEMS and reference 12 facility ranged from 0.97 to 1.03 for CO2, 0.95 to 1.05 for CO, and 0.92 to 1.03 for NOx, 13 indicating that CO2, CO, and NOx measurements from the PEMS are accurate to within 10% of 14 reference measurements. HC measurements are biased low by a factor of approximately two 15 because the PEMS used NDIR and reference method used Flame Ionization Detection (FID) (41, 16 42). PM measurements are analogous to opacity and used for relative comparisons. 17

An engine sensor array is used to record engine revolutions per minute (RPM), intake air 18 temperature (IAT), and manifold absolute pressure (MAP). RPM is measured using an optical 19 sensor in combination with reflective tape placed on a part that rotates at the same rate as the 20 crankshaft. The engine intake air sensor is a thermocouple installed in the intake air flow path. 21 An MAP sensor is installed on a port typically available after the turbocharger. 22

23 Data Collection 24 The time to install the instrument on the study trucks is typically two hours. The measurement 25 system is installed a day before the test. On the day of the test, the PEMS is warmed up for at 26 least 45 minutes before the start of driving. During testing, periodic checks of the system status 27 are conducted. This is done by determining whether engine data is updated on the instrument 28 display in an appropriate manner and whether the gas concentrations are reasonable. 29

The data collection also includes: topping off the fuel tank at start and at end of test and 30 recording the fuel used; weighing the truck at start and at end of test; and recording the odometer 31 reading at start and at end of test. The refueling of trucks is done from the gas pump owned and 32 operated by NCDOT at their Raleigh depot. 33 34 Quality Assurance and Estimation of Emission Rates 35 The quality assurance procedure includes: (1) imputing missing seconds of data when 1 or 2 36 seconds are missing; (2) verification of PEMS internally synchronized concentration and engine 37 data; (3) checking for errors in IAT, RPM, and MAP values and substituting with corrected 38 values when possible; (4) correcting influence of ambient air concentration during lead-in and 39 lead-out when a gas bench is zeroing; (5) checking and correcting when possible consecutive 40 seconds of concentration data that show no change even though engine parameters change; (6) 41 correcting or removing seconds of data that report negative concentrations; (7) correcting or 42 removing seconds of data where the two parallel gas analyzers report significantly different 43 concentrations; and (8) comparing estimated fuel use with gas pump fuel use. 44 After quality assurance, intake airflow, exhaust flow, and mass emissions are estimated 45 using the speed-density method reported by Vojtisek-Lom (43). The method is based on several 46


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key steps. Air flow through the engine is estimated based on the ideal gas law, taking into 1 account the pressure and temperature of air entering the cylinder, the compression ratio, the 2 engine RPM, and a parameter referred to as volumetric efficiency. Volumetric efficiency is the 3 ratio of actual mass flow through the engine to the theoretical mass flow based on piston 4 displacement in each cylinder. Based on the exhaust gas composition, the air-to-fuel ratio can be 5 inferred irrespective of mass air flow. From these estimates, the exhaust flow rate is estimated. 6 Mass emission rates are estimated based on exhaust concentrations of each pollutant and the 7 exhaust flow rate. The mass flow calculations are evaluated by comparison of estimated fuel 8 flow accumulated over a trip to the amount of fuel needed to refill the fuel tank. 9 10 Routes and Duty Cycles 11 The trucks make round trip runs originating at the NCDOT depot in Raleigh, NC and make stops 12 at other NCDOT depots where they unload and/or load cargo. The only change to the regular 13 driving cycle made during the measurement study was to keep the truck running during 14 loading/unloading activity. This was done to maintain continuous operation of the PEMS, and in 15 turn collect idling data. The typical loading/unloading activity duration at each depot is 30-45 16 minutes. 17

Fuel use rate is directly correlated to engine load. A few studies have reported good linear 18 correlation between fuel use and Manifold Absolute Pressure (MAP) (7, 44). In a study of motor 19 graders and another study of cement mixers, MAP had an average rank correlation exceeding 20 93% to fuel use rate (11, 45). Thus, MAP is a good surrogate for engine load with higher MAP 21 values corresponding to higher power demand. 22

23 TABLE 1 Engine and Emissions Control Specifications for Combination Trucks 24

Truck Model Year

Odoa (mi) Make Model Engine Disp.

(L) HP@RPM Emissions Controlb

5715 1999 303,744 International 2574 6X4 Cummins ISM-370 10.8 370@2100 - 6415 2005 235,202 International 9400I 6X4 Cummins ISX-500 15.0 500@2100 EGR 6667 2007 61,008 International 9200I Cummins ISX-500 15.0 500@2000 EGR, DOC, DPF 0009 2009 72,831 International 9200I Cummins ISX-500 15.0 500@2000 EGR, DOC, DPF

0121 2010 29,229 Mack CHU613 Mack MP8-445C 12.8 445@1500 EGR, DOC, DPF, SCR

a Miles on the odometer on test days corresponding to results in Table 3 25 b DOC = Diesel Oxidation Catalyst; DPF = Diesel Particulate Filter; EGR = Exhaust Gas Recirculation; SCR 26

= Selective Catalytic Reduction 27 28

Since the minimum and maximum MAP values are different between truck models, the 29 MAP values need to be normalized before they can be plotted as frequency distribution to 30 compare the power demand distribution between routes. Typical idling MAP for all trucks is 98 31 kPa. The typical peak power demand MAP is 260 kPa for truck 5715, 310 kPa for trucks 6415 32 and 6667, and 340 kPa for trucks 0009 and 0121. Normalized MAP at time t is equal to the 33 difference between MAP value at time t and minimum MAP of the route divided by the span of 34 MAP values for the route. For purposes of comparing driving cycles, the portions of the cycles 35 associated with idling were excluded. About 97% of the removed data represent time when the 36 truck is parked at the NCDOT depot. On a non-measurement run, the truck would have been 37 turned off during such time. 38

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RESULTS 1 Five combination trucks were measured for duty cycles, fuel use, and emission rates on a total of 2 15 days, representing model years from 1999 to 2010. These trucks have engine output ranging 3 from 370 to 500 hp and are similar in gross vehicle weight and tare weight. As shown in Table 4 1, all trucks except the 1999 truck have EGR. The 2007 and 2009 trucks also have DOC and 5 DPF. The 2010 truck also has SCR. Thus, the five trucks represent a wide variety of applicable 6 allowable emission rates and include combinations of the most typical technologies for NOx and 7 PM control. All trucks have 6 cylinder engines, 13-speed manual transmissions, and 5 axles 8 including the trailer. Trucks 5715, 6415, and 6667 were tested in 2008 using petroleum diesel 9 fuel and in 2009 with soy-based B20 biodiesel fuel. Trucks 0009 and 0121 were tested in 2011 10 with soy-based B20 biodiesel fuel. The B20 fuels were procured by NCDOT under strict 11 specifications based on B100 blend stock that is in compliance with applicable ASTM standards. 12 13 The trucks operated on a variety of roundtrip routes to destinations within North Carolina, as 14 shown in Figure 1. Over the period of study from 2008 to 2010 the trucks travelled on 5 routes. 15 Figure 1 shows the geographic locations of the routes and stops. The routes, depot stops, and 16 typical distances are: 17

• Route 1 : Raleigh to North Wilkesboro to Winston-Salem to Raleigh, 320 miles 18 • Route 2 : Raleigh to Greensboro to Raleigh, 150 miles 19 • Route 3 : Raleigh to Wilson to Selma to Raleigh, 130 miles 20 • Route 4 : Raleigh to Castle Hayne to Burgaw to Clinton to Raleigh, 270 miles 21 • Route 5 : Raleigh to Manns Harbor to Hertford to Raleigh, 430 miles 22

23

FIGURE 1 Driving routes from Raleigh to destinations within North Carolina. 24 25

N. WILKESBORO

CASTLE HAYNE

CLINTON

4 BURGAW

RALEIGH

1 GREENSBORO HERTFORD

MANNS HARBOR 3

SELMA

WILSON

5

#

WINSTON-SALEM

Route ID Number

NORTH CAROLINA

2


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1 2 FIGURE 2 Frequency distributions of Manifold Absolute Pressure for real-world duty 3 cycles based on round-trips originating in Raleigh, NC. 4 5 These routes typically involved a high proportion of miles travelled on interstate highways, 6 especially for the trips to Winston-Salem (via I-40), Greensboro (via I-40), and Castle Hayne 7 (via I-40). Portions of the roundtrip for Route 4, for the segment from Burgaw to Clinton, 8 involve travel on a rural arterial with low density of signalized intersections. The trip from 9 Raleigh to Wilson involves travel on U.S. 64, much of which is limited access divided highway. 10 The trip from Raleigh to Manns Harbor also involves travel on limited access divided highway 11 and rural arterials with low density of signalized intersections. 12

The driving cycles for each roundtrip observed from 14 days of measurements are shown 13 as cumulative distribution functions of normalized MAP for non-idle operation in Figure 2. 14 There was one additional day of measurement on Route 3 for which insufficient data were 15 obtained to characterize the round-trip driving cycle. Among the observed driving cycles, 16 average normalized MAP ranges from 0.33 to 0.48. At the 10th percentile, normalized MAP 17 among the observed cycles range from approximately 0.01 to 0.20. At the median (50th 18 percentile), normalized MAP ranges from approximately 0.3 to 0.5. At the 90th percentile, 19 normalized MAP ranges from approximately 0.6 to 0.9. Thus, each duty cycle has a wide range 20 of variability in engine load. The standard deviations of normalized MAP for each duty cycle 21 are in the range of 0.2 to 0.3. 22

The cycle-to-cycle variability in the normalized MAP cumulative distribution as shown 23 in Figure 2 leads to differences in the cycle average rate of fuel consumption and emissions. To 24 quantify such variability, two cycles were selected for analysis that approximately bound the 25 observed cycles. One is based on driving on arterial roads (ARs) as extracted from one of the 26 trips on Route 1, with an average normalized MAP of 0.33. The other is based on driving only 27 on highways (HWs) from the same trip, with an average normalized MAP of 0.52. Thus, the AR 28 and HW cycle represent examples of low and high average engine load duty-cycles compared to 29

00.10.20.30.40.50.60.70.80.9

1

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Cum

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Freq

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Normalized MAP

Route 1Route 1Route 1Route 1Route 1Route 2Route 2Route 3Route 3Route 4Route 4Route 4Route 4Route 5HighwayArterial


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those observed in real-world driving of these trucks. The AR and HW cycle are comprised of 1 991 seconds and 5397 seconds of data, respectively. 2

The normalized MAP modal time-based average emissions and fuel use rates are 3 multiplied with the time spent in each mode, and summed over all modes for the AR and HW 4 duty cycles to arrive at cycle average emissions and fuel use. The cycle average emission is 5 divided by cycle average fuel use to arrive at fuel based (g/gal) results. 6

The effect of variation among cycles on fuel-based emission rates is indicated in Table 2. 7 For NOx and PM, there is only 5 percent or less difference in the emission rate between the AR 8 versus HW cycles among the three trucks that were tested for both biodiesel and petroleum 9 diesel fuel. For HC, all of the cycle average measurements are based on a significant portion of 10 second-by-second exhaust measurements that are below the detection limit of the HC gas 11 analyzer; thus, any apparent differences are not statistically significant. For CO, the emission 12 rate was consistently higher for the AR cycle. 13 Emission rates for driving cycles are also compared in Table 3 for all five measured 14 trucks, based on the use of B20 biodiesel, including the two newest of the trucks. For NOx, the 15 2009 model year truck had a 6 percent higher emission rate on the AR cycle versus the HW 16 cycle. The 2010 model year truck had approximately twice the emissions on the AR cycle as 17 the HW cycle, but the emission rates for both were extremely low at only 1 to 2 g/gal, versus 110 18 g/gal for the 1999 model year truck. Thus, the absolute difference in the NOx emission rate for 19 the 2010 truck between the cycles was small. There was no significant difference in PM or HC 20 emission rates between the cycles for the newer trucks. Similar to the older trucks, the CO 21 emission rate was somewhat higher on the AR cycle. 22

For three of the trucks, a comparison of emission rates for B20 biodiesel versus 23 petroleum diesel is possible, as shown in Table 2. The PEMS used here measured nitric oxide 24 (NO). The results indicate that NO emissions (reported as equivalent mass of NO2) are lower by 25 approximately 10 to 20 percent on a fuel basis for B20. This finding is consistent for both the 26 AR and HW driving cycles, and is similar to findings reported previously based on in-use 27 measurements of dump trucks (8). Furthermore, although a 2002 EPA report is often quoted to 28 imply that NOx emissions increase by a few percent for B20 compared to petroleum diesel, a 29 more careful review of the data that comprises the EPA report reveals substantial inter-engine 30 variability in the results, with some engines having lower and others having higher emission 31 rates (5). Thus, the results obtained here are not inconsistent with prior results, but of course 32 represent only a small number of trucks. As expected, there are reductions in the CO emission 33 rate for the oxygenated B20 versus the non-oxygenated petroleum diesel. The results for PM 34 were somewhat variable, with one truck having approximately 15 percent lower emission rate on 35 B20 while the other two had approximately 10 to 25 percent higher emission rates, but the latter 36 is based on very low emission rates on both fuels. The higher PM emission rates for two of the 37 trucks are contrary to expectations based on comparison to literature, but may merely reflect 38 inter-vehicle variability. From an emission inventory perspective, the main concern is the 39 average difference in emission rate over a large fleet of in-use vehicles, rather than differences 40 merely for an individual vehicle. 41

The comparison of emission rates among different model year vehicles given in Table 3 42 provides clear indication of the efficacy of increasingly stringent emission control standards, as 43 reflected in successively lower emission rates for NO, CO, and PM from the 1999 to 2010 model 44 year vehicles tested. The only minor exception is that the 2005 model year truck appears to have 45

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TABLE 2 Effect of Fuel Type on Fuel-based Emissions Rate 1

NOx [g/gal] HC [g/gal]b,c CO [g/gal] PM [g/gal]

Truck Fuela HW AR HW AR HW AR HW AR

5715 B20 110 110 5.8 6.2 6.5 8.6 0.21 0.22

PD 130 130 1.9 2.3 7.6 10.5 0.25 0.25

B20/PD 0.87 0.88 0.86 0.82 0.84 0.87

6415 B20 30 31 2.2 2.7 9.3 12 0.50 0.50

PD 40 42 1.1 1.4 12.3 15 0.45 0.45

B20/PD 0.76 0.73 0.76 0.82 1.11 1.11

6667 B20 17 17 3.8 4.1 0.5 2.0 0.02 0.02

PD 19 19 2.6 3.0 1.3 3.8 0.02 0.02

B20/PD 0.91 0.89 0.39 0.54 1.26 1.28 HW Highway Duty Cycle 2 AR Arterial Duty Cycle 3 a B20 = soy-based B20 biodiesel. PD = ultra-low sulfur petroleum diesel. The composition of B20 is 84.5 4

weight percent carbon, 13.3 weight percent hydrogen, and 2.2 weight percent oxygen. The composition of 5 petroleum diesel is 86.4 weight percent carbon and 13.6 weight percent hydrogen. 6

b HC modal average concentrations were below detection limit for at least 6 out of 10 MAP modes for each 7 fuel and each truck; hence, ratios between the fuels are not meaningful and thus are not reported. 8

c HC results are bias corrected by a factor of 2.0 because NDIR-based HC measurements are biased low by a 9 factor of approximately two (42). 10 11 12 13

TABLE 3 Effect of Emissions Control Technologies on Fuel based Emissions Ratea 14

NOx [g/gal] HC [g/gal]b,c CO [g/gal] PM [g/gal]

Truck Model Year Data Sized HW AR HW AR HW AR HW AR

5715 1999 16814 110 110 5.8 6.2 6.5 8.6 0.21 0.22

6415 2005 21095 30 31 2.2 2.7 9.3 12 0.50 0.50

6667 2007 25074 17 17 3.8 4.1 0.5 2.0 0.02 0.02

0009 2009 30965 16 17 3.5 3.8 0.3 1.5 0.01 0.01

0121 2010 36120 1 2 4.4 4.8 0.0 0.2 0.01 0.01 HW Highway Duty Cycle 15 AR Arterial Duty Cycle 16 a Trucks operated with soy-based B20 biodiesel fuel 17 b HC modal average concentrations were below detection limit for at least 6 out of 10 MAP modes for each 18

truck. 19 c HC results are bias corrected by a factor of 2.0 because NDIR-based HC measurements are biased low by a 20

factor of approximately two (42). 21 d Number of seconds of test data used in calculating time-based modal average emissions rate. 22 23 24


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higher PM emission rates than the 1999 truck, but otherwise the emission rate decreases for 1 newer vehicles. The comparisons for HC are not statistically significant. 2

As expected based on the applicable emission standards, the 2005 truck has substantially 3 lower NOx emission rate than the 1999 truck. Except for the 1999 truck, the other four trucks are 4 within the useful life over which they are required to maintain compliance with the applicable 5 standards. The 2007 and 2009 trucks have similar NOx emission rates that are approximately 6 half that of the 2005 truck. The 2010 truck, which has SCR, has NOx emissions that are 7 approximately 99 percent lower than that of the 1999 model year truck. For trucks without DPF, 8 NO2 typically comprises 5 percent of total NOx emissions. For trucks with DPF, the fraction of 9 NO2 in NOx may increase to approximately 20 percent. Even if an increase in the proportion of 10 NO2 in the NOx emissions had occurred, the net reduction in total NOx emissions would be 11 above 98 percent when comparing the 2010 truck to the 1999 truck. The PM emission rates of 12 the 2007 to 2010 trucks are substantially lower than those of the 1999 and 2005 trucks. The CO 13 emission rates of the three newer trucks are also substantially lower than those of the two older 14 trucks. Thus, there is a clear difference in the 2007 and newer trucks versus their older 15 counterparts, with the 2010 truck having extremely low emission rates of NOx, CO, and PM 16 compared to the others. The HC exhaust concentrations for all trucks were typically below 17 detection limit and thus comparisons are not statistically significant. 18 19 20 CONCLUSIONS 21 Differences in fuel-based emission rates among the cycles were typically modest at 5 percent or 22 less for NOx and PM and statistically insignificant for HC. The CO emission rate was typically 23 higher on the arterial versus the highway cycle. Furthermore, relative differences in emission 24 rates, such as between fuels or between trucks, were not substantially different for the arterial 25 versus the highway cycle. Thus, comparisons of emission rates by fuel or by vehicle technology 26 are at least somewhat robust to the choice of driving cycle from among the observed real world 27 cycles. An implication is that it is possible to obtain reliable comparisons between fuels or 28 technologies regardless of which of the routes were driven by a given truck on a given day, based 29 on use of modal emission rates and standardization of the comparison to a few duty cycles. 30 For three of the trucks, a comparison was possible for soy-based B20 biodiesel versus 31 petroleum diesel. As expected, CO emission rates are lower for the biodiesel. PM emission 32 rates were lower for one truck, higher for another, and approximately the same for a low-33 emitting truck. NO emission rates were lower for all three of the trucks. The results here 34 illustrate inter-vehicle variability, such as for PM. The NO comparison is similar to that for in-35 use measurements of other vehicles, and thus might be attributed in part to differences in duty 36 cycles compared to other studies that are based on engine dynamometer tests. 37 A comparison among the 1999 to 2010 model years represented by the five trucks 38 provides empirical support that successively more stringent emissions standards are efficacious 39 in reducing real-world emissions under actual driving conditions. Although the vehicle sample 40 sizes here are too small to support conclusions regarding trends in fleet average emission rates by 41 model year, they are consistent with a hypothesis that in-use emissions are substantially lower 42 for 2010 model year trucks than any prior model year, and that trucks manufactured since 2007 43 have substantially lower emission rates than those from prior model years. 44 A key methodological finding of this work is that comparisons between trucks and fuels 45 are robust to variations among driving cycles observed during real-world data collection. This 46


13 Sandhu, Frey

finding provides support for the use of a limited number of ‘bounding’ cycles to characterize 1 cycle-to-cycle variability. 2 3

ACKNOWLEDGEMENTS 4 North Carolina Department of Transportation provided fuels and drivers for each tested truck. 5 This material is partly supported by the National Science Foundation under Grant No. CBET-6 0853766. Any opinions, findings, and conclusions or recommendations expressed in this 7 material are those of the authors and do not necessarily reflect the views of NCDOT or the 8 National Science Foundation. 9 10


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REAL-WORLD MEASUREMENT AND EVALUATION OF HEAVY