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Comparison of Over-the-Rail and Rail Yard Measurements of Diesel Locomotives Brandon Michael Graver, and H. Christopher Frey Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.5b02497 • Publication Date (Web): 30 Sep 2015 Downloaded from http://pubs.acs.org on October 2, 2015

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Environmental Science & Technology

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Comparison of Over-the-Rail and Rail Yard Measurements of

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Diesel Locomotives

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Brandon M. Graver and H. Christopher Frey*

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Department of Civil, Construction, and Environmental Engineering, North Carolina State

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University, Campus Box 7908, Raleigh, NC 27695-7908, Email: [email protected], Phone: (919)

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515-1155, Fax: (919) 515-7908

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ABSTRACT

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Locomotive prime mover engine emission rates are typically measured at steady-state for

10

discrete throttle notches using an engine dynamometer weighted by a standard duty cycle.

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However, this method may not represent real-world locomotive emissions. A method for in-use

12

measurement of passenger locomotives, using a portable emissions measurement system

13

(PEMS), was developed to estimate duty cycle average emission rates. Measurements for 48

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one-way trips between Raleigh, NC and Charlotte, NC were conducted on seven locomotives.

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Eighteen sets of measurements were also conducted in the rail yard (RY). Real-world duty

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cycles differed from those used for regulatory analyses, leading to statistically significant lower

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cycle average NOx and HC emission rates. Compared to RY measurements, notch average NOx

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emission rates measured over-the-rail (OTR) at the highest two notch settings were, on average,

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19 percent lower for four locomotives. At the highest notch, OTR CO2 emission rates were, on

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average, 12 percent lower than RY rates for five locomotives. For a more accurate

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representation of real-world emission rates, OTR measurements are preferred. However, using

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steady-state notch average RY emission rates and standard duty cycles may be tolerable for some

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applications. OTR versus RY cycle average emission rates typically differed by less than 10

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percent.

25 26

INTRODUCTION

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Ridership has increased for inter-city passenger rail in recent years (1). Amtrak, the inter-city

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passenger rail provider in the U.S., transported 31.2 million passengers in fiscal year 2012, its

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ninth ridership record in ten years (2). In some rail corridors, efforts have been made to make

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train travel quicker and more reliable through transportation infrastructure projects. Grants for

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transportation construction are tied to reductions in air pollutant emissions (3). Over 80 percent

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of locomotives deployed for Amtrak service use diesel prime mover engines (PMEs) for

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propulsion (4). Therefore, a goal of ongoing research has been to quantify the real-world activity

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and emissions of passenger rail service.

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In a diesel locomotive, the PME shaft turns an electric generator/alternator. Electricity produced

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is used to drive traction motors, which rotate the locomotive wheels. The PME operates at eight

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discrete throttle notch positions and idle.

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dynamic braking, where the traction motors act as generators and electricity is dissipated as heat

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through an electric resistance grid (5).

One way of slowing the locomotive is through

41 42

Available data on locomotive emissions are typically from steady-state PME dynamometer and

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rail yard (RY) measurements, where exhaust emissions are measured at each notch position (6-

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20). The PME is removed from the locomotive during dynamometer measurements, while the

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PME remains in the locomotive for rail yard measurements. The U.S. Environmental Protection 2 ACS Paragon Plus Environment

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Agency (EPA) locomotive emission standards for nitrogen oxides (NOx), particulate matter

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(PM), carbon monoxide (CO), and hydrocarbons (HC) are based on weighted average time spent

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by the PME in each notch and the associated notch emission factors obtained from federal

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reference method (FRM) measurements (5, 21-22). There are few facilities in the U.S. that can

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measure locomotive emissions using Federal Reference Methods.

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Portable emissions measurement systems (PEMS) have previously been used to measure engine

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exhaust concentrations for a limited number of RY measurements (23-26). Previous research has

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demonstrated that RY measurements produce similar emission rates to dynamometer

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measurements (27). Because RY and dynamometer-based approaches have previously been

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compared, this paper focuses on comparison of OTR and RY-based approaches. However,

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unlike the conditions of dynamometer and RY measurements, PMEs do not continuously operate

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only at steady-state in the real world.

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PEMS can be deployed onboard a locomotive, enabling assessment of engine activity, fuel use,

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and emission rates without removing locomotives from service. Real-world locomotive

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operation involves shifting among notches for both increasing and decreasing engine load. Such

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shifting leads to transitions between notch positions that produce transients in engine load and

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emission rates. For example, transients could account for 40 percent of total PM emissions in a

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duty cycle (28).

66 67

The percent of time spent in idle, dynamic braking, and each of the eight notch positions during

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locomotive operation is the duty cycle. Two distinct duty cycles have been identified by EPA



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for freight locomotives: (1) line-haul, or the movement of freight over a relatively long distance;

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and (2) switching, or the movement of locomotives in a relatively small area to assemble or

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disassemble trains (20). Based on data from Amtrak, an average passenger locomotive duty

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cycle estimated by EPA is similar to the average line-haul duty cycle, with the exception of the

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amount of time spent in idle (20). Variations in duty cycle may lead to variations in cycle

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average emission rates. There has been some change in duty cycle composition over the past 20

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years, especially with the addition of dynamic braking (29).

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The objectives here are to determine: (1) if RY emission measurements are representative of

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emissions produced during real-world locomotive operation; (2) if the regulatory duty cycle

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differs from duty cycles measured during passenger rail service, and whether duty cycles affect

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trip total emission estimates; and (3) if PME transient operation affects trip total emission

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estimates.

82 83

METHODS

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A PEMS is used to quantify fuel use and emission rates of locomotive PMEs during RY and

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over-the-rail (OTR) measurements.

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Field Study Design

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PMEs from seven locomotives were instrumented and exhaust emission concentrations measured

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both in the RY and during revenue-generating passenger rail service. RY measurements were

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conducted at the North Carolina Department of Transportation (NCDOT) Capital Yard

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Maintenance Facility in Raleigh, NC. OTR measurements were conducted during Amtrak 4 ACS Paragon Plus Environment

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Piedmont passenger rail service between Raleigh and Charlotte, NC. The locomotives operated

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on ultra-low sulfur diesel (ULSD) for all measurements.

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Locomotives

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NCDOT owns two EMD F59PHI and four EMD F59PH locomotives, which are used for

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passenger rail service. Each locomotive has a 12-cylinder, 140-Liter, 2,240-kW EMD 12-710

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diesel PME. An EMD GP40 locomotive, with a 16-cylinder, 169-Liter, 2,240-kW EMD 16-645

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diesel PME was previously owned and operated by NCDOT. All seven locomotives were

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remanufactured within the last 4 years, and all measurements were conducted within 2 years of

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remanufacture.

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Data Collection Procedure

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For RY measurements, a mechanic operated the locomotive following a specific, original test

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schedule that is custom to the measurement campaign, but operates the engine at the same notch

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positions and engine loads of the official testing protocol. The engine was run at Notches 8, 7,

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and 6 for a period of 3 to 5 minutes each. After operating at each of these notches, the engine

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was returned to idle to prevent overheating of the dynamic braking grid, since electricity from

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the generator was dissipated as heat. The engine was operated from Notches 5 through idle

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without any intermediate idling. Three replicate RY measurements were conducted on the

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F59PH and F59PHI locomotives, except for one case when only two could be completed because

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of inclement weather conditions. One RY measurement was conducted on the GP40. Shortly

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after the measurements were conducted on the GP40, the locomotive was involved in an at-grade



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crossing accident that destroyed the locomotive. Therefore, it was not possible to conduct

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further repeated tests on this locomotive.

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For OTR measurements, the locomotives were operated normally during revenue-generating

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Piedmont passenger service by Amtrak engineers. The twice-daily Piedmont rail service covers

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a distance of 278 kilometers, with a scheduled duration of 3 hours and 10 minutes. Typically,

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each train is comprised of one locomotive, one baggage/lounge car, and two passenger cars.

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Between 2 and 14 one-way OTR measurements were conducted on each locomotive, with the

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exception of one F59PHI for which only a single one-way OTR measurement was conducted.

123 124

For both RY and OTR measurements, the locomotives were instrumented and exhaust

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concentration and engine activity data were measured continuously. However, for RY

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measurements, data during notch transitions were excluded from analysis. RY measurements are

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meant to be comparable to a dynamometer measurement, and the test procedure used there

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excludes transients (21). Furthermore, the RY transients are not representative of real-world

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transients, in terms of the pairing of notch positions before and after the transition.

130 131

Portable Emissions Measurement System

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The PEMS units used here are the OEM-2100 Montana and OEM-2100AX Axion systems, both

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manufactured by GlobalMRV. These PEMS are composed of two parallel five-gas analyzers, a

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laser light scattering PM detection system, an engine sensor array, and an onboard computer (30-

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31). Similar to the FRM, nondispersive infrared (NDIR) detection is used for CO2 and CO, and

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light scattering is used to measure opacity. These PEMS use NDIR for the detection of HC


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instead of flame ionization detection used in the FRM. For measurement of nitric oxide (NO),

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electrochemical sensing is used, whereas the FRM method is chemiluminescence. A sensor

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array was installed on the engine to measure manifold absolute pressure (MAP), intake air

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temperature (IAT), and engine speed (RPM). Emission concentrations and engine activity data

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were recorded every second.

142 143 144

To validate the PEMS, emissions of several highway vehicles were measured simultaneously at a

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laboratory-grade light duty vehicle chassis dynamometer facility and with the PEMS as part of

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the EPA Environmental Technology Verification program. The results of the analysis indicated

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that the PEMS had good covariation, precision, and accuracy in measuring CO2, CO, and NO

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concentrations (32).

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The PEMS was span calibrated to a known calibration gas mixture for all gaseous pollutants

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before each set of RY and OTR measurements. For PM, the detector was calibrated by the

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manufacturer. The performance of the PEMS in measuring exhaust concentrations typical of

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locomotive exhaust was verified by making measurements in the laboratory of different cylinder

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gas mixtures. The PEMS was able to measure the exhaust concentration to within six percent of

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the cylinder gas concentration for each pollutant, regardless of the cylinder gas concentration

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level.

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Correction factors are used to adjust for biases associated with the PEMS emissions

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measurement methods. A correction factor of 1.053 is used to approximate total NOx, based on



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95 percent NO in NOx (33). The overall response to NDIR to a mixture of hydrocarbons in

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engine exhaust is approximately 23 to 68 percent of the actual total HC (38). A correction factor

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of 2.5 is used to approximate total HC. An evaluation of the light scattering PM measurement

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technique showed emission measurement as much as 80 percent lower versus the FRM (39).

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Thus, PM emission rates are based on a correction factor of 5 to approximate total PM. The

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emission rates reported here are used for relative comparisons between OTR versus RY, actual

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versus EPA duty cycles, and transient versus steady state estimation methods.

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Duty Cycle Derivation

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Each locomotive has an activity data recorder. Real-time RPM, notch positon, and engine output

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data are provided on a digital display in the locomotive cab, but not archived by the data

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recorder. Engine RPM is measured with the sensor array. The engine output at each notch

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position is known, and an analyst records engine output at each notch from the digital display for

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every RY replicate and at least one OTR measurement. The data recorder archives engine

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solenoid operation from which notch is inferred.

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Data Quality Assurance

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Data for PEMS exhaust concentrations, engine activity from sensor array, and locomotive

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activity data are time-aligned. From previous dynamometer and RY measurements, it is known

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that as notch position increases, RPM, MAP, and CO2, NOx, and PM concentrations typically

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increase (25). Exhaust concentrations are time-synchronized with sensor array data by ensuring

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that any change in RPM and MAP corresponds to the appropriate change in measured exhaust

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concentrations. Sensor array and locomotive activity data are synchronized based on a change in 8 ACS Paragon Plus Environment

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notch inferred from activity recorder data and the corresponding change in RPM observed from

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the sensor array.

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Measured data were screened for errors. Emission concentrations from one gas analyzer were

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compared to the other, and if the difference did not exceed a maximum allowable difference

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(MAD) threshold, then the concentrations were averaged. However, if the inter-analyzer

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discrepancy exceeded the MAD, either the data were not used or data from an analyzer suspected

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of producing invalid measurements were excluded and only data from the valid analyzer were

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used. HC and CO concentrations in diesel engine exhaust tend to be low, because these engines

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operate with excess air and have efficient combustion (33). Negative values for these pollutants

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that were within the precision of the instrument were assumed to be zero. Additional details on

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data processing and quality assurance procedures are given elsewhere (34-35).

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Emission Rate Estimation

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For both RY and OTR measurements, fuel-based emission rates, in g/L, are estimated based on

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measurements from which engine mass air flow (Ma) and air-to-fuel ratio (AFR) are inferred.

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Ma is estimated based on key engine parameters using the “speed density” method, which is

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based on the ideal gas law (36-37). Intake air molar flow rate is:

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(1) Where,

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EC

= engine strokes per cycle (2)

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ER

= engine compression ratio (typically 15 to 16)



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ES

= engine speed (RPM)

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EV

= engine displacement (L)

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Ma

= intake air molar flow rate (mole/sec)

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PB

= barometric pressure (101 kPa)

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PM

= engine manifold absolute pressure (kPa)

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Tint

= intake air temperature (°C)

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VE

= engine volumetric efficiency

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Volumetric efficiency (VE) is the ratio of the actual volume of air that flows through the engine

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cylinder versus the physical cylinder volume. VE takes into account factors that affect real air

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flow and is affected by engine design and operational factors, such as notch. VE was found to be

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well correlated with the product of measured RPM and MAP observed during prior

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dynamometer measurements of similar EMD 12-710 and 16-645 PMEs (27).

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Mass emission rates, in g/s, are estimated each second based upon the mole fraction of each

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pollutant on a dry basis, dry exhaust molar flow rate, and molecular weight of exhaust gas. The

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emission rates are estimated based on a carbon balance in which it is assumed that the exhaust

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composition accounts for all of the carbon in fuel, emitted as CO2, CO, and HC. Exhaust molar

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flow rate on a dry basis is estimated based on Ma and AFR inferred from exhaust gas

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composition. Engine output-based emission rates, in g/kW-hr, are estimated based on mass

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emission rate, in g/hr, divided by engine output.

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For PM, the PEMS reports mg/m3 concentration on a dry basis. Dry exhaust flow per liter of

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fuel consumed is estimated by inferring AFR. The volume of exhaust produced per liter of fuel

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is multiplied by the mass per volume concentration of PM to estimate the g/L PM emission rate.

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The latter is multiplied by fuel flow rate and divided by engine output to estimate the engine

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output-based PM emission rate, in g/kW-hr.

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Locomotive emissions for each of many one-way trips were calculated using two approaches.

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Approach 1 is based on time-weighted average notch-based emission rates, which are based on

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steady-state average emission rates for each notch. Approach 2 is based on the summation of

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second-by-second emissions data, which include transients. By comparing Approach 2 versus

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Approach 1, the role of transients in cycle average emissions is assessed.

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Approach 1: Steady-State

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In Approach 1, notch average emission rates at steady-state are estimated for each notch.

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PME is in a specific notch as soon as the engineer changes the throttle position. Only 1 Hz

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emission rates from steady-state operation within a notch are used to estimate notch average

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emission rate. Two criteria were used for steady-state: (1) change in engine speed from one

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second to the next is ≤10 RPM; and (2) engine speed is within ±20 RPM of the expected average

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engine speed at the given notch based on previous dynamometer measurements of the same

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model engine.

The

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Steady-state emission rates are weighted by the percentage of time spent in each notch in the

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EPA line-haul or Piedmont duty cycle. Cycle average emission rates are estimated by summing



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the weighted emission rates. This method is similar to how the EPA estimates PME cycle

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average emission rates for comparison to applicable emission standards (22). Dynamic brake is

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utilized during OTR operation, and cannot be reproduced during RY measurements. Since

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dynamic braking has low engine load, the percent of time allocated to dynamic brake in the duty

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cycle is added to the percent time allocated to idle.

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Approach 2: Transients

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In Approach 2, total emissions for a one-way trip are quantified by summing time-based

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emission rates for each second of data between Raleigh and Charlotte. This approach accounts

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for the emission rates associated with transitions between notches.

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Statistical Comparisons

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Two-sample t-tests were used for comparisons of results taking into account the mean, standard

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deviation of inter-run or inter-replicate variability, and sample size. Comparisons were made for

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individual locomotives and for the entire set of runs or replicates for OTR versus RY-based cycle

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average rates for the EPA line-haul cycle, for Piedmont versus EPA cycle averages based on

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OTR notch rates, and for OTR cycle average rates based on transients versus steady state notch

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average rates.

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RESULTS

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Results include cycle average RY and OTR emission rates for each engine, real-world duty

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cycles observed during OTR measurements, and a comparison of trip total emissions using two

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approaches. This paper focuses on NOx, HC, CO, and PM because they are regulated by 12 ACS Paragon Plus Environment

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emission standards. While CO2 is not regulated, emission rates are estimated to provide insight

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on fuel use. The amount of carbon in the fuel emitted as CO2 averages over 99 percent;

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therefore, relative differences in CO2 emission rate and fuel use rate are approximately the same.

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Approximately 19 and 160 hours of data were collected during RY and OTR measurements,

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respectively. Typically, less than one percent of total data collected were excluded due to errors

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that could not be corrected.

280 281

Rail Yard Measurements

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For each locomotive, notch average engine output-based emission rates were estimated for idle

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and eight notch positions. As engine load increases, engine RPM, MAP, and exhaust CO2

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concentrations increase. This leads to an increase in air, fuel, and exhaust flow for the engine.

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IAT remained relatively constant across all notches for each locomotive. The coefficient of

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variation (CV), which is the ratio of the standard deviation to the mean, for inter-replicate

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variations for a given engine and notch position was 0.04 or less for RPM, IAT, and MAP.

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Thus, engine parameter measurements were highly repeatable.

289 290

Engine output-based NOx emission rates for all locomotives generally decrease as the PME shifts

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from idle to Notch 8. As notch position increases, engine output increases, air-to-fuel ratio

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decreases, and measured NO concentration typically increases. The latter is expected since the

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rate of NO formation typically increases with flame temperature, which in turn increases as AFR

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becomes less lean (33). However, when normalized to engine output, NO emission rate

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decreases with notch position. NOx emission rates, on a g/kW-hr basis, were approximately 81,



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91, and 94 percent lower at Notch 8 versus idle for the GP40, F59PH, and F59PHI locomotives,

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respectively. CV ranged from 0.01 to 0.08 for Notch 8, indicating high repeatability of

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measurements.

299 300

As engine output increases, exhaust PM concentration increases. However, notch average PM

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emission rates were highest at idle for all locomotives, ranging from 3.9 to 10.4 g/kW-hr. For

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each locomotive, PM emission rates at Notches 1 through 8 were similar. For example, the NC

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1810 mean non-idle notch average emission rate was 0.27 g/kW-hr with a 95% confidence

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interval (CI) on the mean of ±0.09 g/kW-hr. Among the six locomotives with EMD 12-710

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engines, the mean non-idle emission rate was 0.35 g/kW-hr with a 95% CI on the mean of ±0.10

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g/kW-hr. For the GP40, the non-idle mean PM emission rate was 1.16 g/kW-hr, with a 95% CI

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on the mean of ±0.30 g/kW-hr. Thus, non-idle emission rates were approximately consistent

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among the eight notches and were substantially lower than during idle. Compared to idle, non-

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idle PM emission rates were approximately 82, 95, and 97 percent less for the GP40, F59PH, and

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F59PHI locomotives, respectively. CV values averaged 0.09 for Notch 8, indicating high

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repeatability of measurements.

312 313

There is substantial inter-replicate variability in notch average HC and CO emission rates for all

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engines, with CV values as high as 1.33 and 1.65, respectively, for a given locomotive and notch

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position. However, concentrations of these pollutants were typically below the detection limit

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for all notches, which contributes to the high relative variation. As expected for diesel engines,

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emission rates of HC and CO tend to be low versus other types of emission sources (33).

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Cycle average emission rates were estimated based on the EPA line-haul duty cycle as shown in

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Table 1. All measured emission rates are of the same magnitude as published emission rates of

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the same locomotive model (5). Cycle average NOx and PM rates for all locomotives are highly

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repeatable across RY replicates for a given locomotive, with CV values between 0.01 and 0.10.

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High inter-replicate variability in notch average HC and CO emission rates lead to high inter-

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replicate variability in cycle average rates. The NOx emission rates were highly variable across

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the measured locomotives. For three locomotives, the rates were relatively low, ranging from

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9.4 to 10.6 g/kW-hr, including the EMD16-645 engine and two mechanically governed EMD12-

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710 engines. Two locomotives had moderate NOx emission rates of 12.0 to 12.7 g/kW-hr, both

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with mechanically governed EMD12-710 engines. Two had relatively high NOx emission rates

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of 14.2 to 15.0 g/kW-hr, both with electronically governed EMD12-710 engines. The results

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indicate substantial inter-engine variability for engines of the same general design. HC and CO

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emission rates are of low magnitude. There is not a clear trend in the relationship between PM

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and NOx emission rates, although there is some hint of a trade-off between these. For example,

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two of the lowest NOx emitting locomotives, NC 1792 and NC 1859, have higher PM emission

334

rates than the highest NOx emitting locomotives, NC 1797. However, NC 1869, which has a

335

moderate NOx emission rate, also tends to have a high PM emission rate compared to all but the

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GP40.

337 338

Over-the-Rail Measurements

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Cycle average emission rates are estimated using the EPA line-haul duty cycle and duty cycles

340

observed during each one-way Piedmont trip.

341



342

Duty Cycles

343

Observed duty cycles for each locomotive model, and the average duty cycle inferred from all

344

measured locomotives, are compared to the EPA line-haul and passenger duty cycles in Table 2.

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Across models, results are similar for the fraction of time spent in Notches 1 through 8. There is

346

variability among locomotive models in the amount of time spent in idle and dynamic braking.

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However, all three locomotive models spent 38.7 to 39.5 percent of the duty cycle, on average, in

348

these lowest engine power demand settings. Differences in the allocation of low engine power

349

demand between idle and dynamic braking are an artifact of engineer preference and not a

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distinguishing feature of locomotive model. Therefore, locomotive model is judged not to be an

351

explanatory factor in duty cycle variability and an average duty cycle based on 48 one-way trips

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was derived. The observed average cycle typically has less time in idle, less time in Notches 1

353

through 7, and more time in Notch 8 than the EPA cycles.

354 355

Emission Rates from Approach 1: Steady-State

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For each locomotive, notch average engine output-based emission rates were estimated for idle,

357

dynamic brake, and the eight notch positions. OTR measured values of RPM, IAT, and MAP for

358

each notch position were similar to those measured in the RY. Therefore, differences, if any, in

359

cycle average emission rates between RY and OTR measurements are not attributed to these

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engine parameters. Furthermore, OTR measured notch average values of RPM, IAT, and MAP

361

were repeatable, with inter-run CV typically less than 0.05. PME output was similar between

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RY and OTR measurements for idle through Notch 6. Engine output at Notches 7 and 8 were

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220 kW higher for OTR versus RY measurements for all locomotives, with the exception of NC


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1755. This is due to the way the engine is programmed for load testing by the engine

365

manufacturer.

366 367

Compared to RY measurements, nearly two-thirds of all NOx emission rates are statistically

368

different and systematically lower during OTR measurements, especially at Notches 7 and 8 for

369

which rates are, on average, 19 percent lower for four locomotives. For CO, HC, and PM,

370

approximately one-third of notch average emission rates measured in the RY and OTR are

371

statistically different and systematically higher during OTR measurements; however, rates at

372

Notches 7 and 8 were statistically similar for four locomotives. Nearly half of OTR notch

373

average CO2 emission rates were statistically different and systematically lower than RY rates,

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especially at Notch 8 for which rates are, on average, 12 percent lower for the F59PH and

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F59PHI locomotives.

376 377

Cycle average emission rates based on both the EPA line-haul and Piedmont duty cycles are

378

given in Table 3. All measured emission rates are of the same magnitude as published emission

379

rates of the same locomotive model (5).

380 381

Differences between RY and OTR cycle average emission rates are based on the RY emission

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rates in Table 1 and the OTR emission rates in Table 3(a). Locomotives NC 1810, 1859, and

383

1893 each had statistically significant lower cycle average NOx rates, by an average of 14

384

percent, based on OTR versus RY notch average rates. For NC 1797 and 1869, differences in

385

cycle average rates were not significantly different. For NC 1755 and 1792, the differences in

386

cycle average rates based on OTR versus RY notch average rates were -19 and 47 percent,



387

respectively. NC 1792 was unusual in that the cycle average rate based on OTR notch rates was

388

higher than based on RY notch rates. Overall, cycle averages for the F59PH and F59PHI

389

locomotives based on OTR notch average rates were a statistically insignificant 3 percent lower

390

than those based on RY average rates. Most engines operated at higher power output in Notches

391

7 and 8 OTR than in the RY.

392 393

For HC, only the NC 1797 cycle average emission rates are statistically different, for which the

394

cycle average based on OTR notch average rates was 230 percent higher than that based on RY

395

notch average rates. For CO, the cycle average OTR emission rates for NC 1859, 1869, and

396

1893 are significantly different than those based on RY notch average rates, differing by -56, 30,

397

and 88 percent, respectively. However, these large differences are typically for rates that are

398

relatively low. There were no significant differences in cycle average PM emission rates based

399

on OTR versus RY notch average rates. Overall, the OTR NOx and HC cycle averages were 1

400

and 9 percent higher, and the PM and CO cycle averages were 3 and 16 percent lower, across the

401

entire locomotive fleet; however, these differences were not statistically significant. This is due

402

to the wide range of differences in the cycle average emission rates between each locomotive in

403

the fleet.

404 405

The comparison of cycle average CO2 emission rates has similar qualitative trends as for cycle

406

average NOx emission rates. NC 1810, 1859, and 1893 each had significantly lower, by 4 to 14

407

percent, cycle average CO2 emission rates based on OTR versus RY notch average rates. For

408

NC 1797 and 1869, differences were not significant. For NC 1755 and 1792, the cycle average

409

rates differed significantly by -16 and 17 percent, respectively. Overall, based on combined data


Page 18 of 38

Page 19 of 38


410

for all replicates and runs over all locomotives, cycle averages for the EMD12-710 engine-

411

equipped did not differ for the EPA line haul cycle when using OTR versus RY notch average

412

rates.

413 414

Based on notch average OTR rates, cycle average emission rates are estimated for and compared

415

between the average Piedmont duty cycle and the EPA line-haul duty cycle for six locomotives

416

for which multiple runs were made. The Piedmont cycle average NOx emission rates for these

417

locomotives were statistically significantly lower by an average of 9 percent, with a range of 2 to

418

16 percent.

419 420

The Piedmont cycle average HC emission rates were a statistically significant 32 percent lower,

421

on average, for all locomotives. The cycle average HC emission rates were lower for all six

422

locomotives and were significantly lower for three locomotives. The Piedmont cycle average

423

emission rates were systematically 1 percent higher for CO and 3 percent lower for PM, with

424

differences in CO significant for two locomotives and for PM for only one locomotive. Observed

425

differences in cycle average emission rates are due to differences in the fraction of time spent in

426

each notch, especially Notch 8.

427 428

Inter-locomotive cycle average CO2 emission rates were 0 to 6 percent lower when estimated

429

using the Piedmont versus EPA duty cycle. The mean Piedmont duty cycle average CO2 rate for

430

the seven locomotives was a statistically significant 2 percent lower than the EPA line-haul duty

431

cycle average CO2 rate.

432



433

Emission Rates from Approach 2: Transients

434

When throttle notch is changed, the time it takes for the engine to reach steady-state differs

435

depending on the number of notches that are skipped. For example, when switching from idle

436

directly to Notch 8, the transition period can be as much as 30 seconds. However, when

437

switching from one notch to an adjacent notch, the transition period is approximately 5 seconds.

438

On average, over 500 notch transitions occur during each one-way Piedmont trip. The

439

interaction between throttle change, engine parameters, and emission rates is observed from

440

second-by-second time traces. Upon a transition to a higher notch, all emission rates decrease

441

before increasing to a steady-state value. Conversely, upon transition to a lower notch, NOx and

442

PM emission rates increase in the seconds immediately after the transition before decreasing to a

443

steady-state value. For example, the NOx and PM emission rates of an F59PH locomotive nearly

444

double and quintuple, respectively, immediately for a short period after downshifting from a

445

higher notch. For CO2, emission rates begin to decrease after a transition to a lower notch.

446 447

Among four locomotives, there were 15 one-way trips for which 95 percent or more of raw data

448

for all pollutants were valid after quality assurance, thereby enabling complete characterization

449

of second-by-second emissions for Approach 2. Trip total emissions are shown in Table 4.

450 451

Trip total NOx emissions estimated from Approach 1 are systematically underestimated by a

452

statistically significant 5 percent over all trips compared to Approach 2. Although the

453

percentage differences for three locomotives, NC 1755, 1810, and 1869, were not statistically

454

significant, they were all negative. For NC 1797, not accounting for transients underestimates


Page 20 of 38

Page 21 of 38


455

total NOx emissions by a statistically significant 5 percent. Approach 1 emission rates were

456

typically higher at lower throttle positions, especially Idle.

457 458

Using Approach 1 to estimate trip total HC and CO emissions produces statistically insignificant

459

overestimates of less than 1 percent and 4 percent, respectively, over all trips.

460 461

Over all one-way trips, trip total PM was systematically underestimated by a statistically

462

significant 9 percent if transients were neglected. For NC 1755 and 1810, PM emissions are

463

underestimated by 33 and 27 percent, respectively, with the former being statistically significant.

464

For NC 1869, PM emissions are not significantly different. For NC 1797, PM emissions are

465

overestimated by a statistically significant 9 percent. Approach 1 emission rates were typically

466

higher at higher throttle positions.

467 468

Although inter-locomotive trip total CO2 emissions were not statistically different for NC 1755,

469

1797, and 1869, the estimates from Approach 1 were higher than for Approach 2. For NC 1810,

470

the Approach 1 trip total CO2 emissions were significantly higher by 17 percent. The mean

471

difference in trip total CO2 emissions over all trips of the four locomotives estimated from

472

Approach 1 versus 2 is significantly overestimated by 10 percent. Approach 1 emission rates

473

were typically higher at higher throttle positions.

474 475

Although differences in cycle average rates for Approach 2 versus 1 were modest or insignificant

476

in many cases, differences are likely to be more substantial at higher spatial and temporal

477

resolution, such as near a train station. Therefore, Approaches 1 and 2 were used to evaluate



478

emission totals for 30 seconds prior to the arrival of NC 1797 at a rail station and 30 seconds

479

after station departure for each of the six trips. The PME was at steady-state Notch 8 prior to

480

downshifting to lower notch positions as the train approached the station, and was ratcheted up to

481

Notch 8 when departing the station. Based on estimating emission totals using notch average

482

emission rates and transient emission rates for the 30 seconds before station arrival and after

483

station departure, Approach 1 overestimated NOx emissions by 28 percent for station arrival and

484

underestimated NOx emissions by 17 percent for station departure, with both differences being

485

statistically significant. Therefore, differences in estimated emission rates at specific locations

486

can be much larger than those for cycle averages over an entire trip.

487 488

DISCUSSION

489

A method is demonstrated for in-use measurement of locomotive activity and emissions during

490

passenger rail service using a portable emissions measurement system.

491 492

RY and OTR measurements produce differences in PME operation between the two

493

measurement methods and statistically different notch average NOx, CO2, CO, HC, and PM

494

emission rates. Therefore, RY measurements may not be representative of emissions produced

495

during real-world locomotive operation.

496 497

However, although notch average rates often differed based on OTR versus RY measurements,

498

the effect on cycle average emission rates was less pronounced. In most cases, cycle average

499

emission rates estimated based on RY notch average rates were within 10 percent of those

500

estimated based on OTR notch average rates. Thus, if errors of 10 percent in cycle average


Page 22 of 38

Page 23 of 38


501

emission rates are tolerable for a given purpose, then measurement of RY notch average

502

emission rates may be adequate. Otherwise, for a more accurate representation of real-world

503

emission rates, OTR measurements are preferred.

504 505

While multiple RY replicates can be completed in one day, the locomotive has to be removed

506

from service while measurements are conducted. With OTR measurements, the locomotive

507

remains in service, but several days are needed to collect multiple one-way trip data to yield

508

replicable notch average emission rates. Cycle average emission rates were repeatable based on

509

typically six one-way trips, or about 20 hours of OTR data, per locomotive. This amount of

510

OTR data is recommended as suitable for future studies.

511 512

Real-world duty cycles differ from those used for regulatory analyses. During Piedmont

513

passenger rail service, a larger percentage of time is typically spent in Notch 8 and a smaller

514

percentage of time in idle and dynamic brake compared to the EPA line-haul duty cycle. These

515

variations in duty cycles lead to statistically significant lower cycle average NOx and HC rates.

516

However, there was no significant difference in cycle average CO and PM rates. Therefore, in

517

practical terms, the regulatory duty cycle could be used to estimate cycle average emission rates

518

within a tolerable error without having to take the extra step of estimating a real-world duty

519

cycle, unless more accurate emission rates are desired or the actual cycle differs from that

520

considered here.

521 522

The impact of transients on real-world locomotive emissions had not previously been quantified.

523

Based on the analysis of 15 one-way OTR measurements, total emissions should be estimated



524

based on the sum of second-by-second emission rates, and not based on steady-state notch

525

average emission rates. Estimating trip total emissions using Approach 2 rather than Approach 1

526

does not add significant time to data analysis. Neglecting to consider transient engine operations

527

underestimated trip total NOx and PM emissions estimates by 5 and 9 percent, respectively, for

528

the four locomotives analyzed, while overestimating trip total CO2 emissions by 10 percent.

529

However, the number of notch transitions over this route may not be representative of all

530

passenger rail service. Engineers typically downshift before entering curves with reduced speed

531

limits. A route with fewer curves may have fewer notch transitions. Also, engineers may

532

increase engine output to climb a hill and decrease engine output when descending. Flatter

533

routes may require fewer notch transitions than the Piedmont route. Estimating second-by-

534

second emission rates will capture microscale emissions changes, which are important in

535

modeling ambient concentrations in areas where locomotives sharply decelerate or accelerate,

536

such as arriving at or departing a rail station.

537 538

Overall, locomotive emission rates are more accurate if measured in the field for actual duty

539

cycles, taking transients into account. However, the errors compared to using RY tests, standard

540

duty cycles, and steady-state notch average rates may be tolerable for some applications.

541 542

ACKNOWLEDGMENTS

543

This material is based upon work supported by NCDOT under Research Project Nos. HWY-

544

2010-12 and HWY-2012-33 and the Federal Railroad Administration under Research Project No.

545

FR-RRD-0023-11-01-00. Hyung-Wook Choi and Jiangchuan Hu collected and analyzed some

546

locomotive emissions and activity data. Herzog Transit Services NC and RailPlan International 24 ACS Paragon Plus Environment

Page 24 of 38

Page 25 of 38


547

Inc. provided technical support. Allan Paul of the NCDOT Rail Division and Curtis McDowell

548

and Lynn Harris of McDowell Engineers provided guidance and logistical support. Any

549

opinions, findings, conclusions or recommendations expressed are those of the authors and do

550

not necessarily reflect the views of the North Carolina Department of Transportation or the

551

Federal Railroad Administration.

552 553

SUPPORTING INFORMATION AVAILABLE

554

The supporting information include: specifications of each locomotive model owned by

555

NCDOT; Piedmont route map and travel duration between rail stations; PEMS precision,

556

accuracy, and calibration; installation of the PEMS; locomotive fuel use and emission rate

557

calculations; PME volumetric efficiency estimation based on dynamometer measurements; notch

558

average RY and OTR engine parameters and engine output-based emission rates for each

559

locomotive; duty cycles for each OTR measurement; and NOx emissions time trace for a small

560

segment of an OTR measurement. This information is available free of charge via the Internet at

561

http://pubs.acs.org/.

562 563

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564

1.

565

Davis, S.C.; Diegel, S.W.; Boundy, R.G. Transportation Energy Data Book: Edition 32; ORNL-6989, Oak Ridge National Laboratory: Oak Ridge, TN, 2013.

566 567 568

2.

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569 25 ACS Paragon Plus Environment


570

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571

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574

Amtrak Fleet Strategy Version 3.1; National Passenger Rail Corporation: Washington, DC, 2012.

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577

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Fritz, S.G. Evaluation of Biodiesel Fuel in an EMD GP38-2 Locomotive; NREL/SR-51033436; Prepared for the National Renewable Energy Laboratory, Golden, CO, 2004.

581 582

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Fritz, S.G. Diesel Fuel Effects on Locomotive Exhaust Emissions; Technical Report SwRI

583

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584

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587

Fritz, S.G. Exhaust Emissions from 2 Intercity Passenger Locomotives. J. Eng. Gas Turbines Power 1994, 116(4): 774-783.

588 589 590

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Fritz, S.G.; Cataldi, G.R. Gaseous and Particulate-Emissions from Diesel Locomotive Engines. J. Eng. Gas Turbines Power 1991, 113(3): 370-376.

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10.

Fritz, S.G.; Hedrick, J.C.; Smith, B.E. Exhaust Emissions from a 1,500 kW EMD 16-645-

593

E Locomotive Diesel Engine using Several Ultra-Low Sulfur Diesel Fuels. Fall Tech.

594

Conf. ASME Intern. Combust. Engine Div. 2005, 37-46.

595 596

11.

597

Bannikov, M.G.; Chattha, J.A. Oxides of Nitrogen (NOx) Emission Levels of Diesel Engines of Switch Locomotives. Proc. Inst. Mech. Eng., Part A 2006, 220(A5): 449-457.

598 599

12.

Bohac, S.V.; Feiler, E.; Bradbury, I. Effect of Injection Timing on Combustion, NOx,

600

Particulate Matter and Soluble Organic Fraction Composition in a 2-Stroke Tier 0+

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Locomotive Engine. J. Eng. Gas Turbines Power 2013, 135(1): 1-7.

602 603

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Bohac, S.V.; Feiler, E.; Bradbury, I. Exhaust Emissions Characterization of a

604

Turbocharged 2-Stroke Tier 0+ Locomotive Engine: NOx, Particulate Matter, and Soluble

605

Organic Fraction Composition. J. Eng. Gas Turbines Power 2012, 134(7): 1-8.

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608

Hedrick, J.C.; Fritz, S.G. Locomotive Idle and Start-Up Exhaust Emissions Testing. Spring Tech. Conf. ASME Intern. Combust. Engine Div. 2008, 385-394.

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611

Hoffman, J.C.; Springer, K.J.; Tennyson, T.A. 4 Cycle Diesel Electric Locomotive Exhaust Emissions – Field Study. Mech. Eng. (Am. Soc. Mech. Eng.) 1975, 97(7): 91-97.

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Bryant, A.H.; Tennyson, T.A. Exhaust Emissions of Selected Railroad Diesel Locomotives. J. Eng. Ind. 1975, 97(3): 1136-1142.



615 616

17.

Markworth, V.O.; Fritz, S.G.; Cataldi, G.R. The Effect of Injection Timing, Enhanced

617

Aftercooling, and Low-Sulfur Low-Aromatic Diesel Fuel on Locomotive Exhaust

618

Emissions. J. Eng. Gas Turbines Power 1992, 114(3): 488-495.

619 620

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Osborne, D.T.; Fritz, S.G.; Glenn, D. The Effects of Biodiesel Fuel Blends on Exhaust

621

Emissions from a General Electric Tier 2 Line-Haul Locomotive. J. Eng. Gas Turbines

622

Power 2011, 133(10): 102803 1-7.

623 624

19.

Osborne, D.T.; Fritz, S.G.; Iden, M.; Newburry, D. Exhaust Emissions from a 2,850 kW

625

EMD SD60M Locomotive Equipped with a Diesel Oxidation Catalyst. Spring Tech.

626

Conf. ASME Intern. Combust. Engine Div. 2007, 441-449.

627 628

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Weaver, C.S. Start-up and Idling Emissions from Two Locomotives; Technical Report

629

SCAQMD No. 00112; Prepared for the South Coast Air Quality Management District,

630

Diamond Bar, CA, 2006.

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633

Emission Standards for Locomotives and Locomotive Engines. Code of Federal Regulations, Part 92, Title 40, 2013.

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Brabb, D.C.; Vithani, A.R.; Punwani, S.K. Onboard Locomotive Exhaust Emissions Measurement. Fall Tech. Conf. ASME Rail Transp. Div. 2007, 69-75.

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642

Frey, H.C.; Choi, H.W.; Kim, K. Portable Emission Measurement System for Emissions of Passenger Rail Locomotives. Transp. Res. Rec. 2012, 2289: 56-63.

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25.

Marchese, A.J.; Bhatia, K.K.; Hesketh, R.P.; McKenna, D. Evaluation of Emissions and

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Performance of NJ TRANSIT Diesel Locomotives with B20 Biodiesel Blends; Prepared

646

for NJ TRANSIT, Newark, NJ, 2009.

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McKenna, D.; Bhatia, K.K.; Hesketh, R.P.; Rowen, C.; Vaughn, T.; Marchese, A.J.;

649

Chipko, G.; Guran, S. Evaluation of Emissions and Performance of Diesel Locomotives

650

with B20 Biodiesel Blends: Static Test Results. Fall Tech. Conf. ASME Rail Transp. Div.

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2008, 167-175.

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Graver B.M.; Frey, H.C. Comparison of Locomotive Emissions Measured During

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Dynamometer Versus Rail Yard Engine Load Tests. Transp. Res. Rec. 2013, 2341: 23-

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Yanowitz, J. Particulate Matter Emissions during Transient Locomotive Operation: Preliminary Study. J. Air & Waste Manage. Assoc. 2003, 53(10): 1241-1247.

659



660

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Dunn, R.; Eggleton, P. Influence of Duty Cycles and Fleet Profile on Emissions from

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Locomotives in Canada; TP 13945E; Transport Canada Transportation Development

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Centre: Montreal, 2002.

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OEM-2100 Montana System Operation Manual; Clean Air Technologies International, Inc.: Buffalo, NY, 2003.

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OEM-2100AX Axion System Operation Manual; Clean Air Technologies International, Inc.: Buffalo, NY, 2008.

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Myers, J; Kelly, T; Dindal, A; Willenberg, Z; Riggs, K. Environmental Technology

671

Verification Report: Clean Air Technologies International, Inc. REMOTE On-Board

672

Emissions Monitor; Prepared by Batelle for U.S. Environmental Protection Agency:

673

Research Triangle Park, NC, 2003.

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Cooper, C.D.; Alley, F.C. Air Pollution Control: A Design Approach; Waveland Press: Long Grove, IL, 2011.

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Frey, H.C.; Unal, A.; Rouphail, N.M.; Colyar, J.D. On-Road Measurement of Vehicle

679

Tailpipe Emissions Using a Portable Instrument. J. Air Waste Manage. Assoc. 2003,

680

53(8): 992-1002.

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Sandhu, G.S.; Frey, H.C. Effects of Errors on Vehicle Emission Rates from Portable Emissions Measurement Systems. Transp. Res. Rec. 2013, 2340: 10-19.

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Burgard, D.A.; Bishop, G.A.; Stadtmuller, R.S.; Dalton, T.R.; Stedman, D.H.

686

Spectroscopy Applied to On-Road Mobile Source Emissions. Appl. Spectrosc. 2006,

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Vojtisek-Lom, M.; Cobb, J.T. Vehicle Mass Emissions Measurement using a Portable 5-

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Gas Exhaust Analyzer and Engine Computer Data. Proc. EPA A&WMA Emiss. Inventory

691

Conf. 1997, 656-669.

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38.

Stephens, R.D.; Mulawa, P.A.; Giles, M.T.; Kennedy, K.G.; Groblicki, P.J.; Cadle, S.H.;

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Knapp, K.T. An Experimental Evaluation of Remote Sensing-Based Hydrocarbon

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Measurements: A Comparison to FID Measurements. J. Air Waste Manage. Assoc. 1996,

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46(2): 148-158.

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Vojtisek-Lom, M.; Allsop, J.E. Development of Heavy-Duty Diesel Portable, On-Board

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Mass Exhaust Emissions Monitoring System with NOx, CO2, and Qualitative PM

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Capabilities; Report 2001-01-3641; Society of Automotive Engineers: Warrenton, PA,

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703

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Andros, Inc. “Concentrations Measurement and Span Calibration Using n-Hexane and

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Propane in the ANDROS 6602/6800 Automotive Exhaust Gas Analyzer”;

705

http://www.andros.com/hmDownloads.htm, accessed January 2007.

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Zhang, K. Micro-Scale On-Road Vehicle-Specific Emissions Measurements and

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Modeling; PhD Dissertation, Department of Civil, Construction, and Environmental

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Engineering, North Carolina State University: Raleigh, NC, 2006.

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Singer, B.C.; Harley, D.A.; Littlejohn, D.; Ho, J.; Vo, T. Scaling of Infrared Remote

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Sensor Hydrocarbon Measurements for Motor Vehicle Emission Inventory Calculations.

713

Environ. Sci. Technol. 1998, 32(21), 3241-3248.

714 715

43.

Stephens, R.D.; Cadle, S.H.; Qian, T.Z. Analysis of Remote Sensing Errors of

716

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46(6), 510-516.

718 719

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Durbin, T.D.; Johnson, K.; Cocker, D.R.; Miller, J.W. Evaluation and Comparison of

720

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722

Environ. Sci. Technol. 2007, 41(17): 6199-6204.

723


Page 32 of 38

Page 33 of 38


724 725 726 727 728

TABLES TABLE 1 Comparison of EPA Line-Haul Duty Cycle Average Emission Rates for Measured Prime Mover Engines Based on Rail Yard Measurements Model

Locomotive

GP40

NC 1792

EMD 16-645E3

1 replicate

F59PHI

NC 1755

EMD 12-710G3 (Electronically governed)

NC 1797

2 replicates 3 replicates

NC 1810 3 replicates

F59PH

NC 1859

EMD 12-710G3 (Mechanically governed)

NC 1869

3 replicates 3 replicates

NC 1893 3 replicates

NOxa

HCb

CO

Opacity-based PMc

CO2

(g/kW-hr)

(g/kW-hr)

(g/kW-hr)

(g/kW-hr)

(g/kW-hr)

10.1 ---d

2.7 ---d

1.2 ---d

1.69 ---d

698 ---d

14.2 (0.02) 15.0 (0.01) 10.6 (0.01) 9.4 (0.02) 12.7 (0.07) 12.0 (0.04)

5.7 (0.92) 1.4 (0.33) 5.1 (0.09) 6.0 (0.18) 0.80 (0.17) 1.1 (0.24)

1.5 (0.44) 0.8 (0.20) 1.6 (0.10) 2.6 (0.15) 1.2 (0.19) 0.5 (0.13)

n/ae

676 (0.02) 677 (0.01) 695 (0.00) 713 (0.00) 712 (0.05) 733 (0.01)

0.26 (0.05) 0.40 (0.10) 0.52 (0.02) 0.59 (0.07) 0.36 (0.08)

729 730

Italicized values in parentheses are coefficients of variation (standard deviation divided by the mean) on the mean emission rate.

731 732 733

a

NOx includes NO and NO2. Only NO was measured. Typically, NOx is comprised of 95 vol-% NO. NOx is always reported as equivalent mass of NO2. Results include multiplicative correction factor of 1.053 to approximate total NOx.

734 735 736

b

HC is measured using non-dispersive infrared (NDIR), which accurately measures some compounds but responds only partially to others. Results include multiplicative correction factor of 2.5 to approximate total HC.

737 738 739

c

Opacity is measured using a light scattering technique, which provides useful relative comparisons of particle levels in the exhaust. Results include multiplicative correction factor of 5 to approximate total PM.

740 741

d

Only one rail yard measurement was completed. Therefore, a coefficient of variation could not be calculated.

742

e

Malfunction of the PEMS photometer lead to no valid opacity-based PM data during measurement.



743 744 745

Page 34 of 38

TABLE 2 Comparison of Measured Duty Cycles during Piedmont Rail Service to EPA Line-Haul Duty Cycle Notch Idle

F59PH 26.5 (10.6, 40.6)

13.0 Dynamic Brake (3.8, 18.6)

1 2 3 4 5 6 7

Percent Time in Notch Locomotive Modela EPA (1998) F59PHI GP40 Averageb Line-Haul Passenger 35.7 24.9 28.4 38.0 47.4

(23.2, 51.8)

(20.9, 28.1)

3.0

14.6

(0.0, 7.0)

(11.6, 17.7)

3.9

3.4

5.1

(0.6, 14.0)

(1.0, 7.9)

(1.7, 8.7)

5.0

4.9

4.3

(1.6, 11.3)

(1.9, 9.9)

(3.7, 4.8)

4.0

3.7

2.5

(1.4, 10.7)

(0.7, 10.3)

(1.5, 3.8)

4.1

4.1

3.0

(1.4, 11.4)

(1.2, 10.7)

(0.9, 5.8)

2.2

2.2

2.3

(0.4, 4.5)

(1.0, 4.6)

(0.9, 3.6)

2.5

2.8

2.0

(0.2, 11.0)

(0.5, 10.2)

(1.2, 2.6)

0.7

1.3

1.1

(0.0, 2.5)

(0.1, 3.7)

(0.3, 2.1)

11.1

12.5

6.2

3.8

6.5

7.0

4.8

6.5

5.1

3.7

5.2

5.7

4.0

4.4

4.7

2.2

3.8

4.0

2.5

3.9

2.9

0.9

3.0

1.4

38.6

16.2

15.6

38.2

38.9

40.3

(22.7, 52.0)

(29.0, 48.0)

(34.6, 45.4)

Number of Runs

32

10

6

48

Avg. Travel Time (s)

11,744

11,918

12,269

11,846

8

746 747

a

Italicized values in parentheses are the minimum and maximum percentages of time spent in a notch position.

748 749 750

b

“Average” is the average of the forty-eight duty cycles from measurements of all locomotives.


Page 35 of 38

751 752 753 754 755


TABLE 3 EPA Line-Haul and Observed Piedmont Duty Cycle Average Emission Rates for Measured Prime Mover Engines Based on Over-the-Rail Measurements Using Approach 1: Steady-State Emission Factors (a) EPA Line-Haul Duty Cycle Model

Locomotive

NOxa (g/kW-hr)

HCb (g/kW-hr)

CO (g/kW-hr)

Opacity-based PMc (g/kW-hr)

CO2 (g/kW-hr)

11.0 ---d

1.77 ---d

0.5 ---d

n/ae

817 ---d

11.7 ---d

1.26 ---d

0.7 ---d

17.9 (0.05)

4.66 (0.46)

1.1 (0.35)

0.21 (0.09)

607 (0.10)

9.1 (0.05)

5.05 (0.34)

1.9 (0.28)

0.37 (0.09)

667 (0.02)

8.1 (0.05)

4.88 (0.77)

1.0 (0.34)

0.56 (0.14)

611 (0.03)

11.0 (0.00)

1.68 (0.19)

1.7 (0.06)

0.67 (0.05)

724 (0.00)

9.7 (0.09)

1.66 (1.27)

0.7 (0.64)

0.32 (0.42)

625 (0.10)

11.2 (0.05)

2.99 (0.61)

1.1 (0.33)

0.40 (0.16)

660 (0.05)

GP40

NC 1792

EMD 16-645E3

(6 trips)

F59PHI

NC 1755


(1 trip)

NC 1797 (6 trips)

NC 1810 (6 trips)

F59PH

NC 1859


(6 trips)

NC 1869 (2 trips)

NC 1893 (14 trips)

Average of All

756

---d

567 ---d

(b) Piedmont Duty Cycle Model

Locomotive

NOxa (g/kW-hr)

HCb (g/kW-hr)

CO (g/kW-hr)

Opacity-based PMc (g/kW-hr)

CO2 (g/kW-hr)

10.8 ---d

1.28 ---d

0.3 ---d

n/ae

771 ---d

9.8 ---d

0.70 ---d

0.8 ---d

0.22 ---d

546 ---d

15.0 (0.03)

2.90 (0.45)

1.0 (0.25)

0.20 (0.10)

592 (0.08)

8.4 (0.05)

3.62 (0.44)

2.0 (0.23)

0.39 (0.08)

667 (0.02)

7.3 (0.03)

4.02 (0.66)

1.1 (0.18)

0.55 (0.12)

599 (0.02)

9.4 (0.00)

0.85 (0.24)

2.0 (0.05)

0.63 (0.01)

713 (0.00)

9.0 (0.10)

0.93 (1.17)

0.7 (0.54)

0.30 (0.37)

614 (0.09)

10.0 (0.04)

2.04 (0.59)

1.1 (0.25)

0.38 (0.14)

643 (0.04)

GP40

NC 1792

EMD 16-645E3

(6 trips)

F59PHI

NC 1755


(1 trip)

NC 1797 (6 trips)

NC 1810 (6 trips)

F59PH

NC 1859


(6 trips)

NC 1869 (2 trips)

NC 1893 (14 trips)

Average of All

757 758 759 760 761 762 763 764 765

0.26

Italicized values in parentheses are coefficients of variation (standard deviation divided by the mean) on the mean emission rate. a


b


c




766 767 768

d

Cycle average emission rates were estimated for only one trip. Therefore, a coefficient of variation could not be calculated.

e

Malfunction of the PEMS photometer lead to no valid opacity-based PM data during measurement.


Page 36 of 38

Page 37 of 38

769 770 771


TABLE 4 Comparison of Steady-State versus Transient Trip Total Emissions for Measured Prime Mover Engines Based on Observed Piedmont Duty Cycles

772

(a) Approach 1 – Steady-State Model

Locomotive

NOxa (kg)

HCb (kg)

CO (kg)

Opacity-based PMc (kg)

CO2 (kg)

NC 1755

31.4 ---d

2.50 ---d

2.22 ---d

0.63 ---d

554 ---d

NC 1797

53.1 (0.04)

10.2 (0.43)

3.48 (0.25)

0.72 (0.09)

690 (0.12)

NC 1810

26.0 (0.10)

11.0 (0.33)

6.18 (0.18)

1.20 (0.12)

747 (0.10)

NC 1869

31.5 (0.03)

1.77 (0.15)

6.18 (0.04)

2.04 (0.07)

755 (0.04)

Locomotive

NOxa

F59PHI

F59PH

773

(b) Approach 2 – Transients Model

(kg)

HCb (kg)

CO (kg)

Opacity-based PMc (kg)

CO2 (kg)

NC 1755

35.7 ---d

2.73 ---d

2.44 ---d

0.93 ---d

553 ---d

NC 1797

56.0 (0.05)

11.0 (0.43)

3.39 (0.25)

0.66 (0.10)

637 (0.14)

NC 1810

27.3 (0.05)

11.1 (0.26)

5.94 (0.15)

1.65 (0.05)

638 (0.06)

NC 1869

31.0 (0.05)

1.81 (0.18)

5.50 (0.01)

2.02 (0.05)

706 (0.06)

F59PHI

F59PH

774

(c) Percent Difference – Approach 1 vs. Approach 2 Model

Locomotive

NOx

HC

CO

Opacity-based PM

CO2

NC 1755

- 12.0

- 8.2

- 9.2

- 32.5

0.0

- 5.2 [ < 0.01 ] - 4.9 [ 0.15 ] - 2.0 [ 0.16 ]

- 7.7 [ 0.01 ] - 1.3 [ 0.91 ] 33.0 [ 0.14 ]

2.8 [ 0.08 ] 3.9 [ 0.32 ] 15.7 [ 0.01 ]

9.0 [ < 0.01 ] - 27.3 [ < 0.01 ] 0.8 [ 0.59 ]

8.0 [ 0.30 ] 17.0 [ 0.02 ] 7.0 [ 0.32 ]

F59PHI NC 1797 NC 1810 F59PH NC 1869

775 776 777 778 779 780 781 782 783 784 785 786 787 788

Italicized values in parentheses are coefficients of variation (standard deviation divided by the mean) on the mean emission rate. Values in brackets are parentheses are p-values. Differences in Approach 1 and Approach 2 emission rates are statistically significant if p ≤ 0.05 and are shaded in light grey. Trip total emission estimates based on the following number of one-way trips: 1 for NC 1755, 6 for NC 1797, 6 for NC 1810, and 2 for NC 1869. a


b


c


d

Trip total emissions were estimated for only one trip. Therefore, a coefficient of variation could not be calculated.



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Comparison of Over-the-Rail and Rail Yard ... - ACS Publications

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