Evaluations of in-use emission factors from off-road construction equipment

Accepted Manuscript Evaluations of in-use emission factors from off-road construction equipment Tanfeng Cao, Thomas D. Durbin, Robert L. Russell, David R. Cocker, III, George Scora, Hector Maldonado, Kent C. Johnson PII:

S1352-2310(16)30750-6

DOI:

10.1016/j.atmosenv.2016.09.042

Reference:

AEA 14911

To appear in:

Atmospheric Environment

Received Date: 22 December 2015 Revised Date:

17 September 2016

Accepted Date: 19 September 2016

Please cite this article as: Cao, T., Durbin, T.D., Russell, R.L., Cocker III., , D.R., Scora, G., Maldonado, H., Johnson, K.C., Evaluations of in-use emission factors from off-road construction equipment, Atmospheric Environment (2016), doi: 10.1016/j.atmosenv.2016.09.042. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Evaluations of In-Use Emission Factors from Off-Road Construction Equipment

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Tanfeng Cao1, Thomas D. Durbin1, Robert L. Russell1, David R. Cocker III1, George Scora1,

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Hector Maldonado2 and Kent C. Johnson1*

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Technology (CE-CERT),1084 Columbia Ave, Riverside, CA 92507, USA

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*Corresponding author: Tel: +1951 781 5786; Fax: +1951 781 5790;

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Email Address: [email protected] (Kent C. Johnson)

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University of California, Riverside, College of Engineering, Center for Environmental Research and

California Air Resources Board, 1001 I Street, P.O. Box 2815, Sacramento, CA 95815, USA

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10 Abstract

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Gaseous and particle emissions from construction engines contribute an important fraction

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of the total air pollutants released into the atmosphere and are gaining increasing regulatory

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attention. Robust quantification of nitrogen oxides (NOx) and particulate matter (PM) emissions

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are necessary to inventory the contribution of construction equipment to atmospheric loadings.

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Theses emission inventories require emissions factors from construction equipment as a function

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of equipment type and modes of operation. While the development of portable emissions

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measurement systems (PEMS) has led to increased studies of construction equipment emissions,

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emissions data are still much more limited than for on-road vehicles. The goal of this research

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program was to obtain accurate in-use emissions data from a test fleet of newer construction

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equipment (model year 2002 or later) using a Code of Federal Requirements (CFR) compliant

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PEMS system. In-use emission measurements were made from twenty-seven pieces of

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construction equipment, which included four backhoes, six wheel loaders, four excavators, two

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scrapers (one with two engines), six bulldozers, and four graders. The engines ranged in model

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year from 2003 to 2012, in rated horsepower (hp) from 92 to 540 hp, and in hours of operation

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from 24 to 17,149 hours. This is the largest study of off-road equipment emissions using 40 CFR

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part 1065 compliant PEMS equipment for all regulated gaseous and particulate emissions.

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*Keywords: PEMS, off-road emissions, non-road emissions, real world emissions, 40CFR1065, emissions

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inventory

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Introduction Off-road equipment is one of the most significant sources of nitrogen oxides (NOx) and

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particulate matter (PM). According to U.S. Environmental Protection Agency (EPA) emissions

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inventory, off-road diesel equipment is estimated to be the 3rd largest source for NOx emissions

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and 2nd largest source for PM emissions among all of the mobile sources, representing 14.5% and

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24.3% of total mobile NOx and PM emissions, respectively (EPA, 2011). Although increasingly

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more stringent emission standards are being implemented for off-road engines, there is still a time

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lag between the implementation of these standards and the implementation of similar standards

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for on-road (Federal Register 2004, 2005). Off-road engines also have relatively long lifespans,

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due to their inherent durability. It is anticipated that the relative contribution of these sources will

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continue to increase as on-road emissions continue to be reduced. These factors make the control

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of emissions from off-road equipment one of the more critical areas in terms of reducing

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emissions inventories and protecting public health.

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Developing emissions factors and emissions inventories for off-road equipment has inherently been more challenging than for on-road vehicles. Off-road engines are typically

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certified on engine dynamometer tests that are not necessarily representative of the engine’s

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diverse in-use operation. Although a number of studies have measured in-use emissions from off-

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road equipment (e.g., Abolhassani et al. 2008, 2013), the available data for off-road equipment is

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still considerably more limited compared to on-road mobiles sources, which have been studied

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extensively for decades. Additionally, data on in-use activity patterns is scarce for off-road

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equipment to identify typical equipment operating modes that’s needed to identify the greatest

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contributors to emissions.

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The development of accurate emissions factors for off-road equipment under in-use

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conditions remains an important factor in improving emissions inventories. The continuing

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development of Portable Emissions Measurement Systems (PEMS) has allowed the

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characterization of in-use emissions from off-road equipment. Over the past few years, there has

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been a considerable effort to standardize PEMS measurement to meet regulatory requirements for

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in-use compliance measurements for on-road vehicles and off-road equipment (e.g., Durbin et al.

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2007, 2009a). Much of this work was performed as part of the Measurement Allowance program,

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which included extensive laboratory testing at Southwest Research Institute (SwRI) and in-use

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testing using the University of California Riverside (UCR), College of Engineering, Center for

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Environmental Research and Technology (CE-CERT)’s Mobile Emission Laboratory (MEL)

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(Fiest et al. 2008, Johnson et al. 2008, 2009, 2010, 2011a, 2011b; Khalek et al. 2010; Khan, et al.

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2012; Miller et al. 2006). The MEL has been demonstrated to conform to Code of Federal

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Regulations (CFR) requirements for laboratory grade emission measurements (Durbin et al.

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2009b).

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73 Studies of construction equipment have been carried out over the years using different

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generations of PEMS technology. Gautam et al. (2002) measured in-use emissions using non-

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CFR compliant prototype portable analyzer on a street sweeper, a rubber-tired front-end loader,

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an excavator, and a track-type tractor in the field in an effort to develop test cycles for subsequent

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engines dynamometer testing. Scora et al. (2007) and Barth et al. (2008, 2012) also measured gas

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phase (NOx, CO, CO2) and PM emissions from heavy-duty construction equipment using a non-

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CFR compliant portable gas analyzer and gravimetric based PM from a self-designed mini-

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dilution tunnel, respectively. The EPA and its collaborators have also conducted an extensive

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study of construction emissions in EPA region 7 using CFR compliant PEMS from Sensors Inc.

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(Kishan et al. 2010; Giasnnelli et al. 2010; Warila et al. 2013). Frey and coworkers conducted

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emission and activity studies of construction equipment and studies of how to model their

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emissions impact using non-CFR compliant PEMS system (Abolhasani et al. 2008, 2013; Frey et

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al. 2003, 2008a, 2008b, 2008c, 2010a, 2010b; Lewis et al. 2009a, 2009b, 2011, 2012; Pang et al.

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2009; Rasdorf et al. 2010). Huai et al. (2005) also measured the activity for different fleets of off-

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road diesel construction equipment.

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The primary purpose of this research is to obtain gaseous and PM emissions from highuse and newer off-road construction equipment using a 40 CFR part 1065 compliant PEMS to

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provide accurate estimates of emissions from off-road construction equipment under real-world

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scenarios. The gaseous and PM exhaust emissions and the engine work were measured using

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CFR compliant PEMS on a second-by-second basis for twenty-seven pieces of construction

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equipment. Videotaping and on-site observations were also used to determine the type of

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construction activity (e.g. digging, pushing, idling, moving, etc.) that the equipment was

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performing. This study represents the most robust dataset available for off-road construction

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equipment in terms of the number of pieces of equipment tested and the use of state-of-the-art

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1065-compliant PEMS system.

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Methodology 2.1 Test Matrix Emission measurements were made for the following equipment: four backhoes, six wheel loaders, four excavators, three scrapers (one with two engines tested), six bulldozers, and four

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road graders. The six different types of equipment tested in this study make up about 80% of the

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equipment population in the State of California (CARB 2014). The basic information for the off-

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road equipment tested is summarized in Table 1. (Table S1 in Supplementary Material contains

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more detailed information about the equipment and engines tested). The twenty-seven pieces of

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equipment included seven pieces of Tier 2 equipment with model years ranging from 2003 to

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2007, with horsepower ratings ranging from 92 to 540 hp, and engine hours ranging from 946 to

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17,149 hours. The other twenty pieces of equipment were Tier 3 and Tier 4i equipment with

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model years ranging from 2006 to 2012, horsepower ratings ranging from 99 to 520 hp and

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engine hours ranging from 242 to 5,233 hours. All diesel fuel used in this study is ultra-low sulfur

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diesel (ULSD) with sulfur content less than 15 ppm.

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Backhoe operation included digging with the backhoe and/or the front end shovel, filling in holes with the front end shovel, idling, and general equipment movement. The primary activity

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for three of the wheel loaders was gravel loading into a truck bed, while two other wheel loaders

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were primarily digging (one also did some filling), and one wheel loader was primarily cleaning

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and smoothing the shoulder of a road (similar to a road grader). One excavator was measured

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during digging, movement, and idling; one excavator had only limited emission data for loading

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and idling; the last two excavators were part of a designed study that included moving from place

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to place, trenching with various arm swings, backfilling, dressing, and idling. Three scrapers were

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tested for this program. One scraper worked near a landfill scraping up dirt to cover the trash.

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This scraper had a front engine that is used to move the machine and a back engine to operate the

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machinery that scrapes the dirt up into the hopper. The second scraper had a single engine and a

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hopper that is lowered so that the front edge cuts into the soil and forces the soil into the hopper.

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The six bulldozers tested were working in either a landfill or a riverbed; their operations included

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idling and pushing trash and/or dirt. The four graders were used for grading (scraping) dirt roads;

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and their operations included idling, moving, and grading.

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2.2 PEMS Description Two different gaseous PEMS systems were utilized over the course of the test campaign for the measurement of gaseous emissions. For the first ten pieces of equipment, the gaseous 4

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emissions were measured with a SEMTECH DS PEMS, and the last seventeen pieces of

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equipment were measured with an AVL 493 PEMS. Both systems measure NOx using a non-

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dispersive ultra-violent (NDUV) analyzer, total hydrocarbons (THC) using a heated flame

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ionization detector (HFID), carbon monoxide (CO), and carbon dioxide (CO2) using a non-

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dispersive infrared (NDIR) analyzer. Both systems collected raw exhaust through a sample line

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heated to 190°C, consistent with the conditions for regulatory measurements for THC. Therefore,

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the two systems were similar, notwithstanding minor differences in design and packaging. The

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reason for the analyzer switch was solely based on PEMS availability at the time of testing.

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Additionally, both PEMS were evaluated by UCR during previous studies and found to be

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accurate for gaseous measurement levels expected during this research (Johnson 2008, Johnson

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2009, Fiest 2008).

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The PM analyzer used for all twenty-seven units was an AVL Micro Soot Sensor (MSS) 483 with a constant filter flow heated gravimetric filter attachment. The MSS measures soot

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concentration on a second–by-second basis using the photo-acoustic principle (Schindler et al.

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2004). The gravimetric filter attachment measurement is used to calibrate the time resolved MSS

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soot measurements by comparing the accumulated soot signal from the MSS with the total mass

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from the filter. The range of calibration factors observed varied from 1.15 to 1.25 for this testing

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project. This very same PM unit participated in the 2010 EPA PM measurement allowance study

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and showed excellent correlation to the reference PM 2.5 method (Johnson et al. 2011a).

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Three different sizes of SEMTECH’s exhaust flow meters (EFM) were used to measure

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real-time exhaust flow in this study depending on the test engine displacement. Other important

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test parameters collected include location (via GPS), ambient temperature, pressure, and humidity.

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The majority of the vehicles tested had ECM data available; when necessary, special or

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manufacturer supplied logging tools were used to log the desired ECM channels. For two vehicles,

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where no ECM was available, the engine speed and engine percent load were estimated using

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real-time exhaust flow and brake-specific fuel consumption (BSFC). Videotaping and on-site

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observations were used to determine the type of construction activity (e.g., digging, pushing,

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idling, moving, etc.) that the equipment was performing.

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2.3 PEMS Installation The complex design of off-road equipment required a unique installation approach for each equipment type. A custom steel frame instrument package with gaseous PEMS, PM PEMS, 5

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EFM, data logging equipment, batteries, battery charger, and other necessary operating auxiliary

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items was built as a single unit complete package. This PEMS package was warmed up and

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calibrated prior to installing it onto the off-road equipment. A calibration procedure was

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performed on-site daily, which includes a leak check and zero-span calibration procedure.

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Additional calibration procedures include monthly linearity and other checks needed for 1065

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compliance. Once the PEMS package was secured with heavy duty ratcheting straps, only the

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routing of the exhaust pipes to the EFM, logging of the ECM signals, and installing the auxiliary

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generator for power was required.

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Depending on the equipment type, the CE-CERT PEMS package generally fit best on the

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roof or large section of the hood due to its relatively large footprint. This study avoided testing

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small sized equipment where the weight of the PEMS package could impact the emissions.

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Vibration isolation mounts installed onto the steel frame along with six-inch-thick high-density

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foam pad between the frame and the vehicle provided vibrational dampening. Weather shielding

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protected the PEMS package from direct sunlight.

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Results

Results from emissions testing of off-road equipment are usually expressed in units of grams of pollutant per horsepower-hour (or per kilowatt-hour) of work done by the engine as it’s

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the reporting units for engine certification purposes. However, emissions can also be expressed in

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units of grams of pollutant per hour (g/hour) or in units of grams of pollutant per kilogram of fuel

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consumed (g/kg-fuel). In terms of precision, emissions in g/hr are the most precise as they are a

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direct measurement from the PEMS, emissions in g/kg-fuel are the next most precise as off-road

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equipment fleet usually track accurate fuel usage, and emissions in g/hp-h are the least precise of

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the three measurement units as the true brake horsepower and torque versus engine speed for the

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particular engine is seldom known for off-road engines. Emissions results are reported using all

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three metrics in Table S2 of Supplementary Material. In this paper emissions comparisons are

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presented in g/hp-h in Table 2. Valid work values were not obtained for unit 8_excavator so no

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brake specific emission values are available for that unit; emissions for this excavator was limited

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to 30 minutes due to failure of the exhaust boot connecting the stack to the EFM, Nevertheless,

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observation of the unit throughout the work day indicated that this unit was repeating the same

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operation throughout the full work day, therefore the data on a g/hr and g/kg of fuel basis

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represent valid measurements can still be found on Table S2 in Supplementary Material.

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The results presented in units of g/hp-h provide a 'high level' comparison against the engine certification standards. It should be noted that the certification test cycle for Tier 2 and

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Tier 3 diesel off-road engines is an 8-mode steady-state engine dynamometer certification test

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cycle, while Tier 4 diesel off-road engines are required to meet emissions standards for both a

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steady state cycle and the nonroad transient cycle. As actual in-use engine/equipment operation is

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highly transient, with rapid and repeated changes in engine speed and load, the comparison of the

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in-use emissions with the certification levels is probably more directly applicable for the Tier 4

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engines that are evaluated for transient operation as part of the certification process. In addition,

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the average engine “load factors” (a measure of how hard the engine is working) can be different

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than the certification test cycle load factors since the in-use testing was not designed to exactly

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mimic the certification cycle. Thus, results are not expected to be directly comparable to the

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certification test results, but nevertheless provide an indication of how emissions from actual, in-

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use diesel engines compare against their engine certification standards.

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3.1 Idle Emissions

Idle emissions represent a large fraction of all equipment usage (by time). Idle emissions for each pollutant are summarized in Table S4 in Supplementary Material in g/hr and g/hr-L,

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where L is the engine displacement in liters. Overall, the idle emissions for CO2 correlate with

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engine displacement, as large engines require more fuel during engine idle. Load-specific idle

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emissions are not presented because the load during idle is near zero, and the idle ECM load

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estimates are far less accurate.

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The overall in-use brake power was typically light (Table 2): 8 units with rated hp’s

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between 92 to 171 had average in-use hp’s <50 with average engine loads between 26.0 and

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52.3%; 11 units with rated hp’s between 148 and 296 had average in-use hp’s between 51.8 and

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90.7 with average engine loads between 27.6 and 56.1%; 4 units with rated hp’s between 193 and

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316 had average in-use hp’s between 100 and 150 with average engine loads between 35.3 and

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58.4%, and 3 units with rated hp’s between 280 to 540 had average in-use hp’s between 161 and

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275 with average engine loads between 54.5 and 72.8 %.

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The California Air Resources Board’s 2011 Inventory Model for off-road diesel equipment

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provides reference load factors (LF) for each type of off-road equipment. The EPA Nonroad

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model also has load factors for many different pieces of equipment. Load factors are used to 7

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adjust the rated horsepower’s of equipment to reflect actual operation conditions. The load factor

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is the ratio of the average horsepower during a working period to the maximum horsepower for

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the given engine. Since this information has not been typically available the inventory models

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have used surrogate methods to estimate load factors. Table 3 compares average measured LFs in

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this study to the current LFs used in the inventory models. With the exception of the scrapers, the

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measured load factors are closer to the ARB load factors than to the EPA load factors. However,

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at two times the standard deviation the measured load factors encompass both the ARB and EPA

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load factors.

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The difficulty with LF being a good metric for emissions estimation is that there is no

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measurable work associated with the idling emissions and thus the total emissions per unit work

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and per unit fuel are higher. Figure 1 shows how two Units can have the same LF but

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significantly different duty cycles. Unit 1 is operated at various load conditions with frequent idle

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modes simulating performing work that requires decision making through the operation and Unit

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2 represents steady work with a simple break between tasks. In both cases the LF is 35, but the

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percentage of idle time and loaded conditions varies significantly between the two Units, thus

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affecting the overall emissions as a function of the load. The emissions impact of the load factor

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will be discussed more in the subsequent section, but future emission models should consider

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evaluations of LF for idle and work conditions separately to truly characterize the emissions from

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a fleet.

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3.3 NOx Emissions

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Plots of the overall brake specific NOx (bsNOx) emissions for each of the units tested are

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presented in Figures 2 and 3. In Figure 2 the results are sorted by Tier and engine hours from left

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to right. The equipment type is indicated by BH for Backhoe/Loader, WL for Wheel Loader, SC

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for Scraper, BD for Bulldozer, HB-BD for Hybrid Bulldozer, EX for Excavator, HB-EX for

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Hybrid Excavator, GR for Grader, and GR-DPF for the grader with an aftermarket DPF. The red

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bars are the CARB zero-hour emission standards as given in the CARB Executive Order for the

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equipment Engine Family Name. For Tier 2 and Tier 3 the CARB standards are for NMHC+NOx

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so the measured bars are for NOx+0.98*THC. CH4 is typically not measured with a PEMS,

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therefore NMHC is calculated as 0.98* THC, as per 40 CFR Part 1065. For Tier 4 the CARB

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standards are for NOx so the measured bars are for NOx. Seven of the twenty-seven units tested

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are Tier 2, fifteen are Tier 3, and five are Tier 4i. For Tier 2, all of the NMHC+NOx are

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essentially equal to or lower than the standards. For Tier 3, 7 of the 15 have NMHC+NOx

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emissions significantly higher than the standards. For Tier 4 all of the NOx emissions are slightly

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above the standards. It should be emphasized that the NMHC+NOx and NOx standards are based

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on engine dynamometer measurements over specific test cycles, so any comparisons with

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emissions from the real-world operation are not meant to imply that an individual piece of

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equipment may or may not be operating within standard limits. There is no indication that

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NMHC+NOx or NOx emissions increase relative to the CARB standards as the engine hours

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increase with this data set.

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The NOx emissions show generally lower trends for engines certified to more stringent

emissions standards. However, the highest brake specific NOx (bsNOx) emissions are from a 2011

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wheel loader (#14, Tier 3). This is attributed to the differences in the type of work being done by

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each test unit; this wheel loader has the lowest engine load of any engine tested. Further, the other

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two wheel loaders (#18 and #20) have the same model engine, similar engine hours, MYs, and

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engine displacements, but shows almost 50% less bsNOx emissions. The average engine percent

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load over the time of operation was 56% and 36%, respectively, for these two units with lower

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NOx emissions compared to the average percent load of 26% for unit #14. For on-road engines

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the percent engine load threshold for Not-to-Exceed (NTE) in-use compliance testing is 30%,

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thus, operation below 30% is excluded from compliance testing. While NTE is not currently

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applied to off-road engines, operation below 30% occurs during in-service operation and can even

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represent the overall average for some in-service operations, as shown by unit #14.

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Figure 3 presents the same emissions as Figure 2 but the data is now sorted by engine Tier level and engine load factor (ELF). The ELF varies from 0.26 to 0.63 for Tier 2, 0.19 to 0.58

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for Tier 3 (doesn’t exceed 0.36 until after 3_WL), and from 0.28 to 0.41 for Tier 4. For a given

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emission standard there is a general trend for the measured emissions to decrease as the ELF

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increases. Higher ELF’s appear to have a more significant effect on the emission factors on a

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work basis than engine hours or MY. The ELF for wheel loader 6_WL and grader 13_GR is 0.32

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and for wheel loader 20_WL and excavator 26_EX_the ELF is 0.33. The NMHC+NOx emissions

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for 6_WL are higher than for 13_GR and the NMHC+NOx emissions for 20_WL are higher than

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for 26_EX. Without considering other information one might conclude that this observation

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indicates that the type of work being performed influences the emissions. However, 6_WL has a

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Komatsu 273 hp, 11.0 liter engine versus the Perkins 163 hp, 6.6 liter engine for the 13_GR and

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the 20_WL has a Perkins 171 hp, 6.6 liter engine versus a Komatsu 155 hp, 4.5 liter engine for

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the 26_EX. Similarly, bulldozer 23_BD has higher NOx emissions than bulldozer 24_BD even

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though they have the same ELF of 0.33. Bulldozer 23_BD has a Caterpillar 316 hp, 15.2 liter

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engine versus a Caterpillar 223 hp, 9.3 liter engine for 24_BD. We attribute the higher emissions

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in these comparisons to the higher engine displacement rather than the physical work being

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performed.

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Plots of the overall PM emissions results for each of the units tested are presented in

Figures 4 and 5. The Tier 2 PM emissions are all below the standards. Six of the 15 Tier 3 PM

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emissions are significantly higher than the standards and 5 of them are for the same engines

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having significantly higher NMHC+NOx emissions than the standards. Unit 11_EX has

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significantly higher PM than the standard whereas for NMHC+NOx it had essentially the same

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emissions as the standard. This is the oldest Tier 3 equipment tested so the higher PM may

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indicate some engine deterioration. All units with diesel particulate filters (DPFs) show

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significant reductions (>90%) in PM in comparison with those units without aftertreatment. Note

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that for Tier 4i the measured PM emissions have been multiplied by 50 so that they will be visible

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in the figures. Equipment 23_BD has a ~50 minute DPF regen included in the emission

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measurements and its PM is still well below the emission standard. If the DPF regen is not

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included then the PM emissions are 0.00121 g/bhp-h and the bar in Figure 4 and 5 would be

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0.0605 g/bhp-h. There is a slight trend of lower brake specific PM (bsPM) emissions for older

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MYs when comparing units without aftertreatment (Figure 4) although any such trend is

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complicated by differences in the load factor between units. It is also possible that the engine

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calibration differences needed to achieve bsNOx emissions for the newer equipment could lead to

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increases in bsPM, although this is likely a secondary factor compared to the engine load

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differences. One of the units (#17, a 2010 grader) is equipped with an aftermarket DPF. The

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bsPM emissions from this unit averaged 29.1 mg/hp-h overall and ranged from 100.8 to 2.4

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mg/hp-h depending on the operating mode. The average bsPM for five Tier 4 interim units was

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1.1 mg/hp-h, suggesting the particular aftermarket DPF is not as efficient as the ones on the

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factory equipped DPF Tier 4 interim machines.

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The trend for lower emissions with increasing ELF (Figure 5), for engines produced to

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the same emissions standards, is not as pronounced as it is for NOx emissions. In Figure 5 the

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comparison between units having exactly the same ELF only holds for 20_WL and 26_EX. The

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most likely reason that the comparison between 6_WL and 13_GR doesn’t hold is that 6_WL has

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an engine produced to a lower PM standard than 13_GR. The DPF regeneration in the emissions

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from 23_BD rules out making a comparison between it and 24-BD.

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3.5 Other Criteria Emissions Plots of the overall THC emissions results for each of the units tested are presented in

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Figures 6 and 7. Since there are no CARB standards for THC emissions only the measured

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emissions are shown in these figures. The general overall trend of THC emissions in Figure 6 is

344

similar to the general overall trend of NOx emissions in Figure 4 with some, but not all, of the

345

same units that had NOx emissions significantly higher than the standards having higher THC

346

emissions than the rest in the Tier group. Two units (#1 and #5, both 410 Deere backhoes)

347

showed relatively high THC emissions of greater than 0.63 g/hp-h, which is almost two times

348

more than the other units tested. As can be seen in Figure 7 equipment 1_BH has the lowest ELF

349

but there are two units having lower ELF’s than equipment 5_BH which suggests the high THC is

350

not necessarily due to light load operation. A similar Deere backhoe model 310 (4_BH) used over

351

a very similar duty cycle, for example, showed about half the emissions of the 410 backhoe. It is

352

unclear what caused the higher THC emissions for the 410 backhoe compared to the 310

353

backhoe. The Tier 4i THC and CH4 emissions were on average 71% and 84% lower than the Tier

354

3 and Tier 2 THC and CH4 emissions on a g/hp-h basis, respectively.

356

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Plots of the overall CO emissions results for each of the units tested are presented in Figures 8 and 9. The general overall trend of CO emissions in Figure 8 is similar to the general

358

overall trend of NOx emissions in Figure 4 with some, but not all, of the same units that had NOx

359

emissions significantly higher than the standards also have CO emissions higher than the

360

standards. The general overall trend of CO emissions in Figure 9 is similar to the general overall

361

trend of NOx emissions in Figure 5 but the decrease in the CO emissions is generally greater than

362

the decrease in NOx emissions as the ELF increases. The CO emissions for the Tier 4i units are

363

essentially at the limits of detection of the PEMS, as indicated by the negative CO emissions

364

values for all but one of the units.

366

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3.6 Comparison with Prior Studies

367

Frey and co-workers performed some of the most recent measurements of emissions from

368

off-road construction equipment (Frey et al. 2010a, 2010b). With the PEMS equipment they were

369

using they measured CO2, CO, NOx, THC and fuel rate in g/sec and reported emissions in g/hr

370

and g/gal of fuel. They did not have measurements of the engine ECM and therefore could not 11

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calculate brake-specific emissions, and also did not measure PM emissions. The majority of their

372

data is for Tier 0 and Tier 1 equipment. Their results in g/gal for Tier 2 and Tier 3 equipment are

373

presented in Table S3 of Supplementary Material, along with our results for comparable Tier 2

374

and Tier 3 equipment. Figure 10 shows a comparison of NOx emissions between Frey et al. and

375

this study sorted by Tier level and equipment types. Tier 2 NOx emissions from Frey study

376

ranged from 73 to 172 g/gal compared to 80 to 96 g/gal in the current study. For Tier 3, the

377

comparison was 58 to 86 g/gal for Frey et al. and 50 to 101 for the current study. Overall, the

378

emissions in g/gal of fuel in our study are similar to the results in the Frey and co-worker studies

379

(Frey 2010a, 2010b). In some cases, however, Frey et al. measured considerably higher emissions

380

for specific pieces of equipment (i.e., MG2-04-0SH, BH3-04MS, BH5-04MS). This suggests the

381

potential importance of high emitters in the construction equipment population, and that further

382

testing of a wide range of in-use equipment could provide a more comprehensive assessment of

383

in-use construction emissions.

384 385 386 387

3.7 Discussion

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The results of this study show that in-use emissions show emissions trends that are somewhat consistent with the different certification levels of specific engines. This is particularly

389

true for the comparisons between the Tier 4 with earlier engine certification levels. Another key

390

finding from this study is that in-use brake-specific emissions for off-road equipment can vary

391

significantly within a given engine Tier, primarily depending on the engine load factor and the

392

engine displacement.

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For NOx emissions, the lowest NOx emissions were found from the Tier 4 engines, while the highest emissions were generally found for the Tier 2 engines with the higher certification

396

standards and high number of engine hours. The NOx emissions for the Tier 4i units are lower

397

than all of the Tier 3 units and, with one exception, all of the Tier 2 units. The NOx emissions for

398

the Tier 2 and 3 units do not show strong trends as a function of model year for any of the units of

399

comparison. Engine load factor appears to be an important factor for NOx emissions, with

400

equipment with low average engine loads factors showing generally higher NOx emissions on a

401

g/hp-h basis. All of the Tier 3 units with a CARB NOx standard of 3.0 g/hp-h had higher NOx

402

emissions than the older Tier 2 units having the same CARB standard. The Tier 2 engines were

403

on the scraper (09_SC and 10_SC) and had relatively high load factors of 0.58 and 0.51,

404

respectively, while the Tier 3 engines had load factors from 0.19 to 0.58, with only 3 of the 13

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Tier 3 engines having load factors above 0.38. This suggests that in some cases the type of engine

406

operation can have a more significant impact on emissions that the age/Tier of the engine for pre-

407

Tier 4 engines. The overall in-use brake power average load factors over all Tiers were between

408

0.19 and 0.41 for nearly all units, with only 7 units having average load factors >0.41, and only

409

one unit having an average load factor of 0.63.

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410 411

Engine displacement or manufacturer could be another important consideration in

comparing emissions from different equipment. The displacements differed for the Tier 2 and

413

Tier 3 units, with the Tier 2 units having displacements of 8.8 and 15.2 liters and Tier 3 engines

414

having generally smaller displacements ranging from 4.5 to 11.0 liters. The possible effect of

415

displacement/manufacturer can be seen when comparing 6_WL with 20_WL, which have engines

416

with 11.0 liter and 6.6 liter displacements, respectively. Although the load factors were similar at

417

0.32 for 6_WL and 0.33 for 20_WL, the NOx emissions were 5.27 and 3.64 g/hp-h, respectively.

418

The PM emissions showed opposite trends for 6_WL and 20 WL, with emissions of 0.0842 and

419

0.333 g/hp-h, respectively, suggesting there is some tradeoff between NOx and PM emissions for

420

these engines.

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421 422

While the data indicate that for a given engine Tier the emissions are primarily influenced by the engine load factor and secondarily by the engine displacement, there are some emissions

424

which cannot be explained only by these factors. There is not enough information available in the

425

present dataset to provide a plausible explanation of other factors influencing these emissions.

427

The Tier 4 units with DPFs all showed significant reductions in PM in comparison with

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those units without aftertreatment. For the Tier 2 and Tier 3 units, the majority of the units had

429

PM emissions lower the CARB standard. Five of the six units that had higher bsPM emissions

430

relative to the standard had load factors of ≤ 0.33, and engines with the same displacement of 6.6

431

liters. These units have PM emissions from 0.10 to 0.34 g/hp-h. One of the units (#17 a 2010

432

grader) was equipped with an aftermarket DPF. The bsPM emissions from this unit averaged

433

0.029 g/hp-h overall, which is above the 0.0016 g/hp-h average of the four Tier 4i units that

434

didn’t have a DPF regeneration, and even above the 0.007 g/hp-h for the Tier 4 unit that had a

435

regeneration. This aftermarket DPF may not be quite as efficient as DPF’s on the Tier 4i units,

436

but it still has average PM emission rates that are considerably lower than those for the non-DPF

437

equipped Tier 2 and Tier 3 units. It is not known how many hours of use this aftermarket DPF has

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438

had, so it could be that the difference in comparison with the tier 4 DPF equipment is due to

439

deterioration with age.

440 The THC emissions ranged from 0.04 to 0.68 g/hp-h. Two units (#1 and #5 both 410

442

Deere backhoes) showed relatively high THC emissions of greater than 0.63 g/hp-h, which is

443

almost two times more than the other units tested. The Tier 4i THC emissions were considerably

444

lower than the Tier 2 and Tier 3 THC and CH4 emissions, averaging 84% and 72% lower on a

445

g/hp-h basis, respectively. CO emissions did not show a trend of increases with hours of engine

446

use. The CO emissions ranged from -0.15 to 3.39 g/hp-h. Three units in the 175 to 600 hp range

447

have average emissions that are higher than the 2.6 g/hp-h standard. Two units in lower power

448

categories (50 hp to 175 hp) also had average CO emissions in the same range, but they were

449

below the 3.7 g/hp-h standard for the smaller engine category. The CO emissions for the Tier 4i

450

units were on average 99% lower than the Tier 3 and Tier 4i units, and were essentially at the

451

limits of detection of the PEMS.

452 453

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The large variability in emissions, especially for NOx and PM, could have important implications for developing accurate emissions inventories and models. This variability is

455

primarily due to differences in engine load factors for different types of work and combinations

456

of work and idle time and the displacement of the engines. Load factors are significantly affected

457

by idle percentage, as more engine idle operation over a given test interval will lower the average

458

power. Thus, idle and loaded conditions should be modeled separately for Load factor and

459

emission estimates. Additional activity studies will be important in understanding the overall

460

emissions profiles of construction equipment and their real-world load factors. This could include

461

data logging of the ECM, GPS data for positional information, as well as video to better

462

differentiate between different modes of operation. As an alternative to activity measurements, it

463

may be possible to investigate construction permits to identify work modes, tons-earth to be

464

moved, and project durations to estimate idle and work based Load Factors and idle/work percent

465

time fractions. In general, the development of emissions factors as a function of load factors will

466

likely also be important in further emissions inventory development.

468 469 470

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Acknowledgements The authors would like to thank the California Air Resources Board and the California Department of Transportation for their financial support, Don Pacocha, Edward O’Neal, and Joe

14

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Valdez for conducting the emission tests, B&B Equipment Rental, Kurt VanDusen and

472

employees of Riverside Waste Management, Luke Trickett and employees of Waste

473

Management Inc., Steve McFarland, Kevin Lough and employees of the County of Riverside

474

who made equipment and testing locations available and provided equipment to place the

475

emission measurement equipment on the construction equipment.

476

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636

Cycles, and Activity of Diesel Nonroad Vehicles. Proceedings of the 23rd CRC Real World

637

Emissions Workshop, San Diego, CA, April.

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Table 1: Detailed information of the off-road equipment tested during in-use operation.

Plot ID

Type

Engine Mfg

Model

Year

1_BH

1_Backhoe

Deere

410J

2007

12/7/2010

2_BH

2_Backhoe

Deere

310SJ

2010

12/8/2010

3_WL

3_Wheel loader

Deere

644J

12/9/2010

4_BH

4_Backhoe

Deere

310SG

12/10/2010

5_BH

5_Backhoe

Deere

2/9/2011

6_WL

6_Wheel loader

2/10/2011

7_WL

3/17/2011

Tier

2

3

M AN U

12/3/2010

EPA

Rated

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Tested

Equipment

Dis. (L)

Power (bhp)

Engine Hours

4.5

99

1182

6.8

99

242

SC

Date

Work Performed

Digging and backfilling Digging and backfilling Digging and

3

6.8

225

1735

2006

2

4.5

92

2599

410G

2006

2

4.5

99

946

Komatsu

WA470-6

2009

3

11.04

273

900

7_Wheel loader

Caterpillar

928G

2004

2

6.6

156

2294

8_EX

8_Excavator

Caterpillar

345D

2008

3

12.5

520

n/a

Loading trucks

4/20/2011

9_SC

9_Scraper

2

8.8

280

>10000

Scraping dirt

4/21/2011

10_SC

10_Scraper

2

15.2

540

>10000

Scraping dirt

5/4/2012

11_EX

11_Excavator

3

12.1

269

5233

Loading trucks

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2007

AC C

638

Caterpillar

637E

Caterpillar

637E

Volvo

EC360B

2006 (Rebuild) 2006 (Rebuild) 2006

21

backfilling Digging and backfilling Digging and backfilling Loading trucks Loading and smoothing asphalt

ACCEPTED MANUSCRIPT

12_BD

12_Bulldozer

Caterpillar

D8R

2003

2

14.8

338

17149

Pushing trash

10/16/2012

13_GR

13_Grader

Perkins

120M

2008

3

6.6

163

3815

Grading shoulder

10/17/2012

14_WL

Caterpillar

928Hz

2011

3

10/18/2012

15_GR

15_Grader

Caterpillar

120M

2010

3

10/22/2012

16_GR

16_Grader

Perkins

120M

2008

3

17_Grader

Caterpillar

120M_DPF

2010

Caterpillar

928Hz

Caterpillar

613G

Caterpillar

928Hz

Caterpillar

D6T

Caterpillar

18_Wheel

18_WL

10/30/2012

19_SC

10/31/2012

20_WL

11/13/2012

21_BD

21_Bulldozer

22_HB-

22_HB

BD

bulldozer

12/6/2012

23_BD

23_Bulldozer

Caterpillar

12/11/2012

24_BD

24_Bulldozer

Caterpillar

25_HB-

25_HB

BD

bulldozer

26_EX

26_Excavator

27_HB-

27_HB

EX

excavator

12/12/2012 3/1/2013 2/28/2013

19_Scraper 20_Wheel loader

171

289

Cleaning ditch

6.6

163

1308

Grading dirt road

6.6

163

2706

Grading dirt road

3

6.6

168

952

Grading dirt road

2011

3

6.6

171

345

Digging dirt

2010

3

6.6

193

439

Scraping dirt

2011

3

6.6

171

242

2012

4i

9.3

223

24

Pushing Rock

D7E (hybrid)

2011

4i

9.3

296

2528

Pushing trash

D8T

2012

4i

15

316

32

Pushing Rock

2012

4i

9.3

223

44

D6T

AC C

12/4/2012

loader

EP

10/29/2012

6.6

SC

DPF

M AN U

17_GR-

loader

TE D

10/23/2012

14_Wheel

RI PT

5/14/2012

Grading road shoulder

Building slope, pushing dirt Building slope,

Caterpillar

D7E (hybrid)

2011

4i

9.3

296

589

Komatsu

PC200

2007

3

4.5

155

2097

Digging Trench

2012

3

6.7

148

245

Digging Trench

Komatsu

HB215 (hybrid)

22

pushing dirt

ACCEPTED MANUSCRIPT

639

EPA Tier

Plot ID

Power 3

eLoad

kg/hr

bhp

%

NOx

THC

mg PM 5

435

0.68

3.72

0.10

133

0.27

624

2.12

4.8

0.28

131

0.37

557

1.51

5.19

0.32

126

44.2

0.39

596

1.97

4.99

0.64

126

61.1

0.58

507

3.06

1.78

0.28

129

54.5

0.51

441

1.88

1.95

0.10

139

32.6

0.26

615

2.51

5.33

0.68

154

55.0

0.50

587

0.93

2.86

0.21

274

81.2

41.0

0.36

572

2.91

4.50

0.08

128

69.0

49.2

0.45

547

1.00

2.65

0.17

109

29.6

214.5

72.8

04

2

7_WL

8.3

42.4

29.8

06

2

4_BH

5.9

33.7

40.4

06

2

5_ BH

7.3

38.8

25.9

161.3

38.3

274.6

9_ SC

1

2

10_ SC

07

2

1_ BH

5.0

25.8

06

3

11_EX

25.1

134.5

07

3

3_WL

14.6

07

3

26_ EX

12.0

3

8_EX

28.4

08

3

13_GR

10.6

08

3

16_GR

09

3

6_WL

10

3

2_ BH

10

3

15_GR

10

3

10 11

4

n/a

n/a

n/a

n/a

n/a

n/a

n/a

n/a

51.8

34.1

0.32

641

2.08

4.24

0.29

365

8.4

45.0

32.2

0.28

581

3.04

3.59

0.26

491

15.5

87.1

n/a4

0.32

567

3.39

5.16

0.11

84.2

8.6

45.3

52.3

0.46

606

1.37

3.35

0.24

97.0

7.4

38.6

28.2

0.24

601

2.49

3.78

0.30

478

17_GR-DPF

12.1

68.4

42.8

0.41

555

1.91

2.89

0.16

29.1

3

19_SC

19.9

100.7

58.4

0.52

622

1.36

3.13

0.05

142

3

14_WL

5.8

31.9

26.0

0.19

573

2.67

5.71

0.30

324

EP

08

TE D

06

0.63

M AN U

12_BD

2

Brake Specific Emissions (g/hp-h) CO

2

06

Factor (ELF)

CO2

03

1

Engine Load

SC

MY 20xx

Fuel 2

RI PT

Table 2: Overall brake specific non-idle averaged brake specific emissions summary for each of the 27 units tested.

AC C

640

23

ACCEPTED MANUSCRIPT

648

18_WL

16.0

89.9

56.1

0.53

558

1.45

3.14

0.15

175

11

3

20_WL

11.3

56.1

36.0

0.33

634

1.74

3.39

0.25

333

11

3

27_HB-EX

9.3

55.6

43.9

0.38

527

0.93

3.07

0.07

152

11

4i

22_ HB-BD

19.9

106.7

35.3

0.36

590

0.43

1.89

0.09

0.36

11

4i

25_HB-BD

14.4

82.2

27.6

0.28

555

-0.09

1.70

0.04

0.18

12

4i

21_ BD

19.1

90.7

40.6

0.41

665

-0.08

1.60

0.04

0.33

12

4i

23_ BD

23.4

104.0

39.4

0.33

712

-0.15

2.14

0.06

7.03 6

12

4i

24_ BD

14.2

74.5

34.5

0.33

605

-0.14

1.62

0.04

0.26

SC

Rebuilt engine Averaged fuel rate calculated based on emissions measurements 3 Power estimated from manufacture supplied lug curves 4 No ECM data 5 Total PM using AVL’s gravimetric span method 6 DPF regen occurred 2

M AN U

1

RI PT

3

Table 3: Comparisons of modeled and measured engine load factors

TE D

641 642 643 644 645 646 647

11

ARB LF, Offroad Inventory Model39 0.43 NA 0.38 NA 0.41 0.36 0.48 0.37

EP

Equipment Type

AC C

Bulldozers Hybrid Bulldozers Excavators Hybrid Excavators Graders Wheel Loaders Scrapers Backhoes

EPA LF, Nonroad Inventory Model42 0.59 NA 0.59 NA 0.59 0.59 0.59 0.21

649

24

LF measured in this study Units Load Factor Tested Average Std. Dev. 4 2 2 1 4 6 3 4

0.43 0.32 0.47 0.38 0.31 0.33 0.54 0.37

0.14 0.06 0.04 NA 0.07 0.11 0.04 0.08

ACCEPTED MANUSCRIPT

650

Unit 1 LF

Unit 2 LF

Unit 1 Ave LF

Unit 2 Ave LF

120 Both Units have the same average LF over the 7 hours but different duty cycles

RI PT

80 60 40

SC

Load Factor

100

0 0

1

2

651 652

M AN U

20

3

4 Time (hours)

5

6

7

Figure 1 Simulated duty cycles for two Units with the same load factor 7

TE D

5

2 1

EP

4 3

CARB Standard

AC C

NOx Emissions (g/hp-hr)

Measured

6

5_BH 1_BH 7_WL 4_BH 9_SC 10_SC 12_BD 2_BH 20_WL 27_HB-EX 14_WL 18_WL 19_SC 6_WL 15_GR 3_WL 26_EX 16_GR 13_GR 11_EX 8_EX 17_GR-DPF 21_BD 23_BD 24_BD 22_HB-BD 25_HB-BD

0

653 654 655

2

3

3-DPF

4i

Figure 2: Measured brake specific NOx emissions by Tier and engine hours and CARB zero hour standards

25

8

5_BH 1_BH 7_WL 4_BH 9_SC 10_SC 12_BD 2_BH 20_WL 27_HB-EX 14_WL 18_WL 19_SC 6_WL 15_GR 3_WL 26_EX 16_GR 13_GR 11_EX 8_EX 17_GR-DPF 21_BD 23_BD 24_BD 22_HB-BD 25_HB-BD

AC C PM Emissions (g/hp-hr)

657 658

659

660 661 0.5 Measured

0.4

0.3

0.2

TE D

656

EP 2

Figure 3: Measured brake specific NOx emissions by Tier and engine load factor and CARB zero hour standards 0.6

M AN U

0

SC

1_BH 7_WL 4_BH 5_BH 10_SC 9_SC 12_BD 14_WL 15_GR 16_GR 6_WL 13_GR 20_WL 3_WL 27_HB-EX 26_EX 2_BH 11_EX 19_SC 18_WL 8_EX 17_GR-DPF 25_HB-BD 23_BD 24_BD 22_HB-BD 21_BD

NOx Emissions (g/hp-hr) 4

3

2

1

RI PT

ACCEPTED MANUSCRIPT

7

6 Measured

3

2

3

26

CARB Standard

5

3-DPF

3-DPF

4i

CARB Standard

0.1

0

4i

Figure 4: Measured brake specific PM emissions by Tier and engine hours and CARB zero hour standards.

ACCEPTED MANUSCRIPT

RI PT

SC

M AN U

CARB Standard

TE D

Measured

EP

0.6

0.5

0.4

0.3

3-DPF 4i

4i

1_BH 7_WL 4_BH 5_BH 10_SC 9_SC 12_BD 14_WL 15_GR 16_GR 6_WL 13_GR 20_WL 3_WL 27_HB-EX 26_EX 2_BH 11_EX 19_SC 18_WL 8_EX 17_GR-DPF 25_HB-BD 23_BD 24_BD 22_HB-BD 21_BD

0.2

0.1

0

3

3-DPF

AC C

PM Emissions (g/hp-hr)

2

Measured

3

Figure 5: Measured brake specific PM emissions by Tier and engine load factor and CARB zero hour standards

0.80

0.70

0.60

0.50

0.40

0.30

0.20

0.10

0.00

2

Figure 6: Measured brake specific THC emissions by Tier and engine hours

27

5_BH 1_BH 7_WL 4-BH 9-SC 10-SC 12_BD 2-BH 20-WL 27-HB-EX 14_WL 18_WL 19_SC 6_WL 15-GR 3_WL 26_EX 16_GR 13_GR 11_EX 8_EX 17_GR-DPF 21_BD 23_BD 24_BD 22_HB-BD 25_HB-BD

662

663 664

665

666

THC Emissions (g/hp-hr)

ACCEPTED MANUSCRIPT

THC Emissions (g/hp-hr)

RI PT

SC

M AN U TE D EP

Measured

3 3-DPF

4i

AC C

0.80

0.70

0.60

0.50

0.40

0.30

CARB Standard

3-DPF

1_BH 7_WL 4_BH 5_BH 10_SC 9_SC 12_BD 14_WL 15_GR 16_GR 6_WL 13_GR 20_WL 3_WL 27_HB-EX 26_EX 2_BH 11_EX 19_SC 18_WL 8_EX 17_GR-DPF 25_HB-BD 23_BD 24_BD 22_HB-BD 21_BD

0.20

0.10

0.00

2

Measured

3

Figure 7: Measured brake specific THC emissions by Tier and engine load factor

0.6

0.5

0.4

0.3

0.2

0.1

0

2

4i

Figure 8: Measured brake specific CO emissions by Tier and engine hours and CARB zero hour standards

28

1_BH 7_WL 4_BH 5_BH 10_SC 9_SC 12_BD 14_WL 15_GR 16_GR 6_WL 13_GR 20_WL 3_WL 27_HB-EX 26_EX 2_BH 11_EX 19_SC 18_WL 8_EX 17_GR-DPF 25_HB-BD 23_BD 24_BD 22_HB-BD 21_BD

667

668

669

670 671

PM Emissions (g/hp-hr)

ACCEPTED MANUSCRIPT

4

Measured

CARB Standard

3 2.5 2

RI PT

CO Emissions (g/hp-hr)

3.5

1.5 1 0.5

SC

2

672 673 674

M AN U

-0.5

1_BH 7_WL 4_BH 5_BH 10_SC 9_SC 12_BD 14_WL 15_GR 16_GR 6_WL 13_GR 20_WL 3_WL 27_HB-EX 26_EX 2_BH 11_EX 19_SC 18_WL 8_EX 17_GR-DPF 25_HB-BD 23_BD 24_BD 22_HB-BD 21_BD

0

3

3-DPF

4i

Figure 9: Measured brake specific CO emissions by Tier and engine load factor and CARB zero hour standards

675 200

Frey, et al

This Study

TE D

160 140 120 100

EP

80 60 40

AC C

NOx emissions (g/gal)

180

20

Tier 2 676 677 678

Tier 3

Figure 10: Comparison of measured fuel specific NOx emissions by Tier and equipment type between Frey et al and this study. 29

11_EX

20_WL

14_WL

3_WL

17_MG

15_MG

MG4-07RE

MG3-07RD

EX1-03MR

BD1-05ST

WL3-05MS

WL1-05_LTC

WL1-05_RHC

4_BH

BH5-04MS

BH3-04LT

BH2-04MEC

BH1-04MHC

BH1-04LTC

MG1-04SH

MG1-04RS

0

ACCEPTED MANUSCRIPT

Highlights

• In-use emission measurements were made from twenty-seven pieces of construction equipment, which included four backhoes, six wheel loaders, four excavators, two scrapers (one with two engines), six bulldozers, and four graders.

RI PT

• This is the largest study of off-road equipment emissions using 40 CFR part 1065 compliant PEMS equipment for all regulated gaseous and particulate emissions.

• The large variability in emissions, especially for NOx and PM, could have important implications for developing accurate emissions inventories and models. This variability is primarily due to differences in engine load factors for different types of work and combinations of work and idle time and the displacement of the engines.

SC

• Engine load factors are significantly affected by idle percentage and thus idle and loaded

M AN U

conditions should be modeled separately for Load factor and emission estimates. Additional activity studies will be important in understanding the overall emissions profiles of construction equipment and their real-world load factors.

• Additional activity studies will be important in understanding the overall emissions

AC C

EP

TE D

profiles of construction equipment and their real-world load factors.