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In-use NOx emissions from diesel and liquefied natural gas refuse trucks equipped with SCR and TWC respectively Chandan Misra, Chris Ruehl, John Francis Collins, Don Chernich, and Jorn Herner Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.6b03218 • Publication Date (Web): 07 Feb 2017 Downloaded from http://pubs.acs.org on February 12, 2017

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Environmental Science & Technology

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In-use NOx emissions from diesel and liquefied natural gas refuse trucks equipped with SCR and TWC respectively

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Chandan Misra*, Chris Ruehl, John Collins, Don Chernich and Jorn Herner

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California Air Resources Board, 1001 I St Sacramento, CA 95814

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*Corresponding author. Tel: +1 (916) 323-1503

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E-mail address: [email protected]

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Abstract

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The California Air Resources Board (ARB) and the City of Sacramento undertook this study to

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characterize the in-use emissions from model year (MY) 2010 or newer diesel, liquefied natural

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gas (LNG) and hydraulic hybrid diesel engines during real-world refuse truck operation.

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Emissions from five trucks: two diesels equipped with selective catalytic reduction (SCR), two

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LNG’s equipped with three-way catalyst (TWC) and one hydraulic hybrid diesel equipped with

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SCR were measured using a portable emissions measurement system (PEMS) in the Sacramento

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area. Results showed that the brake-specific NOx emissions for the LNG trucks equipped with

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the TWC catalyst were lowest of all the technologies tested. Results also showed that the brake

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specific NOx emissions from the conventional diesel engines were significantly higher despite

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the exhaust temperature being high enough for proper SCR function. Like diesel engines, the

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brake specific NOx emissions from the hydraulic hybrid diesel also exceeded certification

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although this can be explained on the basis of the temperature profile. Future studies are

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warranted to establish whether the below average SCR performance observed in this study is a

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systemic issue or is it a problem specifically observed during this work. 40 41 42 43 44 45

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TOC Art

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Introduction

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Oxides of nitrogen (NOx) emitted from heavy-duty diesel engines are major constituents of urban

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air pollution1–3 and can contribute to various environmental issues such as photochemical smog,

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secondary particulate matter (PM) formation and associated visibility debradation,4 and acid

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deposition, in addition to affecting human health directly.5–8 The stringent standards to control

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emissions from the on-road heavy-duty diesel fleet adopted by the Environmental Protection

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Agency (EPA) and the California Air Resources Board (ARB) are already showing an

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improvement in the air quality across various parts of California9–12 due to the reduction of both

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particulate matter (PM) and NOx. While many of these studies have used a stationary platform

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(either remote sensing or plume capture) to measure emissions from heavy-duty engines and thus

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capturing a single mode of operation for large numbers of vehicles, there is a growing need to

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characterize in-use emissions from real-world driving which can be a mix of multiple driving

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modes.

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To meet the stringent NOx emission standards introduced over the years, engine manufacturers

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are utilizing SCR systems to control elevated engine out NOx emissions from MY 2010 and later

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engines.

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temperature and physical system layout. A certain minimum exhaust temperature is required in

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the SCR to achieve hydrolysis of urea to ammonia (NH3) which then reduces NOx into nitrogen

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(N2) and water (H2O).13 As a result, the functioning of SCR is dependent on driving conditions

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because they affect exhaust temperature and urea dosing strategy. A recent study14 showed that

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while the exhaust temperatures are generally sufficient to reduce NOx emissions during highway

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cruise conditions, elevated NOx emissions are observed during cold starts and some situation in

The functioning of SCR is dependent on catalyst material, urea dosing strategy,


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which driving conditions are insufficient to raise and maintain the exhaust temperature above

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SCR light-off conditions. The variability of real-world driving conditions makes it important to

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understand how such conditions affect SCR NOX control including urban driving, stop-and-go

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traffic and other low load/slow speed operations (refuse, drayage truck movement, freight

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delivery etc.) which are challenging for SCR.

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According to some reports15,16 almost the entire nation’s refuse truck fleet of 120,000-136,000

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trucks is powered by heavy-duty diesel engines. A typical diesel refuse truck travels 25,000

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miles/year, burns 2-4 miles/gal and consumes close to 8,600 gallons of fuel each year.

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Considering the United States has about 120,000 refuse trucks in service, these trucks can burn

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up to a billion gallons of fuel each year.16 The refuse truck industry is one of the vocations that

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has taken initiative17,18 to decrease its dependence on petroleum and shift to advanced technology

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or alternative fuels to achieve cost savings and emissions reductions, often utilizing incentive

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funding to upgrade their fleets.

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Stoichiometric natural gas (NG) engines for heavy-duty application are gaining popularity due to

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lower PM and NOx emissions.19–21 These NG engines rely on a three-way catalyst (TWC) to

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remove hydrocarbons (HC), carbon monoxide (CO), and NOx, and have been shown to be

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superior than lean combustion in controlling NOX emissions.19 California cities are leading the

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way on adopting NG engines for vocational use with the state being home to 1,268 of over 2000

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NG fueled refuse haulers in the nation.22 NG has an advantage over diesel fuel as its CO2

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production per unit energy is about 25% lower. NG engines are also 50-90% quieter than the

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diesel engines making them ideal for operation in residential areas. Historically, NG prices have



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been lower than the diesel and less prone to short term spikes. All of these factors make

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stoichiometric NG powered engines a good choice for municipal authorities and they are being

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deployed in many parts of the United States for refuse operations.18,23 While the NOx emitted

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from NG engines with TWC can be well-controlled relative to lean burn diesel engines, the

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transition to NG fleet can pose its own challenges relating to vehicle maintenance and refueling

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infrastructure.16 NG is primarily methane (CH4), a GHG and thus fueling and storage capabilities

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that minimize the leakage of NG into atmosphere are required.

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The use of hybrid technology in refuse operation is also gaining attention to help fleet reduce

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petroleum consumption and achieve costs savings. A typical hydraulic hybrid system captures

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70% of the kinetic energy that otherwise would be lost during braking. Because refuse operation

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involves frequent stop-and-go, recovery of braking energy can improve vehicle fuel economy by

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25-30% compared conventional engines.16

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The goal of this research was to measure the in-use NOx emissions from five different heavy-

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duty engines certified to the MY 2010 (0.2 g NOx/bhp-hr) or interim MY 2010 (0.5 g NOx/bhp-

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hr) standard over typical refuse operation. While emissions characteristics of the heavy-duty

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engines during transient or highway driving modes are widely reported in the literature (for both

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chassis dynamometer and in-use testing), refuse truck operation, is very different characterized

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by frequent stop-and-go operation and there are only a handful studies that describe the in-use

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performance of refuse trucks.24,25 By some accounts, 80% of the refuse truck operation is spent

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in low speed regime.16 Based on ours previous work14 on evaluating SCR functionality on Class

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8 heavy-duty diesel engines, the refuse truck operation could present a challenge to the exhaust


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aftertreatment system due to low average speeds and frequent stops which might not be adequate

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to maintain the exhaust temperature for optimal SCR performance without special attention to

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exhaust temperature management. Hence there’s a need to evaluate aftertreatment performance

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from this vocation to assess if the air quality benefits envisioned under various regulations are

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being achieved by this sector. Results from this study comparing in-use emissions of diesel, LNG

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and hydraulic hybrid diesel refuse trucks with emissions standards for NOx and GHG, could be

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used to refine emissions inventories used for air quality planning and regulatory policy

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development, and to guide potential approaches for further NOx control across a wider engine

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operational envelope.

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Experimental Design and Procedures

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Instruments. A commercially available PEMS (SEMTECH-DS, Sensors Inc., Saline, MI) was

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used throughout this testing to collect emissions, global positioning system (GPS) location and

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engine broadcast data.26 The SEMTECH-DS instrument is recognized by EPA as an instrument

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capable of meeting the accuracy requirements for in-field testing. During this project, the PEMS

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was calibrated and operated per the manufacturer’s recommendations. The procedures described

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in Title 40 Code of Federal Regulations (CFR) 1065 Subpart Part J27 for PEMS field

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measurements were adhered to throughout the study. The PEMS was started and allowed to

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warm-up overnight before sampling for a test. Zero and span gas was used to set zero and span at

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manufacturers recommended concentrations (NO2~250 ppm) while quad gas (a mixture of four

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gases in the same cylinder at these concentrations: CO~1206 ppm, NO~1515 ppm, CO2~12%

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and THC~203 ppm) was used to perform audit checks prior to and at the end of each test.

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Emission samples were drawn into the PEMS analyzer through a heated sample line that was



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connected to the truck’s exhaust stack. The PEMS itself was placed in the vehicle cab on the

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passenger side after removing the seat and frame and was powered by a gasoline generator

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mounted behind the cab. An environmental enclosure without end-covers was used to prevent

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too much heat build-up around the PEMS analyzer and to prevent against shocks.

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The routes corresponded to the normal routine of the truck operation. The routes varied in length

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from 30-81 miles. Each truck operated from Mon-Thu and on different routes each day. PEMS

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zero, span, and audit checks were performed once before these trucks left the Sacramento City

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Yard and once after they returned from completing the day’s shift which was 6-8 hours long

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depending upon the length of the route and drivers efficiency. Data quality was maintained by

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ensuring calibrations were up to date, and that pre- and post-test procedures were followed.

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PEMS tests were deemed invalid if there was a system or procedural error during data collection.

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The SCR inlet temperatures for all the diesel vehicles were collected using an on-board

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temperature sensor in the exhaust stream by the original equipment manufacturer (OEM) using

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the Parameter Group Number (PGN) 64830 and Suspect Parameter Number (SPN) 4360. Table

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S1 in the Supplementary Information lists the minimum set of parameters that were collected for

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each test using the PEMS device.

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Test Vehicles Selection

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Table 1 describes the five vehicles tested in this study. They included: (i) two medium-heavy

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duty diesel engines of identical engine family with displacement of 8.3L and power ratings of

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330 hp, (ii) two heavy-duty LNG engines of identical engine family with the displacement of 8.3

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L with maximum power rating of 320 hp and (iii) a medium heavy-duty hydraulic hybrid diesel

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and displacement of 8.9 L rated at 380 hp. 7 ACS Paragon Plus Environment

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Table 1: Test vehicles ID

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Fuel

Mileage

NOx Control

NOx† Cert

NOx NOx Engine Family † FEL or NTE STD† Diesel-1 Diesel 38,000 SCR 0.18 0.31 0.46 ACEXH0505CAC Diesel-2 Diesel 41,500 SCR 0.18 0.31 0.46 ACEXH0505CAC LNG-1 LNG 38,000 TWC 0.13 0.2 0.3 BCEXH0540LBH LNG-2 LNG 36,500 TWC 0.13 0.2 0.3 BCEXH0540LBH Hybrid Diesel 31,000 SCR 0.22 0.33 0.5 CCEXH0540LAQ † all values in NOx/bhp-hr from http://www.arb.ca.gov/msprog/onroad/cert/cert.php

Engine Make

Engine MY

Engine Model

Engine HP

Cummins Cummins Cummins Cummins Cummins

2010 2010 2011 2011 2012

ISC 8.3 ISC 8.3 ISL G320 ISL G320 ISL 9

330 330 320 320 380



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Testing Protocol.

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Emissions testing was performed while the test vehicles were driven over their normal operating

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routes in and around Sacramento, California.

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different routes each day. Efforts were made to sample each truck for 8 days (i.e., 4 days/week

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for 2 week period) in order to get duplicate data for identical weekdays in two successive weeks

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However, based on logistical issues, problem with PEMS or other circumstances, the testing on

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each truck was generally less than 8 days and varied from 4-7 days.

Each truck operated from Mon-Thu and on

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Before each test, the PEMS was allowed to run overnight using onshore power (wall outlet) in

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order to save time on the morning of test, as PEMS warm-up can take up to an hour. Each

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morning before the test, span and audit checks were performed as described earlier and the

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power source was moved from onshore to offshore source (generator mounted on the truck). The

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data collection was started at least 60 seconds before the engine was turned on to capture cold

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start emissions. At the end of the day when the truck retuned from its normal routine, final span

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and audit checks were done and the data was downloaded using the Semtech post processor.

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Each route began at the Sacramento City Yard (2812 Meadowview Road Bldg 3, Sacramento,

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CA 95832) and utilized arterial driving to reach the neighborhood. This was followed by trash

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collection and a drive to the landfill facility (either using arterial or arterial/highway mix) to drop

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the load. The trucks then returned to another neighborhood for trash pick-up followed by the last

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trip of the day to the landfill. The trucks then drove back to the City Yard. A typical run

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generally started at 6 am and the trucks returned to the City Yard by 2 pm after 8 hours of

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operation. All the trucks tested during this study were side-loader recycle trucks and therefore


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carried the lowest weight of trash per unit compared to regular trash or green waste trucks. This

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can be regarded as worst case scenario for SCR testing as the lower payload will further

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challenge attainment of higher exhaust temperature due to lower power needed for operation

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(both during the trash pick-up as well as during the driving mode).

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PEMS measurements were taken from December 2013 through March 2014. Thus the majority

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of the tests were performed in temperatures that were generally winter (0-15o C) with very few

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days of rain due to drought conditions in California.

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Results and Discussion

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All the data presented in the subsequent graphs are direct emissions measurements and do not

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have any allowance margins added to the emissions data. The following discussion illustrates the

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major findings of our study using a subset of the data. Figure S1 of the supporting information

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provides maps of the test routes described in subsequent sections. The entire dataset from all the

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tests is available in Supplementary Information Table S2.

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Table 2. Segmented NOx emissions, distance and time for all tests Date Engine (MM_DD_YYYY) 12/10/2013 Diesel 1 12/11/2013 Diesel 1 12/12/2013 Diesel 1 12/16/2013 Diesel 1 12/17/2013 Diesel 1 12/18/2013 Diesel 1 12/19/2013 Diesel 1 Average

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NOx (g/bhp-hr) Distance Fraction (%) Time Fraction (%) Trash pick-up Arterial Highway Overall Trash pick-up Arterial Highway Trash pick-up Arterial Highway 1.304 0.711 N/A 1.227 54% 46% 0% 94% 6% 0% 1.043 0.708 N/A 0.991 50% 50% 0% 89% 11% 0% 1.149 0.799 N/A 1.099 54% 46% 0% 91% 9% 0% 1.146 0.900 N/A 1.094 43% 57% 0% 87% 13% 0% 1.201 0.849 2.312 1.153 45% 51% 4% 87% 13% 1% 1.354 0.940 0.423 1.271 47% 50% 3% 88% 12% 0% 1.500 0.857 0.530 1.349 42% 42% 16% 87% 10% 2% 1.242 0.824 1.088 1.169 48% 49% 3% 89% 10% 1%

12/23/2013 Diesel 2 12/24/2013 Diesel 2 12/25/2013 Diesel 2 12/26/2013 Diesel 2 12/31/2013 Diesel 2 1/1/2014 Diesel 2 1/6/2014 Diesel 2 Average

0.729 0.711 0.664 0.684 0.649 0.682 0.842 0.709

0.491 0.489 N/A 0.475 N/A 0.619 0.436 0.514 0.482 N/A 0.501

1/12/2014 LNG 1 1/13/2014 LNG 1 1/14/2014 LNG 1 1/15/2014 LNG 1 1/16/2014 LNG 1 1/20/2014 LNG 1 1/21/2014 LNG 1 Average

0.133 0.127 0.124 0.125 0.139 0.127 0.133 0.130

0.145 0.157 0.144 0.110 0.163 0.158 0.145 0.146

1/27/2014 LNG 2 1/28/2014 LNG 2 Average 3/3/2014 Hybrid 3/4/2014 Hybrid 3/5/2014 Hybrid 3/6/2014 Hybrid Average Legend Trash Pick-up Arterial Highway

0.463

0.758

0.666 0.662 0.630 0.706 0.591 0.621 0.772 0.664

40% 40% 54% 45% 37% 32% 45% 42%

49% 60% 46% 46% 63% 53% 55% 53%

11% 0% 0% 9% 0% 15% 0% 5%

86% 87% 89% 90% 85% 84% 90% 87%

12% 13% 11% 9% 15% 14% 10% 12%

2% 0% 0% 1% 0% 3% 0% 1%

0.049 0.044 0.107 0.062 0.031 0.065 0.049 0.058

0.130 0.130 0.126 0.121 0.139 0.128 0.130 0.129

46% 46% 35% 47% 46% 44% 46% 44%

39% 48% 44% 39% 44% 41% 39% 42%

15% 5% 20% 14% 10% 15% 15% 14%

89% 90% 85% 91% 90% 90% 89% 89%

9% 9% 11% 7% 9% 8% 9% 9%

2% 1% 4% 2% 1% 2% 2% 2%

0.084 0.098 0.091

0.067 N/A 0.161 0.064 0.114 0.064

0.081 0.103 0.092

43% 33% 38%

57% 36% 47%

0% 31% 15%

88% 86% 87%

12% 9% 11%

0% 5% 2%

0.537 0.587 0.564 0.410 0.525

0.241 N/A 0.262 N/A 0.268 N/A 0.231 N/A 0.250 N/A

0.463 0.503 0.497 0.383 0.461

52% 54% 57% 66% 57%

48% 46% 43% 34% 43%

0% 0% 0% 0% 0%

92% 92% 93% 95% 93%

8% 8% 7% 5% 7%

0% 0% 0% 0% 0%

2.023 0.187 0.358

v < 25 mph 25 ≤ v < 50 mph v ≥ 50 mph

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Truck Activity. Table 2 provides distance and time fraction each truck spent in trash pick-up,

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arterial and highway segment. For the purpose of this manuscript, different driving modes are

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defined on the basis of speed as trash pickup (v < 25 mph), arterial (25 ≤ v < 50 mph) and 11 ACS Paragon Plus Environment

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highway (v ≥ 50 mph). This distinction was chosen to make these modes identical to speed bins

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used in EPA’s Motor Vehicle Emission Simulator (MOVES) mode although no data analysis in

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terms of MOVES is being provided in this manuscript. For all purposes, the chosen speed bins

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also well represent the three driving modes observed during this test project.

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As shown in Table 2, all the trucks tested spent majority of time (~ 90%) in the trash pick-up

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mode while arterial accounted for most of the remaining 10% with highway close to 0-2%.

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Diesel Engines. The Diesel-1 refuse truck was tested from 12/10/2013 through 12/19/2013 and

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a total of 7 tests were performed on this vehicle. The distance covered each day varied from 31

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to 81 miles with an average speed of 7.4 mph (SD 1.36). The average fuel consumption during

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the entire testing was around 1.65 mpg (SD 0.17) as reported by the PEMS (and thus derived

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from fuel carbon balance). This value is comparable to data reported during similar emissions

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testing studies for diesel engines.15 The averaged brake specific CO2 emissions were around

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612.8 g CO2/bhp-hr (SD 7.43) while CO emissions averaged at 8.6 g CO/bhp-hr (SD 0.7) The

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CO to CO2 ratio was 0.14% indicating fairly efficient combustion of the diesel fuel.

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The most striking feature of Diesel-1 was the NOx emissions. The average brake-specific NOx

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emissions for all 7 tests on this vehicle were 1.17 g NOx/bhp-hr (SD 0.12). This engine is

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certified at 0.18 gNOx/bhp-hr and these emissions exceeded the certification value by a factor of

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6-7 (i.e., the work specific emissions observed in this study are higher than those observed

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during the Federal Test Procedure or FTP engine dynamometer engine certification cycle). The

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average brake-specific NOx emissions were: 1.24, 0.82 and 1.1 g NOx/bhp-hr for trash pick-up,



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arterial and the highway segments respectively. It should be noted that the elevated averaged

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NOx emissions for highway were heavily influenced by the test on 12/17/2013 (Table 2) which

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probably had a regeneration event at the beginning of the test while the truck transitioned to the

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highway. Figure 1 shows a plot NOx, NO2, CO2, SCR inlet exhaust temperature and speed

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profile against cumulative power for one of the days (12/19/2013) for Diesel-1. The

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corresponding route map is available in Supplementary Information Figure S1. The trend of

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these emissions was identical across various driving modes (arterial, trash collection and

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highway) each day and only one of the days is being shown here for the discussion purposes.

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Figure 1. Emissions and speed profile for Diesel-1 entire route for 12/19/2013

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As evident from Figure 1, the SCR inlet exhaust temperature of about 300 deg C was observed

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during the trash-pick up mode while the temperature during the arterial mode dropped to 225 deg

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C but never below it. The presence of such high temperature during the trash-pick up driving

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mode is important because urea hydrolysis requires an exhaust temperature of at least 180-200oC 13 ACS Paragon Plus Environment

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and below which the SCR efficiency falls rapidly because of cessation in urea hydrolysis.14,28–30

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In order to understand the temperature profile observed during the trash pick-up and to estimate

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NOx emissions during this mode, we plotted derived engine power vs. time for 0.1 mile of

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typical trash pick-up operation (Figure 2). Figure 2 shows that during acceleration from a

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complete stop, the engine may be required to deliver maximum available rated power on

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occasions. This frequent stop-and-go plus the requirements of the arm lift (and compaction) are

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sufficient to keep the exhaust temperature at around 300 deg C. This is further demonstrated by

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plotting the derived engine power against time for arterial mode (Figure 3) which shows the

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lower power consumption during this driving mode and the lack of any power needed for arm lift

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and compaction. While there are events when the demand for power increases to maximum

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available, these events are sparse and spaced out and generally correspond to acceleration from a

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complete stop. The arterial mode is devoid of sudden stop-and-go dropping the exhaust

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temperature to 275 deg C.

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Figure 2. Instantaneous power requirements during trash pick-up (0.1 miles driving shown) 14 ACS Paragon Plus Environment


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Figure 3. Instantaneous power requirements during arterial driving (5 miles driving shown)

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The presence of elevated brake specific NOx emissions despite adequate SCR inlet exhaust

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temperature during trash pick-up mode is surprising and is of concern. While the instantaneous

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DEF usage was not directly measured during these tests, the average DEF usage approximated to

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3-5% of fuel usage which is normal consumption rate as reported by an engine manufacturer.31

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The data in Figure 2 clearly establishes that the NOx emissions during trash pick-up are

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extremely elevated and contribute significantly to the averaged NOx emissions for the entire

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route. The arterial driving emits far lower NOx emissions. While we observed elevated NOx

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emissions during low load/slow speed driving in our earlier work14 that could be explained on

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the basis of the temperature profile, the current study raises a completely new concern where

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extremely high NOx emissions are being observed despite conducive SCR operating conditions.

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While authors agree that accelerations during stop-and-go can certainly produce high engine out

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NOx emissions, the sufficiently high exhaust temperature should also be able to reduce these

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emissions using the SCR. The results however do not reflect that. The highway NOx emissions

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on 12/18/2013 and 12/19/2013 were 0.42 and 0.53 g NOx/bhp-hr. While these emissions are

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about a half of what was observed during the arterial driving, the highway NOx emissions should

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be far lower than arterial driving based on our earlier study which showed that heavy-duty diesel

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SCR performed at its optimum level during highway mode at times emitting lower NOx than the

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certification level. The presence of high NOx during the highway mode can suggest a

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malfunctioning SCR or a problem related to a component and not necessarily to excessive engine

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out NOx emissions which based on our earlier study should be well controlled during the cruise

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mode. The role of frequent stop-and-go operation and its effect on dosing algorithm also needs to

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be explored.

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A total of 7 tests were performed on Diesel-2 from 12/23/2013-1/6/2014. The averaged NOx

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emissions for Diesel-2 were about half of Diesel-1 at 0.66 g NOx/bhp-hr (SD 0.06). Figure 4

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shows emissions and speed profile for one of the days (12/23/2013) for Diesel-2. The

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corresponding route map is available in Supplementary Information Figure S2 .Similar to

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exhaust temperature profile for Diesel-1, the SCR inlet exhaust temperature stayed between 250-

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300 deg C for the entire route. However, the NOx emissions remained elevated by more than 3

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times of the certification level despite the temperature being conducive for SCR functionality for

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almost the entire route.



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Figure 4. Emissions and speed profile for Diesel-2 entire route for 12/23/2013

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Further actions by Cummins to explore causes of subpar SCR performance indicated that the

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diesel particulate filter (DPF) regeneration events were not reaching expected temperatures

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possibly leading to contaminants build up in SCR system reducing its NOx conversion

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efficiency. Cummins technicians performed stationary regeneration events on Diesel-1 which by

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their experience has been confirmed to remove SCR system contaminants and restore SCR

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system performance in similar situations. However, on Diesel 1, the forced regeneration did not

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improve the NOx conversion efficiency. Cummins also removed debris found in the urea tank

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including replacing the internal filter screen that was plugged. As a result, the dosing tank and

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lines were cleaned. All of these actions did not result in any noticeable improvement in SCR

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performance on Diesel-1 as measured by Cummins using their proprietary software to collect

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NOx sensor data. The entire SCR system on Diesel-1 was eventually replaced including the

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catalyst and the NOx sensors. The new catalyst system has not yet been evaluated by us. 17 ACS Paragon Plus Environment

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Regardless, further investigation is warranted to assess whether this is a systemic problem related

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to specific vocations (like trash collection) which may result in catalyst fouling due to frequent

323

stop-and-go and inadequate dosing strategy or is somehow is limited to these two trucks that

324

were tested during this study.

325 326

Liquefied Natural Gas Engines. Truck LNG-1 was tested from 1/13/2014-1/21/2014 and a total

327

of 6 tests were performed on this truck. The distance of the route varied from 45 miles to 78

328

miles with an average speed of 7.3 mph (SD 1.0). The fuel consumption of LNG was not

329

measured directly by the PEMS but was calculated in a similar manner, based on CO and CO2

330

emissions as provided in Table S1. A value of 10.21 kg CO2/gal diesel32 was used to arrive at the

331

diesel equivalent fuel consumption rate for the LNG engines. The LNG-1 emitted on average

332

401 g CO2/bhp-hr (SD 3.36) which is about 34% lower (brake-specific) than the averaged CO2

333

emissions of both Diesel-1 and Diesel-2. Similar reduction in CO2 emissions have been reported

334

for stoichiometric engines with TWC compared against lean burn diesel engine on FTP heavy-

335

duty transient cycle (Crawford et al, 2010) and under real-world city driving conditions.33 It’s

336

worthwhile mentioning here that the CO2 emissions from LNG-1 were lower than the MY2017

337

(555 gCO2/bhp-hr) Federal Phase II GHG standard for heavy-duty engines installed on

338

vocational vehicles. The GHG standard for the vocational engines is defined over the FTP

339

(which is based the Urban Dynamometer Driving Schedule or UDDS chassis dynamometer

340

driving cycle) which is a fairly non-aggressive cycle with an average load factor of roughly 20-

341

25% of the maximum engine power available at a given engine speed.34 Our data showed that the

342

average load factor (all driving modes) for the LNG-1 truck operation was close to 50%. The



Page 20 of 26

343

ability of the LNG-1 to meet the GHG engine standard for both MY2014 and MY2017 on load

344

which is higher than the FTP is noteworthy.

345 346

The averaged segment brake-specific NOx were: 0.13, 0.14 and 0.05 g NOx/bhp-hr for trash

347

pick-up, arterial and the highway segment respectively. The highway NOx emissions for the

348

LNG-1 are extremely low. Figure 5 shows emissions and speed profile for LNG-1 on

349

01/14/2014. The corresponding route map is available in Supplementary Information Figure S3.

350

The plot shows that during cold start, NOx emissions remain elevated for a brief period but as

351

the exhaust temperature rises rapidly, the brake specific NOx emissions drops and remains

352

constant. The overall NOx emissions for this test were 0.12 g NOx/bhp-hr (including the cold

353

start emissions) which was lower than engine certification of 0.13 g NOx/bhp-hr for this engine

354

family.

355 356

Figure 5. Emissions and speed profile for LNG-1 entire route for 01/14/14

357 19 ACS Paragon Plus Environment

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358

Truck LNG-2 was tested from 1/27/2014 through 2/23/2014 for a total of 8 tests. However due to

359

the malfunctioning PEMS CO2 analyzer from the third test onwards, only data from two of the

360

tests performed on LNG-2 are being presented here. Similar to LNG-1, the averaged NOx

361

emissions for LNG-2 were 0.09 g NOx/bhp-hr which were lower than the MY2010 NOx

362

standard as well as the engine certification emissions for this engine family. The averaged

363

segment brake-specific NOx emissions were: 0.09, 0.11 and 0.06 g NOx/bhp-hr for trash pick-

364

up, arterial and the highway segment respectively which are fairly similar to the LNG-1

365

emissions.

366 367

Diesel Hydraulic Hybrid. The diesel hydraulic hybrid engine with Parker hydraulic powertrain

368

was tested from 3/3/2014 to 3/6/2014 and a total of 4 tests were performed. The distance

369

travelled on these four days ranged from 31 to 53 miles with an average speed of 5 mph (SD

370

0.3). The average fuel economy for all tests was 3.35 mpg, which is twice the average fuel

371

economy of Diesel-1 and Diesel 2. The average brake-specific CO2 emissions from the hybrid

372

truck were 470 g CO2/bhp-hr (SD 7.92) which, like LNG-1 and LNG-2, met the vocational

373

vehicles GHG engine standard for both MY2014 and MY2017.

374 375

The average NOx emissions from all four tests were 0.46 g NOx/bhp-hr which exceeds the

376

certification value. The average brake-specific NOx emissions were: 0.52 and 0.25 g NOx/bhp-

377

hr for trash pick-up and arterial segments respectively. The hybrid engine was not driven on

378

highway and therefore those emissions were not recorded as a result. It’s highly likely that if the

379

truck was driven on highway and the emissions data was collected, it would have been more in

380

line with the FTP work specific NOx emission rate.14



Page 22 of 26

381 382

Figure 6. Emissions and speed profile for diesel hydraulic hybrid entire route for 03/03/14

383 384

The plot in Figure 6 (route map shown in Supplementary Information Figure S4) shows that the

385

SCR inlet temperature in a hydraulic truck is highly variable and at times falls below 200 deg C,

386

the operating temperature of an SCR. The plot also shows that if the SCR inlet exhaust

387

temperature stays above 200 deg C and achieves some kind of stability, NOx emissions are

388

controlled. In Figure 6, this can be observed between 165-195 cumulative bhp-hr, 205-275

389

cumulative bhp-hr and from 285 cumulative bhp-hr to the end of the test. It’s clear that during

390

the periods mentioned above, the SCR inlet temperature is well above 200 deg C and NOx

391

emissions control is achieved. This is in contrast to Diesel-1 and Diesel-2 engines tested during

392

this study which did not show optimal SCR activity even when the exhaust temperature was

393

adequate for NOx control.

394


Page 23 of 26


395

The test data presented here does not establish why SCR activity is observed for the hydraulic

396

hybrid engine and not for the diesel engines tested. The hybrid engine tested during this study is

397

MY2012 vs. the diesel engines which were MY2010. It’s possible that the SCR catalyst on the

398

diesel engines may have deteriorated by the time this study was performed while the hydraulic

399

engine being newer still had the SCR functionality intact. As mentioned previously, the exact

400

cause of these differences need to be explored further before a definitive argument can be made

401

for lack of expected NOx control on the diesel engines tested.

402 403

The data for hydraulic engine also shows that maintaining a temperature for SCR functionality

404

needs to be explored in future technology development. While the hydraulic component can have

405

substantial effects on fuel cost savings (with concomitant effect on cutting down GHG

406

emissions), the diesel engine and the hydraulic components in a hybrid system should also work

407

in tandem to control NOx emissions during all the modes of driving.

408 409

Acknowledgements and Disclaimer

410

Authors would like to thank the staff at the Depot Park Facility or their support during the

411

experimental phase of this study. Authors would also like to acknowledge kind support of Steve

412

Barker, Ron Kammerer and Christopher Kerhulas of the City of Sacramento without which this

413

project would have been impossible. Acknowledgements are also due to Mike Cooper of

414

Cummins for providing assistance with the aftertreatment system diagnosis. The statements and

415

opinions expressed in this paper are solely the authors’ and do not represent the official position

416

of the California Air Resources Board or the City of Sacramento. The mention of trade names,

417

products, and organizations does not constitute endorsement or recommendation for use.



418

Page 24 of 26

Supporting Information Available

419

Route maps for selected runs presented in the manuscript, PEMS parameters and

420

summary of all runs

421

References:

422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458

(1) (2)

(3) (4)

(5) (6) (7) (8) (9)

(10)

(11)

(12)

(13) (14)

(15)

Lloyd, A. C.; Cackette, T. A. Diesel engines: environmental impact and control. J. Air Waste Manag. Assoc. 1995 2001, 51 (6), 809–847. Sawyer, R. F.; Harley, R. A.; Cadle, S. H.; Norbeck, J. M.; Slott, R.; Bravo, H. A. Mobile sources critical review: 1998 NARSTO assessment. Atmos. Environ. 2000, 34 (12–14), 2161–2181. Yanowitz, J.; McCormick, R. L.; Graboski, M. S. In-Use Emissions from Heavy-Duty Diesel Vehicles. Environ. Sci. Technol. 2000, 34 (5), 729–740. Wiley: Atmospheric Chemistry and Physics: From Air Pollution to Climate Change, 2nd Edition - John H. Seinfeld, Spyros N. Pandis http://www.wiley.com/WileyCDA/WileyTitle/productCd-0471720186.html Humans, I. W. G. on the E. of C. R. to. Diesel and Gasoline Engine Exhausts and Some Nitroarenes; International Agency for Research on Cancer, 2014. Houghton, M. Final Staff Report: Update to the Toxic Air Contaminant List http://www.arb.ca.gov/toxics/Finalreport.PDF Health Assessment Document for Diesel Engine Exhaust http://nepis.epa.gov CDC - NIOSH Publications and Products - Carcinogenic Effects of Exposure to Diesel Exhaust (88-116) http://www.cdc.gov/niosh/docs/88-116/ Bishop, G. A.; Hottor-Raguindin, R.; Stedman, D. H.; McClintock, P.; Theobald, E.; Johnson, J. D.; Lee, D.-W.; Zietsman, J.; Misra, C. On-road Heavy-duty Vehicle Emissions Monitoring System. Environ. Sci. Technol. 2015, 49 (3), 1639–1645. Dallmann, T. R.; DeMartini, S. J.; Kirchstetter, T. W.; Herndon, S. C.; Onasch, T. B.; Wood, E. C.; Harley, R. A. On-Road Measurement of Gas and Particle Phase Pollutant Emission Factors for Individual Heavy-Duty Diesel Trucks. Environ. Sci. Technol. 2012, 46 (15), 8511–8518. Dallmann, T. R.; Harley, R. A.; Kirchstetter, T. W. Effects of Diesel Particle Filter Retrofits and Accelerated Fleet Turnover on Drayage Truck Emissions at the Port of Oakland. Environ. Sci. Technol. 2011, 45 (24), 10773–10779. Bishop, G. A.; Schuchmann, B. G.; Stedman, D. H.; Lawson, D. R. Emission changes resulting from the San Pedro Bay, California Ports Truck Retirement Program. Environ. Sci. Technol. 2012, 46 (1), 551–558. Diesel Emissions and Their Control http://books.sae.org/r-303/ Misra, C.; Collins, J. F.; Herner, J. D.; Sax, T.; Krishnamurthy, M.; Sobieralski, W.; Burntizki, M.; Chernich, D. In-Use NOx Emissions from Model Year 2010 and 2011 Heavy-Duty Diesel Engines Equipped with Aftertreatment Devices. Environ. Sci. Technol. 2013, 47 (14), 7892–7898. Farzaneh, M.; Zietsman, J.; Lee, D.-W. Evaluation of In-Use Emissions from Refuse Trucks. Transp. Res. Rec. J. Transp. Res. Board 2009, 2123, 38–45.


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459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503


(16) Parker Hannifin Corporation. The Clean Side of Garbage: A Technical Paper on Emission Reductions with Hydraulic Hybrid Drive Systems http://www.parker.com (17) West Coast Diesel Emissions Reduction Collaborative Heavy-Duty Refuse Trucking Project https://westcoastcollaborative.org/files/sectortrucking/CleanEnergyTruckingREFUSE-ProjectDescrDec.pdf (18) LA Checks Refuse Truck Emissions at the Curb. Government Engineering August 2005. (19) Yoon, S.; Collins, J.; Thiruvengadam, A.; Gautam, M.; Herner, J.; Ayala, A. Criteria pollutant and greenhouse gas emissions from CNG transit buses equipped with three-way catalysts compared to lean-burn engines and oxidation catalyst technologies. J. Air Waste Manag. Assoc. 1995 2013, 63 (8), 926–933. (20) Turrio-Baldassarri, L.; Battistelli, C. L.; Conti, L.; Crebelli, R.; De, B.; Iamiceli, A. L.; Gambino, M.; Iannaccone, S. Evaluation of emission toxicity of urban bus engines: Compressed natural gas and comparison with liquid fuels. Sci. Total Environ. 2006, 355 (1-3), 64–77. (21) Thiruvengadam, A.; Besch, M. C.; Thiruvengadam, P.; Pradhan, S.; Carder, D.; Kappanna, H.; Gautam, M.; Oshinuga, A.; Hogo, H.; Miyasato, M. Emission rates of regulated pollutants from current technology heavy-duty diesel and natural gas goods movement vehicles. Environ. Sci. Technol. 2015, 49 (8), 5236–5244. (22) Krupnick, A. Energy, Greenhouse Gas, and Economic Implications of Natural Gas Trucks http://www.rff.org/files/sharepoint/WorkImages/Download/RFF-BCK-KrupnickNaturalGasTrucks.pdf (23) Shea, S. Clean Cities Niche Market Overview: Refuse Haulers http://www.afdc.energy.gov/pdfs/51588.pdf (24) Fontaras, G.; Martini, G.; Manfredi, U.; Marotta, A.; Krasenbrink, A.; Maffioletti, F.; Terenghi, R.; Colombo, M. Assessment of on-road emissions of four Euro V diesel and CNG waste collection trucks for supporting air-quality improvement initiatives in the city of Milan. Sci. Total Environ. 2012, 426, 65–72. (25) Sandhu, G. S.; Frey, H. C.; Bartelt-Hunt, S.; Jones, E. In-use measurement of the activity, fuel use, and emissions of front-loader refuse trucks. Atmos. Environ. 2014, 92, 557–565. (26) On Board Emissions Analyzers http://www.sensors-inc.com/onboard.html (27) Federal Register | Test Procedures for Testing Highway and Nonroad Engines and Omnibus Technical Amendments https://www.federalregister.gov/articles/2005/07/13/0511534/test-procedures-for-testing-highway-and-nonroad-engines-and-omnibus-technicalamendments#h-40 (28) Urban off-cycle NOx emissions from Euro IV/V trucks and buses | International Council on Clean Transportation http://www.theicct.org/urban-cycle-nox-emissions-euro-ivvtrucks-and-buses (29) Internal Combustion Engine Fundamentals http://www.mheducation.com/highered/product.M007028637X.html (30) Vehicular Emissions in Review http://papers.sae.org/2012-01-0368/ (31) Cummins Filtration. Diesel Exhaust Fluid (DEF) Q & A https://www.cumminsfiltration.com/pdfs/product_lit/americas_brochures/MB10033.pdf (32) LNG quick facts http://www.prometheusenergy.com/_pdf/LNGQuickFacts.pdf (33) Pelkmans, L.; De Keukeleere, D.; Lenaers, G. Emissions and fuel consumption of natural gas powered city buses versus diesel buses in real-city traffic; 2001.



504 505 506

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(34) Emission Test Cycles: HD FTP Transient http://www.dieselnet.com/standards/cycles/ftp_trans.php


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