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Heavy duty diesel exhaust particles during engine motoring formed by lube oil consumption Panu Karjalainen, Leonidas Ntziachristos, Timo Murtonen, Hugo Wihersaari, Pauli Simonen, Fanni Myllari, Nils-Olof Nylund, Jorma Keskinen, and Topi Rönkkö Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.6b03284 • Publication Date (Web): 13 Oct 2016 Downloaded from http://pubs.acs.org on October 17, 2016

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Environmental Science & Technology

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Heavy duty diesel exhaust particles during engine

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motoring formed by lube oil consumption

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Panu Karjalainen1, Leonidas Ntziachristos1,*, Timo Murtonen2, Hugo Wihersaari1, Pauli

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Simonen1, Fanni Mylläri1, Nils-Olof Nylund2, Jorma Keskinen1, Topi Rönkkö1

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1

Aerosol Physics Laboratory, Department of Physics, Tampere University of Technology, P.O.

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Box 692, 33101 Tampere, Finland 2

VTT Technical Research Centre of Finland Ltd., P.O. Box 1000, 02044 VTT, Espoo, Finland

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*Corresponding author. Email: [email protected], tel: +30 23 10 99 60 03, fax: +30 23 10 99 60 12

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ACS Paragon Plus Environment

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ABSTRACT

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This study reports high numbers of exhaust emissions particles during engine motoring. Such

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particles were observed in the exhaust of two heavy duty vehicles with no diesel particle filter

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(DPF), driven on speed ramp tests and transient cycles. A significant fraction of these particles

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was non-volatile in nature. The number-weighted size distribution peak was below 10 nm when a

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thermodenuder was used to remove semivolatile material, growing up to 40 nm after semivolatile

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species condensation. These particles were found to contribute to 9-13% of total particle number

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emitted over a complete driving cycle. Engine motoring particles originated from lube oil and

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evidence suggests that these are of heavy organic or organometallic material. Particles of similar

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characteristics have been observed in the core particle mode during normal fired engine

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operation. Their size and chemical character has implications primarily on the environmental

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toxicity of non-DPF diesel and, secondarily, on the performance of catalytic devices and DPFs.

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Lube oil formulation measures can be taken to reduce the emission of such particles.

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KEYWORDS

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particulate emissions; diesel emissions; lube oil; core mode; nucleation mode

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TOC / ABSTRACT ART

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INTRODUCTION

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Diesel exhaust aerosol emissions have been in detail studied since at least the late 1970s.1 Over

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these years, exhaust particle physical and chemical characteristics from a variety of vehicle and

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engine types operating on different fuels have been measured around the world. In parallel,

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health studies have revealed the association of untreated diesel exhaust with short-term2 and

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long-term3 health effects in humans. The collective efforts from thousands of scientists and

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researchers around the world, together with the solutions achieved by engineers in the

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development side and policy makers in the regulatory front, have brought significant

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improvements to emissions control, including engine technology measures, stringent fuel quality

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specifications, and enhanced methods of monitoring real-world particulate matter (PM)

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emissions. Undoubtedly though, the breakthrough in diesel particle emissions control has been

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achieved with the commercialization of the diesel particle filter (DPF). DPFs effectively filter the

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exhaust gas before it is emitted to the atmosphere and have been shown to lead to real-world

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reductions of at least ~90% in PM mass emissions4 and 66% reduction in total particle number

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(PN)5, compared to typical pre-DPF levels. Heavy duty engines equipped with DPF and

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complying with the US2010 standards were reported to emit two orders of magnitude less mass

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and number of total particles compared to pre-DPF ones in a comprehensive laboratory study.6

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DPFs have also been shown to result to very low non-volatile particle (soot) emissions.7, 8 Most

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importantly, recent studies demonstrated the potential of DPFs to reduce health effects9 and

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revealed the positive impacts of DPF-equipped vehicles to air quality.10

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Current emission limits in regions like China, India and Latin America still do not mandate the

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use of DPFs in new vehicles.11 Understanding and monitoring emissions from vehicles without

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DPFs is still necessary in these regions. Even in countries with world-class emission standards,


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DPF equipped vehicles only correspond to a fraction of the fleet. In 2015, only about one third of

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the truck fleet was equipped with DPFs in US9 and 10% of the fleet in the EU.12 As the average

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service life of a heavy duty diesel (HDD) vehicle is in the excess of 20 years both in US13 and

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the EU12, non-DPF diesel exhaust emissions will continue to be a dominant PM source in the

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future. In EU, this is what projections show until at least 2035.14 PM control measures for

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existing vehicles are therefore still necessary.

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PM characteristics at the inlet of catalytic aftertreatment devices and DPFs have implications

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on long-term performance and durability. Soot load in the DPF is continuously (passive systems)

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or periodically (active systems) oxidized in a process known as regeneration. The frequency of

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active regenerations mostly depends on the soot loading of the filter. Regenerations become

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more frequent as the vehicle ages, both because engine out soot emissions deteriorate with time

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but also because the DPF effective volume decreases by ash layers formed in the DPF channels.

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Ash layers mostly form due to accumulation of lube oil residues or additives which are not

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eliminated during regenerations. DPF ash accumulation increases fuel consumption by

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increasing the average backpressure levels in the exhaust and by increasing regeneration

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frequency due to the smaller DPF effective volume. Some of the ash components, like P or Ca

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are known catalyst poisons hampering selective catalytic reduction (SCR) and diesel oxidation

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catalyst (DOC) performance.15

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A previous study16 reported a significant number of ash and semivolatile particles formed

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during engine motoring. These particles mostly resided in the sub-20 nm size range while a

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significant fraction was still observed below 7 nm. Because of their small size and often metallic

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character, these particles potentially pose a direct environmental and health risk. For example,

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nanometer-sized magnetite particles associated to combustion have recently been observed in


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human brain samples.17 Moreover, such non-volatile nanoparticles are linked to various

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ecotoxicity endpoints.18, 19 But even for DPF vehicles, such particles may potentially contribute

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to ash formation in the DPF thus compromising the environmental performance, including

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increased fuel consumption and DPF regeneration frequency, of the vehicle. In this paper we

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study the characteristics of these particles from controlled experiments on two HDD vehicles

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with the objective to improve our understanding on how to reduce their direct and indirect

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environmental impacts.

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EXPERIMENTAL

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Vehicles, fuel and lubricant oil. The test vehicles included a local delivery Euro IV truck (2007

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model year, 879 thousand km) and a Euro III city bus (2005 model year, 997 thousand km) in

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operation at the Helsinki Metropolitan area. The vehicles were not equipped with DPF but they

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were both fitted with exhaust gas recirculation (EGR) and the truck was also equipped with an

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oxidation catalyst (Table S1 in supplemental information – SI). Vehicles of such specifications

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are common in local transportation and, usually, older busses like the one tested here are used to

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increase service capacity during rush hours. Commercially available diesel fuel with less than

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10 ppm sulfur and a typical market-grade lube oil (10W-40) were used in all tests for both

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vehicles. A sample of the oil used in the bus was analyzed for residues after testing (more info in

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SI).

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Testing pattern. Chassis dynamometer measurements were conducted over repetitive cycles of

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acceleration, steady speed driving, deceleration, and steady speed driving at lower speed. The

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lower speed was 20 km/h, and the higher one was either 40 km/h or 80 km/h in different cycles.

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Steady speed driving lasted for 30 s, and acceleration ramps were executed with an average load


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of 70-90% of maximum engine load. Deceleration ramps were performed by the engine braking

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the vehicle, without applying wheel brakes or any exhaust throttling. The dynamometer tractive

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resistance was adjusted to represent half-full vehicle loading. Tests over the World Harmonized

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Vehicle Cycle (WHVC) were also performed for comparison. Recordings and more details on

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the cycles executed are given in the SI.

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Exhaust sampling and instrumentation. Particle samples were collected following partial

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dilution sampling, directly in the exhaust line, with a primary dilution ratio of 12:1. Removal of

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aerosol volatile material was conducted in some tests using a thermodenuder (TD) operating at

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265ºC. Particle concentration was measured by three parallel condensation particle counters with

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cutpoints at 2.5 nm, 7 nm, and 23 nm, respectively. An EEPS (TSI, Inc.) provided real-time size

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distributions. Individual particle characterization and elemental speciation was conducted by

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observing individual particles by transmission electron microscope (TEM) combined with energy

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dispersive X-ray spectrometry (EDS). Several engine operation parameters were also extracted

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using the SAE J1939 communication protocol. SI presents more details on the experimental

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setup implemented.

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RESULTS

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Figure 1 shows a 200 s long emission recording of two consecutive 20-40 km/h speed ramps of

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the truck. The top panel shows that fuel rate scales with vehicle speed and the highest values are

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reached during acceleration. At decelerations, the fuel delivery is interrupted and the engine is

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motored by vehicle inertia, thus braking the vehicle without application of the wheel brakes. The

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three following panels in Figure 1 show particle number emission rates and size distributions

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with and without the use of the TD. The concentration practically in all sizes and regardless of


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the use of the TD follows the fuel rate profile when the engine is fired, with accelerations leading

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to highest concentrations followed by steady speed driving at 40 km/h and then 20 km/h. The

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distribution in these cases shows a distinct soot mode peak in the range of 40-80 nm, a range

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typically expected from in-cylinder fuel combustion, and, occasionally, a second peak of sub-

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20 nm particles.


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Figure 1. Truck operation and particle emissions over two 40-20 km/h speed ramps. The top

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panel shows vehicle speed and fuel rate to the engine, the second panel from top shows particle

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number traces with and without use of TD and the two remaining panels show EEPS particle size

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spectra, again with and without TD use.


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The scaling of particle concentration with fuel rate is lost during decelerations. Braking from

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40 km/h to 20 km/h initially leads to a local peak of particle number, especially when no TD is

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used. This finding confirms the observation first made by Rönkkö et al.16 on new particle

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formation during engine motoring events. Particle number drops with time over the 20 s period

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that the deceleration lasts and, when no TD is used, gradually reaches the concentration level at

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20 km/h, despite no fuel has been delivered to the engine during the entire deceleration period.

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The particle size distribution differs during decelerations, compared to the one at fired operation.

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No soot mode is observed during deceleration, hence the particle formation mechanism during

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engine motoring is not based on combustion. The different size distribution also confirms that

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these particles are not late combustion residuals in the exhaust or the sampling system but actual

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exhaust products of the engine.

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The majority of those particles are volatile in nature. Their concentration downstream of the

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TD is one order of magnitude lower compared to upstream conditions, while a significant

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fraction of those resides in the 2.5-7 nm region. In fact, the number of non-volatile particles

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larger than 20 nm is negligible. This means that these particles would not be captured by the

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regulatory particle number protocol currently applicable for Euro VI trucks in EU that only

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addresses particles larger than 23 nm.20

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Typical particle size distributions from different operation phases of the truck are shown in

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Figure 2. When no TD is used, size distributions seem to significantly overlap, with those under

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fired conditions being either bimodal or monomodal with a measurable number concentration

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above 50 nm. Deceleration is the only phase practically producing no particles above 50 nm. All

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distributions are dominated by semi-volatile compounds. Removing semi-volatiles by the TD


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reveals that fired conditions produce bimodal distributions with a distinct distribution below

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20 nm and a soot mode with a median above 50 nm. Engine motoring results to an almost

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identical sub-20 nm mode with fired conditions but no soot mode. The number peak of the sub-

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20 nm mode is consistently found in the range of 6-10 nm, regardless of whether the engine is

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fired or not. The similarity indicates that the sub-20 nm mode, often called nonvolatile ‘core’

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mode21-24 or solid nucleation mode (NM)25, contains a strong fraction which is not combustion

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generated. As almost all of the many studies on non-DPF diesel exhaust have shown, this

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primary core mode acts as a condensation pool for volatile and semi-volatile material addition.

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The new material addition transforms these primary size distributions to the ones shown w/o TD

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in Fig. 2 (left panel).

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Figure 2. Typical particle size distributions at different operation conditions from the truck

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recordings, corrected for dilution ratio. Left, measurements w/o TD and right with the TD on.

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The particle number concentration and size distribution as a function of engine temperature are

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shown in Figure 3. The coolant temperature starting the engines from a cold start is shown on the


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top panels in both cases. Some initial data points were actually missing for the truck case due to

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error in recording (Figure S2 in SI). As shown by the EEPS size distributions with time, the soot

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mode appears from engine start and little changes as temperature gradually increases. The

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contribution of the sub-20 nm mode to total particle concentration is higher when the engine is

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cold. This is evident for all driving conditions and both vehicles by looking at the EEPS size

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distributions or by comparing the number concentration of particles larger of 23 nm with the

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concentration of particles above 7 nm or 2.5 nm. In fact, the majority of particles during cold

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start are in the sub-20 nm range. The NM concentration gradually weakens at steady speed

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conditions in time, in particular for the bus and the 40 km/h truck cases, while the soot mode

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becomes relatively stronger. This is a typical behavior of combustion generated aerosol where

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higher in-cylinder temperatures improve fuel volatilization and reduce volatile and semi-volatile

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particle formation.26

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On the contrary to fired conditions, the mean particle size and concentration of sub-20 nm

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particles during decelerations do not decrease as the engines of both vehicles warm up. In fact,

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the mean size of sub-20 nm particles increases with time, a trend which is more obvious for the

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truck. This is shown in the bottom panels of Figure 3, which provide three characteristic

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instances of size distributions during decelerations. In the bus case, NM practically disappears at

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fired periods and it remains present only during engine motoring periods. The growth in size is

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not as remarkable as in the truck case, but the engine temperature increase in the bus was more

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moderate in this test, from 40ºC to only 60ºC, compared to up to 80ºC for the truck. The general

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findings in Figure 3 were also observed in other driving profiles, which are shown in the SI.


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Figure 3. Time-series of particle characteristics recordings for the truck (left-hand side) and bus

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(right-hand side) over consecutive 20-40-20 km/h speed steps, starting from cold start. From top:

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(a) Engine operation parameters, (b) Particle number concentrations in three different size

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ranges, (c) Real-time particle distributions spectra obtained by EEPS, (d) Typical size

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distributions at decelerations, corresponding to points (i), (ii) and (iii) of panels (b).

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Additional evidence on the source and characteristics of the particles produced during fuel cut-

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off periods is provided by the TEM images combined with EDS analysis (Figure 4). These

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particles were sampled only while the vehicles decelerated, by switching on the TEM-sampler


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pump only during these phases of the driving cycle. Panel (a) shows at relatively low

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magnification the scarce presence of individual particles on the collection medium and the other

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panels focus on individual particles. Some particles (g) are larger than 200 nm and are abundant

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in metal species as a result of component attrition. Other large particles (f) are rich in S and K –

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the latter most often found as a residual of biodiesel production process. Smaller particles, in the

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range of 50 nm (b, c), are found to contain lube oil derived components such as Zn, Ca, and Mg.

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Si has also been observed in some of the particles but some studies consider Si to be a detector

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artifact in such measurements.27, 28 If this is not an artifact, Si can be found directly in engine

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intake if ambient air is not efficiently filtered or in the aged lube oil from the clean-up of ambient

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Si particles that have made their way into the engine. In fact, aluminosilicates and other Si-rich

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particles, similar in morphology to the one shown in panel (e) have been also observed by

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Popovicheva et al.29, 30

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Most interesting are particles in the (c, d, e, h) panels where dark spots smaller than 10 nm

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appear within a halo background. No elemental speciation by EDS could be identified for these

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small particles. Such particles of small “nuggets” within a moderately optical dense material

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were identified by Miller et al.31 when operating on hydrogen fuel and were recognized to be of

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lube oil origin. Kirchner et al.28 also spotted such particles in normal diesel exhaust at idle and

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quoted evidence32,

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surrounded the particles and rapidly evaporated at the TEM conditions. Their conclusion was

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that such a break-up was enhanced in the case of hygroscopic sulfate associated particles. This

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latter hypothesis is supported by Hinkley et al.34 who also observed such shapes under TEM

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observation of high-sulfur coal-fired power station particles and attributed those to crystallization

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of residues from evaporation of acidic sulfate. Kirchner et al.28 noticed that these dark spots

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that attributed the halo background to water ‘explosion’ that originally


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quickly disappeared under the TEM beam. Regardless of the exact origin of the nuggets, the

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original particles these come from are associated with sulfur in all studies. In our case, sulfate

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can only be associated with lube oil as the fuel practically contained only traces of sulfur.

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Figure 4. TEM images of typical particles observed during engine deceleration events

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downstream of the thermodenuder for the truck (a-d) and the bus (e-h). Main elements for each

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particle identified by EDS are designated in the figure. Yellow circles show individual particles

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and green areas show dispersed dark spots (nuggets) in halo. Bottom ribbon shows analysis of

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species found in oil after bus tests. Note different degrees of magnification in each case.

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The contribution of particles observed during decelerations can be a significant fraction of total

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particle emissions (Figure 5). For decelerations from low speeds typical for urban driving (e.g.

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40-20 km/h), the share of such particles can reach one quarter of total number emissions. This is

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due to the relatively high contribution of the number peak observed when deceleration starts


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(Fig.3). For mild decelerations of longer duration from higher speed, the importance of this

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initial peak to total emissions drops and this also decreases the contribution of engine motoring

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particles to total emissions. Over typical transient driving cycles with mixed driving conditions,

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the contribution of engine motoring particles was found to be 9-13%. This is a significant

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contribution from an environmental perspective if one combines their small size, non-volatile

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character, and the fact that the engine is not fueled while these are emitted. It should be again

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repeated that these particles, which are non-volatile and far from an artifact of the sampling

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system, would be excluded from measurement if the sampling protocol used by the Euro VI

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regulation had been followed. This protocol limits control of non-volatile particles above

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23 nm.20 Lowering this cutpoint to 10 nm, as is currently being discussed35, would be beneficial

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in taking into account engine motoring particles as well.

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Figure 5. Share of particles during engine motoring to total particle number emissions for the two

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vehicles and over different driving conditions.

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DISCUSSION

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A high number of nanoparticles at the exhaust of two HDD vehicles during deceleration events

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is observed in this study, confirming previous evidence.16 The particles consisted of a non-

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volatile core below 15 nm, extending down to 2.5 nm (low limit of the instrumentation used),

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and condensation of additional semi-volatile material resulted to the formation of a typical NM

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in the 15-40 nm size range. The number of these particles peaked immediately after the engine

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load was released and the decelerating vehicle started motoring the engine (engine braking). The

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particle number remained at measurable high levels for several seconds (~20 s) after deceleration

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started. Following a cold-start, the particle number and size during repeating decelerations

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increased as the engine warmed up, in contrast to the NM produced during fired conditions

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which became weaker with engine temperature.

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Lube oil is the only possible origin of such particles, as no fuel was injected during engine

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deceleration. Release of stored material from aftertreatment devices like oxidation catalysts

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might have been a secondary source36 but we observed these particles by both vehicles tested and

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one of them was equipped with no aftertreatment device. In fact, their appearance pattern can be

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well explained by the lube-oil consumption model developed by Tornehed & Olofsson37 for

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diesel heavy duty engines. According to this, lube oil is consumed in an engine primarily through

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its exposure to the combustion chamber by means of three mechanical and one physical process.

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The mechanical processes include throw-off during the upward piston movement, reverse blow-

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by during the expansion and intake strokes, and top-land scrapping, especially when deposits

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have accumulated on the piston top land. These processes lead to highest oil consumption over

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the exhaust stroke, owed to the upward piston movement. Evaporation scales with wall and

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piston temperatures, which maximize in fired conditions during the expansion stroke.


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Mechanical processes contribute to liquid oil consumption and hence result to both semivolatile

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and ash PM emissions while evaporation mostly results to vapor oil consumption and hence is

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assumed to contribute to semivolatile PM emissions only.

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Based on these processes, the particle emission peak at the start of the non-fired conditions can

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be explained by oil throw-off and some reverse blow-by as the cylinder pressure in the first

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exhaust strokes during deceleration is considerably relieved compared to the fired conditions and

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a new pressure difference between the cylinder and the crankcase is established. Both vehicles

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had an open crankcase ventilation system so no crankcase gas was returned back to the intake. A

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closed crankcase ventilation system might further augment the presence of these particles during

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decelerations. In parallel, temperature decrease with time reduces oil evaporation and, as a result,

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a large source of semivolatile material ceases. This can explain why particle concentration

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gradually drops during the deceleration but it is not eliminated for at least a 20 s period.

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Knowledge of the composition of these particles could provide hints regarding their formation

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pathways. However, these are too small to reliably detect composition, even when using EDS

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combined with TEM. Hence, one may only hypothesize they originate either from ash or heavy

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organic material. Volatilization of lube oil ash particles can occur at the high temperature zone of

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combustion. Vapors can then re-nucleate to form such smaller particles, repeatedly found in the

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5-8 nm range. This is a high-temperature process and is possible when the flame consumes the

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lube oil mist while this is mixed with fuel and air in the combustion zone. However, this cannot

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be the main mechanism during engine motoring, when no combustion occurs. During engine

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motoring, lube oil ash should rather end up unprocessed to exhaust PM, similar to those larger

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particles shown in Figure 4(c,e,f,g).


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Heavy organic compounds with metals, sulfur, or other minerals, are a more probable origin of

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core mode particles during engine motoring. The majority of hydrocarbon species in the lube oil

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are above C34, reaching at least up to C50.38 Pentacontane (C50H102), for example, has a boiling

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point of ~580ºC at ambient pressure, hence it would definitely survive in the particulate phase

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while lube oil mist is scavenged out of the cylinder during engine motoring. Partial oxidation of

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lube oil droplets may also lead to heavier oxygenated lube oil derived species; lube oil thermal

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oxidation is the main mechanism of heavy sludge formation in the crankcase. These mostly

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organic core particles would then act as sites for sulfate and lighter organics condensation to

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occur in the tailpipe or during sampling, which would increase their mean size to the 15-40 nm

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range. The pattern of small nuggets in halo observed with TEM (Figure 4c,d,e,h) would confirm

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such a mechanism, where nuggets are the heavy organic or organometallic species and

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condensed semi-volatile species, partly removed at TEM conditions, make up the halo.

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We may hypothesize that the core mode particles observed under engine motoring conditions

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due to lube oil may also partly explain core mode particles under fired conditions for both

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diesel21,

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significantly vary in terms of size between motored and fired conditions. Previous studies with

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TEM images28, 31 also observed nuggets in halo for fired conditions. The primarily organic origin

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of these spots would also be consistent to their translucent image under some TEM

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observations25 and their quick disappearance under the electron beam.28 The significant role of

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lube oil in core mode particles may also explain why Lähde et al.39 could not establish a link

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between core mode and fuel injection pressure, while such a link was clear for the soot mode size

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and concentration. Also, the fact they could not observe a core mode at low load may be

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associated with the low consumption of lube oil at low load.37

25, 39, 40

and premixed combustion.31,

41

Figure 2 showed that the core mode did not


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The formation of core mode due to organics in the cylinder would be consistent to the charge

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of these particles being equivalent to a Boltzmann distribution of around 600ºC,25, 42 i.e. much

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lower than typical combustion temperatures. Indeed, most of the lube oil is exposed to the

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cylinder at the end of the exhaust stroke, i.e. when the temperature has dropped below 800ºC.37

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This does not imply that all core mode particles under fired mode are produced in this manner.

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Core mode concentrations can be much higher than what we have observed here21 while high

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concentrations of nanoparticles have been also observed in flames when no lube oil is present.43,

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44

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the core mode.25, 39 Combustion processes43 and ash volatilization at high temperature may be

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additional sources of core mode particles at fired conditions. Additional core mode formation

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during combustion though does not contradict the fact that a large number of non-volatile

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nanoparticles under fired or motoring conditions is the direct result of unburned lube oil

333

emission.

Finally, it is not clear how a pure lube-oil mechanism could explain observed EGR effects on

334

Understanding and characterizing core mode particles is important. Primary organometallic

335

particles of this small size would be fully or totally combusted during DPF regeneration and

336

could liberate inorganic species at an almost molecular level that gradually penetrate through the

337

filter wall45 or contribute to the formation of new particles by recondensation downstream of the

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DPF during regenerations.46, 47 Identifying the oil species related to the process and introducing

339

relevant lube oil refinements could therefore reduce much of the problem. Most importantly, as

340

these particles act as core for the formation of nucleation mode, refinement of the lube oil could

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have a direct effect on emissions of non-DPF equipped diesel vehicles still in operation in

342

millions around the world today. This would offer a potential emissions reduction remedy that

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could readily be achieved without expensive retrofits of aftertreatment devices of often


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344

questionable effectiveness. In fact, similar particles have been observed in the exhaust of spark

345

ignition engines during engine motoring,16, 48 therefore lube oil refinement is expected to have

346

positive effects on the emissions of light duty vehicles as well.

347

The association of core mode particles during decelerations to lube oil consumption was

348

largely phenomenological in the current study, in the absence of an alternative plausible

349

mechanism. Moreover, the tests were performed in diesel engines of long service life and

350

subsequent wear. Repeating the research with different engine technologies and more recent

351

engines, including spark ignition ones, would be necessary to potentially generalize the

352

conclusions of this study. Experiments using lube oils of different formulation and ash and sulfur

353

content would shed more light to the formation mechanisms of such particles.

354

ASSOCIATED CONTENT

355

Supporting

356

instrumentation; time series of particle concentration and size distributions over transient tests.

357

This material is available free of charge via the Internet at http://pubs.acs.org.

358

AUTHOR INFORMATION

359

Corresponding Author

360

*Phone: +30 23 10 99 60 03, Facsimile: +30 23 10 99 60 12, email: [email protected]

361

ACKNOWLEDGMENT

Information.

Vehicle

details;

description

of

experimental

setup

and

362

Authors would like to express their gratitude to VTT’s heavy duty chassis dynamometer staff

363

for their work in the experiments. Finnish Transport Safety Agency (Trafi) is acknowledged for

364

the financial support of the study.


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Heavy Duty Diesel Exhaust Particles during ... - ACS Publications

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