Evaluation of the Engine Exhaust Particle Sizer (EEPS) for real-time measurements of diesel and biodiesel exhaust particulate matter (PM).

1. Electrical Mobility
Measurements of Agglomerate
Particulate Matter
Jim Dunshee
MS Thesis Defense
November 11th, 2015

2. Slide 2
Historical Perspective: Particle Uncertainty
“…but how many particles are really
present under any conditions, and how
the number varies, we have at present
very little idea.”
- John Aitken, 1888
SOURCES: Aitken, 1888; Wellcome Library; Seinfeld & Pandis, 2006

3. ≥10 microns (µm)
visible to the human eye
Slide 3
Particulate Matter (PM)
IMAGE SOURCE: ciese.org
“A complex mixture of extremely small
particles and liquid droplets” (US EPA)
PM10 PM2.5

4. Slide 4
PM & Health
• Class 1 Carcinogen
• No evidence of safe exposure level
(World Health Organization, 2013)
IMAGE SOURCE: alencorp.com (Everything You Need to Know About Airborne Particulate Matter)

5. Slide 5
Particle Size Distribution
Low←Number→High Small ← Particle Diameter → Large

6. Slide 6
Diesel PM Size Distribution
IMAGE SOURCE: Kittelson,, 1998

7. Slide 7
Spark vs. Compression Ignition Engine Emissions
IMAGE SOURCE: dieselnet.com
SI engine with catalyst
Diesel engine (100%)
RelativeEmissions(%)

8. Slide 8
Engine Cycles
Gasoline - Otto Cycle
• Spark Ignition (SI)
• Homogeneous combustion
• Burns “rich”
• Air-fuel ratio < stoichiometric
Diesel - Diesel Cycle
• Compression Ignition (CI)
• Heterogeneous combustion
• Burns “lean”
• Air-fuel ratio > stoichiometric
IMAGE SOURCE: Reactive Flow Modeling Laboratory (rfml.kaust.edu.sa)

9. Slide 9
Diesel PM/NOx Tradeoff
Diffusion Flame Combustion
Oxidation
• Decreases soot (PM)
• Increases NOx
SOURCES: Kittelson & Kraft, 2014; Dec, 1997

10. Slide 10
Diesel PM Formation
IMAGE SOURCES: Khalek, 2006; Twigg & Phillips, 2009
Elemental
Carbon (EC)
Organic
Carbon (OC)

11. Slide 11
PM Formation by Particle Size
IMAGE SOURCE: Guarieiro & Guarieiro, 2015
Re-
entrainment
Engine wear

12. Slide 12
Diesel Properties
Medium petroleum distillates: C8 – C21
Ultra-Low Sulfur Diesel (ULSD):
Naturally occurring sulfur (a lubrication agent)
reduced to 15ppm = less soot formation
~75% Alkanes ~25%
May result in toxic
aromatic emissions
IMAGE SOURCE: criticalfueltech.com

13. Slide 13
Biodiesel Properties
Fatty Acid Methyl Esters (FAMEs)
Potential to reduce PM:
• Oxygen content of molecule (complete combustion/soot oxidation)
• Absence of sulfur
• Absence of aromatic compounds
(Lapuerta et al., 2007)
IMAGE SOURCE: biofuelsystems.com/biodiesel-chemistry

14. Slide 14
Biodiesel PM Properties
Chung et al., 2008 (diesel generator):
Irregular compact particles with more
organic carbon relative to ULSD
SOURCE: Chung et al., 2008
Diesel
Biodiesel

15. Slide 15
PM Measurement
The Gravimetric Method
Operational Definition:
“mass collected on a filter”
under specified conditions
(Swanson et al., 2012)
Units: Mass Concentration (µg/m³) =
Issues:
1) Temporal Resolution
requires time to collect sample
2) Measurement Error
low modern vehicle emission rates

16. Diesel PM Emission Standards
Slide 16SOURCES: (a) Twigg & Phillips, 2009; (b) Vouitsis et al., 2003
(b) US and EU diesel PM
emission limits for
heavy-duty vehicles
from 1992-2010
(a) EU legislated diesel PM
emission limits for
passenger cars from
1983-2010

17. Slide 17
Gravimetric Accuracy
SOURCE: Vouitsis et al., 2003; ACEA report 99000524
Note: emission rates and standards for heavy-duty engines

18. Slide 18
New Method: IPSD (Integrated Particle Size Distribution)
Basic procedure
1. Measure particle size
distribution (PSD) by
number
2. Assume spherical
particles to calculate
volume
3. Apply size dependent
density values to
calculate mass
m = ρV
mass = density x volume
Low←Number→High
d
2 = r
V = 4
3 πr3
IMAGE SOURCES: vironova.com, rkm.com.au
Method formalized by Liu et al. (2009)

19. • Light-duty vehicles (gas & diesel)
• Empirically based particle effective density values
• Good correlation (R² = 0.79) between IPSD and
Gravimetric
• Systematic bias (MassIPSD = 0.63 x MassGrav)
Slide 19
Li et al. (2014) : IPSD Study

20. Slide 20
Problem With PSD Measurements (EEPS)
Discrepancies reported between
Engine ExhaustParticle Sizer (EEPS or FMPS)
and Scanning Mobility Particle Sizer (SMPS)
for agglomerate particles (e.g., diesel soot)
(Kaminski et al., 2013; Quiros et al., 2014; Zimmerman
et al., 2014)

21. Slide 21
SMPS (Scanning Mobility Particle Sizer)
IMAGE SOURCES: Guha et al., 2012; redwoodareahospital.org
Considered the “gold standard” particle sizing/counting system

22. Slide 22
SMPS: Bipolar Diffusion Charging
Roughly independent of particle morphology
Note: Particle charging efficiency drops dramatically below 20nm for Boltzmann distribution (shown).
Fuchs charging theory is better for Dp < ~50nm.
Charge distribution forms over time (Hinds, 1999):
< -3 -3 -2 -1 0 +1 +2 +3 > +3
0.01 0.007 0.3 99.3 0.3
0.02 0.104 5.2 89.6 5.2
0.05 0.411 0.6 19.3 60.2 19.3 0.6
0.1 0.672 0.3 4.4 24.1 42.6 24.1 4.4 0.3
0.2 1.00 0.3 2.3 9.6 22.6 30.1 22.6 9.6 2.3 0.3
0.5 1.64 4.6 6.8 12.1 17.0 19.0 17.0 12.1 6.8 4.6
1.0 2.34 11.8 8.1 10.7 12.7 13.5 12.7 10.7 8.1 11.8
2.0 3.33 20.1 7.4 8.5 9.3 9.5 9.3 8.5 7.4 20.1
5.0 5.28 29.8 5.4 5.8 6.0 6.0 6.0 5.8 5.4 29.8
10.0 7.47 35.4 4.0 4.2 4.2 4.3 4.2 4.2 4.0 35.4
Percentage of particles carrying the
indicated number of charges
Dp
(µm)
Average
No. of
Charges
IMAGE SOURCE: palas.de/en/product/kr8557

23. Slide 23
EEPS (Engine Exhaust/Fast Mobility Particle Sizer)
Unipolar charger:
SOURCES: Krinke & Zerrath, 2011; TSI, 2015

24. Slide 24
EEPS: Unipolar Diffusion Charging
Default calibration underestimates
charge for agglomerates
IMAGE SOURCE: TSI, 2015
TSI Solution:
New, empirically
based, EEPS data
inversion matrices
Problem:
EEPS unipolar charge distribution
calibrated for spheres (emery oil)

25. turbocharged, 4 cylinder, 4.5L, 75kW, Tier 3 diesel engine
fueled with BP6 diesel fuel with a sulfur content of 6ppm
Slide 25
New EEPS Matrix Development by TSI
SOURCE: TSI, 2015

26. Slide 26
New EEPS Matrices: Soot & Compact
Instrument matrix calibrated for soot Comparison of current matrices
at 420nm and 42nm
electrometer columns

27. Slide 27
Soot Matrix Results: Heavy-duty Engine
IMAGE SOURCE: TSI, 2015
Low Load:
High Load:
Number Volume

28. Slide 28
Soot Matrix Results: Light-duty Engine
IMAGE SOURCE: TSI, 2015
GM A20DTH 2.0L light duty turbo charged diesel engine

29. Slide 29
GMD Agreement with Soot Matrix
No longer underestimates larger
agglomerate particles (Dp > ~100nm)
IMAGE SOURCE: TSI, 2015

30. 1) How accurate are new EEPS matrices for various
vehicle exhaust particles?
a) Biodiesel - unique morphology/chemical composition?
b) Transient drive-cycle
2) Do new EEPS matrices improve mass estimates
with IPSD method?
a) IPSD vs. Gravimetric
b) Transient events (e.g., cold-start)
Slide 30
Research Questions?

31. Slide 31
Current Study
Experiments/Dataset 1: EEPS Evaluation
Experiments/Dataset 2: Cold-start Emissions
EEPS measurements for first 30sec of engine start at
10, 15, and 25°C (nominally)

32. Slide 32
Data Collection Sequence
Event Setting Duration
Instrument Blank (preIB) Instrument on HEPA filter ≥10min
Tunnel Blank (preTB) Dilution System On ≥10min
Engine Idle Engine On 7.5min
Engine Warm-up 3300rpm, 40 or 60% Throttle 7.5min
Test Cycle Various ~90min
Engine Cool-down (Idle) Engine On 7.5min
Tunnel Blank (postTB) Dilution System On ≥10min
Instrument Blank (postIB) Instrument on HEPA filter ≥10min
Test Cycles
1) Steady State (75% engine load)
2) Transient (60min) + 3x10min Steady State Phases
- Depicted in Slide 37

33. Slide 33
Experimental Setup
Engine exhaust
Dry, filtered air
Key:
Differential
Pressure Gage
Temp. Control
Setpoint (°C)
2 stage
diluter
Diluted Sample
Dilution Ratio ~80:1
Engine drive cycle and dilution system developed by by Tyler Feralio (image credit)
Engine:
Volkswagen 1.9L SDi (similar to Euro II LDD)
• 4 Cylinders
• No aftertreatment devices

34. Slide 34
Fuel Properties
SOURCE: GC-MS analysis conducted by John Kasumba
ULSD (0.81g/cm³) Soybean Biodiesel (0.86g/cm³)

35. Slide 35
Density Distribution

36. Slide 36
Quality Assurance: SMPS & Filters
SMPS (units: #/cm³)
90min Filter Blanks (Tunnel)
N 5
Avg 4 µg/m³
StDev 2.4
Minimum value from tests:
35.5 µg/m³
Reported as: MEAN [95% One-sided Upper Confidence Limit]

37. Slide 37
QA: EEPS Dataset 1 – Box Plots

38. Slide 38
QA: EEPS Dataset 1 – Detection Limit
EEPS pre-test instrument blank data

39. Slide 39
ULSD Steady State PSDs
Log-log plot Semi-log plot

40. Slide 40
ULSD Modal Fit Parameters

41. Slide 41
Xue et al. (2015): Generator on ULSD
SOURCE: Xue et al., 2015

42. Slide 42
ULSD PM Mass Data

43. Slide 43
Soot vs. Default: Transient Cycle w/ ULSD

44. Slide 44
ULSD Transient Phase: Fractional Contributions

45. Slide 45
ULSD Steady State: Fractional Contributions

46. Slide 46
Betha & Balasubramanian (2011): ULSD Particle Fractionation
Idle 30% 70% 100%
Engine Load (%)
100%
80%
60%
40%
20%
0%
ParticleNumberFraction(%)
Nanoparticles
(>50nm)
Ultrafine
(50-100nm)
Fine
(>100nm)
FMPS data (i.e., Default EEPS matrix) for diesel generator exhaust
SOURCE: Betha & Balasubramanian, 2011

47. Slide 47
Biodiesel Steady State PSDs
Log-log plot Semi-log plot

48. Slide 48
Biodiesel Modal Fit Parameters

49. Slide 49
Xue et al. (2015): Generator on Biodiesel
SOURCE: Xue et al., 2015

50. Slide 50
Biodiesel PM Trend
Gravimetric PM
data by biodiesel
blend for the light-
duty diesel engine
from this study
(dashed line &
blue data points)
General trend
reported by EPA
(2002) - solid line
and black data
points
Giakoumis et al. (2012)
Majority of data for
EPA (2002) &
Giakoumis et al.
(2012) for heavy-
duty diesel engines
Bielaczyc et al. (2009)
data for a LDD engine

51. Slide 51
Biodiesel PM Mass Data

52. Slide 52
EEPS Report Card
Key
SP: Satisfactory Progress
UP: Unsatisfactory Progress
IMAGE SOURCE: diplomabuy.com

53. Slide 53
QA: EEPS Dataset 2 – Box Plots

54. Slide 54
QA: EEPS Dataset 2 – Detection Limit
EEPS pre-test instrument blank data

55. Slide 55
ULSD Cold-start Emissions

56. Slide 56
Cold-start: Fractional Contributions

57. Slide 57
Sakunthalai et al. (2014): ULSD Cold-starts
Cambustion Differential
Mobility Spectrometer
(DMS500) data for LDD
engine exhaust
SOURCE: Sakunthalai et al., 2014

58. • EEPS Soot Matrix
• Good agreement for ULSD (SMPS and Filter)
• Applied to cold-start emissions
• Biodiesel Exhaust Particles
• Not characterized well by EEPS
• Poor agreement with SMPS and Filter
Slide 58
Conclusions

59. • Biodiesel exhaust particle effective density
• Additional EEPS matrices
• Or user calibration
• EEPS evaluation for biodiesel blends
• EC/OC analysis by engine load
• Compared to particle size fractionation trend
Slide 59
Future Work

60. UVM Transportation Air Quality Lab
Britt Holmén
Tyler Feralio
John Kasumba
Karen Sentoff
Yao Tan
Acknowledgements

61. Questions & Answers

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Chung, A., A. A. Lall, and S. E. Paulson. "Particulate emissions by a small non-road diesel engine: Biodiesel and diesel characterization
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Agency (2002).
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