Sedimentation field flow fractionation (SdFFF) · Sedimentation field flow fractionation (SdFFF) of...

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Sedimentation field flow fractionation (SdFFF)of soot particles emitted by a light duty diesel

James R. Kassab1,2, Annett Wollmann3, Richard Zahoransky2, Michael Claussen3, Philippe J.P. Cardot1*

1 Laboratoire de Chimie Analytique et de Bromatologie, Université de Limoges Faculté de Pharmacie, 2 Rue du Dr. Marcland, F-87025 Limoges

2 Fachhochschule Offenburg, University of Applied Sciences, Badstr. 24, D-77652 Offenburg

3 CUTEC Institut GmbH, Leibnizstr. 21 & 23, D-38678 Clausthal-Zellerfeld

8th ETH Conf. on Combustion Generated Nanoparticles Aug. 2004

Content

• Field Flow Fractionation: Subtechnique Sedimentation FFFSdFFF; theory of retention and field programming

• Off-line hyphenation of SdFFF with Optical MultiwavelengthTechnique (OMT) for particle analysis

• SdFFF system in use

• Soot collection and sample preparation

• Soot fractionation and size analysis by OMT

• Comparison to size analysis by SMPS

• Conclusion


Field Flow Fractionation (FFF)

• First conceptualized by Giddings 1960s

• Separation occurs inside a thin ribbonlike channel clamped between two highly polished plane and parallel walls

Parabolic flow profile

Flow in Flow out

External field


Overview on FFF subtechniques

+semipermeable

walls

Hot plate (metal)

Cold plate (metal)

dTdx

Thermal FFF

E

-Electrical FFF

U (cross flow)

inflow

outflow

Flow FFF


Sedimentation FFF (SdFFF)

SdFFF separator principle Cross sectional view of the channel

Accumulation wall

Spin DirectionFlow in

Flow out

Inlet streamOutletstream

Thickness

Zone A

w

Parabolicflow profile

Injection

Exit port(to detector)

Rotation Flow

Zone B

rω2r


Retention in the normal mode

External field

Flow

Zone A (slow) Zone B (fast)

Parabolicflow profile

Accumulation wall

x

z

lA

lBV1

V2

V1

V2


Sedimentation field programming

Accumulation wall

Relaxation time

l1l2 l3 l4

0

0.05

0.1

0 30 60 90Time (min)

Det

ecto

r sig

nal (

mV

)

1 2 3 4


Off-line hyphenation of OMT with SdFFF

Combining the size separation technique SdFFFwith the particle sensor

OMT (Optical Multiwavelength Technique WIZARD DQ):Benefit from the separation potential of SdFFF to measure the mean particle sizes of collected fractions obtained frombroadly distributed particulate sample

Confirmation whether a selective FFF separation occurred according to the concerned elution mode

Obtained sizes can be compared to those determined by other sizing techniques such as EM and PCS


Dispersion Quotient Technique (1): OMT principle

monodisperseI = I0·exp{-N·L·π·r2·Qext(r,λ,n)}

polydisperseI = I0·exp{-L·N·π·∫ r2·Qext(λ,r,n)·p(r)dr

LASER

L

Detector

IntensityI0

IntensityI

Particle Cloud

with:I = intensityI0 = initial intensityN = particle concentrationL = optical path lengthr = particle radius Qext = extinction coefficientλ = wavelength n = refractive indexp(r) = number distribution


Dispersion Quotient Technique (2)OMT Principle

2ln

1ln

0

0

1

λ

λ

⎟⎠⎞

⎜⎝⎛

⎟⎠⎞

⎜⎝⎛

=

IIII

DQ

measured values),,(

),,(

2

12

2

nrQnrQ

rLNrLN

ext

ext

λλ

ππ

⋅⋅⋅⋅−⋅⋅⋅−

=


Transient Measurements (ECE)

OMT Particle Analyzer(WIZARD-DQL)

ECE Cycle

LD Engine

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.10

0 20 40 60 80 100 120 140 160 180

Time [sec]

Mea

n di

amet

er [µ

m]

0.0E+00

1.0E-09

2.0E-09

3.0E-09

4.0E-09

5.0E-09

6.0E-09

7.0E-09

8.0E-09

9.0E-09

Volu

me

conc

entr

atio

n [m

3 /m3 ]

Diameter

Concentration

0

500

1000

1500

2000

2500

3000

0 20 40 60 80 100 120 140 160 180

Time [sec]

Spee

d of

rot.

[rpm

]

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

90.0

Torq

ue [N

m]

Pow

er [k

W]

Speed

Power

Torque

0%

20%

40%

60%

80%

100%

120%

0 20 40 60 80 100 120 140 160 180

Time [s]

Inte

nsiti

es

635 nm

810 nm

1310 nm


Schematic of the OMT

LASER 1

LASER 2

LASER 3

LASER -CONTROL

OPTICS

Reference Detector

TIME CONTROL SIGNAL INTERFACE

POWER SUPPLY

Signal DetectorMeasurement chamber

Central Unit

Sensor Head

Data Acquisition


OMT: WIZARD DQLLight Beam, 3 Wave Lengths

ControlUnit

Sensor Head

to Measure-ment Chamber& Detector(Not Shown)


Off-line hyphenation set up

SdFFFseparator

Time dependent fraction collection

Fraction concentrationOMT unit

Fraction collector

CentrifugationVolume reductionSonication & vortexing

Microcuvette of 160 µL volume capacity

1 cm optical path length

Elution after retention


FFF System: SdFFF

DetectorInjection System

Pump

Channel

External Field

Spin DirectionFlow in

Flow out

Inlet streamOutletstream



SdFFF separator

rotor bowl

inlet tubing

rotor axisrotating seal

inlet tubing

outlet tubing

motor anti-vibrationsystem

rotating seal

outlet tubing

Rotor bowl

Tachometer

Rotatingseal

Front View

Rotor bowl

3-phase engine

Rotating seal

Back View

Diesel engine at CUTEC site

• 4 cylinder LD VW EURO III 85 KW engine, displacement volume 1.9 L

• Variable geometry torroidal technology (VGT)

• Exhaust gas recirculation (EGR)

• Pump unit injection (PUI)


Engine Set-up at CUTEC Site


Dilution system

Second injectordilution ratio:1:5 - 1:30

Filter holder

Heated hose200ºC

Pump70 L/min

Flowmeter

Injectordilution ratio:1:7 - 1:10

Micro dilutiontunnel

• Micro dilution tunnel

• Rapid mixing with the conditioned ambient air or dilution air

• Constant volume sampling (CVS)

• Teflon coated glass fiber filters Pallflex (70 mm diameter)


Sample preparation

• Soot recovery by bath-sonication in 10 ml ethanol

• Mixture of ethanol+soot with 10 ml n-hexane

• After the removal of n-hexane, 5 ml distilled water containing 0.1% (w/v) and 0.02% NaN3 are added

• Dispersion by 10 min bath-sonication

• Ethanol evaporation by heating at 70ºC

• Sonication by a sonic dismembrator for 90 min and vortexing

• Carrier liquid and suspension media: doubly distilled water containing 0.1% (w/v) and 0.02% NaN3

• Injection volume: 100 µL


Surfactant concentration effect

Elution conditions: initial field strength = 600g (1972 rpm); injection flow rate=0.2 ml/min; Predecay time= 5 min; stop flow time=15 min; final field strength=29.60g (439 rpm); elution flow rate= 1.2 ml/min


Sonication effect


Soot elution by SdFFF


TEM pictures of soot (aerosol)


Engine speed effect on particle size at 180 Nm torque

Engine speed effect on particle size at 80 NM

0

60

120

180

1 2 3

Soot samples

Mea

n pa

rticl

e siz

e (n

m)

0

6

12

18

PM p

r hou

r (m

g)

OMTSdFFFSMPSPM per hour

1800 RPM 2400 RPM 3000 RPM

0

40

80

120

160

1 2 3

Soot samples

Mea

npa

rtic

lesi

ze(n

m)

0

2

4

6

PM p

er h

our(

mg)

1800 rpm 2400 rpm 3000 rpm


In exhaust (aerosol)

In suspension

SMPS

OMT: primary particles

SdFFF OMT


Torque effect on particle size at 3000 rpmTorque effect on particle size at 1800 RPM

0

60

120

180

1 2Soot samples

Mea

n pa

rticl

e siz

e (n

m)

0

6

12

18

PM p

er h

our (

mg)


80 NM 180 NM

Torque effect on particle size at 2400 RPM

0

70

140

1 2Soot samples

Mea

n pa

rticl

e siz

e (n

m)

0

2

4

6

PM p

er h

our (

mg)


80 NM 180 NM0

40

80

120

160

1 2

Soot samples

Mea

npa

rtic

lesi

ze(n

m)

0

4

8

12

PM p

er h

our(

mg)

80 Nm 180 Nm

In suspensionOMT


In exhaust (aerosol)

SMPS

OMT: prim. particles

SdFFF


Conclusion

• Soot particle size variation analyzed by OMT and SdFFFin the collected PM amount is related to the different engine load conditions

• The detected mean soot particle sizes in liquid suspen-sions differ appreciably to those in aerosols:

- SdFFF and OMT measurements in liquid: 120 – 160 nm- OMT measurements in the raw exhaust: approx. 20 nm

(primary particles)- SMPS measurements in the diluted exhaust: 60 – 80 nm

• Different soot agglomerates in liquid and aerosol

• Surprisingly, the suspended soot particles keep specific characteristics related to engine load conditions


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