sampling system effects on emission measurements: airing ... · ¾line losses greater than...
TRANSCRIPT
Bruce Anderson
and the
AAFEX Science Team
Sampling System Effects on Emission Measurements: Airing our Dirty
Laundry
AAFEX Data Workshop—Orlando
January 8, 2009
Sampling lines:
• What are the size dependent particle losses in the sampling lines?
• Do the particle losses change as the lines age?
• Are gas phase measurements influenced by the sampling lines?
• Do volatile particles nucleate and grow in the sample lines?
Sampling probes:
• Are particles lost in the 1-m probes due to inertial impaction or thermophoresis?
• Are the complex “particle” probes required for representative particle sampling or are existing “gas” probes good enough
• Are particle size distributions skewed by non-isokinetic sampling
• Does chemistry occur on the hot probe surfaces that destroys soot and carbon species
Sampling System Questions addressed during AAFEX
Particle Loss to Sampling Lines a Major Concern
Common aerosol sampling lines varied from 24 to 46 m long
Right 1 M LineLine Line Tube Residence (s) Residence (s)
Diameter (in) Length (in) Volume (l) 75 lpm 125 lpm0.04 0.02 0.00 0.00 0.000.25 1.55 0.05 0.04 0.020.31 1.84 0.09 0.07 0.040.56 0.03 0.00 0.00 0.000.31 0.54 0.03 0.02 0.010.62 19.92 4.62 3.70 2.22
24 meters 4.8 liters 3.8 seconds 2.3 seconds
Left 1 M LineLine Line Tube Residence (s) Residence (s)
Diameter (in) Length (m) Volume (l) 75 lpm 125 lpm0.04 0.02 0.00 0.00 0.000.25 1.53 0.05 0.04 0.020.31 1.94 0.09 0.07 0.040.56 0.03 0.00 0.00 0.000.31 1.33 0.06 0.05 0.030.62 35.45 8.23 6.58 3.95
40 meters 8.4 liters 6.75 4.05
Left 30 M LineLine Line Tube Residence (s) Residence (s)
Diameter (in) Length (in) Volume (l) 75 lpm 125 lpm0.62 46 9.03 7.23 4.34
46 meters 9.0 liters 7.2 seconds 4.3 seconds
Right 30 M LineLine Line Tube Residence (s) Residence (s)
Diameter (in) Length (m) Volume (l) 75 lpm 125 lpm0.62 38.2 7.44 5.95 3.57
38.2 meters 7.4 liters 6 seconds 3.6 seconds
Re > 32000 in all lines—Flows fully turbulentMeasured residence times 3x greater than calculated
Aerosol Sampling Line Characteristics
MST
ARI
NASA
3/8” St. St. Manual Valves
HEPA1/2 “ Air Actuated Ball Valves
Manifold
pump
Critical Flow Orifice
Right rake
Background
Left rake
30 m Right
30 m Left
Valve Box
3/8” Electrically Actuated Solenoids
AFRL
Vent
Sample Manifold Located in MST Trailer
Valve box plumbed to draw exhaust sample continuously though transmission lines to avoid stagnation; this could have led to soot build-up on surfaces
1 m left
30 m left
1 m right
30 m right
Calculations Suggest Lines have Small Impact
UTRC model assumes clean, smoothbore tubing; Predicts >90% mass transmission
LongDMA
ballast
Furnace
Contains Crucible w/NaCl
Pump
20 lpm
Filter
200 lpmTSI FM
hepa Eductor
N2 gas
regulator
hepa
Sampling LineTSI 3772
P
TSI 3772
P
RotameterMetering Valve (MV)
Line Losses Measured at End of Mission
Monodisperse particles generated and injected into sample lines, measured at each end using identical particle counters
10 1000.0
0.2
0.4
0.6
0.8
1.0
50%
30 m Left 30 m Right
Sam
ple
Line
Tra
nspo
rt Ef
ficie
ncy
Diameter (nm)
10 1000.0
0.2
0.4
0.6
0.8
1.0
1 m Left 1 m Right
Sam
ple
Line
Tra
nspo
rt Ef
ficie
ncy
Diameter (nm)
50%
Transmission Efficiencies Lower than Predicted
Lines from 30 m Inlet Probes
Lines from 1 m sampling rakes
Measured Particle Transmissions range from 50 to 90%
Clean Lines Typically Exhibit Fairly Low Losses
AAFEX Line Losses Assessed after 35 hours of Engine Runs
Penetration Efficiency of APEX‐3 Sample Lines
10 1000.0
0.2
0.4
0.6
0.8
1.0
30 m 1 m
Sam
ple
Line
Tra
nspo
rt E
ffici
ency
Diameter (nm)
50%
Results suggest lines should be frequently cleaned or that back-purging lines might be better than pulling continuous flow
Evidence Suggests Line Loses Increased with Age
0 1 2 3 4 5 6 70.0
0.2
0.4
0.6
0.8
1.0
R
elat
ive
Bla
ck C
arbo
n E
I
Experiment Day
Slope = -5%/day
#2 engine BC emissions at 30 m at 65 and 85% power
Lines also Influence Gas Measurements
Sticky molecules take time to come to equilibrium with tubing walls
Lag in signal depends on length and age of tubing
Decreasing vapor pressure
Time Constants Derived from Decay Curves
Low Volatility Gases Best Measured with Short Sampling Lines
10 20 30 40 50 60 70 800
100
200
300
400
500
Mas
s Em
issi
on In
dex
(mg/
kg)
Engine Power (%)
10 20 30 40 50 60 70 801015
1016
1017
Aero
sol N
umbe
r EI (
#/kg
)
Engine Power (%)
30 m Probe
30 m Probe
1 m Probe
1 m Probe
Do Lines Promote Volatile Aerosol Formation and Growth?
Number EIs typically 10 to 20 times higher in 30 m samples than 1 m due to nucleation of volatile aerosols
#2 engine, JP-8 Fuel
#2 engine, JP-8 Fuel
Volatile aerosol mass sometimes much greater than BC mass in 30 m samples
All near-field observations to date made using long sampling lines
Line Effects Assessed by Comparing Box vs. Truck
Sampling Line Residence Times <1 sec vs. 16 seconds
~1 m
29.5 m
0 20 40 60 80 1000.0
2.0x1016
4.0x1016
6.0x1016
8.0x1016
1.0x1017
1.2x1017
Deathbox EEPS NASA EEPS
Num
ber E
I (#/
kg)
Engine Power
Jan 28, morning, JP-8 fuel
0 20 40 60 80 1000
50
100
150
200
250
300
350
Deathbox EEPS NASA EEPS
Volu
me
EI (u
m3/
kg)
Engine Power
Jan 28, morning, JP-8 fuel
Measurements Indicate Volatile Aerosols Nucleate in Plume
Volume EIs Comparable
Deathbox Number EIs 2X higher than Truck Values
Sampling Line Residence Times <1 sec for box, 16 seconds for truck
10 100
0
100
200
300
400
500
600
UTRC NASA
V
olum
e E
I (um
3/kg
)
D iameter (nm)
Jan 28, 7% power
10 100
0
20
40
60
80
100
120
140
UTRC NASA
Vol
ume
EI (
um3/
kg)
D iameter (nm)
Jan 28, 45% power
10 100
0
20
40
60
80
100
120
UTRC NASA
Vol
ume
EI (
um3/
kg)
D iameter (nm)
Jan 28, 65% power
10 100-20
0
20
40
60
80
100
120
140
160 UTRC NASA
Vol
ume
EI (u
m3/
kg)
D iameter (nm)
Jan 28, 85% power
Sampling Lines Influence Shape of Size Distributions
Small aerosols are lost to tubing surfaces or undergo coagulation
Does it matter if probe velocity matches the exhaust velocity?
Calculations suggest mismatched velocities may effect large particle numbers
Number and mass EIs show a decreasing trend
with sample concentration (except for jump at highest point)
Isokinetic Sampling Effects Assessed (imperfectly) by Varying Dilution Flow
Data recorded at 85% thrust where exhaust velocity -> mach 1
Increased dilution flow raises pressure in probe, reduces inlet velocity; iso‐kinetic effects convolved with changing line losses
Number EI
Mass EI
~5X change in flow velocity
0 50 100 150 200 250 300 350
0.0
0.5
1.0
1.5
2.0
2.5
3.0
CO2-1100 CO2-1900 CO2-2900 CO2-3700 CO2-530
Tota
l Aer
osol
Vol
ume
EI (
um3/
kg)
Diameter (nm)
10 100
0.5
1.0
1.5
2.0
2.5
3.0
3.5
530 ppm 1100 ppm 1900 ppm 2900 ppm
Rat
io o
f Vol
ume
Dis
tribu
tions
(SM
PS
1)
Diameter (nm)
85% Power, Ratio of X size distribution to 3700 ppm size dist
Results are inconclusive—further study warranted; better experiment needed
Large Particles Enriched, but is Flow Velocity the Cause?
Total sample flow changes by up to 75% across dilution range; this may be primary cause for changes in number and mass EI
Mean Diameter
AAFEX WORKSHOPOrlando FloridaBruce Anderson, NASA LaRC Jan 8, 2010
Are Particles Lost to the 1 m inlet probes?
Probe Losses Assessed by Comparing 1 and 30 m NV Particle EIs
Recall that 50% of particles are lost in 30 m sample line, only 10% in 1 m line
Mass EI
Number EI
Left Engine--All DataRed=Individual Points
Blue=average
30 m EIn values high at low power due to re-condensation
of volatile material after heater; no evidence of this at
>45% power
Right Engine--All DataRed=Individual Points
Blue=Average
30 m EIn values high at low power due to re-condensation
of volatile material after heater; no evidence of this at
>45% power
Losses More Pronounced on Right Engine because of Similar Sampling Line Transmission Characteristics
Losses may be caused by impaction, diffusion, thermophoresis or catalytic oxidation
Mass EI
Number EI
0 5 0 1 0 0 1 5 0 2 0 0 2 5 0 3 0 0 3 5 0-2 0
0
2 0
4 0
6 0
8 0
1 0 0
1 2 0
1 4 0
1 6 0
1 8 0
2 0 0
3 0 m 1 m
Non
vola
tile
Vol
ume
EI (
um3/
kg)
D ia m e te r (n m )
L e f t E n g in e , 8 5 % P o w e r , J 2 7
0 5 0 1 0 0 1 5 0 2 0 0 2 5 0 3 0 0 3 5 0
0
5 0
1 0 0
1 5 0
2 0 0
3 0 m 1 m
Non
vola
tile
Vol
ume
EI (
um3/
kg)
D ia m e te r (n m )
L e f t E n g in e , 8 5 % P o w e r , J 2 8
0 5 0 1 0 0 1 5 0 2 0 0-2 0
0
2 0
4 0
6 0
8 0
1 0 0
1 2 0
1 4 0
1 6 0
1 8 0
3 0 m 1 m
Non
vola
tile
Vol
ume
EI (
um3/
kg)
D ia m e te r (n m )
L e f t E n g in e , 8 5 % P o w e r , J 2 9
0 5 0 1 0 0 1 5 0 2 0 0 2 5 0-2 0
0
2 0
4 0
6 0
8 0
1 0 0
1 2 0
1 4 0
1 6 0
1 8 0
3 0 m 1 m
Non
vola
tile
Vol
ume
EI (
um3/
kg)
D ia m e te r (n m )
L e f t E n g in e , 8 5 % P o w e r , J 3 0
1 m values at sizes >100 nm always lower; is this caused by inertial losses at 1 m or by contributions from background aerosols at 30 m?
Loss of Large Particles at 1 m Drive Lower Mass EIs
To examine benefit of dilution probe, a gas probe was re‐plumbed to introduce
dilution gas ~1 m downstream of the inlet tip, then data was recorded as we
switched back and forth between the aero and gas probes at different power settings
Is it necessary to use “dilution” probes for particle sampling?
Special rakes required to support probes, add greatly to cost and complexity of tests
= Water
= Diluent
A
A
Section A-A= Sample
AEDC Dilution Probe
Right Engine‐‐JP‐8 FuelRed=Aerosol ProbeBlue=Gas Probe
Number and Mass EIs Roughly Equivalent
Right EngineJP‐8 Fuel
Red=Aerosol ProbeBlue=Gas Probe
Some Indication that Nucleation Occurs in Gas Probe
Line losses greater than predicted, probably due to build-up of surface contaminants during testing. Losses clearly a major problem—sampling approaches need to be strictly defined.
Sticky gases require a long time to reach equilibrium with sample line walls, makes accurate determination of alcohols, acids and PAHs difficult.
Volatile aerosols condense in plume, but continue to form and grow within the long sampling lines.
Evidence suggests that probe inlet velocity matters, but is difficult to resolve from other sampling effects.
Results clearly indicate that particles are lost to the 1 m inlet probes, but the exact mechanisms responsible are difficult to define.
Gas probes yield OK particle mass emissions data, but can lead to number EI enhancements due to nucleation in undiluted section
Summary