particulate emission measurements from aviation gas

Particulate Emission

Measurements from Aviation

Gas Turbine Engines 10th November, 2016 University of Birmingham, UK Mark Johnson Rolls-Royce Global Emissions Measurement Expert

Particle distribution from a combustion exhaust (typically <100nm diameter) consists of

• Non-volatile primary and agglomerate particles (solid carbon/smoke)

And

• Volatile (condensation) particles (hydrocarbons and sulfate)

Difference between non-volatiles and volatiles defined by temperature of 350degC.

Current belief - volatile combustion generated particles do not exist at the engine exit.

They form only in sampling lines and/or downstream of engine

TEM examples below (note Electro-mobility diameter shape difference)

Gas Turbine non volatile Particulate Matter (nvPM)

What are we trying to measure

Aerosol Society Meeting – Birmingham 10th November 2016

Cleaning Mechanisms

• Removal from alveolar region by

interaction with macrophages -inefficient

for particles < 80 nm.

Majority of gas

turbine

combustion

particles fall in

this size range

Aviation PM driver: LAQ – Human health impact

• The smaller the particle the deeper

it enters the human body

• Ultrafine particles have a strong

impact on human health

• Ultrafine particles are under-

represented in mass-based metrics

• Key property is the particle

surface area.

• Interaction mechanisms are not

yet understood.


Existing ICAO regulation - Smoke Number (visibility)

SAE Smoke Number method determined over 60 years ago

based on reflectance of smoke stained filters

Inaccurate at current technology smoke levels & no easy link to LAQ or

climate impact

ICAO/Regulators asked for nvPM mass and number


Aviation GT nvPM Sampling & Measurement System

Development & experimental trials

2009- Official regulatory request to SAE E31 Accurate measurement of nvPM Mass & Number

2008-14 EASA SAMPLE Programme (€2.5m) Sampling system development - European reference system designed and

tested including several intercomparisons

2011- … APRIDE- SR Technics Zurich (€4m + €5m ) Swiss fixed reference system and sampling probe integrated to test cell –

numerous 2-way & 3-way inter-comparisons with other reference systems

2012- … PARTNER & ASCENT (€6m) North American reference system comparisons,

2013- … OEM Testing (€>10m) R-R, GE, HW, P&W & SNECMA, operability

2014-16 VARIAnT I&II (€1.3m) System Inter-comparisons & System Loss

2014-16 DG-MOVE (€1m) System Inter-comparisons


6 6

Rolls-Royce data - In

Comparison of

2 x compliant

sampling

systems

System 1

System 2

Mass1

Mass2

Number 1

Size

Number 2

Example nvPM certification methodology test

at Zurich (2012)

ICAO / SAE regulation setup Annex 16 Vol II Appendix 7 / ARP6320 (2016)

10 systems now in operation worldwide (circa £500k to build/buy per system)


Aircraft engine sampling

systems are much longer than

automotive due to:

- Harsh (vibration and

temperature) environment

close to large engines

- Complex probes for exhaust

representativeness

Results in sampling line lengths

>25m and therefore significant

particle loss

nvPM Measurement

system

Thick Te

stbe

d W

all

Difficulties in Aero large engine sampling…


Typical Aero gas turbine particle size distributions measured at end of sampling system, after particle loss

Aero gas turbine particle sizes range typically between 20 and

50nm and are significantly affected by size dependent particle

loss mechanisms


Particle loss mechanisms

UTRC model (tool published in SAE AIR6241)


Mass instrument

Number instrument

Volatile particle remover

Component loss defined by performance specifications

Diluter

Sample line loss defined by line geometry,

flowrate temperature & pressure

Component loss defined by calibration

measurements

Cyclone

Thermophoretic (assumed size independent) loss. Corrections for large

temperature gradient from sampling probe in hot exhaust (upto 600 °C

to Diluter at 160 °C

Size dependent particle line loss defined by line geometry, flowrate

(estimated), temperature & pressure

nvPM System loss locations


Regulatory nvPM measurements - Sampling system standardised as far as possible

- Thermophoretic correction (not size dependent) are included in

regulatory EI measurements. Correction typically 0 (mixed flow probe) to

~30% (core flow probe)

LII300

But for Airport Inventories need reasonable estimates of ‘real’ engine exit nvPM emissions

to do so means correcting for all particle system loss

SAE AIR6504 To estimate the nvPM system loss correction factors, an estimation of nvPM

mass and number concentrations at the engine exhaust exit plane are

needed and a number of assumptions are required:

o Lognormality of nvPM size distribution at engine exit

o constant fixed effective density

o fixed geometric standard deviation (width of distribution)

o no coagulation in sampling system


System Section 1 Sampling Probe

Practicality compromise to use existing Annex 16 compliant Gaseous probes

>12 spatial points, 80% pressure drop (tip dilution discounted as too complex)

Different engine manufacturers have vastly different compliant sampling probes

Theoretical penetration comparisons of 4 x engine manufacturer

probe (different designs) performed - Differences are within 5%


nvPM system Sections 3 & 4 nvPM Transfer Line – long 25 m length plus cyclone & splitter

Ideally sampling chain as short as possible

(to minimise loss), practicality compromise

for large test cells (e.g. 14x14m)

Geometry/operation standardised to obtain

similar particle losses between

systems/testbeds/operators

Large (super micron) particles from random

shedding - affect mass measurement

10 μm particle has 125 millon times more mass

than 20 nm particle

Cyclone Sharp cut - 1μm


Measurements vs theoretical size dependent penetration

of 25m line

LII300

SAMPLEIII.1 (2011) VARIAnT 2 (2016)

• Similar measurements also performed using lab soot on North American & Swiss reference nvPM systems


Section 5

Measurement Section

Examples:

nvPM mass instrument (real-time):

AVL MSS 483 – photoacoustic technique

Artium LII-300 – laser induced incandescence technique

nvPM number instrument:

Dekati DEED+CS with CPC (Grimm 5.421, TSI 3775)

AVL APC advanced (TSI 3790E)


Number Measurement Technique

CPC spec smaller than automotive, D90<15nm D50 <10nm

Need to remove volatiles...

Use Volatile Particle Remover (VPR)

upstream of CPC, consisting of

Evaporation tube & Catalytic Stripper

AND additional dilution to ensure

CPC in single count mode

Condensation Particle Counter


VPR penetration curve fit

LII300

• As part of calibration VPR must meet minimum penetration specifications at 4 particle sizes

• As part of calibration CPC

must meet minimum efficiency specifications at 10 and 15 nm, of 0.9 & 0.5 respectively


CPC lower size cut-off

efficiencies curve fit

15nm 30nm 50nm 100nm

≥0.3 ≥0.55 ≥0.65 ≥0.70

Example of Individual and Combined System loss

LII300

FORUM-AE Workshop – Amsterdam 15th April 2016

Iterative procedure for estimation of nvPM mass and

number concentrations corrected for nvPM sampling and

measurement nvPM loss:

estimate particle size distribution at engine exit

LII300

Some examples of nvPM system correction factors

LII300

APRIDE4

APRIDE5

Honeywell

P&W

SAMPLE III.5

VARIANT I & II

kSL_num Range: Average

2.0 to 3.6

2.3 to 6.0 4.15

3.6

4.6

2.1 to 5.5

3.8 to 9.0 5.5

kSL_mass Range : Average

1.2 to 1.4

1.1 to 1.2 1.1

1.5

1.3 1.4 to 1.6

1.3 to 1.9

1.5

fuels Jet A Jet A Jet A Jet A Jet A JetA,

camelina, and blends

nvPM number correction factors 2 to 9 nvPM mass correction factors 1.1 to 1.9


Use of system loss corrections for Airport Inventories or

Possible future regulation

LII300

There is certainty that significant particle system losses occur for

aviation nvPM measurement

For airport inventories, knowledge of ‘real’ engine exit emissions is

needed – Using this correction methodology, these can be estimated.

But the uncertainty on these estimations could be larger than ± 25%

(still to be determined)

For regulatory standard setting, the sampling particle losses have

been standardised (as far as practical) so that repeatable/

comparable measurements are taken. Large differences in engine

technology particle size distributions could impact the comparability

for the future.

Possible use in a future standard

System loss correction methodology could be used

in other applications where particle size is not available


Summary

Aircraft Gas Turbine nvPM mass & number

measurements passed into international regulation (Feb 2016)

• Multiple emissions certification quality tests been conducted

by reference systems & engine manufacturers

• nvPM mass and number reproducibility typically within ±25%

• Mass LOQ at ~5 μg/m3 equivalent to ~50 μg/m3 at engine exit

o nvPM mass emissions below this level observed…

• Improvements in mass calibration ongoing – source important

• System Loss correction method defined

• Work ongoing to improve measurement and system loss

uncertainties

• System optimised for nvPM not suitable for Total PM


Thank you for listening

Many thanks to the large number of people globally

involved in this work

Any further questions, feel free to contact me:

[email protected]


Additional back-up slides

Operating mode Power setting Time in mode

1. Taxi / Idle 7% take-off thrust 26.0 minutes

2. Take-off 100% Std. day take-off thrust 0.7 minutes

3. Climb 85% take-off thrust 2.2 minutes

4. Approach 30% take-off thrust 4.0 minutes

Landing

Aviation regulatory LTO (Landing Take-off cycle)


ICAO Regulatory nvPM standard – maximum mass

concentration equivalent to Smoke standard (only for GT’s with thrust >26.7 kN

includes probe thermophoretic loss

= ~15 to 30% correction for unmixed (core only) sampling


The constant 22.4 is the volume of one mole of air in litres at STP conditions rounded to one decimal place

ICAO Regulatory nvPM standard (only for GT’s with thrust >26.7 kN

report nvPM Emission Indices at each LTO point

includes probe thermophoretic loss

System Loss correction factors reported for airport

inventories

kSL_mass and kSL_num at each of the 4 LTO points


particulate emission measurements from aviation gas

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