conference 2014-afmc-sheet-ver1

Life Impact | The University of Adelaide

Delivering innovative technologies for a clean energy future

Centre for Energy Technology

A novel algorithm to estimate soot sheet dimensions in Delft-Adelaide Flame

19th Australasian Fluid Mechanics

Conference

Dr Shaun Chan

Dr Paul R. Medwell

Professor G.J. (Gus) Nathan

Dr Shawn Kook

Life Impact | The University of AdelaideSlide 1


Background

Soot in turbulent flame is distributed in thin

sheets & has high intermittency

Local flame dynamics can influence soot

distribution & emission behavior

• Recirculation of reactants within fuel-rich eddies

can result in regions with high soot concentration.

• Layers with large, dense soot sheet can

penetrate reaction zone.

Soot sheet dimension & concentration

information are important to understand soot

oxidation & emission



Motivation

Automated method to statistically quantify soot sheet

dimensions is desired

• To reduce manual labor.

• To improve statistical reliability.

Challenges

• Soot sheets in turbulent flames are not straight, have irregular

shapes or orientations.

• Previous studies mostly rely on over-simplistic approach that is

prone to error.



Aims & methodology

Aim

• To develop an automated approach that permit statistical

quantification of soot sheets with random orientations and shapes

Methodology

• Combines & adapts two computational methods from literature:

• Qamar et al., Combustion and Flame (2011)

• Holroyd, Journal of Computing in Civil Engineering (1999)



Limitation

Characteristic dimensions extracted from planar images, do not

represent the true dimensions of the 3-dimensional soot sheets

Proposed method could potentially be extended into the third

dimension with the application of parallel light sheets



Dimensions

• Nozzle diameter: 6mm

• Primary air annulus: 45mm.

Main jet

• Natural gas (~81% CH4, 14% N2)

Pilot

• C2H2/H2/Air

Flow conditions

• Ujet: 21.9m/s (Re = 9,700)

• Uann: 4.4m/s

• Ucoflow:0.3m/s

Adelaide-Delft flame

Pilot

Main

* Qamar et al., Combustion and Flame (2009)



LII optical setup

Excitation

• Wavelength: 1064nm.

• Fluence: 0.9J/cm2.

Detection

• Wavelength: 430nm.

• Gate width: 40ns.

• Prompt detection.

• 1000 images at each measurement position.

Calibration

• Laser extinction measurement.

* Qamar et al., Combustion and Flame (2009)



Website: http://www.adelaide.edu.au/cet/isfworkshop/

International sooting flame workshop

Laminar flames:

• Chemical kinetics

• Particle dynamics

Turbulent flames:

• Jet flames

• Bluff body flames

• Swirl flames

• Pool fires

• Influence of scale

Pressurised flames & sprays:

• Simplified IC engines

• Pressurised jet flames

• Shock tubes

ISF Workshop



Algorithm steps

Selected instantaneous LII image at x/d = 80±5, with scale.

Soot sheet #15, with a bend shape, is chosen for analysis.



Algorithm steps

Numbered steps in algorithm for soot sheet #15

• Soot sheet (shaded grey), line segment (red dashed lines).

• Anchor points (red dots), boundary boxes (black boxes).



Characteristic length and width

Characteristic length is determined by fitting straight line

segments through anchor points

Characteristic width is derived from the averaged widths of

equivalent ellipses fitted onto the subdivided regions

• Anchor points (red diamond points).

• Ellipses (black dashed lines).



Shape & orientation

Demonstration for (a) highly corrugated & (b) trifurcated soot

sheets

• Anchor points (red diamond points).

• Ellipses (black dashed lines).



Uncertainty

“True” length (L) versus automated characteristic length value

(L) for soot sheets

• Anchor point method underestimated “true” length by 11%.

• Equivalent width method was previously assessed to overestimate

“true” width by 5%.

L*=0.89L

R2=0.94



Joint pdf for soot characteristic width & length

Joint pdf for soot sheet characteristic width & length is

computed for LII images at x/d = 115±5

• Single population, linear relationship suggest correlation between

soot sheet characteristic width & length.

Best fit line



Conclusions

A novel automated method that permits statistical

quantification of the soot sheet dimensions is developed

• Uncertainty of ~11%.

• Accounts for bending, irregular shapes & orientation.

The measurements reveals new findings in Adelaide-Delft flame

• Correlation between characteristic length & width.

Further work

• Chan et al., Experiments in fluids (2014)



Question

conference 2014-afmc-sheet-ver1

Science

life impact

university of adelaideslide

soot sheet dimensions

energy technology website

dense soot sheet

dimensional soot sheets

challenges soot sheets

high soot concentration