Application of optical diagnostic techniques to oxy-coal flames

Pál Tóth, Terry A. Ring, Árpád B. Palotás, Eric G. Eddings Dept. of Chemical Engineering

University of Utah Dept. of Combustion Technology

University of Miskolc

Overview

• Motivation: CFD model validation • Experimental systems used • Different methodologies to be discussed

– Particle measurements by shadowgraphy – Radiative flux, temperature and soot

concentration mapping by multi-color pyrometry

– Velocity measurement in flames by high-speed imaging

Experimental Systems

Laboratory-scale pulverized coal flame

Larger-scale (100 kW) pulverized coal combustor

Shadowgraphy

Laboratory-scale pulverized coal flame

Larger-scale (100 kW) pulverized coal flame

• Simultaneous measurement of particle concentration, size, velocity and shape

• Developed advanced image analysis software to be able to study flames larger than laboratory-scale

• Yields information on particle swelling, burnout, clustering, fragmentation and indirectly devolatilization and tar/soot formation

DIP of Shadowgraphs

• Shadowgraphs of larger scale flames are degraded, noisy and full of imaging artifacts due to beam steering and non-ideal conditions

• Commercial software can typically only handle images taken under laboratory conditions

• Developed a new method based on supervised learning and self-organizing neural networks

Lab-Scale Studies

Projected Area vs. Eccentricity at different heights in flame and different equivalence ratios

100 KW-Scale Studies

• Particle swelling can be quantified • Oxygen mixing affects and displaces zones of swelling along the flame axis • Joint statistics show weak correlation

0% O2

20% O2

O2% in Primary Stream

Validation Data

• Shadowgraphy can be combined with simultaneous infrared imaging to also obtain temperature information

• Provides high-fidelity data for model validation

100 KW combustor Lab-scale flame

IR image – coal particles, soot and volatiles

IR image after filtering out soot/HC

Radiation Imaging

• Simultaneous high-speed measurement of flame radiation and flame velocity

• Measurement of geometric properties (flame length, standoff)

• Deduced temperature and soot information

Beam splitter

High-speed visible camera

High-speed MWIR camera

Radiation Imaging

Red

chan

nel

Radiation Imaging

Illinois #6

Skyline

PRB

Axial coordinate, m Axial coordinate, m

Radiation Imaging

• Stand off measurements as detected by the visible camera. Compares with previous plots by Wendt et al. using visual detection based on images from a digital camera.

– Uses an intensity threshold (5X background) for “ignition” or attachment. – The results were not very sensitive to this arbitrary threshold value.

• IR images show the flame attached always.

Optical Flow Velocimetry • Fast and simple method to measure apparent flame velocity • Flame velocity is defined as the apparent motion field that optimally warps an

image frame into the next • Needs at least two consecutive frames • No lasers needed • Non-intrusive

Optical flow velocimetry • Mean velocity well approximates PIV mean

velocity in 100 KW combustor • Standard deviation is higher due to inclusion of

out-of-plane motion • Advantages

– Simple – Cheap – Fast (real-time)

• Disadvantages – Not planar – Flame must be luminous and turbulent (most practical

flames)

Col-axial Flames Swirling Flames

Under Development

Optical flow velocity in non-luminous regions from infrared images – high speed infrared velocimetry

Direct measurement of Stokes number in flames seeded with nanoparticles – combined PIV-like tracking of nanoparticles for gas and coal particles via shadow velocimetry

Three dimensional mapping of particle temperature, concentration, velocity, emissivity and size – stereo streaking pyrometry

Visible IR

Concluding Comments

• Different methodologies discussed – Particle measurements by shadowgraphy

• Velocity, diameter, shape and concentration

– Radiative flux, temperature and soot concentration mapping by multi-color pyrometry

– Velocity measurement of flames by high-speed imaging

– Some new methodology developments

• Oxycoal datasets (papers) forthcoming

The authors wish to thank Mr. Zhonghua Zhan and Ms. Teri Draper for their assistance with aspects of this work. This material is based upon work supported by the Department of Energy under Award Number DE-NT0005015. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

Acknowledgements