Activities at Combustion Physics Department of Physics within the area of soot diagnostics

1. Activities at Combustion Physics Department of Physicswithin the area of soot diagnostics Per-Erik Bengtsson, Henrik Bladh, Jonathan Johnsson

2. Combustion Physics (at Physics Dep., TF) ~35 people Soot diagnostic group Per-Erik Bengtsson Henrik Bladh Jonathan Johnsson Facilities 12 modern laser laboratories (1 soot diagnostic lab.) 1 engine laboratory 1 fire laboratory 1 high-pressure combustion rig Combustion Centre in Lund! Large Scale Facility in Europe! Enoch Thulin-laboratory inaugurated in 2001, belonging to Lund Combustion Centre.

3. Main activities at Combustion Physics • Development of optical diagnostic techniques (often laser-based) for combustion processes for measurements of e.g. • temperature • species concentrations • velocities • particle characteristics • Application of these techniques to different flame systems for phenomenological studies and model validation • Measurements in practical devices such as internal combustion engines, gas turbines, etc. Laser techniques have unique features such as non-intrusivity, and high spatial as well as temporal resolution!

4. Brief historical background • Combustion Physics has long tradition in soot diagnostics in flames. • Elastic scattering measurements in combination with extinction measurements absorption were developed at the end of 1980´s for soot concentration and size measurements in flames. • A soot diagnostic technique (for soot volume fractions) was developed in Lund during the 1990´s based on soot vaporization and subsequent excitation of produced C2-fragments. • More focus is now put on soot measurements using laser-induced incandescence (LII), which is the dominating technique nowadays for non-intrusive soot volume fraction and soot particle size measurements. • 2003-2007 we were partners in a European programme, AEROTEST, developing an LII-system that remotely and non-intrusively can measure soot volume fraction in aerocraft engine exhausts (on ground). Discussions on a follow-up programme has started.

5. Present projects • Project Development of a laser-diagnostic tool for characterization of nanoparticles from combustion. Time period 2008 – 2010 Financed by Swedish Research Council • Project Soot diagnostics within a project ”Transient spray combustion”. To develop laser-induced incandescence (LII) as a tool for soot measurements, especially for soot particle sizing. The project involves experimental laboratory studies, theoretical development and applied measurements in IC engines. Time period 2006 – 2009 Financed byStrategic Science Foundation through the Centre of Combustion Science and Technology

6. Heat conduction Sublimation Absorption Radiation (LII signal) Laser-induced incandescence (LII) • Soot particles are exposed to a laser pulse. • The particles are heated by the laser light to temperatures around 4000 K. • The resulting temperature radiation from this process is the LII signal. • The LII signal can be used for soot particle measurements (volume fraction and size) Schematic illustration of the LII process Time in soot formation process Flat flame burning ethylene and air on a McKenna flat flame burner

7. Basic LII setup for particle sizing Beam dump Lens combination Burner Signal strength Lens Optical filter transmitting at visible wavelengths Time Photomultiplier

8. Evaluation of soot particle size distributions Laser pulse • The time decay of the LII signal can be used to evaluate the soot particle size and the width of the distribution. • This is done using a heat and mass transfer model for laser-heated particles. • Best-fit data is found of particle size and size distribution in numerical comparison between model and experiment. 1 Time-resolved LII signal Normalised signal d=50 nm d=10 nm 0 0 50 100 150 200 250 300 Time (ns) Heat transfer model Absorption Heat conduction Sublimation Radiation Internal energy change

9. Model signal Experiment 100 80 LII signal 60 40 20 0 0 200 400 600 800 1000 1200 1400 1600 1800 Time (ns) 10 9 Best-fit lognormal size distribution 8 7 6 Intensity 5 4 3 2 1 0 10 15 20 25 30 35 40 45 50 Particle size (nm) Example of results from size distribution evaluation • Experimental time-resolved LII signal from a sooting flame has been evaluated using • the Lund heat and mass transfer model • a fitting procedure developed within this project. • As a result a best-fit lognormal size distribution was obtained

10. Present and future work • Installation of new laser Nd:YAG laser system • Characterization of measurement system (experimental equipment, theoretical model, fitting procedure) • Apply the measurement system to simple sooting laboratory flames, such as the McKenna burner. • Continue the discussion with other groups in the transient spray project about common tasks, especially the chemical kinetic sub-project and the engine experiment sub-project. • Identify projects that can be performed together with partners working with aerosols in Lund. • Development of soot generator and characterization of exhausts • Comparisons of different aerosol measurement techniques • LII can be used for non-intrusive transient particle measurements

11. Drawing: Jonathan Johnsson

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