Laser induced incandescence imaging for the investigation of soot formation in laminar flames

Student thesis: Doctoral Thesis

Abstract

This work has been aimed at applying laser induced incandescence imaging for the measurement of soot concentration within a variety of novel flame sources and setups. Laser induced incandescence (LII) is an optical technique used in laser diagnostics to measure soot volume fraction and estimate particle size in-situ. Using imaging to measure LII allows for a range of combustion environments to be investigated and soot volume fractions to be measured. An experimental methodology had to be setup to measure the LII signal using a Nd:YAG laser, ICCD camera and flat flame burner and calibrated along with another optical technique known as extinction. This allowed for the soot volume fraction to be calibrated and measured and this gives the standard case for calibrating other measurements in different flames.From burner setup it is possible to change the boundary temperature of the flame. It was thought that by changing this temperature it would be possible to change the soot concentration within the flame. However, using LII imaging it was shown that despite this change in temperature the soot volume fraction remains the same, this was also eventually found to be the case when modelling these types of flames. This gives confidence in different experimental setups between groups can be used for comparison.The burner being characterised by a standard setup allows for comparison when using a different excitation source, a long-pulsed fibre laser. Using a long pulse fibre laser has benefits and it is shown in this work that it is possible to get a comparable result with LII centre line height above burner (HAB) profiles matching. Modelling also allows for comparisons and understanding on how the laser temporal and spatial profile can affect the LII signal.The rise of the interest in sustainable energy generation has led to the increase of using alternative fuel sources such as biofuels. Using the method developed it was possible to record soot volume fraction images within a wick diffusion flame which used a selection of biofuels and show improvement on previously published temporal profiles produced in these flames. The sooting propensity of each fuel was able to be characterised more accurately using spatially resolved profiles over temporally measured profile.
Date of Award7 Jun 2019
Original languageEnglish
Awarding Institution
  • University Of Strathclyde
SponsorsUniversity of Strathclyde
SupervisorIain Burns (Supervisor) & Jun Li (Supervisor)

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