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Title: Studies of turbulent burning rates and flame structures using 3D optical measurement techniques
Author: Ahmed, Shaik Pervez
ISNI:       0000 0004 8504 6453
Awarding Body: University of Leeds
Current Institution: University of Leeds
Date of Award: 2019
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Burning velocities and Markstein numbers of premixed n-butanol explosion flames have been investigated under laminar and turbulent conditions at 360 K with pressures ranging between 0.1 to 1.0 MPa and equivalence ratios, φ, from 0.7 to 1.4. For instabilities arising during laminar explosions, pressure dependencies were sought to exploit the leading role of the critical Peclet number in the phenomena. The critical Karlovitz number for flame stability decreased with increase in the strain rate Markstein number, Ma_sr. As a result, it is possible to predict the extent of the unstable regime for laminar flames as a function of Ma_sr and pressure. It is shown that such data can be used to estimate the severity of large scale atmospheric explosions. For turbulent burning velocity, u_t , measurements, rms velocities, u', between 0.5- 6.0 m/s were employed. Correlations of u_t normalized by the effective rms turbulent velocity, U, were sought in terms of Karlovitz stretch factor, K, and the extent of validity of these correlations is extended to an Ma_sr value of 9. The present work also focuses on the development of a 3D swinging laser imaging technique to reconstruct 3D turbulent explosion flames. Experiments were conducted using CH₄ and H₂ air mixtures over a range of pressures, temperatures and φ covering different Ma_sr. Flame parameters such as total flame surface areas, A, and mean surface areas, a, were determined. Enhancement of the flame surface area, A/a, measured in both 2D and 3D is compared with the corresponding flame speed enhancement, u_t/u_l . As K is increased, the 3D A/a is unable to account entirely for the measured u_t/u_l for negative Ma_sr mixtures. For these mixtures, the discrepancy observed is tentatively explained by a theory based on turbulent diffusivity enhancement. Finally, quenched flame kernel mean diameters, d_k, are determined for a variety of fuels including CH₄, H₂, and n-butanol, at different φ and pressures. Normalised quenched flame kernel mean diameters, d_k/δ_k, are correlated with K and Ma_sr. Values of d_k/δ_k were found to increase with both K and Ma_sr. The existing data on the onset of turbulent flame quenching are extended to higher K and lower Ma_sr.
Supervisor: Lawes, Malcolm ; Bradley, Derek Sponsor: University of Leeds
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available