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Title: New fuels, flame quenching and DDT
Author: Shehata, Moustafa Mohamed Attya Okily
ISNI:       0000 0004 8498 697X
Awarding Body: University of Leeds
Current Institution: University of Leeds
Date of Award: 2019
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Two limiting conditions of burning rate are considered, culminating in either flame extinction, or transition to a detonation. A 2D schlieren technique, for flame imaging of quenching kernels has been employed, supported by 3D swinging sheet measurements. The study was able, for the first time, to determine the kernel mean diameters at the point of quench. It was found that the burning regime on the U/K diagram covered higher values of K and strain rate Markstein numbers, Ma_Sr, than previously reported. Hydrogen, methane, n-butanol and i-octane air mixtures were studied at different pressures and temperatures, up to 1 MPa and 365 K. Kernel mean diameters are normalised with laminar flame thicknesses, and correlated, through measurement of turbulent length scales, with K and Ma_Sr. It is also shown how the quenching, through blow-off, of jet flames is closely related to that of single kernel quenching of premixed flames. Just as excessive air entrainment causes quenching of jet flames, entrainment of pilot flame gases by a highly turbulent mixture, can ensure its survival. As a part of the assessment of H2 as a fuel, its autoignition and transition to detonation were studied, with emphasis on laminar flow. This necessitated micro-tubes for flame acceleration. Stoichiometric H2/O2 mixtures were studied at pressures where autoignition delay times are short. The probability of a purely laminar propagation leading to a detonation is marginal only when the initial temperature is raised to 375 K, do purely laminar detonations become possible, in tubes of between about 0.5 and 1.35 mm diameter. The tendency of mildly turbulent mixtures to auto-ignite, for an initial temperature of 300 K is greater than with laminar flames on the same initial conditions and tube sizes. A further related study demonstrates a proposed detonation engine for the laminar transition to detonation, but this reveals practical design limitations.
Supervisor: Bradley, Derek ; Lawes, Malcolm Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available