D. Bradley

University of Leeds, Leeds, ENG, United Kingdom

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Publications (7)0 Total impact

  • G ANDREWS, D BRADLEY, S LWAKABAMBA
    Combustion and Flame - COMBUST FLAME. 01/1976; 26:271-272.
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    ABSTRACT: Current theories of turbulence that seem relevant to the structure of turbulent flames are reviewed. The compatibility of such theories with different turbulent flame models is discussed. It is suggested that the turbulent Reynolds number, Rλ, of the reactants is an important controlling parameter in turbulent flame propagation. When Rλ>100, a wrinkled laminar flame structure is unlikely and the turbulent flame propagation is probably associated with small dissipative eddies. It is proposed that the ratio of turbulent burning velocity to laminar burning velocity can be correlated with Rλ.
    Combustion and Flame. 01/1975;
  • G.E. Andrews, Derek Bradley, S.B. Lwakabamba
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    ABSTRACT: Turbulent burning velocities have been measured in an explosion vessel equipped with four fans driven by air turbines. This arrangement created a central region of uniform isotropic turbulence in which measurements were made of flame speed, turbulent burning velocity and gas velocity just ahead of the flame front. Two techniques were used for such measurements: one involving anemometer measurements of the gas velocity ahead of the flame and the other involving the creation of two kernels of gas originating from two separated, simultaneous sparks. Measurements were made for a range of methane-air and ethylene-air mixtures at an initial pressure of one atmosphere and at different fan speeds. An increase in fan speed resulted in increases in flame speed and turbulent burning velocity, but the gas velocity ahead of the flame showed little change. This last is explained by significant increase in flame thickness with fan speed. A consideration of current ideas of turbulent structure suggests a rational basis for the correlation of burning velocity data is to plot the ratio of turbulent to laminar burning velocity against the turbulent Reynolds number for the unburnt gas. An increase in fan speed gives an increase in the Reynolds number. The experimental results show there is indeed a primary correlation between this ratio and the turbulent Reynolds number. Reference to results of other workers also gives some confirmation of this.
    Symposium (International) on Combustion 01/1975; 15(1):655–664.
  • G.E. Andrews, D. Bradley
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    ABSTRACT: The existing methods of measuring the limits of flammability are critically reviewed. Experimental results are presented that were obtained with a cylindrical vessel equipped with windows. Flame propagation was recorded using a laser source, schlieren-interferometric techniques, and a high-speed camera. Gas velocities ahead of the flame front were measured with a hot-wire anemometer. These techniques also provided information on hot-gas kernels produced by the spark, but with no flame propagation. Limits of flammability were observed for upward and downward propagation, and burning velocities in near limit flames were measured, together with hot-gas convective rise velocities.A theory is developed for the effects of natural convection, in which the buoyancy force acting on the hot kernel is equated to the kernel's rate of change of momentum. The reasons for the neglect of drag in the early stages are discussed. The theory gives the time for the top of the flame to move a given distance, and the convective rise velocity. There is fair agreement with the experimental results.The role of natural convection in determining the limit for downward propagation is discussed. The limit for upward propagation is discussed in terms of wall quenching, gas-phase quenching, and initial failure to ignite the mixture.
    Symposium (International) on Combustion 01/1973; 14(1):1119-1128.
  • G.E. Andrews, D. Bradley
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    ABSTRACT: The use of the double kernel method of obtaining burning velocities is described and discussed. Experimental results are presented for the variations of methane-air burning velocity with equivalence ratio and initial pressure. Measurement of the higher burning velocities of some hydrogen-air mixtures is difficult with this technique, but some values are presented showing the variation of burning velocity with mixture strength. Values of burning velocity determined in this way are in good agreement with those obtained using other reasonably reliable techniques.
    Combustion and Flame. 01/1973;
  • G.E. Andrews, D. Bradley
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    ABSTRACT: Results are presented for the variation of burning velocity with equivalence ratio for methane-air mixtures at one atmosphere pressure. Values were determined by the bomb-hot wire and corrected density ratio techniques, for combustion during the prepressure period. The former of these methods gives a maximum burning velocity of 45 + 2 cm/see, at an equivalence ration of 1.07. Results are compared with those of other workers and the reasons for discrepancies are discussed. The influence of pressure and unburnt gas temperature upon burning velocity are discussed also.
    Combustion and Flame. 01/1972; 19(2):275-288.
  • G.E. Andrews, D. Bradley
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    ABSTRACT: A critical survey is presented of the different experimental techniques for the measurement of burning velocity. Where possible, correction factors are derived to compensate for errors. The survey is carried out with particular reference to the maximum burning velocity of methane-air mixtures. Recommendations are made as to the most suitable methods of measuring burning velocity for both closed vessels and burners. The recommended value of the maximum burning velocity of methane-air is 45 ± 2 cm/sec at 1 atm and 298°K.
    Combustion and Flame. 01/1972; 18(1):133-153.

Publication Stats

194 Citations
451 Views

Institutions

  • 1972–1973
    • University of Leeds
      • School of Mechanical Engineering
      Leeds, ENG, United Kingdom