摘要:

This paper presents a numerical analysis of combustion and multimode heat transfer in inert porous media. The work is directly relevant to the understanding of premixed flame stabilization in porous radiant burners. The influence of the flame location, the radiative properties of the porous material, the solid thermal conductivity, and stoichiometry on the flame speed and stability are determined using a one-dimensional conduction, convection, radiation, and combustion model. The porous medium is allowed to emit, absorb, and scatter radiant energy, Non-local thermal equilibrium between the solid and gas is accounted for by introducing separate energy equations for the two phases. Heat release is described by a single-step, global reaction. The results indicate that stable combustion at elevated flame speeds can be maintained in two different spatial domains. Flame propagation near the edge of the porous layer is controlled mostly by solid-phase conduction; whereas, in the interior both solid conduction and radiation heal transfer are important. The radiative characteristics of the porous matrix such as the optical depth and scattering albedo were also shown to have a considerable effect on flame stability

ISSN:0010-2202    

DOI:10.1080/00102209008951615

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Time- and space resolved measurements have been made, for the first time using simultaneous Raman, Rayleigh and LIF techniques in a turbulent jet diffusion flame of CH4, diluted alternatively with N2and air. The spontaneous Raman/Rayleigh data are processed to yield instantaneous species mass fractions of CH4, O2, N2, H2O, H2, CO and CO2as well as temperature, densily and mixture fraction. The LIF data is used to obtain the OH radical mass fraction.

ISSN:0010-2202    

DOI:10.1080/00102209008951616

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

A vertical tube furnace was used to obtain kinetics data for the reaction of sized fractions of residual fuel oil coke particles with oxygen. Temperatures were in the range 1287 to 1795 K and oxygen concentrations were between 0.29 and 4.95%, and were chosen to simulate large boiler plant conditions. The chemical and physical characteristics of the material were determined.

ISSN:0010-2202    

DOI:10.1080/00102209008951617

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The solution of the one-dimensional premixed flame equations is considered with Arrhenius kinetics, not only with the assumption of large activation energy, but also large heat release. Previous studies have shown that under these circumstances, the chemical zone widens considerably with the pre-heat zone no longer able to be modelled as a separate, chemically frozen region.

ISSN:0010-2202    

DOI:10.1080/00102209008951618

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The effectiveness as pulsed igniters of plasma jets originally designed as continuous-flow radical generators, developed for flame stabilisation, is investigated with particular reference to ignition in aircraft gas turbines. It is found that these devices are able to ignite kerosene sprays in aircraft flame tubes more effectively than conventional high energy igniters, with either nitrogen or air as the plasma medium, in spite of the very low mean enthalpy of the plume and at the shortest of times attainable with a manual “on-off” switch. Further reductions in discharge times down to orders of 100ms permit the use of a compact capacitor-based power supply and this device was tested, at various levels of turbulence and pressures down to 1/4 atmospheric, using equipment at Leeds University. In tests with lean methane/air mixtures it proved to be as effective as the most incendiary fuel-wetted pulsed plasma jets in previous tests, in spite of the further dilution of the lean mixtures by the inert plasma medium. Sporadic tests at a high altitude test facility for jet engine combustors, however, suggested that it was rather less effective in igniting aviation kerosene sprays at the low initial rcactant temperatures which are likely to be encountered following extinction and loss of compression at high altitudes. It was inferred that this limitation was due to the low vapour pressure causing insufficient fuel vapour to be entrained into the plasma plume and this suggested as a remedy the use of a gaseous hydrocarbon as the plasma medium. Tests with methane resulted in the ejection of a massive ball of flame extending to about 25 cm in less than 10 ms, with very little carbon being deposited on the electrodes. This highly incendiary combination or flame and chemically active plasma involves the use of quite small amounts of fuel (such that the requirement of some 20 one second firings could be contained within the volume of one cylinder of lighter fuel, for example)

ISSN:0010-2202    

DOI:10.1080/00102209008951619

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

By coupling a well-stirred microjet reactor with Vacuum Ultraviolet (VUV) photoionization and a time of flight mass spectrometer (TOF-MS), we have developed a useful technique for studying hydrocarbon combustion and pyrolysis kinetics. The reaction occurs in a microjet reactor which allows immediate free jet expansion into vacuum, preserving trace non-equilibrium reaction intermediate species. The detection of these products with minimal fragmentation using single photon VUV ionization allows the direct determination of reaction intermediate parent species, simplifying the identification of probable reaction pathways. Preliminary results show products from the pyrolysis of ethyl acetylene at tempera lures from 300-1600 K. for ms reaction times. These results illustrate the advantages of using VUV-ionization mass spectrometry for the simultaneous detection of a wide-spectrum of pyrolysis and combustion products, especially where complex mixtures of hydrocarbons at ppm levels are present

ISSN:0010-2202    

DOI:10.1080/00102209008951620

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor