Combustion Science and Technology

BOYER, LeMOYNE; QUEIROZ, MARDSON

doi: 10.1080/00102209108951755pmid: N/A

Abstract Temperature dissipation measurements have been completed in a lifted turbulent non-premixed propane flame issuing from a converging nozzle at several axial stations and along the centerline. The radial and axial components of the temperature dissipation were measured directly. The assumption of lognor-mality is shown to be a good approximation of the temperature dissipation character in the core of the flame out to ro. the radius where the mean temperature is at a maximum. Significant deviations from the lognormal distribution are observed on the outer side of the shear layer. The radial and axial components of the dissipation are reasonably isotropic in the region close to the jet's centerline. However, in direct contrast to the results found in nonreacting flows, detailed comparisons of the radial and axial temperalure dissipation profiles in the off-axis region of 0.1 < r/ ro < 1.3 indicate that there are definite anisotropic and non self-similar characteristics in the temperature dissipation. Furthermore, joint probability density functions between temperature and its dissipation components have shown that they are uncorrelated on axis, yet both negative and positive correlation existed further outward from ro at all the axial stations measured.

HOU, SHUHN-SHYURNG; CHANG, CHIN-KUAN; LIN, TA-HUI

doi: 10.1080/00102209108951756pmid: N/A

Abstract The characteristics of multiflame burnings are investigated through modification of the boundary conditions in conserved systems. The experiments measure the maximum temperature and the thickness of the high-temperature zone in counterflows. To provide a conserved system, the total volume flow rate of mixtures through each burner and the total volume flow rates of methane, oxygen, and nitrogen flowing out of both burners are kept constant The possible burning structures are observed to be single-flame, double-flame and triple-flame burnings in which the individual flame can be burned independently. or burned beyond the fiammability limit by the support of another stronger flame. Results show that an optimum burning identified by the highest values of the maximum temperature and the thickness of the high-temperature zone is achieved under the condition of a triple-flame burning which has a closer approach to the equilibrium combusiton state. However, the enrichment of nitrogen in the flow will produce a double-flame burning which has a highest value of maximum temperature but a smaller high-temperature zone. The local minima of the maximum temperature and the thickness of the high-temperature zone are obtained under the critical condition of the lean or rich premixed flame being ready to propagate away from the diffusion flame. Finally, a complete process of flame transition is addressed.

BITTKER, DAVID A.

doi: 10.1080/00102209108951757pmid: N/A

Abstract A detailed mechanism for the oxidation of benzene is presented and used to compute experimentally obtained concentration profiles and ignition delay limes over a wide range of equivalence ratio and temperature. The computed results agree qualitatively with all the experimental trends, and quantitative agreement is obtained with several of the composition profiles and ignition delay limes. There are indications, however, that some important reactions are as yet undiscovered, because of differences between experimental and computed results. Among these is a weaker computed temperature dependence of the computed ignition delay times than that observed experimentally. Available literature expressions have been used for the rate coefficients of all reactions, except for two involving phenol. The phenol pyrolysis rate coefficient used in this work is 25% lower than a recent literature expression and that for the hydroxyl radical attack on phenol had to be increased significantly.

FARAGȮ, ZOLTȦN

doi: 10.1080/00102209108951758pmid: N/A

Abstract Although less than one tenth of the global sulfur emission originates from domestic heating, this portion increases to 50-100% during the winter months in overcrowded European regions. Therefore, both the further reduction of the domestic oil sulfur content and the flue gas desulfurization for domestic heating are important determinants improving the air quality in built-up areas. In this paper, a method is introduced to predict the concentration of sulfur-Irioxide, the water and the acidic dewpoint of the flue gas as a function of the oil sulfur level and the usual parameters of combustion. Calculation results of the corrosion rate in condensing heat exchangers are discussed, and possible operating conditions are described to reduce corrosion in heating plants and in condensing heat exchanger.

YETTER, R. A.; DRYER, F. L.; RABITZ, H.

doi: 10.1080/00102209108951759pmid: N/A

Abstract A comprehensive reaction mechanism for the oxidation of carbon monoxide in the presence of hydrogen is described. Model predictions are compared with experimental data over wide ranges of physical conditions. The data, obtained from shock tube experiments and various types of reactor experiments, encompassed a combined temperature range of 823-2870 K, fuel-oxidizer equivalence ratios between 0.0005 and 6.0, C/H ratios between 0005 and 128, and pressures between 0.3 and 2.2 atmospheres, Validation of the reaction mechanism is obtained with reproduction of the experimental results by the model predictions and from sensitivity analysis calculations Results from the latter calculations provided a quantitative measure of the sensitivity of the model predictions to the imposed input parameters over the complete range of experimental parameters noted above.

YETTER, R. A.; DRYER, F. L.; RABITZ, H.

doi: 10.1080/00102209108951760pmid: N/A

Abstract New data on the kinetics of CO/H2O/O2 and H2/O2 mixtures in the temperature range of 852—1138 K and at I atmosphere pressure are reported. The data were obtained from adiabatic. constant pressure flow reactor experiments for variations in the initial carbon, hydrogen, and oxygen contents of the mixture and also for variations in the initial temperature. In particular, the results define explosion limit temperatures for near stoichiometric mixtures of CO/H2O/O2 and H2/O2 systems at atmospheric pressure without the presence of surfaces and also demonstrate the complex relationship between water vapor concentration and the carbon monoxide oxidation rate.

MCINTOSH, C.; WILCE, S. A.

doi: 10.1080/00102209108951761pmid: N/A

Abstract The interaction of high frequency acoustic waves with premixed flames is discussed and the results presented for a simple one-dimensional theory involving the solution of the acoustic equation in the presence of a strong temperature gradient. The wavelength of the disturbance is very small on an acoustic scale, being on a level with a typical diffusion length. Thus one is considering effectively the interaction of “ultra sound” with flames (frequencies of the order of mHz). The effect of the flame is to introduce a small but significant jump in the velocity perturbation as the pressure disturbance passes through the flame. Plots showing the effect on the waveform of transmitted and reflected waves are displayed and discussed. In particular one can observe the small but significant effect of the reaction zone on the amplitude and phase of the waves emitted from the flame. It is thus possible that ultra sound could be used as a diagnostic tool to analyse flame structure. The theory can also be extended to larger amplitude pressure inputs where a non-linear wave equation must be invoked. In this case one can consider the effect of a pressure pulse passing through the flame with all the attending effects of wave steepening and non-linear growth or decay in the amplitude of the response.

WEBER, R. O.

doi: 10.1080/00102209108951762pmid: N/A

Abstract Dimensional analysis is combined with experimental results to infer the effect of gravitational acceleralion upon the rate of flame spread over a solid combustible, such as a PMMA cylinder. The conclusion is that the rate of flame spread is insensitive to gravitational acceleration.

GUTMARK, E.; SCHADOW, K. C.; SIVASEGARAM, S.; WHITELAW, J. H.

doi: 10.1080/00102209108951763pmid: N/A

Abstract Measurements of pressure fluctuations in sudden-step expansion flows of round cross-section are examined to determine the effect of matching the fluid-dynamic frequency associated with large scale coherent structures in the near field of the jet to the acoustic or bulk-mode frequency of the confining duct. In one case, the fuel and air were premixed with an equivalence ratio of 1.0 and in the other the fuel was injected radially through discrete holes a short distance upstream of the expansion with an overall equivalence ratio of 0.52. The results show substantial increases in the amplitude of the instability when the two frequencies are matched and the linear relationship between the velocity and frequency implied by a constant Strouhal number of around 0.3 leads to frequencies outside the range previously shown to be associated with the much higher amplitudes of oscillations of rough combustion.