Molecular Transport Effects in Turbulent Diffusion Flames at Moderate Reynolds Number PDF Download
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Author: R. W. Bilger Publisher: ISBN: Category : Languages : en Pages : 38
Book Description
In flames molecular diffusivities are enhanced by the high temperatures and can be of the same order as turbulent diffusivities in flames of moderate Reynolds number. A perturbation analysis is used to quantify effects in a hydrogen/air diffusion flame which arise from differential molecular diffusivities. The analysis uses perturbations about the equal diffusivity, adiabatic, equilibrium theory commonly used and yields solutions for the average and higher moments for the departures in normalized element mass fractions and enthalpy. The results are compared with the laser-Raman measurements of Drake et al. in a relatively low Reynolds number flame. Generally the agreement is excellent. (Author).
Author: R. W. Bilger Publisher: ISBN: Category : Languages : en Pages : 38
Book Description
In flames molecular diffusivities are enhanced by the high temperatures and can be of the same order as turbulent diffusivities in flames of moderate Reynolds number. A perturbation analysis is used to quantify effects in a hydrogen/air diffusion flame which arise from differential molecular diffusivities. The analysis uses perturbations about the equal diffusivity, adiabatic, equilibrium theory commonly used and yields solutions for the average and higher moments for the departures in normalized element mass fractions and enthalpy. The results are compared with the laser-Raman measurements of Drake et al. in a relatively low Reynolds number flame. Generally the agreement is excellent. (Author).
Author: Nedunchezhian Swaminathan Publisher: Cambridge University Press ISBN: 1139498584 Category : Technology & Engineering Languages : en Pages : 447
Book Description
A work on turbulent premixed combustion is important because of increased concern about the environmental impact of combustion and the search for new combustion concepts and technologies. An improved understanding of lean fuel turbulent premixed flames must play a central role in the fundamental science of these new concepts. Lean premixed flames have the potential to offer ultra-low emission levels, but they are notoriously susceptible to combustion oscillations. Thus, sophisticated control measures are inevitably required. The editors' intent is to set out the modeling aspects in the field of turbulent premixed combustion. Good progress has been made on this topic, and this cohesive volume contains contributions from international experts on various subtopics of the lean premixed flame problem.
Author: Publisher: ISBN: Category : Languages : en Pages : 23
Book Description
A numerical simulation of entrainment, turbulent advection, molecular import and chemical kinetics in a turbulent diffusion flame is used to investigate effects of molecular transport on turbulence-chemistry interactions. A fun finite-rate chemical mechanism is used to represent the combustion of a hydrogen-argon mixture issuing into air. Results based on incorporation of differential diffusion and variable Lewis number are compared to cases with the former effect, or both-effects, suppressed. Significant impact on radical species production and on NO emission index (based on a reduced mechanism for thermal NO) is found. A reduced mechanism for hydrogen-air combustion, omitting both effects and incorporating other simplifications, performs comparably except that its NO predictions agree well with the case of full chemistry and molecular transport, possibly due to cancellation of errors.
Author: Paul A.. Libby Publisher: ISBN: Category : Languages : en Pages : 25
Book Description
Previous application of the Bray-Moss model for premixed turbulent combustion to planar, oblique and normal flames is extended to include the effect of large but finite values of the two dominant characteristic numbers, a turbulence Reynolds number providing a measure of the intensity of the turbulence and a Damkoehler number relating a turbulence time to a chemical time. A classical perturbation analysis involving two small parameters proportional to the inverse of these two numbers is carried out to account separately for the effects of molecular transport and of altered scalar dissipation and for the effects of finite chemical reaction rates. Two limiting cases corresponding to highly oblique confined flames and normal or unconfined oblique flames are treated. Of particular interest in the former case is the effect of the perturbations of the predicted orientation of the turbulent reaction zone. For the unconfined flames attention focuses on the effect of the perturbations on the turbulent flame speed and on the change in turbulent kinetic energy across the reaction zone.
Author: R. Borghi Publisher: Springer Science & Business Media ISBN: 146139631X Category : Science Languages : en Pages : 958
Book Description
Turbulent reactive flows are of common occurrance in combustion engineering, chemical reactor technology and various types of engines producing power and thrust utilizing chemical and nuclear fuels. Pollutant formation and dispersion in the atmospheric environment and in rivers, lakes and ocean also involve interactions between turbulence, chemical reactivity and heat and mass transfer processes. Considerable advances have occurred over the past twenty years in the understanding, analysis, measurement, prediction and control of turbulent reactive flows. Two main contributors to such advances are improvements in instrumentation and spectacular growth in computation: hardware, sciences and skills and data processing software, each leading to developments in others. Turbulence presents several features that are situation-specific. Both for that reason and a number of others, it is yet difficult to visualize a so-called solution of the turbulence problem or even a generalized approach to the problem. It appears that recognition of patterns and structures in turbulent flow and their study based on considerations of stability, interactions, chaos and fractal character may be opening up an avenue of research that may be leading to a generalized approach to classification and analysis and, possibly, prediction of specific processes in the flowfield. Predictions for engineering use, on the other hand, can be foreseen for sometime to come to depend upon modeling of selected features of turbulence at various levels of sophistication dictated by perceived need and available capability.
Author: Publisher: ISBN: Category : Languages : en Pages :
Book Description
In current study Numerical simulation of turbulent combustion process is approached using One Dimensional Turbulence (ODT) model. The ODT model is based on the coupling of molecular processes (reaction and diffusion) with turbulent transport in a spatially- and temporally-resolved fashion over a one-dimensional domain. The domain corresponds to a transverse (or radial) direction; while, the transient evolution of the thermo-chemical scalars on the 1D domain represents the spatial evolution downstream of the jet inlet. The linear-eddy approach for modeling molecular mixing in turbulent flow involves stochastic simulation on a 1D domain with sufficient resolution to predict all relevant physical length scales properly. Firstly ODT is carried out to predict the hydrogen and air jet diffusion flame with helium dilution in the fuel. The comparison with existing experimental data was made for the numerical result of ODT simulation of jet diffusion flames in both conditional means and rms of scalars of measurements and computational results. Another application of ODT was made in present work to verify the capability of prediction of autoignition (self-ignition) of one of free shear layer flow -- jet diffusion flow. Different range of pressure and Reynolds number are set to identify the effects of turbulence intensity and mixture properties on the self-ignition chemistry. Autoignition delay time was studied based on these different conditions. At the same time the ability of the prediction of mixture temperature and species mass fraction profile were tested. A principle numerical result is expected and discussed. Conditional pdf and progress variable were used to analyze the computational result of ODT. Analysis was focus on the temperature growth and the mass fraction distribution of intermediate species and product.
Author: R. W. Bilger
Author: R. W. Bilger
Author: Nedunchezhian Swaminathan
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Author: Rodney O. Fox
Author: Paul A.. Libby
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Author: R. Borghi
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Author: Lawrence Talbot