Laminar diffusion flamelet models in non-premixed turbulent combustion

Modeling chemical and physical processes of wood and biomass pyrolysis

Over the last two decades, our understanding of soot formation has evolved from an empirical, phenomenological description to an age of quantitative modeling for at least small fuel compounds. In this paper, we review the current state of knowledge of the fundamental sooting processes, including the chemistry of soot precursors, particle nucleation and mass/size growth. The discussion shows that though much progress has been made, critical gaps remain in many areas of our knowledge. We propose the roles of certain aromatic radicals resulting from localized π electron structures in particle nucleation and subsequent mass growth. The existence of these free radicals provides a rational explanation for the strong binding forces needed for forming initial clusters of polycyclic aromatic hydrocarbons. They may also explain a range of currently unexplained sooting phenomena, including the large amount of aliphatics observed in nascent soot formed in laminar premixed flames and the mass growth of soot in the absence of gas-phase H atoms. While the above suggestions are inspired, to an extent, by recent theoretical findings from the materials research community, this paper also demonstrates that the knowledge garnered through our longstanding interest in soot formation may well be carried over to flame synthesis of functional nanomaterials for clean and renewable energy applications. In particular, work on flame-synthesized thin films of nanocrystalline titania illustrates how our combustion knowledge might be useful for developing advanced yet inexpensive thin-film solar cells and chemical sensors for detecting gaseous air pollutants.

Formation of nascent soot and other condensed-phase materials in flames

http://staff.mechmining.uq.edu.au/klimenko/pub/pdf/Prog_Energy_Combust_Sci_1999_p.pdf

Conditional moment closure for turbulent combustion

Several hybrid regression models that predict hot stabilized vehicle fuel consumption and emission rates for light-duty vehicles and light-duty trucks are presented in this paper. Key input variables to these models are instantaneous vehicle speed and acceleration measurements. The energy and emission models described in this paper utilize data collected at the Oak Ridge National Laboratory (ORNL) that included fuel consumption and emission rate measurements (CO, HC, and NOx) for five light-duty vehicles and three light-duty trucks as a function of the vehicle’s instantaneous speed and acceleration levels. The fuel consumption and emission models are found to be highly accurate as compared to the ORNL data, with coefficients of determination ranging from 0.92 to 0.99. Given that the models utilize the vehicle’s instantaneous speed and acceleration levels as independent variables, these models are capable of evaluating the environmental impacts of operational-level projects including intelligent transporta...

Estimating vehicle fuel consumption and emissions based on instantaneous speed and acceleration levels

A representation of curved boundaries for the solution of the Navier-Stokes equations on a staggered three-dimensional Cartesian grid

The causes of smoke emission from free gaseous laminar diffusion flanles are investi-gated. Soot concentration, temperature and velocity profiles were measured around the smokepoint for a range of fuels. Smoke was emitted when the temperature in the burnout region droppedbelow about 1300 K.A smoking flame stopped emitting smoke when the temperature in the burnout region wasslightly raised locally by absorption of energy from a COz laser beam.The temperature drop in the flame is strongly coupled to soot concentration through radiationlosses. Soot formation rates are in turn influenced by heat losses and residence times near thefuel nozzle tip. Thus conditions near the nozzle influence the smoke point. The results are alsodiscussed in context with turbulent diffusion flame smoke emission.

Who do Diffusion flames Emit smoke

Modeling soot formation in turbulent methane–air jet diffusion flames

Soot volume fraction measurements are made in turbulent ethylene diffusion flames and are compared with predictions. The theoretical model is based on mixture fraction distributions in the flame and measured soot volume fractions are correlated against predicted mixture fraction. The results show that in the lower parts of the flame this formulation is not adequate. However, the maximum soot concentrations further up the flame are less dependent on residence time and a mixture fraction approach may be useful here.

Soot and Mixture Fraction in Turbulent Diffusion Flames

Experimental results are presented for turbulent diffusion flames of a round jet of hydrogen in a co-flowing stream of air. The aim of the work is to provide comprehensive data which will assist in refining the newer and more-powerful theories coming into use. The jet diameter was 7.62 mm and the tunnel cross section large enough so that the flames were essentially unconfined and near to zero pressure gradient. Buoyancy effects were also negligible. Measurements were made at jet to external stream-velocity ratios of 2, 5, 8, and 10 to 1. Measurements made include jet exit-plane velocity and turbulence profiles, and concentration, temperature, and momentum flux within the flame. Some results for turbulence levels and nitric oxide concentrations are also presented. The general level of accuracy of the experiments is believed to be good. However, it was found that derivation of velocity is extremely sensitive to small errors in concentration measurements in the outer part of the flow, where the density gradients and fluctuations are steepest. The results are discussed in the light of the theories of Libby and Spalding. It is considered that such theories should use the time-mean density, which takes into account the fluctuating composition at a point in the flow, and that current models of turbulence may need modification. Peak nitric oxide concentrations are found to lie considerably on the rich side of the stoichiometriccontour. Nitric oxide production rates on the centerline have been deduced from the experimental data and show a peak at a mean composition having 60 per cent of theoretical air. No reasonable theoretical explantation has been found for these results.

J.H. Kent

Papers

A representation of curved boundaries for the solution of the Navier-Stokes equations on a staggered three-dimensional Cartesian grid

Who do Diffusion flames Emit smoke

Modeling soot formation in turbulent methane–air jet diffusion flames

Soot and Mixture Fraction in Turbulent Diffusion Flames

Turbulent diffusion flames