Uintah and Related C-SAFE Publications


N.D. Marsh, I. Preciado, E.G. Eddings, A.F. Sarofim, A.B. Palotas, J.D. Robertson. “Evaluation of Organometallic Fuel Additives for Soot Suppression,” In Combustion Science and Technology, Vol. 179, No. 5, pp. 987--1001. 2007.
DOI: 10.1080/00102200600862497


In this work, we investigate the utility of the smoke lamp for evaluating the soot-reducing potential of additives, by comparing it to a more complex liquid-fed laminar diffusion flame. The additives, ferrocene (bis(cyclopentadienyl) iron-Fe(C5H5)2), ruthenocene (bis(cyclopentadienyl)ruthenium-Ru(C5H5)2), iron naphthenate (a 12% iron salt of naphthenic acid, which is a mixture of fatty carboxylic acids, some of which may include a cyclopentane ring), and MMT (Methylcyclopentadienyl manganese tricarbonyl-CH3C5H4Mn(CO)3) are evaluated at various concentrations in the jet fuel JP-8. Although the smoke lamp is a simple, inexpensive, and widely-available test for evaluating the sooting potential of liquid fuels, it does not provide an effective measure of soot suppression by metal-containing additives. The drop-tube reactor more accurately captures the physical conditions and processes—droplet vaporization, ignition, and rich vs. lean operation—typically found in more complex systems. We find in the smoke lamp that ferrocene, and to a lesser degree ruthenocene, are effective soot suppressors when used in JP-8, and that their effectiveness increases with increasing concentration. In the smoke lamp, MMT and iron naphthenate have minimal effect. On the other hand, in the drop-tube reactor, all four additives are quite effective, especially at fuel lean conditions, where soot suppression reaches 90–95%. Under fuel-rich conditions, where in some cases the additives elevate the yield of soot aerosol slightly, we find a significant increase in the production of the soluble organic fraction of the aerosol, i.e., tar. In order to understand why the smoke lamp sometimes fails to indicate a soot suppressing potential (i.e., from MMT and iron naphthenate), soot samples were collected from a wick lamp burning ferrocene and iron naphthenate additives in JP-8. These samples, as well as several from the drop-tube reactor, were analyzed by X-Ray Fluorescence (XRF) in order to determine their metal content, and we find that the soot aerosol produced by the wick lamp using ferrocene-containing fuel had roughly 30 times the iron content of the soot aerosol produced by the wick lamp using iron-naphthenate-containing fuel. This difference in metal content is not found in samples produced in the drop-tube reactor. We conclude that the poor performance of iron naphthenate in the smoke lamp is likely the result poor vaporization of the additive from the wick, a consequence of its high molecular weight (average 465).

J. Van Rij, T. Harman, T. Ameel. “The effect of creep flow on two-dimensional isoflux microchannels,” In International Journal of Thermal Sciences, Vol. 46, No. 11, pp. 1095--1103. November, 2007.
DOI: 10.1016/j.ijthermalsci.2007.04.007


Microchannel convective heat transfer and friction loss characteristics are numerically evaluated for gaseous, two-dimensional, steady state, laminar, constant wall heat flux flows. The effects of Knudsen number, accommodation coefficients, second-order slip boundary conditions, creep flow, and hydrodynamically/thermally developing flow are considered. These effects are compared through the Poiseuille number and the Nusselt number. Numerical values for the Poiseuille and Nusselt numbers are obtained using a continuum based three-dimensional, unsteady, compressible computational fluid dynamics algorithm that has been modified with slip boundary conditions. To verify the numerical results, analytic solutions of the hydrodynamically and thermally fully developed momentum and energy equations have been derived subject to both first- and second-order slip velocity and temperature jump boundary conditions. The resulting velocity and temperature profiles are then utilized to obtain the microchannel Poiseuille and Nusselt numbers as a function of Knudsen number, first- and second-order velocity slip and temperature jump coefficients, Brinkman number, and the ratio of the thermal creep velocity to the mean velocity. Excellent agreement between the numerical and analytical data is demonstrated. Second-order slip terms and creep velocity are shown to have significant effects on microchannel Poiseuille and Nusselt numbers within the slip flow regime.

Keywords: Microchannel, Slip, Creep, Viscous dissipation, Nusselt number, Poiseuille number

A. Santamaria, E.G. Eddings, F. Mondragon. “Effect of Ethanol on the Chemical Structure of the Soot Extractable Material of an Ethylene Inverse Diffusion Flame,” In Combustion and Flame, Vol. 151, No. 1-2, pp. 235--244. October, 2007.
DOI: 10.1016/j.combustflame.2007.06.004


The effect of fuel-side ethanol addition on the chemical structure of the soot extractable material generated in an ethylene inverse diffusion flame was evaluated by means of average structural parameters. The results indicate that the ethanol effect on the aromatic components was more pronounced, with an increase of about 40% in the average number of aromatic fused rings (R a) as compared to the results of a neat flame. This observation also helps explain the low percentage of chloroform-extractable material in the soot samples obtained from the flame with ethanol addition. In contrast, the aliphatic component of the extractable material did not demonstrate significant changes with ethanol addition.

A. Santamaria, F. Mondragon, W. Quinones, E.G. Eddings, A.F. Sarofim. “Average Structural Analysis of the Extractable Material of Young Soot Gathered in an Ethylene Inverse Diffusion Flame,” In FUEL, Vol. 86, No. 12-13, pp. 1908--1917. August, 2007.
DOI: 10.1016/j.fuel.2006.12.002


Conventional analytical methods such as 1H NMR, vapor pressure osmometry (VPO) and elemental analysis were used to characterize the soot precursor material represented by the chloroform extractable fractions of the young soot gathered at different heights of an ethylene inverse diffusion flame in terms of average structural parameters. The results indicate that the soot soluble fraction obtained at a 6 mm height has a relatively large molecular weight and has long aliphatic chains which later disappear with an increase in height above the burner base, especially in the region where the temperature is high (1200 K). This behavior is also accompanied by an increase in the aromaticity (fa) of the samples.

P.C. Wallstedt, J.E. Guilkey. “Improved Velocity Projection for the Material Point Method,” Subtitled “Computer Modeling in Engineering and Sciences,” Vol. 19, No. 3, pp. 223--232. 2007.
DOI: 10.3970/cmes.2007.019.223


The standard velocity projection scheme for the Material Point Method (MPM) and a typical form of the GIMP Method are examined. It is demonstrated that the fidelity of information transfer from a particle representation to the computational grid is strongly dependent on particle density and location. In addition, use of non-uniform grids and even non-uniform particle sizes are shown to introduce error. An enhancement to the projection operation is developed which makes use of already available velocity gradient information. This enhancement facilitates exact projection of linear functions and reduces the dependence of projection accuracy on particle location and density for non-linear functions. The efficacy of this formulation for reducing error is demonstrated in solid mechanics simulations in one and two dimensions.

H.R. Zhang, E.G. Eddings, A.F. Sarofim. “Combustion Reactions of Paraffin Components in Liquid Transportation Fuels Using Generic Rates,” In Combustion Science and Technology, Vol. 179, No. 1-2, pp. 61--89. 2007.
DOI: 10.1080/00102200600805975


The approach of mechanism generation is the accepted one of assigning generic rates to reactions in the same class. The procedure has been successfully applied to higher paraffins that include detailed sub-models of n-hexane, cyclohexane, n-heptane, n-decane, n-dodecane, and n-hexadecane and semi-detailed sub-models of iso-octane and methyl cyclohexane, in addition to reactions of aromatic formation and oxidation. Comparison between predictions and experimental data were found to be satisfactory for n-heptane, iso-octane, n-decane and gasoline premixed flames. The mechanism was also able to reproduce the measured concentrations for a n-hexadecane experiment in a jet stirred reactor. The numerical accuracy in predicting the flame structures of soot precursors, including acetylene and benzene, is one of the major foci of this study. The predicted maximum concentrations of acetylene and benzene are within 20% for most flames in this study.

H.R. Zhang, E.G. Eddings, A.F. Sarofim. “Olefin Chemistry in a Premixed N-Heptane Flame,” In Energy and Fuels, Vol. 21, No. 2, pp. 677--685. 2007.
DOI: 10.1021/ef060195h


Three different n-heptane mechanisms were used to simulate a fuel-rich normal heptane premixed flame in order to identify major reaction pathways for olefin formation and consumption and areas of uncertainties of these reactions. Olefins are formed mainly via β-scission and hydrogen abstraction, and smaller olefins are sometimes formed by combination of allylic radicals and H/CH3 radicals. Olefins are consumed by direct decomposition, radical-addition, and hydrogen-abstraction reactions. Isomerization between alkyl radicals plays an important role in olefin formation and in determining olefin species distribution. Peroxy radicals contribute to the olefin formation in the low-temperature region, but further studies are needed to resolve many uncertainties. Simulation results using the Pitsch, LLNL, and Utah heptane mechanisms were compared to experimental concentration profiles of selected species, and the uncertainties in the olefin chemistry thus identified are discussed. The discrepancies in the computed concentrations of most olefin species are usually due to the combined effects of uncertainties in the kinetics of β-scission and isomerization reactions. Resolving these uncertainties in n-heptane combustion chemistry is critical for building practical mechanisms for the larger paraffins that are major components of liquid aviation and diesel transportation fuels. In addition, olefin chemistry is critical to any combustion mechanisms that focus on the soot formation, because products of olefin decomposition such as C3Hx and C4Hx species are well-known precursors for the formation of the first aromatic ring.

H.R. Zhang, E.G. Eddings, A.F. Sarofim, C.K. Westbrook. “Mechanism Reduction and Generation Using Analysis of Major Fuel Consumption Pathways for n-Heptane in Premixed and Diffusion Flames,” In Energy and Fuels, Vol. 21, No. 4, pp. 1967--1976. 2007.
DOI: 10.1021/ef060092z


Reaction pathway analyses were conducted for three mechanisms (designated as the Pitsch, Utah, and Lawrence Livermore National Lab) for a normal heptane premixed flame (Φ = 1.9) and a normal heptane opposed diffusion flame, in order to identify the relative importance of the major fuel consumption pathways in the two flame classes. In premixed flames, hydrogen abstraction is found to be the major fuel consumption route although it is surpassed by thermal decomposition when the flame temperature exceeds 1400 - 1500 K. At the higher temperatures, however, little fuel remains in a premixed flame so that thermal decomposition provides a minor pathway for overall fuel decomposition. The principal abstractor is the hydrogen radical in all three mechanisms with the hydroxyl radical having a secondary role. In opposed diffusion flames, thermal decomposition competes with hydrogen abstraction in providing the major pathway for fuel consumption. Thermal decomposition becomes important when a large fraction of the fuel reaches the high-temperature zone in a flame. By understanding the relative importance of competing fuel consumption pathways, mechanisms can be tailored to each specific application by eliminating or lumping insignificant reactions. The results obtained in this study for n-heptane may be used to guide the reduction of existing mechanisms for a particular application or the generation of mechanisms for the combustion of larger paraffins that are major components of liquid aviation and transportation fuels.

H.R. Zhang, L.K. Huynh, N. Kungwan, Z. Yang, S. Zhang. “Combustion modeling and kinetic rate calculations for a stoichiometric cyclohexane flame. 1. Major reaction pathways,” In Journal of Physical Chemistry, A, Vol. 111, No. 19, pp. 4102--4115. 2007.
DOI: 10.1021/jp068237q
PubMed ID: 17388269


The Utah Surrogate Mechanism was extended in order to model a stoichiometric premixed cyclohexane flame (P = 30 Torr). Generic rates were assigned to reaction classes of hydrogen abstraction, beta scission, and isomerization, and the resulting mechanism was found to be adequate in describing the combustion chemistry of cyclohexane. Satisfactory results were obtained in comparison with the experimental data of oxygen, major products and important intermediates, which include major soot precursors of C2-C5 unsaturated species. Measured concentrations of immediate products of fuel decomposition were also successfully reproduced. For example, the maximum concentrations of benzene and 1,3-butadiene, two major fuel decomposition products via competing pathways, were predicted within 10% of the measured values. Ring-opening reactions compete with those of cascading dehydrogenation for the decomposition of the conjugate cyclohexyl radical. The major ring-opening pathways produce 1-buten-4-yl radical, molecular ethylene, and 1,3-butadiene. The butadiene species is formed via beta scission after a 1-4 internal hydrogen migration of 1-hexen-6-yl radical. Cascading dehydrogenation also makes an important contribution to the fuel decomposition and provides the exclusive formation pathway of benzene. Benzene formation routes via combination of C2-C4 hydrocarbon fragments were found to be insignificant under current flame conditions, inferred by the later concentration peak of fulvene, in comparison with benzene, because the analogous species series for benzene formation via dehydrogenation was found to be precursors with regard to parent species of fulvene.

H.R. Zhang, Z. Yang, E.G. Eddings, A.F. Sarofim. “Pollutant Formation in Premixed and Diffusion Flames of Paraffinic Fuels Using the Reduced Utah Surrogate Mechanisms,” In American Chemical Society, Division of Fuel Chemistry, Vol. 52, No. 1, pp. 144--147. 2007.


Normal heptane, isooctane and cyclohexane have been the most interested surrogate components for liquid transportation and aviation fuels, due to their roles as indicative fuels for octane number and the representative compounds for normal, iso and cyclo-paraffins. Methodologies of mechanism generation for these representative fuel fractions have been discussed in detail in literature. The basics of fuel consumption in flames have been discussed by Vovelle1, Ranzi2, Zhang3 and coworkers, among others. Ranzi et al.2 presented a lumping technique that was also discussed in detail in an earlier study3 and used for generation of reaction mechanisms that can be used to model flames of liquid fuels. The lumping approach is an effective reduction technique for models of large aliphatic fuels. Reaction pathway analysis presents another reduction technique that was used to reduce a complete kinetic set to smaller models. Doute et al.4 reduced a n-decane model by removing less important reaction routes systematically and still obtained satisfactory agreement between the experimental data and predicted results. Bollig et al.5 proposed a reduced n-heptane mechanism and modeled a diffusion flame with the emphasis on pollutant-related intermediates. The mechanism was further reduced using another technique with the assumption of partial equilibrium for intermediates. There are many important applications that need reduced kinetic mechanism, especially in those that require expensive computations but are less demanding in kinetic details. For example, only a few dozen reactions can be comfortably acquired in aerodynamic applications. In this study, the detailed Utah Surrogate Mechanisms of about 1200 reactions and 210 species3 will be reduced by a combined technique. The resultant mechanism will be used to simulate premixed and counter-flow diffusion flames of normal heptane, iso-octane and cyclo-hexane fuels. And the pollutant formation of soot precursors, e.g. benzene and acetylene, will be investigated for the three common surrogate components.

H.R. Zhang, E.G. Eddings, A.F. Sarofim. “Criteria for Selection of Components for Surrogate of Natural Gas and Transportation Fuels,” In Proceedings of the Combustion Institute, Vol. 31, No. 1, pp. 401--409. January, 2007.
DOI: 10.1016/j.proci.2006.08.001


The present paper addressed the production of soot precursors, acetylene, benzene and higher aromatics, by the paraffinic (n-, iso-, and cyclo-) and aromatic components in fuels. To this end, a normal heptane mechanism compiled from sub-models in the literature was extended to large normal-, iso-, and cyclo-paraffins by assigning generic rates to reactions involving paraffins, olefins, and alkyl radicals in the same reaction class. Lumping was used to develop other semi-detailed sub-models. The resulting mechanism for components of complex fuels (named the Utah Surrogate Mechanism) includes detailed sub-models of n-butane, n-hexane, n-heptane, n-decane, n-dodecane, n-tetradecane and n-hexadecane, and semi-detailed sub-models of i-butane, i-pentane, n-pentane, 2,4-dimethyl pentane, i-octane, 2,2,3,3-tetramethyl butane, cyclohexane, methyl cyclohexane, tetralin, 2-methyl 1-butene, 3-methyl 2-pentene and aromatics. Generic rates of reaction classes were found adequate to generate reaction mechanisms of large paraffinic components. The predicted maximum concentrations of the fuel, oxidizer, and inert species, major products and important combustion intermediates, which include critical radicals and soot precursors, were in good agreement with the experimental data of three premixed flames of composite fuels under various conditions. The relative importance in benzene formation of each component in the kerosene surrogate was found to follow the trend aromatics > cyclo-paraffins > iso-paraffins > normal-paraffins. In contrast, acetylene formation is not that sensitive to the fuel chemical structure. Therefore, in formulation of surrogate fuels, attention should be focused on selecting components that will yield benzene concentrations comparable to those produced by the fuel, with the assurance that the acetylene concentration will also be well approximated.


J. Bigler, J. Guilkey, C. Gribble, C.D. Hansen, S.G. Parker. “A Case Study: Visualizing Material Point Method Data,” In Proceedings of Euro Vis 2006, pp. 299--306, 377. May, 2006.

W. Ciro, E.G. Eddings, A.F. Sarofim. “Experimental and Numerical Investigation of Transient Soot Buildup on a Cylindrical Container Immersed in a Jet Fuel Pool Fire,” In Combustion Science and Technology, Vol. 178, No. 12, pp. 2199--2218. 2006.
DOI: 10.1080/00102200600626108


Soot buildup and its effects on heat transfer have been investigated as part of an effort to understand the thermal response of containers of high-energy materials immersed in fires. Soot deposition rates were measured for cooled and uncooled cylindrical containers immersed in a jet fuel pool fire. The soot buildup was measured at different time intervals with a wet film gage with an uncertainty of 20%. These rates were compared with those calculated by solving the boundary layer equations along the cylinder surface including the thermophoretic transport of soot particles. Thermophoresis was the dominant soot transport mechanism controlling the deposition of soot on the container wall and gave deposition rates in good agreement with the measured values. The soot buildup was found to have an important insulating effect on the heat transfer to the container. A soot deposit thickness of 1.2 mm resulted in as much as a 35% reduction in heat flux.

J.E. Guilkey, J.B. Hoying, J.A. Weiss. “Computational Modeling of Multicellular Constructs with the Material Point Method,” In Journal of Biomechanics, Vol. 39, No. 11, pp. 2074--2086. 2006.

Y. Guo, J.A. Nairn. “Three-Dimensional Dynamic Fracture Analysis using the Material Point Method,” In Computer Modeling in Engineering and Sciences, Vol. 1, No. 1, pp. 11--25. 2006.


This paper describes algorithms for three-dimensional dynamic stress and fracture analysis using the material point method (MPM). By allowing dual velocity fields at background grid nodes, the method provides exact numerical implementation of explicit cracks in a predominantly meshless method. Crack contact schemes were included for automatically preventing crack surfaces from interpenetration. Crack-tip parameters, dynamic J-integral vector and mode I, II, and III stress intensity factors, were calculated from the dynamic stress solution. Comparisons to finite difference method (FDM), finite element method (FEM), and boundary element method (BEM), as well as to static theories showed that MPM can efficiently and accurately solve three-dimensional dynamic fracture problems. Since the crack description is independent of the object description, MPM could be useful for simulation of three-dimensional dynamic crack propagation in arbitrary directions.

I. Ionescu, J.E. Guilkey, M. Berzins, R.M. Kirby, J.A. Weiss. “Simulation of Soft Tissue Failure Using the Material Point Method,” In Journal of Biomechanical Engineering, Vol. 128, No. 6, pp. 917--924. 2006.

G. Krishnamoorthy, R. Rawat, P.J. Smith. “Parallelization of the P-1 Radiation Model,” In Numerical Heat Transfer, Part B: Fundamentals, Vol. 49, No. 1, pp. 1--17. 2006.
DOI: 10.1080/10407790500344068


The P-1 radiation model is spatially decomposed to solve the radiative transport equation on parallel computers. Mathematical libraries developed by third parties are employed to solve the linear systems that result during the solution procedure. Multigrid preconditioning accelerated the convergence of iterative methods. The parallel performance did not depend strongly on the radiative properties of the medium or the boundary conditions. Predictions from coupling the weighted-sum-of-gray-gases model with the P-1 approximation are compared against benchmarks for model problems. The P-1 approximation resulted in only a moderate loss in accuracy while being significantly faster than the discrete ordinates method.

S. Parker, K. Zhang, C. Damevski, C.R. Johnson. “Integrating Component-Based Scientific Computing Software,” In Parallel Processing for Scientific Computing, Edited by M.A. Heroux and P. Raghavan and H.D. Simon, SIAM, pp. 271--288. January, 2006.

R.P. Pawlowski, J.N. Shadid, J.P. Simonis, H.F. Walker. “Globalization Techniques for Newton--Krylov Methods and Applications to the Fully-coupled Solution of the Navier-Stokes Equations,” In SIAM Review, Vol. 48, No. 4, pp. 700--721. 2006.
DOI: 10.1137/S0036144504443511


A Newton-Krylov method is an implementation of Newton's method in which a Krylov subspace method is used to solve approximately the linear subproblems that determine Newton steps. To enhance robustness when good initial approximate solutions are not available, these methods are usually globalized, i.e., augmented with auxiliary procedures (globalizations) that improve the likelihood of convergence from a starting point that is not near a solution. In recent years, globalized Newton-Krylov methods have been used increasingly for the fully coupled solution of large-scale problems. In this paper, we review several representative globalizations, discuss their properties, and report on a numerical study aimed at evaluating their relative merits on large-scale two- and three-dimensional problems involving the steady-state Navier–Stokes equations.

A. Santamaria, F. Mondragon, A Molina, N.D. Marsh, E.G. Eddings, A.F. Sarofim. “FT-IR and 1H-NMR Characterization of the Products of an Ethylene Inverse Diffusion Flame,” In Combustion and Flame, Vol. 146, No. 1-2, pp. 52--62. July, 2006.
DOI: 10.1016/j.combustflame.2006.04.008


Knowledge of the chemical structure of young soot and its precursors is very useful in the understanding of the paths leading to soot particle inception. This paper presents analyses of the chemical functional groups, based on FT-IR and 1H NMR spectroscopy of the products obtained in an ethylene inverse diffusion flame. The trends in the data indicate that the soluble fraction of the soot becomes progressively more aromatic and less aliphatic as the height above the burner increases. Results from 1H NMR spectra of the chloroform-soluble soot samples taken at different heights above the burner corroborate the infrared results based on proton chemical shifts (Ha, Hα, Hβ, and Hγ). The results indicate that the aliphatic β and γ hydrogens suffered the most drastic reduction, while the aromatic character increased considerably with height, particularly in the first half of the flame.

Keywords: Soot, FT-IR, 1H NMR, Inverse diffusion flame