The Combustion and Reacting Flows group at the University of California, Davis is made up faculty from the Departments of Mechanical and Aeronautical Engineering, Civil and Environmental Engineering, Biological and Agricultural Engineering, Chemistry, Chemical Engineering and Materials Science, Environmental Toxicology and the Facility for Advanced Instrumentation.

Some current research projects are described below with the funding source indicated in parentheses. Project descriptions are followed by faculty biographies. Laboratory facilities are described on the last page.

RESEARCH PROJECTS IN COMBUSTION AND CHEMICALLY REACTING FLOWS

DIAMOND SYNTHESIS (UC DAVIS; Aldredge) - Diamond films are synthesized by chemical vapor deposition on silicon and molybdenum substrates, with an acetylene-oxygen or plasma torch as the activation energy source. The aim of the research is the fundamental understanding of chemical mechanisms in both the gas phase above the substrate and on the substrate surface, and the understanding of the influence of chemistry and gas-phase fluid dynamics on the growth rates and quality of the deposited diamond films. Potential industrial applications of this research are the coating of tools to increase surface hardness and the design of thin-film heat sinks to increase heat dissipation from computer chips.

TURBULENT PREMIXED FLAMES (ONR; Aldredge) - This research is directed toward a fundamental understanding of the influence of large-scale turbulence on the propagation of turbulent or wrinkled premixed flames. Mathematical conservation equations are solved by a combination of analytical and computational techniques to investigate the role of flame stretch and flame broadening by the turbulent flow. The aim of the research is accurate prediction of the dependence of the average flame speed on the turbulence intensity and Reynolds number of the turbulent reactive flow.

COMBUSTION OF BINARY MISCIBLE DROPLETS IN REDUCED GRAVITY (NASA; Shaw) - This research aims at studying the combustion characteristics of individual and unsupported two-component miscible droplets in reduced-gravity environments. Attention is focused upon droplets that are initially in the millimeter size range. Droplet components are selected so that their volatilities are significantly different. Some phenomena of interest are transient gas-phase processes (e.g., sudden flame contraction caused by rapid increases of the surface mass fraction of the less volatile component, and extinction), transient liquid-phase processes (e.g., droplet diameter histories, bubble nucleation, and disruption), and sooting and transport of observable soot particles (from thermophoretic and aerodynamic forces). Experiments will be carried out in the NASA LeRC 2.2 sec drop tower, with data obtained by cine photography of the burning droplets. Films will be analyzed both manually and with digital image processing techniques. Time histories of droplet and flame diameters and other observables will be measured. In conjunction with the experiments, theoretical studies will be undertaken to aid interpretation of the experimental results. An objective of these studies will be to clarify the influence of liquid-phase species and energy transport on transient combustion behaviors.

A DROP-TUBE APPARATUS TO PROMOTE SPHERICALLY-SYMMETRICAL DROPLET GASIFICATION (NSF; Shaw) - A unique drop-tube apparatus to promote spherically-symmetrical evaporation and combustion of freely-falling droplets is being developed and constructed. Design of the apparatus is based upon the principle that gravitationally-induced pressure gradients in gases may be significantly reduced by accelerating the gases with properly contoured tubes. Droplets traveling with the gases will experience greatly reduced buoyancy and forced convection environments, thereby promoting spherical symmetry. The apparatus will be used to study nearly spherically-symmetrical droplet evaporation and combustion under conditions that have heretofore not been experimentally achieved (i.e., combustion of droplets initially ≈ 100 µm in diameter at atmospheric pressure). Experimental studies will focus on; 1. combustion and extinction of hydrocarbon droplets; 2. measurement of transient droplet and flame diameters; and 3. combustion and disruption of droplets with strong sooting tendencies. Results from these experiments will be useful in practical applications of droplets and sprays, and also in fundamental combustion research.

PARTICULATE FORMATION IN FLAMES (NSF; Kennedy) - This project is concerned primarily with soot production in turbulent diffusion flames. Laser extinction measurements of soot volume fractions and luminous radiation are made in a wind tunnel under varying conditions of axial pressure gradient. Temperature, velocity and mean gas concentrations are also being measured to determine the impact of pressure gradients on flame structure. A second aspect of this program of research is the use of an isothermal analog of soot formation in a turbulent jet. The relatively slow reaction of NH3 and HCl is used to form NH4Cl particles. Laser visualization of the aerosol is used to discern regions of product formation and biacetyl fluorescence is used to measure the mixture fraction field at the same time.

THERMAL TREATMENT OF HAZARDOUS WASTE (NIH; Kennedy) - Particle formation in a diffusion flame of chlorinated hydrocarbons is being investigated experimentally in a laminar, counterflow diffusion flame. Laser extinction and scattering measurements of the soot aerosol characterize its properties. The impact of the H to Cl ratio on the production of hazardous products of incomplete combustion is studied; the absorption of these gas phase species onto particles is of interest in this project. In the second phase of the project, metal emissions from diffusion flames will be studied. Particular attention will be given to the formation of arsenic and chromium particles in flames.

TURBULENT SPRAYS (AFOSR; Kennedy) - An experiment has been developed to study the dispersion of 50 to 100 mm droplets in a turbulent jet of air. A novel laser scattering and imaging technique permits us to track the motion of these particles through a sheet of laser light so that Lagrangian statistics of droplet dispersion are obtained as functions of time of flight. A droplet lasing technique has been developed that allows us the measure the change of the tagged droplet to within 20 to 50 nm, hence permitting measurements of vaporization rates to be obtained in a turbulent flow. The results will be used to test the validity of current correlations of droplet drag and mass transfer in a turbulent flow.

HEALTH EFFECTS OF ULTRAFINE AEROSOLS (Health Effects Institute; Kennedy) - This project represents a collaboration between researchers in Mechanical and Aeronautical Engineering, Civil and Environmental Engineering and Veterinary Medicine. It aims to determine the consequences for pulmonary health of inhalation of ultrafine aerosols that are generated by combustion sources.

SYNTHESIS OF QUANTUM DOTS OF GALLIUM NITRIDE (Kennedy) - Very small particles of GaN can exhibit interesting properties as a result of their three dimensional spatial confinement. Laser ablation of a gallium target by a UV laser beam is being studied as a promising strategy for the synthesis of GaN. Particles less than 10 nm have been successfully created by this method. Fundamental research into the mechanisms that are involved is required.

FACULTY BIOGRAPHIES

RALPH C. ALDREDGE, III, Assistant Professor

(530) 752-5016

EDUCATION

1985 B.S. Mechanical Engineering & French Carnegie-Mellon University
1987 M.A. Mechanical & Aerospace Engineering Princeton University
1990 Ph.D. Mechanical & Aerospace Engineering Princeton University

POSITIONS

1987-1988 Teaching Assistant, Princeton University
1985-1990 Research Assistant, Princeton University
1990-1991 Chancellor's Postdoctoral Fellow, University of California, San Diego
1991-1992 James Irvine Research Fellow, California Institute of Technology
1992-Pres. Assistant Professor, University of California, Davis

REPRESENTATIVE PUBLICATIONS

1. "Influence of Wrinkled Premixed-Flame Dynamics on Large-Scale, Low-Intensity Turbulent Flow", R.C. Aldredge and F.A. Williams, Journal of Fluid Mechanics, Vol. 228, pp. 487-511 (1991).
2. "The Propagation of Wrinkled Premixed Flames in Spatially Periodic Shear Flow", R.C. Aldredge, Combustion and Flame, Vol. 90 (to appear).

RESEARCH INTERESTS

Turbulent-Combustion Modeling; the coupling between combustion instabilities and noise-generated turbulence; combustion-controlled synthesis of diamond films.

Email Professor Aldredge

HARRY A. DWYER, Professor

(530) 752-1777

EDUCATION

1962 B.S. Mechanical Engineering Rutgers University
1964 M.S. Mechanical Engineering Rutgers University
1966 Ph.D. Mechanical Engineering Rutgers University

POSITIONS

1962-1964 Research Engineer, Rutgers University, New Brunswick, NJ
1966-1967 Theoretical Fluid Physicist, General Electric Space Sciences Laboratory, King of Prussia, PA
1967-Pres. Professor, University of California, Davis

REPRESENTATIVE PUBLICATIONS

1. "A Study of Flow Interactions During Axisymmetric Spin-Up," S. Ibrani and H.A. Dwyer, AIAA Paper 86-0036, 24th AIAA Aerospace Sciences Meeting, Jan. 6-9, Reno, NV. (1986).
2. "Numerical Calculation of the Interaction of Pressure Waves and Flames," H.A. Dwyer, A. Lutz, R.J. Kee, Reacting Flows. G.S.S. Ludford Editor, Lectures in Applied Mathematics, AMS Vol. 24, pp. 185-198 (1986).

RESEARCH INTERESTS

Simulation of laminar and turbulent flow with the use of the digital computer with a special interest in flows with chemical reactions.

IAN M. KENNEDY, Professor and Vice Chairman

(530) 752-2796

EDUCATION

1975 B. Eng. Mechanical Engineering Sydney University, Australia
1980 Ph.D. Mechanical Engineering Sydney University, Australia

POSITIONS

1976-1979 Research Student, Dept. of Mechanical Engineering, Sydney University, Australia
1979-1981 Post Doctoral Research Associate, Dept. of Mechanical and Aero Engineering, Princeton University
1981-1983 Research Staff Member, Dept. of Mechanical and Aero Engineering, Princeton University
1983-1986 Research Scientist, Aero Research Labs, Melbourne, Australia
1986-1989 Assistant Professor, University of California, Davis
1989-1993 Associate Professor, University of California, Davis
1993 Professor

REPRESENTATIVE PUBLICATIONS

C. Call and I. M. Kennedy, A technique for measuring Lagrangian and Eulerian Particle Statistics in a Turbulent Shear Flow, Experiments in Fluids 12, 125 - 130 (1991).

C. Call and I. M. Kennedy, Measurements and Simulations of Particle Dispersion in a Turbulent Flow, Int. J. Multiphase Flow, 18, 891 - 903 (1992).

I. M. Kennedy, C. Yam, D. Rapp and R. Santoro, Modeling and Measurements of Soot and Species in a Laminar Diffusion Flame, Combustion and Flame 107, 368 - 382 (1995).

I. M. Kennedy, Models of Soot Formation and Oxidation, Prog. Energy Combust. Sci. 23, 95 - 132 (1997).

T. M. Allen, D. Z. Bezabeh, C. H. Smith, E. M. McCauley, A. D. Jones, D. P. Y. Chang, I. M. Kennedy and P. B. Kelly, Speciation of Arsenic Oxides using Laser Desorption Ionization Time-of-Flight Mass Spectrometry, Analytical Chemistry 68, 4052 - 4059 (1995).

S. Yuan, Y. Yoon, M. Muller-Roosen and I. M. Kennedy, A Two Dimensional Discrete-Sectional Model for Metal Aerosol Dynamics in a Flame, accepted in Aerosol Sci. Tech. (1997). [see abstract]

T. J. Goodwin, V. J. Leppert, S. H. Risbud, I. M. Kennedy and others, Synthesis of gallium nitride quantum dots through reactive laser ablation, Applied Physics Letters 9, 70 N23, 3122 - 3124 (1997).

Ian M. Kennedy, Yanda Zhang, A. Daniel Jones, Daniel P. Y. Chang, Peter B. Kelly and Youngbin Yoon, The Morphology Of Chromium Emissions From A Laminar Hydrogen Diffusion Flame, to appear in Combustion and Flame 1998. [see abstract]

RESEARCH INTERESTS

Combustion; laser diagnostics; aerosol formation; health effects of combustion.

An image of a spray in a turbulent flow generated by exciting acetone vapor fluorescence to show vapor concentration and fluorescence from droplets.

Email Professor Kennedy

WOLFGANG KOLLMANN, Professor

(530) 752-1452

EDUCATION

1967 Dipl-Ing Aerospace Engineering Technical University, Stuttgart, Germany
1972 Dr-Ing Mechanical Engineering Technical University,Aachen, Germany
1979 Habilitation Mechanical Engineering Technical University, Aachen, Germany

POSITIONS

1968-1969 Research Assistant, Technical University, Stuttgart, Germany
1969-1977 Assistant Professor, Technical University, Aachen, Germany
1977-1980 Assistant Professor, Von Karman Institute, Belgium
1981-1985 Associate Professor, University of California, Davis
1985-Pres. Professor, University of California, Davis

REPRESENTATIVE PUBLICATIONS

1. "Pdf Modelling of Turbulent Nonpremixed Methane Jet Flames," J.-Y. Chen, W.Kollmann and R.W. Dibble, Combustion Science and Technology, Vol. 64 pp. 315-346 (1989).
2. "The Pdf Approach to Turbulent Flow," W. Kollmann, Theoretical Comput. Fluid Dynamics, Vol. 1, pp. 249-285 (1990).
3. "Segregation Parameters and Pair-Exchange Mixing Models for Turbulent Nonpremixed Flames," J.-Y. Chen, W. Kollmann, 23rd Symposium on Combustion, Orleans, France (1990).

RESEARCH INTERESTS

Turbulence modeling; turbulent combustion; numerical fluid mechanics.

Email Professor Kollmann

BENJAMIN D. SHAW, Associate Professor

(530) 752-4130

EDUCATION

1981 B.S. Mechanical Engineering Colorado State University
1984 M.S. Mechanical Engineering Colorado State University
1989 Ph.D. Mechanical/AerospaceEngineering Princeton University

POSITIONS

1982-1984 Research Assistant, Colorado State University
1986-1987 Teaching Assistant, Princeton University
1984-1988 Research Assistant, Princeton University
1988-1989 Staff Research Associate, University of California, San Diego
1989-1991 Assistant Professor, University of Connecticut
1991-1995 Assistant Professor, University of California, Davis
1995 - present Associate Professor, University of California, Davis

REPRESENTATIVE PUBLICATIONS

1. "Asymptotic Analysis of the Lumped Capacitance Approximation," B.D. Shaw, International Journal of Heat and Mass Transfer (in press).
2. "Theory of Azeotropic Gasification of Miscible Multicomponent Droplets," B.D. Shaw, Combustion Science and Technology, 84: p. 295 (1992).
3. "A Model for the Deflagration of Aqueous Solutions of Hydroxylammonium Nitrate," B.D. Shaw and F.A. Williams, to be presented at the Twenty-Fourth International Symposium of Combustion, Sydney, Australia, July 5-10 (1992).
4. "A Drop-Tube Apparatus to Promote Spherically-Symmetrical Evaporation and Combustion of Unsupported Droplets," D.F. Wang, J.S. Woo and B.D. Shaw, Review of Scientific Instruments, 62: pp. 3029-3036 (1991).

RESEARCH INTERESTS

Combustion; fluid mechanics; heat transfer.

Email Professor Shaw

STUDENT SUPPORT

Support for graduate studies is available for well qualified students. Contact one of the professors listed above for further information about specific funding and projects.

COMBUSTION LABORATORY FACILITIES

The combustion laboratory at U.C. Davis is housed in approximately 2,000 square feet of well-equipped space. The major items of equipment are listed below.