The efforts of our research team focus on the quantitative kinetic characterization of reaction systems that have the potential to lead to more efficient and lower carbon power generation (e.g., solid oxide fuel cells, alternative fuels). Some examples of our approach are given below.
Impact of gas-phase reactions in solid oxide fuel cells
The gas-phase reactions in the fuel channel of a solid oxide fuel cell produce intermediates that can profoundly influence performance. We seek to understand the detailed chemical pathways that lead to production of the smaller hydrocarbons that might be catalytically converted within the anode before being electrochemically oxidized. We also seek to characterize the molecular weight growth processes that can lead to deposit formation within the anode channels. Some representative publications:
"Hydrocarbon Fuel Effects in SOFC Operation: An Experimental and Modeling Study of n-hexane Pyrolysis" K. L. Randolph and A. M. Dean, Phys. Chem. Chem. Phys., 9, 4245 - 4258 (2007).
"Kinetic Modeling of Ethane Pyrolysis at High Conversion", C. Xu, A.Shoaibi, C. Wang, H-H. Carstensen, and A. M. Dean, J. Phys. Chem. A, 115, 10470-10490 (2011).
Impact of alternative fuels on the performance of diesels and turbines
We have developed improved detailed kinetic and fuel vaporization models to quantitatively characterize the impact of alternative fuels on combustor performance. Changes in the chemical kinetics due to the use of alternative fuels can impact combustion characteristics such as cetane number, flame speed, and emissions. Performance changes might also be caused by changes in the fuel physical properties that affect vaporization and mixing. Some representative publications:
"The effects of multicomponent fuel droplet evaporation on the kinetics of strained opposed-flow diffusion flames," C. Wang, A. M. Dean, H. Zhu, and R. J. Kee, Combust. Flame, 160, 265-275 (2013).
"Detailed Modeling of Low-temperature Propane Oxidation: 1. The Role of Propyl+O2 Reaction", L. K. Huynh, H-H Carstensen, A. M. Dean, J. Phys. Chem A, 114, 6594-6607 (2010).
Development of theoretically based rate rules for free radical reactions
We continue to focus on the kinetics of elementary reactions, especially in the context of using electronic structure calculations to examine a series of similar reactions and then using these results to generate rate rules that are applicable to a wide range of such reactions. Some representative publications:
"Rate Constant Rules for the Automated Generation of Gas-Phase Reaction Mechanisms" H-H. Carstensen and A. M. Dean, J. Phys. Chem. A, 113, 367-380 (2009).
"High-Pressure Rate Rules for Alkyl + O2 Reactions: Part 1 - The Dissociation, Concerted Elimination, and Isomerization Channels of the Alkyl Peroxy Radical", S. M. Villano, L. K. Huynh, H-H. Carstensen, and A. M. Dean, J. Phys. Chem. A, 115, 13425-13442 (2011).
"High-Pressure Rate Rules for Alkyl + O2 Reactions: Part 2 - The Isomerization, Cyclic Ether Formation, and ?-Scission Reactions of Hydroperoxy Alkyl Radicals", S. M. Villano, L. K. Huynh, H-H. Carstensen, and A. M. Dean, J. Phys. Chem. A, 116, 5068-5089 (2012).
Development of theoretically-based detailed chemical mechanisms for hydrocarbon pyrolysis and oxidation
To develop mechanisms in terms of the actual elementary reactions in high-temperature, free radical systems, we use an iterative approach: (1) measure stable species and reactive intermediates in well-defined experiments, (2) compare these data to predictions of detailed kinetic models, (3) use the discrepancies to focus on those aspects of the chemistry that need more analysis, and (4) apply theoretical methods to attempt to resolve the discrepancies. An important component of this approach is the need to predict the temperature and pressure dependence of the branching reactions of chemically-activated reactions. The improved models that resulted from this approach allow more efficient identification of process concepts, so as to minimize the "experimental phase space." Some representative publications:
"The Kinetics of Pressure-Dependent Reactions" H-H. Carstensen and A. M. Dean in Comprehensive Chemical Kinetics, 42, 105-187 (2007).
"Modeling High Pressure Ethane Oxidation and Pyrolysis" C.V. Naik and A. M. Dean, Proc. Combustion Institute, 32, 437-443 (2009).
Extension of approaches used to analyze hydrocarbon kinetics to thermochemical conversion of biomass
Our group is becoming heavily involved in the production of fuels and power from the thermal conversion of biomass. We are particularly interested in characterizing the elementary chemical reactions occurring during biomass pyrolysis and gasification. As part of this analysis, we are characterizing the gas-phase reactions that lead to tar formation during biomass gasification as well as exploring gas-phase pathways to selectively remove tars from biomass and coal derived syngas streams. Some representative publications:
"Development of Detailed Kinetic Models For The Thermal Conversion of Biomass Via First Principle Methods And Rate Estimation Rules" H-H. Carstensen and A.M. Dean, in Computational Modeling in Lignocellulosic Biofuel Production, ACS Symposium Series 1052, 201-243 (2010).
"Selective Removal of Ethylene, a Known Deposit Precursor, from a 'Dirty' Synthesis Gas Stream via Gas-Phase Partial Oxidation", S. M. Villano, J. Hoffmann, H-H. Carstensen, and A.M. Dean, J. Phys. Chem. A, 114, 6502-6514 (2010).
"A Quantitative Kinetic Analysis of CO Elimination from Phenoxy Radicals" H-H. Carstensen and A. M. Dean, Int. J. Chemical Kinetics, 44, 75-89 (2012).
Coupling detailed kinetics with transport
Chemical reactions can be strongly influenced by multiple transport processes, including interactions between gas-phase reactions and those occurring on catalytic surfaces and the impact of mixing. Some representative publications:
Effects of Fuel Physicochemical Properties on Autoignition in the Ignition Quality Tester (IQT)", G. E. Bogin Jr, A. DeFilippo, J.Y. Chen, G. Chin, J. Luecke, M. A. Ratcliff, B.T. Zigler, A. M. Dean, Energy Fuels, 25, 5562-5572. (2011).
"Investigation of Gas-Phase Reactions in the Mixing Region for Hydrocarbon Autothermal Reforming Applications", S. Kim, H-H. Carstensen, A. M. Dean, and J. Bae, Int. J. Hydrogen Energy, 37, 7545-7553 (2012).
o Scale-bridging Modeling Tools to Assist the Design and Development of Electrochemical Power Sources, Office of Naval Research
o Kinetic Mechanism of Biomass Pyrolysis, National Advanced Biofuels Consortium, Department of Energy
o Pyrolysis Reactions of Butene Isomers at Low Temperatures, Petroleum Institute
o Fundamental Research On The Biological Stability Of Future Naval Fuels And Implications For The Biocorrosion Of Metallic Surfaces, Office of Naval Research
o Kinetic Ignition Model Validation for Hydrocarbons and Oxygenates in Heterogeneous Fuel-Air Mixtures, National Renewable Energy Lab
o Heterogeneously Catalyzed Endothermic Fuel Cracking, Air Force Office of Scientific Research