Rate-controlled constrained-equilibrium theory of chemical reactions in complex systems

The Rate-Controlled Constrained-Equilibrium method (RCCE) is a powerful technique for simplifying the treatment of chemical reactions in complex systems. The method is based on the assumption that slow chemical reactions impose constraints on the allowed composition of such systems. Since the number of constraints can be very much smaller than the number of species, the number of rate equations to be integrated can be considerably reduced. In the present work, a kinetic scheme with 55 species and 366 reactions has been used to investigate stoichiometric Ethanol-oxygen mixture in a constant energy constant volume chamber. The state of the system was determined by three fixed elemental constraints: elemental carbon, elemental oxygen and elemental hydrogen and six variable constraints: moles of fuel, moles of fuel radicals, total number of moles, moles of free valence, moles of free oxygen, moles of OH+O+H. The 9 rate equations for the constraint potentials (LaGrange multipliers associated with the constraints) were integrated over a range of 1400 K-1700 K for initial temperature and 1atm-10atm for initial pressure. The RCCE calculations were in good agreement with detailed calculations and were faster than detailed calculations, which required integration of 55 species rate equations.

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Rate Controlled Constrained-Equilibrium Simulation of Ethanol Combustion Using SVD Derived Constraints

Volume 6: Energy ◽

10.1115/imece2019-10994 ◽

2019 ◽

Author(s):

Shrabanti Roy ◽

Fatemeh Hadi ◽

Omid Askari

Keyword(s):

Chemical Reactions ◽

Fluid Dynamic ◽

Equilibrium States ◽

Chemical System ◽

Accurate Identification ◽

Combustion Modeling ◽

Number Of Species ◽

Constrained Equilibrium ◽

Ethanol Combustion ◽

Rate Controlled

Abstract In this study, the fully automatable Approximate Singular Value Decomposition of the Actual Degrees of Disequilibrium (ASVDADD) method is used for combustion modeling of ethanol. Due to the importance of ethanol as one of the most common type of biofuels, modeling its reaction kinetics and chemical composition evolution during combustion is necessary. The detailed kinetic mechanism (DKM) considered here is generated by authors using reaction mechanism generator (RMG) technique and it consists of 66 species and 1031 reactions. Tracking this number of species and chemical reactions in computational fluid dynamic (CFD) analysis of engineering problems is prohibitive. To alleviate this issue, Rate-Controlled Constrained-Equilibrium (RCCE) model reduction scheme for chemical kinetics is employed. It describes the evolution of a complex chemical system with acceptable accuracy with a number of rates controlling constraints on the associated constrained-equilibrium states of the system, much lower than the number of species in the underlying DKM. Successful approximation of the constrained equilibrium states requires accurate identification of the constraints. One promising procedure is the ASVDADD method that is capable of identifying the best constraints for a given range of thermodynamic conditions and a required level of approximation. ASVDADD is based on simple algebraic analysis of the results of the underlying DKM simulation and is focused on the behavior of the degrees of disequilibrium (DoD) of the individual chemical reactions. In this paper, ASVDADD is used to derive the RCCE constraints and ethanol combustion is modeled using both DKM and RCCE. Comparison of RCCE results with those of DKM shows the effectiveness of the ASVDADD derived constraints which demonstrates the potential of the RCCE method for combustion modeling of heavy and complex fuels.

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On the structure and analysis of complex systems of first-order chemical reactions containing irreversible steps—II Projection properties of the characteristic vectors

Chemical Engineering Science ◽

10.1016/0009-2509(68)89027-x ◽

1968 ◽

Vol 23 (10) ◽

pp. 1191-1200 ◽

Cited By ~ 11

Author(s):

A.J. Silvestri ◽

C.D. Prater ◽

J. Wei

Keyword(s):

Complex Systems ◽

Chemical Reactions ◽

First Order ◽

Projection Properties

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Combustion Simulation of Propane/Oxygen (With Nitrogen/Argon) Mixtures Using Rate-Controlled Constrained-Equilibrium

Journal of Energy Resources Technology ◽

10.1115/1.4041289 ◽

2018 ◽

Vol 141 (2) ◽

Cited By ~ 14

Author(s):

Guangying Yu ◽

Hameed Metghalchi ◽

Omid Askari ◽

Ziyu Wang

Keyword(s):

Experimental Data ◽

Energy System ◽

Kinetic Mechanism ◽

Chemical Kinetic ◽

Oxygen Mixture ◽

Free Valence ◽

Wide Range ◽

Constrained Equilibrium ◽

Rate Controlled ◽

Good Agreement

The rate-controlled constrained-equilibrium (RCCE), a model order reduction method, has been further developed to simulate the combustion of propane/oxygen mixture diluted with nitrogen or argon. The RCCE method assumes that the nonequilibrium states of a system can be described by a sequence of constrained-equilibrium states subject to a small number of constraints. The developed new RCCE approach is applied to the oxidation of propane in a constant volume, constant internal energy system over a wide range of initial temperatures and pressures. The USC-Mech II (109 species and 781 reactions, without nitrogen chemistry) is chosen as chemical kinetic mechanism for propane oxidation for both detailed kinetic model (DKM) and RCCE method. The derivation for constraints of propane/oxygen mixture starts from the eight universal constraints for carbon-fuel oxidation. The universal constraints are the elements (C, H, O), number of moles, free valence, free oxygen, fuel, and fuel radicals. The full set of constraints contains eight universal constraints and seven additional constraints. The results of RCCE method are compared with the results of DKM to verify the effectiveness of constraints and the efficiency of RCCE. The RCCE results show good agreement with DKM results under different initial temperature and pressures, and RCCE also reduces at least 60% CPU time. Further validation is made by comparing the experimental data; RCCE shows good agreement with shock tube experimental data.

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THE CHARACTERIZATION OF COMPLEX SYSTEMS OF CHEMICAL REACTIONS

Chemical Engineering Communications ◽

10.1080/00986448908940663 ◽

1989 ◽

Vol 83 (1) ◽

pp. 221-240 ◽

Cited By ~ 16

Author(s):

JOHN HAPPEL ◽

PETER H. SELLERS

Keyword(s):

Complex Systems ◽

Chemical Reactions

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Comparison Between RCCE and Shock Tube Ignition Delay Times at Low Temperatures

Journal of Energy Resources Technology ◽

10.1115/1.4030493 ◽

2015 ◽

Vol 137 (6) ◽

Cited By ~ 13

Author(s):

Ghassan Nicolas ◽

Hameed Metghalchi

Keyword(s):

Free Energy ◽

Shock Tube ◽

Ignition Delay ◽

Low Temperatures ◽

Reduction Technique ◽

Experimental Measurements ◽

Ignition Delay Times ◽

Delay Times ◽

Constrained Equilibrium ◽

Rate Controlled

The rate-controlled constrained-equilibrium (RCCE) method is a reduction technique based on local maximization of entropy or minimization of a relevant free energy at any time during the nonequilibrium evolution of the system subject to a set of kinetic constraints. In this paper, RCCE has been used to predict ignition delay times of low temperatures methane/air mixtures in shock tube. A new thermodynamic model along with RCCE kinetics has been developed to model thermodynamic states of the mixture in the shock tube. Results are in excellent agreement with experimental measurements.

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