Rate-Controlled Constrained-Equilibrium Calculations of Ethanol-Oxygen Mixture

2006 ◽  
Author(s):  
Mohammad Janbozorgi ◽  
Yue Gao ◽  
Hameed Metghalchi ◽  
James C. Keck
Keyword(s):  
Chemical Reactions ◽  
Initial Pressure ◽  
Kinetic Scheme ◽  
Rate Equations ◽  
Oxygen Mixture ◽  
Free Valence ◽  
Free Oxygen ◽  
Constant Volume Chamber ◽  
Constrained Equilibrium ◽  
Rate Controlled

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.

Methanol Oxidation Induction Times Using the Rate-Controlled Constrained-Equilibrium Method

2003 ◽  
Author(s):  
Sergio Ugarte ◽  
Mohamad Metghalchi ◽  
James C. Keck
Keyword(s):  
Methanol Oxidation ◽  
Ignition Delay ◽  
Rate Equations ◽  
Oxygen Mixture ◽  
Free Oxygen ◽  
Equilibrium Method ◽  
Ignition Delay Times ◽  
Delay Times ◽  
Constrained Equilibrium ◽  
Rate Controlled

Methanol oxidation has been modeled using the Rate-Controlled Constrained-Equilibrium method (RCCE). In this method, composition of the system is determined by constraints rather than by species. Since the number of constraints can be much smaller than the number of species present, the number of rate equations required to describe the time evolution of the system can be considerably reduced. In the present paper, C1 chemistry with 29 species and 140 reactions has been used to investigate the oxidation of stoichiometric methanol/oxygen mixture at constant energy and volume. Three fixed elemental constraints: elemental carbon, elemental oxygen and elemental hydrogen and from one to nine variable constraints: moles of fuel, total number of moles, moles of free oxygen, moles of free oxygen, moles of free valence, moles of fuel radical, moles of formaldehyde H2CO, moles of HCO, moles of CO and moles of CH3O were used. The four to twelve rate equations for the constraint potentials (LaGrange multipliers conjugate to the constraints) were integrated for a wide range of initial temperatures and pressures. As expected, the RCCE calculations gave correct equilibrium values in all cases. Only 8 constraints were required to give reasonable agreement with detailed calculations. Results of using 9 constraints showed compared very well to those of the detailed calculations at all conditions. For this system, ignition delay times and major species concentrations were within 0.5% to 5% of the values given by detailed calculations. Adding up to 12 constraints improved the accuracy of the minor species mole fractions at early times, but only had a little effect on the ignition delay times. RCCE calculations reduced the time required for input and output of data in 25% and 10% when using 8 and 9 constraints respectively. In addition, RCCE calculations gave valuable insight into the important reaction paths and rate-limiting reactions involved in methanol oxidation.

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

2018 ◽  
Vol 141 (2) ◽  
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.

Constrained-Equilibrium Modeling of Methane Oxidation in Air

2013 ◽  
Author(s):  
Ghassan Nicolas ◽  
Mohammad Janbozorgi ◽  
Hameed Metghalchi
Keyword(s):  
Combustion Process ◽  
Rate Equations ◽  
Experimental Measurements ◽  
Combustion Modeling ◽  
Ignition Delay Times ◽  
Wide Range ◽  
Constrained Equilibrium ◽  
Detailed Kinetic Model ◽  
Rate Controlled ◽  
Oxidation In Air

The Rate-Controlled Constrained-Equilibrium (RCCE) has been further developed and applied to model methane/air combustion process. The RCCE method is based on local maximization of entropy or minimization of a relevant free energy at any time during the non-equilibrium evolution of the system subject to a set of constraints. The constraints are imposed by slow rate-limiting reactions. Direct integration of the rate equations for the constraint potentials has been employed. Once the values of the potentials are obtained, the concentration of all species can be calculated. A set of constraints has been developed for methane/air mixtures in the method of Rate-Controlled Constrained-Equilibrium (RCCE). The model predicts the ignition delay times, which have been compared to those predicted by detailed kinetic model (DKM) and with shock tube experimental measurements. The DKM includes 60 H/O/C1–2/N species and 352 reactions. The RCCE model using 16 constraints has been applied for combustion modeling in a wide range of initial temperatures (900–1200 K), pressures (1–50 atmospheres) and fuel-air equivalence ratio (0.6–1.2). The predicted results of using RCCE are within 5% of those of DKM model and are in excellent agreement with experimental measurements in shock tubes.

Rate-Controlled Constrained-Equilibrium Theory of Chemical Reactions

2008 ◽  
Author(s):  
James C. Keck ◽  
Gian Paolo Beretta ◽  
Ahmed Ghoniem ◽  
George Hatsopoulos
Keyword(s):  
Chemical Reactions ◽  
Equilibrium Theory ◽  
Constrained Equilibrium ◽  
Rate Controlled

A Study of Interactions between Mixing and Chemical Reaction Using the Rate-Controlled Constrained-Equilibrium Method

2016 ◽  
Vol 41 (4) ◽  
Author(s):  
Fatemeh Hadi ◽  
Mohammad Janbozorgi ◽  
M. Reza H. Sheikhi ◽  
Hameed Metghalchi
Keyword(s):  
Chemical Kinetics ◽  
Chemical Reaction ◽  
Computational Cost ◽  
Methane Combustion ◽  
Rate Equations ◽  
Wide Range ◽  
Constrained Equilibrium ◽  
Rate Controlled ◽  
Detailed Kinetics ◽  
Reacting Systems

AbstractThe rate-controlled constrained-equilibrium (RCCE) method is employed to study the interactions between mixing and chemical reaction. Considering that mixing can influence the RCCE state, the key objective is to assess the accuracy and numerical performance of the method in simulations involving both reaction and mixing. The RCCE formulation includes rate equations for constraint potentials, density and temperature, which allows taking account of mixing alongside chemical reaction without splitting. The RCCE is a dimension reduction method for chemical kinetics based on thermodynamics laws. It describes the time evolution of reacting systems using a series of constrained-equilibrium states determined by RCCE constraints. The full chemical composition at each state is obtained by maximizing the entropy subject to the instantaneous values of the constraints. The RCCE is applied to a spatially homogeneous constant pressure partially stirred reactor (PaSR) involving methane combustion in oxygen. Simulations are carried out over a wide range of initial temperatures and equivalence ratios. The chemical kinetics, comprised of 29 species and 133 reaction steps, is represented by 12 RCCE constraints. The RCCE predictions are compared with those obtained by direct integration of the same kinetics, termed detailed kinetics model (DKM). The RCCE shows accurate prediction of combustion in PaSR with different mixing intensities. The method also demonstrates reduced numerical stiffness and overall computational cost compared to DKM.

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

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.

Constrained-Equilibrium Modeling of Ethanol Combustion in Air

2014 ◽  
Author(s):  
Ghassan Nicolas ◽  
Mohammad Janbozorgi ◽  
Hameed Metghalchi
Keyword(s):  
Batch Reactor ◽  
Kinetic Scheme ◽  
Equilibrium Modeling ◽  
Constrained Equilibrium ◽  
Ethanol Combustion ◽  
Rate Controlled ◽  
Ignition Characteristics

The rate-controlled constrained-equilibrium technique is used to study the ignition characteristics of mixtures of ethanol/air in an isolated batch reactor. A set of 16 constraints was identified which is able to reproduce the ignition characteristics very well within the specified range of thermodynamics conditions. The detailed kinetic scheme involves 37 species and 238 reactions without nitrogen chemistry.

Rate Controlled Constrained-Equilibrium (RCCE) Method Applied to Di-Methyl Ether (DME) Combustion

2008 ◽  
Author(s):  
Mohammad Janbozorgi ◽  
Donald Goldthwaite ◽  
Hameed Metghalchi
Keyword(s):  
High Pressure ◽  
Low Temperature ◽  
Methyl Ether ◽  
Batch Reactor ◽  
Kinetic Scheme ◽  
Constrained Equilibrium ◽  
Rate Controlled ◽  
Ignition Characteristics

The rate-controlled constrained-equilibrium technique is used to study the ignition characteristics of Di-Methyl Ether (DME) under high pressure, low temperature in a batch reactor. A set of 9 constraints was identified which is able to exactly reproduce the ignition characteristics within the specified range of thermo dynamics conditions. The detailed kinetic scheme involves C1-C2 chemistry and comprises 54 species and 308 reactions without nitrogen chemistry.

The Rate-Controlled Constrained-Equilibrium Combustion Modeling of n-Pentane/Oxygen/Diluent Mixtures

2019 ◽  
Vol 141 (8) ◽  
Author(s):  
Linghao Du ◽  
Guangying Yu ◽  
Ziyu Wang ◽  
Hameed Metghalchi
Keyword(s):  
Experimental Data ◽  
Hydrocarbon Fuel ◽  
Chemical Mechanism ◽  
Pure Oxygen ◽  
Oxygen Mixture ◽  
Ignition Delay Times ◽  
Constraint Set ◽  
Constrained Equilibrium ◽  
Rate Controlled ◽  
Reacting Systems

Rate-controlled constrained equilibrium (RCCE) is a reduction technique used to describe the time evolution of complex chemical reacting systems. This method is based on the assumption that a nonequilibrium system can reach its final equilibrium state by a series of RCCE states determined by maximizing entropy or minimizing relevant free energy. Those constraints are imposed by some small number of slow reactions. Much research has been done on this method and many RCCE models of C1−C4 hydrocarbon fuel combustion have been established by the previous researchers. Those models show good performance compared with the result of detailed kinetic model (DKM). In this study, RCCE method is further developed to model normal pentane (n-C5H12) combustion with least number of constraints. The chemical mechanism for DKM contains 133 species and 922 reactions. Two sets of constraints were found during the study: (1) 16 constraints for the normal pentane and pure oxygen mixture and (2) 14 constraints for the mixture of normal pentane and oxygen with argon as diluent. Results of the first constraint set were compared with result of DKM and results of the second constraint set were compared with those of DKM and experimental data by calculating their ignition delay times. Comparisons showed that the first set of constraints had relatively good accuracy and the second set of constraints agreed very well with the experimental data.

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