A Comparison of Constraint and Constraint Potential Forms of the Rate-Controlled Constraint-Equilibrium Method

2015 ◽  
Vol 138 (2) ◽  
Author(s):  
Fatemeh Hadi ◽  
M. Reza H. Sheikhi
Keyword(s):  
Performance Studies ◽  
Computation Time ◽  
Rate Equations ◽  
Detailed Chemical Kinetics ◽  
Effective Implementation ◽  
Computational Performance ◽  
Stirred Reactor ◽  
Wide Range ◽  
Rate Controlled ◽  
Detailed Chemical

A comparative assessment is made of two implementations of the rate-controlled constrained-equilibrium (RCCE) method. These are the constraint and constraint potential formulations in which rate equations are solved for the RCCE constraints and constraint potentials, respectively. The two forms are equivalent mathematically; however, they involve different numerical procedures and thus show different computational performance. The main objective of this study is to compare the accuracy and numerical efficiency of the two formulations to attain the most effective implementation of the RCCE in turbulent combustion simulations. The RCCE method is applied to study methane oxygen combustion in an adiabatic, isobaric well stirred reactor. Simulations are carried out over a wide range of initial temperatures and equivalence ratios. Performance studies are conducted and RCCE results are compared with those obtained by direct integration of detailed chemical kinetics. The results show that both methods provide very accurate representation of the kinetics. It is also demonstrated that while the constraint form involves less numerical stiffness, the constraint potential implementation results in more saving in computation time.

A Comparison of Rate-Controlled Constrained-Equilibrium Formulations

2015 ◽  
Author(s):  
Fatemeh Hadi ◽  
Mohammad Janbozorgi ◽  
M. Reza H. Sheikhi
Keyword(s):  
Performance Studies ◽  
Turbulent Combustion ◽  
Gas Mixtures ◽  
Direct Integration ◽  
Stirred Reactor ◽  
Wide Range ◽  
Constrained Equilibrium ◽  
Rate Controlled ◽  
And Performance ◽  
Detailed Kinetics

In this study, constraint potential and constraint forms of the Rate-Controlled Constrained-Equilibrium (RCCE) method have been investigated in terms of accuracy and performance. Although the two formulations are equivalent mathematically, they show quite different performances from the computational standpoint. The main objective of this work is to determine the most efficient implementation of RCCE to be used in turbulent combustion simulations. Simulations are conducted of an adiabatic, isobaric stirred reactor. The kinetics includes methane oxygen combustion using 133 reaction steps and 29 species. RCCE calculations are performed by 12 constraints. The simulations are carried out over a wide range of initial temperatures for stoichiometric gas mixtures. Performance studies of the two RCCE formulations are carried out and the results are compared with those obtained by direct integration of detailed kinetics.

Modeling Static Instabilities of Biogas Flames in a Stirred-Reactor Using Detailed Chemical Kinetics Simulations

2013 ◽  
Author(s):  
Christopher D. Bolin ◽  
Abraham Engeda
Keyword(s):  
Gas Turbines ◽  
Static Stability ◽  
Gas Turbine Combustor ◽  
Detailed Chemical Kinetics ◽  
Reduced Mechanism ◽  
Stirred Reactor ◽  
Primary Zone ◽  
Stability Limits ◽  
Different Sources ◽  
Detailed Chemical

Kinetic modeling of lean static stability limits of the combustion of biogas type fuels in a model of an ideal primary zone of a gas turbine combustor is presented here. In this study, CH4 is diluted with CO2 to simulate a range of gases representative of the products of anaerobic digestion of organic materials from different sources (e.g., landfill and animal waste digester). Fuels of this type are of interest for use in small gas turbines used in distributed generation applications. Predictions made by two detailed mechanisms (GRI-Mech 3.0 and San Diego) and one reduced mechanism (GRI-Mech 1.2, reduced) are employed to investigate the underlying kinetics near lean extinction. Approximate correlations to lean extinction are extracted from these results and compared to those of other fuels.

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.

Development of the Rate-Controlled Constrained-Equilibrium Method for Modeling of Ethanol Combustion

2015 ◽  
Vol 138 (2) ◽  
Author(s):  
Ghassan Nicolas ◽  
Hameed Metghalchi
Keyword(s):  
Ignition Delay ◽  
Stable Equilibrium ◽  
Combustion Process ◽  
Detailed Chemical Kinetics ◽  
Equilibrium Method ◽  
Constrained Equilibrium ◽  
Ethanol Combustion ◽  
Rate Controlled ◽  
Detailed Chemical

The rate-controlled constrained-equilibrium method (RCCE) has been further developed to model the combustion process of ethanol air mixtures. The RCCE 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. An important part of RCCE calculation is determination of a set of constraints that can guide the nonequilibrium mixture to the final stable equilibrium state. In this study, 16 constraints have been developed to model the nonequilibrium ethanol combustion process. The method requires solution of 16 differential equations for the corresponding constraint potentials. Ignition delay calculations of ethanol oxidizer mixtures using RCCE have been compared to those of detailed chemical kinetics using 37 species and 235 reactions. Agreement between the two models is very good. In addition, ignition delay of C2H5OH/O2/Ar mixtures using RCCE has been compared with the experimental measurements in the shock tube and excellent agreement has been reached validating the RCCE calculation.

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.

Use of Detailed Chemical Kinetics to Study HCCI Engine Combustion With Consideration of Turbulent Mixing Effects

2002 ◽  
Vol 124 (3) ◽  
pp. 702-707 ◽  
Author(s):  
S.-C. Kong ◽  
R. D. Reitz
Keyword(s):  
Chemical Kinetics ◽  
Turbulent Mixing ◽  
Combustion Process ◽  
Reaction Rates ◽  
Detailed Chemical Kinetics ◽  
Wide Range ◽  
Hcci Engines ◽  
Heavy Duty Diesel ◽  
Flame Chemistry ◽  
Detailed Chemical

Detailed chemical kinetics was used in an engine CFD code to study the combustion process in HCCI engines. The CHEMKIN code was implemented in KIVA such that the chemistry and flow solutions were coupled. The reaction mechanism consists of hundreds of reactions and species and is derived from fundamental flame chemistry. Effects of turbulent mixing on the reaction rates were also considered. The results show that the present KIVA/CHEMKIN model is able to simulate the ignition and combustion process in three different HCCI engines including a CFR engine and two modified heavy-duty diesel engines. Ignition timings were predicted correctly over a wide range of engine conditions without the need to adjust any kinetic constants. However, it was found that the use of chemical kinetics alone was not sufficient to accurately simulate the overall combustion rate. The effects of turbulent mixing on the reaction rates need to be considered to correctly simulate the combustion and heat release rates.

S.I. Engine Operation on H2, CO, CH4 and Their Mixtures

2004 ◽  
Author(s):  
Hailin Li ◽  
Ghazi A. Karim ◽  
A. Sohrabi
Keyword(s):  
Operating Conditions ◽  
The Other ◽  
Oxidation Reactions ◽  
Detailed Chemical Kinetics ◽  
Engine Operation ◽  
Wide Range ◽  
Variable Compression Ratio Engine ◽  
Fuel Mixtures ◽  
Detailed Chemical ◽  
Good Agreement

Experimental data are presented of the knock and combustion characteristics of a wide range of fuel mixtures of CO, H2 and CH4 while using a variable compression ratio engine. A predictive model was employed for predicting such characteristics where the oxidation reactions of mixtures of H2, CO, and CH4 were simulated using detailed chemical kinetics. Predicted results were validated against those determined experimentally and showed good agreement for a wide range of fuel compositions and operating conditions. However, it was noted that the predicted knock limited equivalence ratios for dry CO-air operation, in comparison to the other fuel applications, tended to display deviation from the experimentally established values. The reasons for this tendency are discussed and measures to permit the prediction of such a behavior are presented.

Numerical CFD evaluation of a flameless burner using detailed chemical kinetics

2017 ◽  
Author(s):  
Marco Antonio Nascimento ◽  
Lucilene Oliveria Rodrigues ◽  
Fagner Luis Goulart Dias
Keyword(s):  
Chemical Kinetics ◽  
Detailed Chemical Kinetics ◽  
Flameless Burner ◽  
Detailed Chemical

PARALLEL SOLVER FOR THE SIMULATIONS OF DETONATION WAVES ON UNSTRUCTURED GRIDS

2020 ◽  
Author(s):  
A. I. Lopato ◽  
◽  
A. G. Eremenko ◽  
Keyword(s):  
Chemical Kinetics ◽  
Numerical Scheme ◽  
Unstructured Grids ◽  
Numerical Study ◽  
Numerical Approach ◽  
Detonation Waves ◽  
Detailed Chemical Kinetics ◽  
Parallel Solver ◽  
Further Development ◽  
Detailed Chemical

Recently, we developed a numerical approach for the simulation of detonation waves on fully unstructured grids and applied it to the numerical study of the mechanisms of detonation initiation in multifocusing systems. Current work is devoted to further development of our numerical approach, namely, parallelization of the numerical scheme and introduction of more comprehensive detailed chemical kinetics scheme.

scholarly journals New general mixed-integer linear programming model for mobile workforce management

2021 ◽  
Author(s):  
András Éles ◽  
István Heckl ◽  
Heriberto Cabezas
Keyword(s):  
Programming Model ◽  
Time Windows ◽  
Mutual Exclusion ◽  
Parallel Execution ◽  
Mixed Integer ◽  
Management Problem ◽  
Routing Problem ◽  
Workforce Management ◽  
Computational Performance ◽  
Wide Range

AbstractA mathematical model is introduced to solve a mobile workforce management problem. In such a problem there are a number of tasks to be executed at different locations by various teams. For example, when an electricity utility company has to deal with planned system upgrades and damages caused by storms. The aim is to determine the schedule of the teams in such a way that the overall cost is minimal. The mobile workforce management problem involves scheduling. The following questions should be answered: when to perform a task, how to route vehicles—the vehicle routing problem—and the order the sites should be visited and by which teams. These problems are already complex in themselves. This paper proposes an integrated mathematical programming model formulation, which, by the assignment of its binary variables, can be easily included in heuristic algorithmic frameworks. In the problem specification, a wide range of parameters can be set. This includes absolute and expected time windows for tasks, packing and unpacking in case of team movement, resource utilization, relations between tasks such as precedence, mutual exclusion or parallel execution, and team-dependent travelling and execution times and costs. To make the model able to solve larger problems, an algorithmic framework is also implemented which can be used to find heuristic solutions in acceptable time. This latter solution method can be used as an alternative. Computational performance is examined through a series of test cases in which the most important factors are scaled.

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