Rate-controlled constrained equilibrium calculation of ignition delay times in hydrogen-oxygen mixtures

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

Energy Conversion and Resources: Fuels and Combustion Technology, Energy, Nuclear Engineering, and Solar Engineering ◽

10.1115/imece2003-55289 ◽

2003 ◽

Cited By ~ 1

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.

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Constrained-Equilibrium Modeling of Methane Oxidation in Air

Journal of Energy Resources Technology ◽

10.1115/1.4027692 ◽

2014 ◽

Vol 136 (3) ◽

Cited By ~ 12

Author(s):

Ghassan Nicolas ◽

Mohammad Janbozorgi ◽

Hameed Metghalchi

Keyword(s):

Kinetic Model ◽

Ignition Delay ◽

Combustion Process ◽

Rate Equations ◽

Time Step ◽

Ignition Delay Times ◽

Wide Range ◽

Delay Times ◽

Constrained Equilibrium ◽

Detailed Kinetic Model

Rate-controlled constrained-equilibrium method has been further developed to model methane/air combustion. A set of constraints has been identified to predict the nonequilibrium evolution of the combustion process. The set predicts the ignition delay times of the corresponding detailed kinetic model to within 10% of accuracy over a wide range of initial temperatures (900 K–1200 K), initial pressures (1 atm–50 atm) and equivalence ratios (0.6–1.2). It also predicts the experimental shock tube ignition delay times favorably well. 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. The underlying detailed kinetic model involves 352 reactions among 60 H/O/N/C1-2 species, hence 60 rate equations, while the RCCE calculations involve 16 total constraints, thus 16 total rate equations. Nonetheless, the constrained-equilibrium concentrations of all 60 species are calculated at any time step subject to the 16 constraints.

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Use of Virtual Kinetics Chemistry for Ignition Delay Times Predictions

10.26678/abcm.encit2020.cit20-0633 ◽

2020 ◽

Author(s):

Augusto Pacheco ◽

Amir Antonio Martins Oliveira

Keyword(s):

Ignition Delay ◽

Ignition Delay Times ◽

Delay Times

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Ignition Characteristics of a Fischer-Tropsch Synthetic Jet Fuel

Volume 3: Combustion, Fuels and Emissions, Parts A and B ◽

10.1115/gt2008-51211 ◽

2008 ◽

Cited By ~ 4

Author(s):

P. Gokulakrishnan ◽

M. S. Klassen ◽

R. J. Roby

Keyword(s):

Kinetic Model ◽

Ignition Delay ◽

Flow Reactor ◽

Kinetic Mechanism ◽

Jet Fuel ◽

Synthetic Jet ◽

Jet Fuels ◽

Ignition Delay Times ◽

Delay Times ◽

Ignition Characteristics

Ignition delay times of a “real” synthetic jet fuel (S8) were measured using an atmospheric pressure flow reactor facility. Experiments were performed between 900 K and 1200 K at equivalence ratios from 0.5 to 1.5. Ignition delay time measurements were also performed with JP8 fuel for comparison. Liquid fuel was prevaporized to gaseous form in a preheated nitrogen environment before mixing with air in the premixing section, located at the entrance to the test section of the flow reactor. The experimental data show shorter ignition delay times for S8 fuel than for JP8 due to the absence of aromatic components in S8 fuel. However, the ignition delay time measurements indicate higher overall activation energy for S8 fuel than for JP8. A detailed surrogate kinetic model for S8 was developed by validating against the ignition delay times obtained in the present work. The chemical composition of S8 used in the experiments consisted of 99.7 vol% paraffins of which approximately 80 vol% was iso-paraffins and 20% n-paraffins. The detailed kinetic mechanism developed in the current work included n-decane and iso-octane as the surrogate components to model ignition characteristics of synthetic jet fuels. The detailed surrogate kinetic model has approximately 700 species and 2000 reactions. This kinetic mechanism represents a five-component surrogate mixture to model generic kerosene-type jets fuels, namely, n-decane (for n-paraffins), iso-octane (for iso-paraffins), n-propylcyclohexane (for naphthenes), n-propylbenzene (for aromatics) and decene (for olefins). The sensitivity of iso-paraffins on jet fuel ignition delay times was investigated using the detailed kinetic model. The amount of iso-paraffins present in the jet fuel has little effect on the ignition delay times in the high temperature oxidation regime. However, the presence of iso-paraffins in synthetic jet fuels can increase the ignition delay times by two orders of magnitude in the negative temperature (NTC) region between 700 K and 900 K, typical gas turbine conditions. This feature can have a favorable impact on preventing flashback caused by the premature autoignition of liquid fuels in lean premixed prevaporized (LPP) combustion systems.

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