Chemical-Kinetic Studies

Reduced Chemical-Kinetic Mechanisms

Numerical simulations of combustion in realistic flows with high Reynolds numbers and complex geometries are severely limited by computational capabilities, so that computations incorporating detailed-chemistry schemes can only be performed for simple flow problems. Theoretically based simplifications are needed to provide a more manageable chemistry description that still has sufficient accuracy to yield reliable computational results. To that end, we make use of analytic methods for chemistry reduction employing rigorous approximations based on time disparities, such as the quasi-steady-state approximation for intermediates and the partial-equilibrium approximation for reversible elementary reactions. The procedure leads to reduced descriptions with a small number of overall reactions that are useful in analytical studies and can also be implemented readily in existing numerical codes, thereby facilitating the computation of practical combustion devices. Different fuels have been treated over the years, in particular methane and hydrogen and, more recently, syngas, obtained from gasification of coal and biomass. Besides reduced mechanisms for specific combustion conditions, the work includes development of multipurpose reduced mechanisms able to describe all different combustion phenomena with acceptable accuracy.

Figure1.1

Minimum skeletal mechanism for syngas combustion

Related publications

  1. Four-step and three-step systematically reduced chemistry for wide-range H2-air combustion problems
    P. Boivin, A. L. Sánchez, F. A. Williams, Combust. Flame, 160 76–82 (2013). [DOI]
  2. An explicit reduced mechanism for H2-air combustion
    P. Boivin, C. Jiménez, A. L. Sánchez, F. A. Williams, Proc. Combust. Institute, 33 517–523 (2011). [DOI]
  3. A four-step reduced mechanism for syngas combustion
    P. Boivin, C. Jiménez, A. L. Sánchez, F. A. Williams, Combust. Flame, 158 1059–1063 (2011). [DOI]
  4. One-step reduced kinetics for lean hydrogen-air deflagration
    D. Fernández-Galisteo, A. L. Sánchez, A. Liñán, F. A. Williams, Combust. Flame, 156 985–996 (2009). [DOI]
  5. A simple one-step chemistry model for partially premixed hydrocarbon combustion
    E. Fernández-Tarrazo, A. L. Sánchez, A. Liñán, F. A. Williams, Combust. Flame, 147 32–38 (2006). [DOI]
  6. The Reduced Kinetic Description of Lean Premixed Combustion
    A. L. Sánchez, A. Lépinette, M. Bollig, A. Liñán and B. Lázaro, Combust. Flame, 123, 436–464 (2000). [DOI]

Studies of Hydrogen Combustion

Hydrogen is a clean energy carrier that can be produced from any primary energy source, including renewable sources. It is bound to become key in the solution of the energy supply problem for the 21st century, enabling clean efficient production of power and heat. Although fuel cells are envisioned as a central component in many applications, providing an efficient conversion tool to produce electricity from the chemical reaction of hydrogen, direct combustion in Internal Combustion Engines and Gas Turbines is also currently considered of technological interest. Besides these technological applications associated with power generation, combustion is viewed as a fundamental issue in the development of the hydrogen economy, with safety concerns associated with accidental explosion events entering when considering options for hydrogen storage. A better understanding of the hydrogen combustion processes is therefore necessary both to improve designs of hydrogen combustion devices and to develop safety regulations and counter-measures for explosion protection. Over the years, we have investigated a wide range of hydrogen reactive phenomena that include spontaneous and forced ignition, deflagrations, flame balls, and diffusion flames. Low-temperature ignition of hydrogen has been considered in recent work because of its relevance for gas-turbine applications and explosion hazards in storage plants. The work has led to clarification of the so-called third-explosion limit, thereby providing the answer to a long-standing problem.

Figure1.2

The reduced chemistry of low temperature hydrogen-oxygen ignition. The left-hand-side plot represents the variation of the ignition time with equivalence ratio as obtained numerically with detailed chemistry (dashed curves) and with our two-step reduced chemistry (solid curves). The right-hand-side plot shows as a dashed curve the experimentally determined explosion limits of hydrogen-oxygen combustion, with the solid line denoting the analytic prediction developed for the third explosion limit on the basis of our reduced chemistry.

Related publications

  1. The chemistry involved in the third explosion limit of H2-O2 mixtures
    A. L. Sánchez, E. Fernández-Tarrazo, F. A. Williams, Combust. Flame, 161 111–117 (2014). [DOI]
  2. Recent advances in understanding of flammability characteristics of hydrogen
    A. L. Sánchez, F. A. Williams, Prog. Energy Combust. Sci., 41 1–55 (2014). [DOI]
  3. Hydrogen-air mixing-layer ignition at temperatures below crossover
    E. Fernández-Tarrazo, A. L. Sánchez, F. A. Williams, Combust. Flame, 160 1981–1989 (2013). [DOI]
  4. Explicit analytic prediction for hydrogen-oxygen ignition times at temperatures below crossover
    P. Boivin, A. L. Sánchez, F. A. Williams, Combust. Flame, 159 748-752 (2012). [DOI]
  5. Flammability conditions for ultra-lean hydrogen premixed combustion based on flame-ball analyses
    E. Fernández-Tarrazo, A. L. Sánchez, A. Liñán, F. A. Williams, Int. J. Hydrogen Energy, 37 1813-1825 (2012). [DOI]
  6. Ignition time of hydrogen-air diffusion flame.
    A. L. Sánchez, E. Fernández-Tarrazo, P. Boivin, A. Liñán, F. A. Williams, C. R. Mecanique, 340 882–893 (2012). [DOI]
  7. The structure of lean hydrogen-air flame balls
    E. Fernández-Tarrazo, A. L. Sánchez, A. Liñán, F. A. Williams, Proc. Combust. Institute, 33 1203–1210 (2011). [DOI]