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Dynamics of thermal ignition of spray flames in mixing layers

  • D. Martínez-Ruiz (a1), J. Urzay (a2), A. L. Sánchez (a1) (a3), A. Liñán (a4) and F. A. Williams (a3)...
Abstract
Abstract

Conditions are identified under which analyses of laminar mixing layers can shed light on aspects of turbulent spray combustion. With this in mind, laminar spray-combustion models are formulated for both non-premixed and partially premixed systems. The laminar mixing layer separating a hot-air stream from a monodisperse spray carried by either an inert gas or air is investigated numerically and analytically in an effort to increase understanding of the ignition process leading to stabilization of high-speed spray combustion. The problem is formulated in an Eulerian framework, with the conservation equations written in the boundary-layer approximation and with a one-step Arrhenius model adopted for the chemistry description. The numerical integrations unveil two different types of ignition behaviour depending on the fuel availability in the reaction kernel, which in turn depends on the rates of droplet vaporization and fuel-vapour diffusion. When sufficient fuel is available near the hot boundary, as occurs when the thermochemical properties of heptane are employed for the fuel in the integrations, combustion is established through a precipitous temperature increase at a well-defined thermal-runaway location, a phenomenon that is amenable to a theoretical analysis based on activation-energy asymptotics, presented here, following earlier ideas developed in describing unsteady gaseous ignition in mixing layers. By way of contrast, when the amount of fuel vapour reaching the hot boundary is small, as is observed in the computations employing the thermochemical properties of methanol, the incipient chemical reaction gives rise to a slowly developing lean deflagration that consumes the available fuel as it propagates across the mixing layer towards the spray. The flame structure that develops downstream from the ignition point depends on the fuel considered and also on the spray carrier gas, with fuel sprays carried by air displaying either a lean deflagration bounding a region of distributed reaction or a distinct double-flame structure with a rich premixed flame on the spray side and a diffusion flame on the air side. Results are calculated for the distributions of mixture fraction and scalar dissipation rate across the mixing layer that reveal complexities that serve to identify differences between spray-flamelet and gaseous-flamelet problems.

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Email address for correspondence: jurzay@stanford.edu
References
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Aggarwal S. K. 1998 Review of spray ignition phenomena: present status and future research. Prog. Energy Combust. Sci. 24, 565600.
Annamalai K. & Ryan W. 1992 Interactive processes in gasification and combustion. 1. Liquid-drop arrays and clouds. Prog. Energy Combust. Sci. 18, 221295.
Arrieta-Sanagustín J., Sánchez A. L., Liñán A. & Williams F. A. 2011 Sheath vaporization of a monodisperse fuel-spray jet. J. Fluid Mech. 675, 435464.
Arrieta-Sanagustín J., Sánchez A. L., Liñán A. & Williams F. A. 2013 Coupling-function formulation for monodisperse spray diffusion flames with infinitely fast chemistry. Fuel Process. Technol. 107, 8192.
Baba Y. & Kurose R. 2008 Analysis and flamelet modelling for spray combustion. J. Fluid Mech. 612, 4579.
Bermúdez A., Ferrín J. L. & Liñán A. 2007 The modelling of the generation of volatiles, inline-graphic $({\mathrm{H} }_{2} $ and CO, and their simultaneous diffusion controlled oxidation, in pulverized coal furnaces. Combust. Theor. Model. 11, 949976.
Bilger R. W. 2011 A mixture fraction framework for the theory and modelling of droplets and sprays. Combust. Flame 158, 191202.
Chapman D. R. 1949 Laminar mixing of a compressible fluid. NACA-TN-1800.
Chiu H. H. & Liu T. M. 1977 Group combustion of liquid droplets. Combust. Sci. Technol. 17, 127142.
Ciezki H. K. & Adomeit G. 1993 Shock-tube investigation of self-ignition of n-heptane-air mixtures under engine relevant conditions. Combust. Flame 93, 421433.
Correa S. M. & Sichel M. 1982 The group combustion of a spherical cloud of monodisperse fuel droplets. Proc. Combust. Inst. 19, 981991.
Crowe C., Sommerfeld M. & Tsuji Y. 1998 Multiphase Flows with Droplets and Particles. CRC Press.
Danis A. M., Namer I. & Cernansky N. P. 1988 Droplet size and equivalence ratio effects on spark ignition of monodisperse n-heptane and methanol spray. Combust. Flame 74, 285294.
Faeth G. M. 1983 Evaporation and combustion of sprays. Prog. Energy Combust. Sci. 9, 176.
Fernández-Tarrazo E., Sánchez A. L. & Williams F. A. 2013 Hydrogen–air mixing-layer ignition at temperatures below crossover. Combust. Flame 160, 19811989.
Franzelli B., Fiorina B. & Darabiha N. 2013 A tabulated chemistry method for spray combustion. Proc. Combust. Inst. 34, 16591666.
Godsave G. A. E. 1953 Evaporation and combustion of sprays: the burning of single drops of fuel. Proc. Combust. Inst. 4, 818830.
Gutheil E. 1995 Numerical analysis of the autoignition of methanol, ethanol, n-heptane and n-octane sprays with detailed chemistry. Combust. Sci. Technol. 34, 16591666.
Harrje D. T. 1972 Liquid Propellant Rockets. NASA monograph.
Jenny P. B., Roekaerts D. & Beishuizen N. 2013 Modelling of turbulent dilute spray combustion. Prog. Energy Combust. Sci. 38, 846887.
Knudsen E. & Pitsch H. 2010 Large eddy simulation of a spray combustor using a multi-regime flamelet approach. In Annual Research Briefs, pp. 337350. Center for Turbulence Research, NASA Ames/Stanford University.
Labowsky M. & Rosner D. E. 1978 Group combustion of droplets in fuel clouds, I. Quasi-steady predictions. In Evaporation–Combustion of Fuels (ed. Zung J. T.), pp. 6379. American Chemical Society.
Lefebvre A. 1998 Gas Turbine Combustion. Taylor and Francis.
Lessen M. 1950 On the stability of the laminar free boundary between parallel streams. NACA-R-979.
Li S. C. 1997 Spray stagnation flames. Prog. Energy Combust. Sci. 23, 303347.
Liñán A. 1985 Theory of droplet vaporization and combustion. In Modélisation des Phénomènes de Combustion (ed. Borghi R., Clavin P., Liñán A., Pelcé P. & Sivashinsky G. I.), CEA-EDF INRIA 59, pp. 73103. Editions Eyrolles.
Liñán A. & Crespo A. 1976 An asymptotic analysis of unsteady diffusion flames for large activation energies. Combust. Sci. Technol. 14, 95117.
Liñán A. & Williams F. A. 1993a Ignition in an unsteady mixing layer subject to strain and variable pressure. Combust. Flame 95, 3146.
Liñán A. & Williams F. A. 1993b Fundamental Aspects of Combustion. Oxford University Press.
Longmire E. & Eaton J. K. 1992 Structure of a particle-laden round jet. J. Fluid. Mech. 236, 217257.
Luo K., Pitsch H., Pai M. G. & Desjardins O. 2011 Direct numerical simulations and analysis of the three-dimensional n-heptane spray flames in a model swirl combustor. Proc. Combust. Inst. 33, 21432152.
Mastorakos E. 2009 Ignition of turbulent non-premixed flames. Prog. Energy Combust. Sci. 35, 5797.
Moin P. & Apte S. V. 2006 Large-eddy simulation of realistic gas turbine combustors. AIAA J. 44, 698708.
Neophytou A., Mastorakos E. & Cant R. S. 2012 The internal structure of igniting turbulent sprays as revealed by complex chemistry DNS. Combust. Flame 159, 641664.
Peters N. 2000 Turbulent Combustion. Cambridge University Press.
Pitsch H. & Peters N. 1998 A consistent flamelet formulation for non-premixed combustion considering differential diffusion effects. Combust. Flame 114, 2640.
Reveillon J. & Versvich L. 2000 Spray vaporization in non-premixed turbulent combustion modelling: a single droplet model. Combust. Flame 121, 7590.
Reveillon J. & Vervisch L. 2005 Analysis of weakly turbulent dilute-spray flames and spray combustion regimes. J. Fluid Mech. 537, 317347.
Sánchez A. L. 1997 Nonpremixed spontaneous ignition in the laminar wake of a thin splitter plate. Phys. Fluids 9, 20322044.
Santasu D., Lakshmisha K. N. & Bilger R. W. 2011 Modelling of nonreacting and reacting turbulent spray jets using a fully stochastic separated flow approach. Combust. Flame 158, 19922008.
Shashank 2011 High-fidelity simulations of reactive liquid-fuel jets, PhD thesis, Stanford University.
Sirignano W. A. 1983 Fuel droplet vaporization and spray combustion theory. Prog. Energy Combust. Sci. 9, 291322.
Sirignano W. A. 2010 Fluid Dynamics and Transport of Droplets and Sprays. Cambridge University Press.
Urzay J., Pitsch H. & Liñán A. 2011 Source terms for calculations of vaporizing and burning fuel sprays with non-unity Lewis numbers in gases with temperature-dependent thermal conductivities. In Annual Research Briefs, pp. 199211. Center for Turbulence Research, NASA Ames/Stanford University.
Wang Y. & Rutland C. J. 2007 Direct numerical simulation of ignition in turbulent n-heptane liquid-fuel spray jets. Combust. Flame 149, 353365.
Williams F. A. 1985 Combustion Theory, 2nd edn. pp. 446484. Benjamin Cummings.
Ying H. & Yang V. 2009 Dynamics and stability of lean-premixed swirl-stabilized combustion. Prog. Energy Combust. Sci. 35, 293–264.
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Journal of Fluid Mechanics
  • ISSN: 0022-1120
  • EISSN: 1469-7645
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