摘要:

A theoretical model is presented that can be used to predict the structure and rate of spread of an attached diffusion flame moving over a thermally thin, pyrolyzing combustible placed in a gravity-free, quiescent, oxidizing environment. The gas-phase model includes steady-state, two-dimensional momentum, energy, and species equations while the solid-phase model consists of continuity and energy equations, the solution to which provide boundary conditions for the gas-phase problem. The spread rate appears as an eigenvalue in both the gas- and solid-phase equations. The numerical procedure developed to solve the system of equations is stable even for spread rates comparable to normal velocities present at the fuel-gas interface. Solid fuel pyrolysis is modelled using a first-order Arrhenius decomposition while both finite-rate and infinite rate chemistry in the gas phase are considered.

ISSN:0010-2202    

DOI:10.1080/00102209008951599

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The behavior of stationary and rotating polyhedral Bunsen flames of butane/air under systematic thermal and chemical modification of the reactive mixture is experimentally investigated. As the concentrations of additives CF3Br, N2and O2are gradually increased in the combustible mixture, the variation of the temperature in the trough and crest regions of the polyhedral flames is examined. It is found that addition of 0.36 (5.0) molar percentage of CF2Br (N2) completely removes the cellular structure of the polyhedral flame. Also, in butane/air mixtures at different velocity, the critical temperatures corresponding to the onset of cell formation are found to be nearly identical. The results suggest that in conjunction to the hydrodynamics and thermodiffusive flame instability mechanisms, chemical-kinetic effects also play some role in the formation, amplification or sustenance of cellular flame structures. The observations are consistent with the recent flame stability theories which are based on multi-step chemical reaction mechanisms. Also, the rotation velocity of polyhedral flames is measured using two thermocouples which are connected in series. In oxygen-enriched air, it is found that secondary cellular structures may form, on top of the stationary 6-sidcd polyhedral flames, whose cells grow radially with oxygen concentration.

ISSN:0010-2202    

DOI:10.1080/00102209008951600

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

A phenomenological model simulating stratification of temperature and species concentration was developed to predict engine misfire. The model incorporates the coalescence dispersion model for finite rate mixing and the mass entrainment model for flame propagation. The fuel mixture in the combustion chamber is divided into equal mass particles, each having a thermodynamic state. A first order chemical rate reaction for the combustion of propane in air is used. A set of ordinary differential equations for the evolution of temperature and species concentration for each particle is formulated. A predictor corrector method was developed to solve the system of equations.

ISSN:0010-2202    

DOI:10.1080/00102209008951601

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The modelling of the mean reaction rate in a premixed turbulent flame is approached by means of a library of laminar flame solutions. A formulation of such a library is presented and the detailed data requirements are investigated. Laminar flame calculations are performed in an asymmetrical counterflow configuration with a cold, reactive methane-air mixture flowing against the corresponding hot equilibrium combustion products. The flamelet properties required for the library are shown to be independent of the definition of a reaction progress variable c. Stoichiometric flames at pressures of 1 bar, 1.5 bar and 2 bar are considered, with corresponding initial temperatures of 328, 386 and 433 K. The results are examined in the light of the demands of the library, and suitable definitions of key quantities are proposed. A specimen laminar flamelet library is then assembled.

ISSN:0010-2202    

DOI:10.1080/00102209008951602

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor