Laminar Flame Properties Research Articles

An experimental investigation of strain-induced extinction of diluted hydrogen-air counterflow diffusion flames

Previous studies about turbulent combustion in hydrogen-air systems for application in supersonic-combustion devices such as the National Aerospace Plane have suggested that combustion in such devices takes place in thin reaction sheets that are convoluted, distorted, and in some cases locally extinguished by turbulence. Sharing this view, a number of researchers have focused their attention on characterizing the structure and extinction properties of laminar hydrogen-air diffusion flames. Most of the research has been of a numerical or theoretical nature and only a few experiments have been performed to test the detailed numerical diffusion-flame models. The objective of the present communication is to report results of some experiments designed to characterize the extinction properties of diluted laminar counterflow diffusion flames between air and hydrogen-nitrogen mixtures.

Effects of turbulence on flame radiation from diffusion flames

Enhancement of heat transfer by flame radiation in furnaces can increase the efficiency and decrease the volume of a furnace. Flame radiation from turbulent diffusion flames, which prevail in furnaces, depends both on the chemistry of soot formation and the turbulent mixing processes of the flow. Previous work has shown that thermochemical effects (i.e. fuel or air preheating, oxygen enhancement, etc.) related to soot formation chemistry and flame radiation can be correlated in turbulent diffusion flames by using smoke-point properties of laminar diffusion flames. This work addresses the other part of the turbulent flame problem which involves the effects of the turbulent flow field on soot formation and radiation for given fuel and thermochemicla conditions. Radiation measurements in turbulent momentum, controleld jet flames were made by using five nozzles (1 mm, 1.5 mm, 2 mm, 3 mm, 4 mm) having a large contraction ratio and burning three fuels: acetylene (C 2 H 2 ), propylene (C 3 H 6 ) and methane (CH 4 ). By employing the relatively well understood flow of a turbulent jet flames, the following fundamental issue was addressed: it soot formation in turbulent diffusion flames determined by the overall residence (macroscale) time or by the straining rate of the small (Kolmogorov) scales wherein combustion occurs? Correlations of the present data obtained by using a simple soot formation and radiation model support the small scale (Kolmogorov) straining rate hypothesis.

A Comprehensive Chemical Kinetic Reaction Mechanism for Oxidation and Pyrolysis of Propane and Propene

Abstract Abstract—A detailed chemical kinetic reaction mechanism is developed to describe the oxidation and pyrolysis of propane and propene. The mechanism consists of 163 elementary reactions among 4l chemical species. New rate expressions are developed for a number of reactions of propane, propene, and intermediate hydrocarbon species with radicals including H, 0, and OH. The mechanism is tested by comparisons between computed and experimental results in shock tubes and the turbulent flow reactor. The resulting comprehensive mechanism accurately reproduces experimental data for pressures from 1 to 15 atmospheres, temperatures from 1000 to 1700 K, and fuel-oxidizer equivalence ratios from 0.066 to pyrolysis conditions. The mechanism also predicts correctly laminar flame properties for propane and propene, and detonation properties for propane.

Numerical Modeling of Flame Inhibition by CF3Br

Abstract A numerical model is used to investigate the properties of laminar flames inhibite d by CF3Br. Fuels include hydrogen, methane, methanol, and ethylene, with both oxygen and air as the oxidizers. A detailed chemical kinetic reaction mechanism for the fuel oxidation is combined with a mechanism describing reactions of CF3Br and its halogenated products. The effects of CF3Br on the flammability limits and burning velocity of laminar flames are predicted by the model, and the effects of variations in pressure, unburned gas temperature, and equivalence ratio on inhibition efficiency are examined.

A comprehensive mechanism for the pyrolysis and oxidation of ethylene

A detailed chemical kinetic reaction mechanism is developed for the intermediate and high temperature pyrolysis and oxidation of ethylene. The mechanism, consisting of 93 elementary reactions among 26 chemical species, is validated by comparison between computed results and measured data from shock tube and turbulent flow reactor experiments. New rates expressions are determined for a number of reactions between C/sub 2/H/sub 4/ molecules and H, O, and OH radicals. The comprehensive mechanism accurately reproduces available experimental data for pressures ranging from 1 to 12 atmospheres and for fuel-air equivalence ratios from 0.125 to pyrolysis conditions. The resulting mechanism then predicts correctly laminar flame and detonation properties for ethylene-air mixtures.

Simplified Reaction Mechanisms for the Oxidation of Hydrocarbon Fuels in Flames

Abstract Simplified reaction mechanisms for the oxidation of hydrocarbon fuels have been examined using a numerical laminar flame model. The types of mechanisms studied include one and two global reaction steps as well as quasi-global mechanisms. Reaction rate parameters were varied in order to provide the best agreement between computed and experimentally observed flame speeds in selected mixtures of fuel and air. The influences of the various reaction rate parameters on the laminar flame properties have been identified, and a simple procedure to determine the best values for the reaction rate parameters is demonstrated. Fuels studied include n-paraffins from methane to n-decane, some methyl-substituted n-paraffins, acetylene, and representative olefin, alcohol and aromatic hydrocarbons. Results show that the often-employed choice of simultaneous first order fuel and oxidizer dependence for global rate expressions cannot yield the correct dependence of flame speed on equivalence ratio or pressure and can...

Prediction of laminar flame properties of methanol-air mixtures

A numerical model has been used to study the propagation of laminar methanol-air flames. The model consists of a one-dimensional time-dependent treatment of the conservation equations together with a detailed chemical kinetic oxidation mechanism having 84 elementary chemical reactions involving 26 chemical species. Solutions are used to study the dependence of laminar flame speed and flame structure on pressure, equivalence ratio, and unburned-gas temperature, and computed flame properties are compared with available experimental data. At low pressures, flame properties vary only slightly with changes in pressure, but at high pressures, this variation is considerably larger. This change in behavior from low to high pressures is a result of the increasing importance of radical recombination reactions. Most of this pressure-dependent inhibition is caused by the competition of a single reaction H + O 2 + M = HO 2 + M, with the key chain branching reaction H + O 2 = O + OH.

A theoretical study of some properties of laminar steady state flames as a function of properties of their chemical components

Laminar mixing flames as a function of the chemical properties of the gas mixture - mathematical analysis

Dependence of laminar flame properties on the mechanism of chain reaction

The theory of stationary laminar flames must provide not only for calculation of flame-propagation velocities, but also for studies of flame properties under different conditions, and make possible the description of these properties by means of very simple analytical functions which would be of help in solving scientific or practical problems that require knowledge of laminarflame properties. A no less important object of the theory is to ensure the possibility of studying kinetic laws which govern chemical reactions at high temperatures when direct measurement of reaction rates is practically impossible. The process of flame propagation in systems involving straight TM and branched 5' 6 chain reactions was investigated earlier. The dependence of certain laminar-flame properties on the type of chain reaction effecting the chemical process in the flame can be determined from the results obtained. Thus the type of reaction which proceeds in the given combustible mixture can be established from flame properties which are determined experimentally. Once the reaction type is known, experimental values of elementary reaction-rate constants at high temperatures can be obtained from the dependence of the burning velocity on temperature, pressure and transfer coefficients. A comparison of basic properties and functions of burning velocity in chain-branching and nonbranching systems will be made in this work. P1 + Z--~ C + P2, (1) QI nl = hi F1 nl = hi K l (T ' )nz nl