A general technique for predicting properties of highly turbulent, chemically reacting diffusion flames with regions of recirculating flow and with radial pressure gradients is described. The technique is explicitly written for calculations on low altitude, axisymmetric rocket exhaust flames, but may readily be applied to other combustion systems where coupling between chemical reactions and turbulent mixing processes is strong. The application of the method is illustrated: agreement between results obtained and experimental measurements is good, although more stringent further testing is needed.

A list of recommended rate coefficients for chemical reactions occurring in flames is given. Rate coefficients, expressed as functions of temperature for the range 1000 ⩽ T ⩽ 3000 K, are either taken from experiments described in the scientific literature or estimated by comparison with rate coefficients for analogous reactions. Brief notes on the origins of recommended coefficients are included and rough uncertainties are attached to the listed values. A table showing reaction equilibrium constants as functions of temperature is also provided.

In such nonequilibrium combustion systems as rocket exhaust plumes, reactions of the types X + H Y ⇌ X Y + H , (A) and X + Y + M ⇌ X Y + M , (B) where X is a metal atom or free electron, Y is a free radical and M is a collision partner, compete to determine concentration ratios [XY]/[X]. Competition criteria suggested by Sugden are modified, extended, and exemplified by reference to particular reactions of practical interest. The criteria help the chemist to select the minimum number of chemical reactions for computer calculations on the properties of combustion systems. Recommended rate coefficients and uncertainties are offered for several reactions of types (A) and (B).

Application of basic chemical kinetic and gasdynamic considerations to the problem of calculating electrical properties of turbulent afterburning exhaust plumes of solid propellant rocket motors is discussed. The sources of free electrons are described, and the importance of incorporating chemical kinetic (rather than thermochemical equilibrium) data is illustrated by reference to several sample calculations. It is shown that for systems in which potassium is the dominant impurity, above-equilibrium electron concentrations are formed, principally via K + C 1 → K + + C 1 - followed by C 1 - + H → H C 1 + e - The free radical concentrations are produced in above-equilibrium concentrations from the H 2 -CO-Cl-O 2 afterburning reactions. Exhaust plume properties are shown to be sensitive to values selected for rate coefficients of several reactions, and the need for more accurate determinations of these rate coefficients is thus demonstrated. The accuracy of the calculations is further limited by uncertainties in the gasdynamics of the turbulent mixing process. Within the limits of error imposed by these uncertainties, however, the model described does account adequately for experimental observations.

Four different experimental techniques (flame-ion mass spectrometry, microwave cavity resonance, electrostatic probe and absorption spectrophotometry) are employed in a study of fuel-rich, laminar, atmospheric-pressure premixed H2/O2/N2 flames containing potassium and molybdenum. Addition of molybdenum-containing compounds to flames seeded with potassium causes large reductions in concentrations of potassium atoms and extensive electron attachment. The results are interpreted in terms of a homogeneous reaction mechanism involving formation of the stable species KHMoO4, MoO3−, and HMoO4−, and the following enthalpy changes and equilibrium constants are inferred: The electron affinities of HMoO4 and MoO3 implied are approximately 410 and 249 kJ mole−1, respectively.

Electron concentrations produced by calcium, strontium and barium in atmospheric-pressure hydrogen-nitrogen oxygen flames have been measured by the microwave cavity resonance method, and enthalpy changes and equilibrium constants obtained as follows: Download : Download full-size image Discrepancies between Second Law and Third Law values of ΔH00 are interpreted as indicating kinetic limitations in the ionization reactions. The results would be consistent with upper limits to the pre-exponential factors in the rate constants for the above reactions of about 2 × 10−10cm3molecule−1sec−1.

Values of the recombination constants of alkali metal ions with electrons in H2−O2−N2 flames are calculated from measured rate constants for the reverse ionization step. These values are compared with similar, but measured recombination constants for certain other metals in the same H2−O2−N2 flames (to which have been added 1% proportions of acetylene). The good correlation obtained lends strong support to the view that the processes under study are those represented by the two reactions Me++e−+M ahMe*+M, where Me* represents an electronically excited metal atom and M a bulk flame-gas molecule. For chromium, an additional heterogeneous process ivolving involatile oxide particles may also be involved.