Two-step Combustion Research Articles

NUMERICAL ANALYSIS OF TWO-RING FLAME STABILIZER FLOWS IN AIRCRAFT AFTERBURNERS

A computational procedure is described for the calculation of isothermal flow fields of two-ring flame stabilizers in practical afterburners and also for the reacting flow parameters in a research afterburner. The predictions have been obtained using a finite volume solution procedure for the steady three-dimensional elliptic equations of fluid flow. The physical models include the κ-e turbulence model, eddy breakup model, two-step reaction model, droplet vaporization and combustion model, and six-flux radiation model. The presence of radial gutters and staggering the distance between two-ring gutters alter the afterburner flow patterns considerably, including the elimination of diffuser stall and flow separation losses near the diffuser. The predicted and measured emissions in the research afterburner geometry agree qualitatively. The effect of the fuel to air ratio and location of the fuel injector on the temperature and species concentration distribution are presented in detail.

AN ANALYTICAL DESIGN METHODOLOGY FOR AN ANNULAR COMBUSTOR

SUMMARY This paper describes a computational procedure for the optimization of the performance parameters of a simulated annular combustor. This method has been applied to analyze the influence of the performance parameters and geometries on the annular combustor characteristics and provide a good understanding of combustor internal flow fields, and therefore it can be used for guiding the combustor design process. The approach is based on the solution of governing nonlinear, elliptic partial differential equations for 3-D axisymmetric recirculating turbulent reacting swirling flows and the modelling of turbulence, combustion, thermal radiation and pollutant formation. The turbulence effects are introduced via the modified two-equation κ-e model. Turbulent combustion is modelled using the κ-e-g model and a two-step turbulent combustion model is employed for the excess emission of carbon monoxide CO. For the evaluation of the NO pollutant formation rate, the NO pollutant formation model, which takes into a...

Nitric oxide conversion in hydrocarbon-fuel flames in two-step combustion

On the basis of the kinetic model of nitrogen oxide conversion in hydrocarbon-fuel combustion, the stages of NO conversion are calculated and the degree of conversion in multistage combustion is determined. The calculation results are compared with industrial test data. The limiting degree of conversion in industrial-furnace conditions is estimated.

Recovery of silica from aqueous silicate solutions via trialkyl or tetraalkylammonium silicomolybdate

Reaction of aqueous silicate with ammonium molybdate at pH 1.5 affords the β form of silicomolybdic acid. The latter can be precipitated by the addition of a variety of quaternary ammonium salts. The precipitated silicomolybdate can then be decomposed to silica in a two-step combustion process (at 350 and 1000 °C). Recoveries of Si are nearly complete, but the starting silicate solution must be made strongly basic prior to the reaction with molybdate. The overall process can be utilized for the recovery of silicon isotopes and as a method of silica purification. Key words: silica, silicate, silicomolybdate, silicon-29.

Thermal Separation of Soot Carbon

We present here a simple and versatile variant of the thermal analysis of soot carbon, and a discussion on the encountered analytical artifacts. The method is based on a two-step combustion procedure; the removal of the organic material that does not absorb visible light is optimized during a precombustion step at 340°C during 2 hours under a pure oxygen flow, and the remaining carbon is then determined by coulometric titration of the CO2 evolved from the combustion of the samples. These analytical conditions minimize the crossover between the different components of the aerosol, but better to a clear-cut division between organics and soot carbon, the quantitative evaluation of their thermal evolution is obtained. Artifacts have been tested thoroughly with various standards and replicates of ambient air samples collected. The method gives reliable soot carbon determination at the microgram level in samples from a wide variety of environments. Combined H / C atomic ratio measurements and investigations of ...

Control of dioxins from municipal solid waste incinerator

The purpose of this study is to establish whether intermediate products, which are remained as unburned components and become the precursors to form the PCDD, can be reduced by improvement of the plant operation. The change of the PCDD levels was analyzed along the stream of the flue gas. Two test programs were conducted to reduce the emission levels of PCDD at municipal solid waste (MSW) incinerators. They were as follows; 1. (1) High temperature incineration to reduce unburned components. 2. (2) Investigation of the relationship between CO contents and PCDD levels at an incinerator which was operated by reductive two-step combustion mode to reduce NOx emission level.

Traveling Wave Solutions Arising from a Two-Step Combustion Model

The combustion process $A \to B \to C$ may give rise to many traveling wave solutions, each traveling with a different velocity. The first reaction, $A \to B$, may produce a flame F1 with speed $\theta _1 $, while the second reaction may produce a second flame F12 with speed $\theta _2 $. If $\theta _1 < \theta _2 $, then the rear flame F12 will approach the forward one, Fl. One may expect that what eventually evolves is a single configuration moving with constant velocity. This corresponds to a third traveling wave solution. In this paper it is shown that if $\theta _1 < \theta _2 $, then such a third wave does indeed exist.

Combustion analysis with gas temperature diagrams measured in a prechamber spark ignition engine

Up to date, a pressure indicator diagram has been usually used to estimate the heat release rate and mass burned fraction and thereby analyse the combustion process in a spark ignition engine. However, this analysis has only provided unitary information on the combustion process in the engine. Recently, gas temperature diagrams measured by an infrared absorptionemission pyrometer were recognized to give information on the combustion process at various stations in the combustion chamber. The temperature measuring technique and its results are already described in a previous paper. In this paper, to make a more reasonable model of torch combustion in a spark ignition engine with an auxiliary chamber, gas temperature diagrams measured under a wide range of air-fuel ratio and torch nozzle diameter are analysed to determine such combustion characteristics show a reasonable agreement with those estimated from the pressure diagrams. Accordingly, the combustion analysis with gas temperature diagrams are found to provide such a lot of useful local information for combustion modeling as optimum diameter of torch nozzle, two-step combustion and reverse flow through torch nozzle.

Reduction in nitrogen oxide concentration in homogeneous combustion of methane and its mixtures with nitrogenous substances in air

Experiments were carried out with a jet apparatus with laminar flame at atmosperic pressure in order to study the two-step combustion of pure methane-air mixtures and similar mixtures with nitrogenous substances - methylamine and pyridine - added. The first series of experiments used methane-air mixtures. During combustion, nitrogen oxide was formed from atmospheric nitrogen. In the second series of experiments the methane contained 1.5-2.5% of a nitrogenous additive. In this case, the quantity of nitrogen oxide formed was many times lower. Analogous experiments were performed with addition of 1.5-2.5% pyridine, and similar results were obtained. Under the conditions described, two-step combustion of methane-air mixtures with methylamine or pyridine added also proves quite effective.

Droplet decomposition in a reactive atmosphere: Complete responses for large activation energies

A two-step combustion process, consisting of monopropellant (i.e. one-reactant) burning followed by bipropellant (i.e. two-reactant) burning, is considered. The original reactant, namely vapor from a liquid droplet, decomposes into a fuel that combines with oxidant in the surrounding atmosphere. Complete responses M( D 1, D 2) of the evaporation rate M of the droplet to the Damköhler numbers D 1, D 2 of the two reactions are determined in the limit of large activation energies. Conditions under which the response is monotonic or multi-valued (thereby exhibiting auto-ignition and auto-extinction) are identified. Previous conjectures, based on Damköhler-number asymptotics, are found to be mostly correct. Once more the efficacy of activation-energy asymptotics in dealing with the strongly nonlinear Arrhenius term of reactive fluid mechanics is demonstrated.