Jet-stirred Combustor Research Articles

The Maximum Mixedness Model Applied with Detailed Reaction Mechanisms

Abstract The Zwietering maximum mixedness model (MMM) is extended for use with detailed chemical reaction mechanisms in a combustion setting. Both MMM species and energy balances are offered with a Chemkin-consistent nomenclature. The solution algorithm is discussed. Several reactor residence time distributions are currently offered for use with the MMM program. The MMM is used here to simulate observed literature species concentration data in a turbulent, jet-stirred combustor. For comparison, the results are also compared to simulations from perfectly stirred reactor (PSR) and partially stirred reactor (PaSR) models. The MMM model predicts the observed higher-than-PSR fuel conversions using a residence time distribution based on two unequal CSTRs-in series.

Simulation of a toroidal jet-stirred combustor using a partially stirred reactor model with detailed kinetic mechanisms

The detailed chemistry in a jet-stirred laboratory combustor has been computed with a partially stirred reactor (PaSR) model that uses interaction by exchange with the mean as a turbulent moment closure to simulate finite time micro-mixing. Ideal macro-mixing is assumed as characterized by an exponential residence time distribution. Local conditions are relaxed toward the mean at a rate defined by the mixing frequency that is a ratio of the turbulent dissipation to the turbulent mixing energy. The solution technique approximates mean conditions, and solves the deterministic model to refine the approximation, and eventually converge on a solution. The approximation and convergence technique compared favorably with the Monte Carlo modeling calculations presented in the literature, while using, on average, less than 1/100th of the CPU time. The comparison of PaSR model predictions to literature experimental data from a toroidal jet-stirred laboratory combustor operating in both fuel-lean and fuel-rich conditions also showed reasonable agreement with data. Moreover, the PaSR proved valuable as a research tool. It provided an indication of the sensitivity of reactor kinetics to the effects of micro-mixing delay, and predicted temperature and species distributions, while using detailed thermo-kinetic mechanisms. These features, which are beyond the scope of the perfectly stirred reactor (PSR) model, are provided within reasonable computational times.

Experimental and Numerical Studies of PIC Formation During Chlorocarbon Combustion: Development of a Failure Mode Diagnostic System for Hazardous Waste Incinerators

The major concern regarding organic emissions from hazardous waste incineration systems is the formation of products of incomplete combustion (PICs). Previous studies have shed light on the mechanisms of formation and emission of PICs, showing that the formation of these by-products is highly dependent upon the local ratio of fuel and oxidant, and that their amount and composition are sensitive to both turbulent mixing and chemical kinetic constraints. PIC emissions are closely related to the fluctuations in mixture ratio that result from the turbulent mixing process. Experimental and modeling studies are carried out in order to develop a fault diagnostic system for commercial hazardous waste combustors. The experimental facility has been designed to investigate the effects of both mixing and chemical kinetics on product formation. It consists of a Toroidal Jet-Stirred Combustor (TJSC) followed by a Plug Flow Reactor (PFR). An injector positioned at the PFR entrance allows one to inject a selected species directly into the PFR. A mixture of hydrocarbons and chlorocarbons is used as a hazardous waste surrogate. Benzene is injected into the PFR in order to investigate the combined effects of turbulent mixing and chemical kinetic inhibition on PIC emissions. The development of the fault diagnostics is approached by establishing a relationship between the PIC speciation measured in the exhaust and the kinetic and/or mixing failure mode that has led to the emissions. Finally, a numerical simulation of the turbulent reacting flow is attempted by incorporating a highly simplified reaction mechanism in a commercial CFD code. Results for injection of benzene into the PFR are compared to experimental data.

A Turbulent Reacting Flow Model that Incorporates Detailed Chemical Kinetics

ABSTRACT A turbulent reacting flow model has been developed, based upon a stochastic modeling approach that is applicable over a wide range of Reynolds and Schmidt numbers. All relevant length scales are resolved in one dimension which allows for direct implementation of detailed chemical kinetic calculations and molecular transport. Experiments were performed in a turbulent plug flow reactor for validation and application of the model to investigate the combined effects of turbulent mixing and chlorine chemistry on the formation of products of incomplete combustion. Methyl chloride was injected into the plug flow reactor whose baseline flow was the hot-product stream of a Toroidal Jet-Stirred Combustor. The micromixing and chemical reaction of the injected material with the baseline flow was monitored as a function of distance from the point of injection. Measurements of pulsed laser Rayleigh scattering were used to determine the extent of mixing while species concentrations were measured via extractive ...

Chlorocarbon-lnduced Incomplete Combustion In A Jet-Stirred Reactor

Abstract The chemistry leading to products of incomplete combustion, as affected by chlorocarbons, was studied by modeling data from a jet-stirred reactor, verifield experimentally to be at nearly perfectly-stirred conditions. Premixed, fuel-rich mixtures of C2H4, CH3Cl, and air were burned in a toroidal jet-stirred combustor. Instantaneous measurements of local temperature were obtained using laser Rayleigh scattering. and extractive probe sampling followed by gas chromatography was used to determine concentrations of stable species. Reactor temperature, and equivalence ratio (φ) were held constant, while the chlorine content was varied by modifying the C2H4, CH3Cl, and diluent N2 flows. The instantaneous temperature measurements showed that the reactor remains nearly perfectly-stirred, even to the point of blowout. A perfectly stirred reactor (PSR) model indicated that the principal effect of chlorine addition was that of inhibiting the burnout of CO to CO2, consistent with the experimental observation ...

Jet-Stirred Combustor Behavior Near Blowout: Observations and Implications

Abstract The behavior of jet-stirred combustors near blowout has been examined. Such units nominally emulate perfectly stirred reactors (PSR). Previous experimental data on instantaneous temperatures and stable species from a toroidal design have suggested non-PSR behavior as overall extinction is approached. Detailed mechanistic modeling in this work shows that such combustors experience global blowout at significantly lower mass flow rates than predicted by a PSR model. It is suggested that, as overall blowout is approached, only a fraction of the physical reactor volume is under active combustion as localized extinction occurs while apparent global stability still exists. This hypothesis is used to successfully predict observed global extinction points for C2H4/air and CO/H2/ air in a toroidal unit, and CH4/air in a spherical unit. In order to judge whether a stirred combustor is experiencing significant departures from PSR behavior, a test is offered for carbon-containing fuels burned under fuel-lean conditions. It compares the measured CO concentration with the predicted CO concentration obtained from a PSR computer simulation based on an elementary CO/H2 reaction mechanism and a modified feed composition. In this feed, the actual fuel is replaced with a stoiehiomelrically equivalent amount of CO and H2O, and the 02 feed is reduced accordingly. If localized instability is occuring, the measured CO level will exceed the predicted CO level. This test has been confirmed for fuel-lean C2H4 oxidation in air in a toroidal jet-stirred combustor.

Measurements and modeling of light hydrocarbons in rich C 2H 4 combustion in a jet-stirred reactor

Premixed fuel and air were burned at atmospheric pressure and 1750 K in a jet-stirred combustor. A water-cooled stainless-steel probe was used to sample stable species over an equivalence ratio range of 1.3–2.0. In general, the major stable species measured showed good agreement with a model consisting of a single well-stirred reactor and a reaction mechanism proposed by Glarborg, Miller, and Kee. Radical reactions occurring in the sampling probe were also modeled using a measured probe temperature profile. At low equivalence ratios (1.3–1.5), where the concentration of stable species are small relative to the concentrations of radical species (H, OH, O, CH3, etc.), radical reactions in the probe produce large changes in the measured species concentrations. At higher equivalence ratios (above 1.5), the effects of probe quenching are diminished due to the small radical concentrations relative to the concentrations of the major stable species.

A study on the effect of temperature on soot formation in a jet stirred combustor

In an attempt to understand soot formation mechanisms and predict soot yields in practical combustion systems, experiments were conducted in a toluene/air turbulent premixed flame in a jet stirred combustor (JSC). Soot mass concentrations were measured via a laser extinction technique and soot particle diameter and number density were measured via a laser extinction technique and soot particle diameter and number density were measured via a combination laser extinction/scattering technique. A global soot model was utilized to analyze rates of particle nucleation, coagulation, and specific surface growth. In order to study the effect of flame temperature on soot formation, one uncooled and three water cooled JSCs were prepared. Soot mass concentration measurements showed strong dependency of the soot production on stoichiometry, residence time, and flame temperature. It was found that as temperature became lower the incipient soot limit became lower, which indicated a greater sooting tendency at a lower flame temperature. The soot mass concentration was found to maximize at a flame temperature of approximately 1200∼1400°C. It was also found that the soot particle diameter increased with temperature. The measurements and the results of a global soot model calculation showed that particle nucleation decreased and the specific surface growth rate increased with an increase in temperature above the maximum sooting temperature.

Inhibition of a Fuel Lean Ethylene/Air Flame in a Jet Stirred Combustor by Methyl Chloride: Experimental and Mechanistic Analyses

Abstract Probability density functions (PDFs) of instantaneous temperature have been obtained for fuel lean C2 H4 /air burning in a toroidal jet stirred combustor (TJSC) using pulsed laser Rayleigh scattering. The PDFs provide a very sensitive measure of departures from perfectly stirred reactor (PSR) behavior, Narrow PDFs were obtained under stable operating conditions. As the mean combustion temperature was reduced or the reaction kinetics decelerated by the addition of CH3,C1, the PDFs exhibited a bimodal distribution indicative of localized blowout. Modeling of the reactions indicates that chlorine primarily destabilizes this hydrocarbon oxidation system by inhibiting the burnout of CO. This inhibition is affected through significant depletion of OH in the presence of relatively high levels of HC1 by the reaction OH + HC1 = H2O + CI. Inhibition is further affected by the termination reaction CI + HO2 + HCI + O2 because HO2 is a source of OH.

Identification of aromatic alkynes and acyclic polyunsaturated hydrocarbons in the output of a jet-stirred combustor

Analyse des produits de la combustion de l'ethylene (C 4 -C 12 ) par chromatographie en phase gazeuse, spectrometrie de masse et spectrometrie IR a transformation Fourier

Identification of acetylenes in the output from a jet-stirred combustor by gas chromatography-mass spectrometry and gas chromatography-fourier transform infrared spectrometry

When analyzed by gas Chromatographic mass Spectrometry (GC-MS), some combustion-derived components yield equivocal mass spectra whose simple patterns suggest aromatic rings but whose molecular mass rule out such structures. Although acyclic polyunsaturated molecules are strongly suggested, the lack of structural detail and the scarcity of reference compounds lowers confidence in GC-MS data. Fortunately, Fourier-transform infrared Spectrometry is well-suited to the identification of unsaturated molecules and often provides the complementary information required for complete characterization.

Dependence of Soot Production on Fuel Blend Characteristics and Combustion Conditions

Liquid synthetic fuels derived from nonpetroleum resources will play a major role in meeting future national energy demands. In the case of gas turbine applications, it is known that the different properties of these fuels can result in substantially altered combustion performance. Most importantly, decreased fuel hydrogen content resulting from an increased aromatic content has been observed to result in increased exhaust smoke and particulates as well as greater flame luminosity. This paper contributes empirical information and insight which allows the greater soot formation tendencies of low hydrogen content fuels to be better understood. A small scale laboratory device which simulates the strongly backmixed conditions present in the primary zone of a gas turbine combustor is utilized. The Jet Stirred Combustor provides for very rapid mixing between a premixture of vaporized fuel and air and the combustion products within a 5.08 cm dia hemispherical reactor. Results to be presented are gaseous combustion product distributions, incipient soot limits, and soot production (mg/l) for a variety of fuels. The influences of combustor inlet temperature and reactor mass loading have been evaluated and the sooting characteristics of fuel blends have been studied. These results have been analyzed to develop useful correlations which are in general agreement with existing mechanistic concepts of the soot formation process.

Experimental and theoretical studies of NO xformation in a jet-stirred combustor

As an approach to testing kinetic models which couple NO formation to combustion reactions, a jet-stirred combustor was used to study NO(x) formation under kinetically controlled combustion conditions. The experimental data were compared with kinetic calculations for a well-stirred reactor. The agreement between theory and experiment was quite good for the combustion of hydrogen/air and carbon monoxide/air, for which detailed mechanisms were used. A quasi-global mechanism for the combustion of propane/air resulted in substantial underprediction of NO(x) formation.