摘要:

A Natural Gas Premixed Forced Internal Recirculation Burner (FIR) developed at the Institute of Gas Technology (IGT) reduces NOxemission level to sub-1O vppm. The FIR burner incorporates air staging and internal recirculation of combustion products. which greatly enhances heat removal. In the primary zone, combustion of rich natural gas/air mixtures occurs at low-temperatures (800 to 13ooK), therefore, NOxformation is unaffected by the thermal NOxmechanism - the main source of NO in typical natural gas burners. In the primary zone of the FIR burner, the composition of NOxemissions mainly consists of (70 to 80%) N02. This composition significantly differs from typical natural gas burners and from the FIR exit composition. where NO2concentration is less than 5% of the total NOx, amount. The low-temperature (800 to 13ooK) ignition and combustion in the primary zone of the FIR burner was modeled by admixing products with initial methane-air mixture. The developed approach predicts methane ignition and oxidation within typical residence times in the primary zone of the burner. NOxformation in low-temperature methane combustion was analyzed and attributed to the prompt NO mechanism. High concentration levels of HO2in the rich low-temperature flame in the FIR primary zone resulted in NO conversion to NO2. To further investigate low-temperature methane combustion a plausible kinetic mechanism was developed. Using the developed mechanism, the ignition of methane was found to be strongly promoted by the internal recirculation of combustion products. When the recirculation ratio is about 20 to 30%, the difference in ignition delays between methane and natural gas is insignificant.

ISSN:0010-2202    

DOI:10.1080/00102200008935793

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

We consider the propagation speed of thin premixed flames disturbed by the fluid flow and suggest a new approach based on using the generalized curvilinear system of coordinates and tensor calculus. The suggested technique is shown to be more simple than the traditional technique used by Sivashinsky (1976), Matalon and Matkowsky (1982) and also in other publications. The result of Matalon and Matkowsky (1982) is generalized for an arbitrary temperature dependent diffusion coefficient.

ISSN:0010-2202    

DOI:10.1080/00102200008935794

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Chromium has been identified as a carcinogenic metal. Incineration is the useful method for disposal of toxic chromium hazard waste and a chromium kinetic model in a flame is very important to study chromium oxidation. Chromium chemical kinetics over a range of temperatures of a hydrogen/air flame is proposed. Nine chromium compounds and fifty-eight reversible chemical reations were considered. The forward reaction rates are calculated based on the molecular collision approach and Arrhenius's Law. The backward reaction rates were calculated according to forward reaction rates. the equilibrium constants and chemical thennodynamics. The kinetic model is verified for two premixed equilibrium cases and is tested for a hydrogen/air diffusion flame. A chemical flux analysis is employed to reveal the significant chemical reactions. The results show that the kinetic model is precise enough and the chromium kinetics play an important role in the Hydrogen/Air diffusion flame.

ISSN:0010-2202    

DOI:10.1080/00102200008935795

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The effects of uncertainty in mass flux and initial temperature on the predictions of NO and OH from a detailed chemical kinetics model are determined. The Sandia steady laminar one-dimensional premixed flame code is used to solve the chemical kinetics model for a series of flames from 1 to 9.16 atm. The model allows the determination of the variation in the predictions of NO and OH concentrations from small changes in mass flow rate and in the initial gas temperature. The mass flow rate and initial gas temperature are two quantities for which experimental uncertainty exists, but the effect of which is not often considered in chemical kinetics modeling. The results indicate that uncertainty in the mass flow rate can significantly affect the quantitative predictions of NO and OH, while the initial gas temperature has little effect on the flame modeling results.

ISSN:0010-2202    

DOI:10.1080/00102200008935796

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

An asymptotic analysis of the multi-dimensional detonation instability has been developed in the limit that the ratio q of the reaction heat release over the enthalpy at the leading shock is much smaller than unity. The leading order solution corresponds to a wave equation describing the dynamics of the inert shock wave. By considering the next order destabilizing effects related to the heat release fluctuation and the non-uniform distribution of the stationary solution, an expression of the dispersion relation. which is valid in the vicinity of the bifurcation limits, has been obtained. The present work extends our previous analysis (He I996a) in the Newtonian limit to general situation for q≪1. It is found that the dispersion relation so determined is identical to that presented in (He 1996a), which was obtained in the Newtonian limit and q≪1 by carrying out an asymptotic analysis to the second order. The theoretical results for the growth rate and the bifurcation limits agree well with the numerical solutions of the exact linear instability problem. The physical mechanisms involved in the cellular detonations have been discussed.

ISSN:0010-2202    

DOI:10.1080/00102200008935797

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Experimental results of N2-diluted counterflow diffusion flames of CH4and C3H18vs, air with local extinction are reponed. The local extinction was caused by inert jet impingement on flames at selected locations either from the fuel or oxidizer side of the reaction zone. This was done to simulate how local extinction affects flame extinction over a larger flame area. The results are: (1) Local extinction of both CH4and C3H8flames occurs at a lower strain rate when the inert jet impingement originates from the airside. (2) The global extinction strain rate for CH4flames is insensitive to the location and number (one vs. three) of local extinction sites. (3) For C3H8flames, one single inert jet impinging from the airside along the centerline is more effective in causing global extinction than three inert jets impinging at regions away from the centerline. This suggests that flame extinction over a larger area may depend on strategically selected smaller local extinction sites. Furthermore, since similar results of (3) are not observed in this study for CH4flames, fuel chemistry may also play a role in the effectiveness of local extinction transitioning to global extinction. Differences between flame stabilization mechanisms with and without local extinction are discussed and the implications for turbulent diffusion flames are outlined.

ISSN:0010-2202    

DOI:10.1080/00102200008935798

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A new flamelet model has been developed for large-eddy simulation of turbulent premixed cornbustion in the thin-reaction-zones regime. In this regime of turbulent combustion, turbulent eddies smaller than the flame thickness exist and this small-scale turbulence disturbs the flame structure. Recent experimental observations show that turbulence interacts mostly with the chemically inert preheat zone while the thin reaction zone of the flame where all chemical processes occur remains unchanged. Therefore, flamelet models can be extended to this regime. The present model accounts for the different type of interactions between the flame and turbulence of different scales. The large-scale (larger than the flame thickness) turbulence increases the turbulent burning velocity by wrinkling the flame. On the other hand, the small-scale (smaller than the flame thickness) turbulence modifies the laminar flame propagation by enhancing the intensity of transport processes within the preheat zone. The developed model has been validated by carrying out a posteriori tests using a realistic gas turbine combustor problem. Comparisons with experimental data and conventional thin-flame model simulations show that the new model can significantly improve the predictions.

ISSN:0010-2202    

DOI:10.1080/00102200008935799

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

In 1921 an analysis by von Karman demonstrated that viscous pumping action occurs when a flat disk is rotated in a fluid of semi-infinite extent. The rotation draws material inward normal to the disk, forcing it radially outward, thereby causing a swirling motion. A similarity exists near the disk, in the vicinity of the centerline, such that the radial and tangential velocity components are propor-tionalto the radius, while all other flow properties depend only on the distance normal to the disk. If the disk is a fuel and the ambient fluid is an oxidizing gas, then a flat laminar diffusion flame parallel to the disk can be established in the swirling flow drawn in. Theoretical descriptions of such flames have been developed previously, and some experiments have been performed, notably for disks of polymethyl methacrylate (PMMA) in air. The present contribution provides quantitative measurements of burning rates and flame stand-off distances for such rotating disks and demonstrates that time-dependent heating of the fuel is important under these conditions, while nearly steady-state conditions apply in the gas. The fully steady-state solutions that have been published would apply to PMMA only for combustion in oxygen-enriched atmospheres for the sample sizes and rotational rates of the present experiments.

ISSN:0010-2202    

DOI:10.1080/00102200008935800

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Quantitative measurements of soot concentration made in an oscillating propane-air counterflow diffusion flame are presented. The non-intrusive laser induced incandescence (LII) technique was used to make spatially and temporally resolved measurements of soot volume fraction in these transient flames as a function of initial steady strain rate, forcing frequency, and forcing amplitude of the strain rate fluctuation. The results of this study show that the soot formation process becomes insensitive to fluctuations in strain rate at high initial strain rates. At low initial strain rates, however, the maximum soot concentration is drastically reduced with high frequency, high amplitude fluctuations compared to the corresponding steady strain soot volume fraction. Low frequency oscillations are found to always increase the maximum soot concentration, by up to a factor of six for some conditions. These measurements provide important insight into the response of the chemistry control1ing the soot formation process in flamelets subject to unsteady rates of strain.

ISSN:0010-2202    

DOI:10.1080/00102200008935801

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

ISSN:0010-2202    

DOI:10.1080/00102200008935802

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor