摘要:

The differences in the flow field of an unforced unstable flame and a forced stable flame was examined through velocity and temperature measurements. Measurements were made in open atmosphere with an air-assist atomizing nozzle consisting of a central liquid-fuel (ethanol) stream, and a swirling primary air stream. Measurements made include the temperature, and CH/C2emission spectra for the forced stable flame, and cold-flow velocity measurements for both the air stream and the fuel droplets with and without primary-air forcing. The temperature distributions indicate that the stable flame is characterized by three distinct zones in the axial direction: (1) a low-temperature droplet heat-up and vaporization zone near the base of the flame, (2) an intermediate zone with three regions in the radial direction: a low-temperature droplet vaporization region straddled by two high-temperature combustion regions, one in the center and the other along the outer edges respectively, and (3) an upper high-temperature zone with combustion across the entire cross-section. The intermediate zone is most effected by forcing with substantial increases in the velocities, entrainment or volume flow rate, and turbulence levels. These increases contribute to improved vaporization and fuel-air mixing and therefore higher temperatures near the base of the flame. The forcing-induced improved mixing and the higher temperatures near the base of the flame are responsible for the flame stabilization.

ISSN:0010-2202    

DOI:10.1080/00102200008952124

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A detailed N/H reaction mechanism has been developed and validated in comparison with experimental data for ammonia pyrolysis in shock waves (Davidson et al.,Int. J. Chem. Kinet, 1990, 22:513). It has been shown that incorporation of the reactions with N2H3and N2H4into the mechanism significantly influences calculated rise-time and peak concentrations of the NH and NH2radicals if the currently adopted rate constant of the reaction

ISSN:0010-2202    

DOI:10.1080/00102200008952125

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

This paper describes a prediction method applicable to turbulent non-premixed combustion, constrained by the influences of finite rate chemistry. The method is an eulerian particle hybrid based on earlier proposals by Borghi. Such methods are readily adapted to complex numerical grids and offer the potential of computational economy which is acceptable for engineering applications. The present treatment has been extended to encompass extinction. Predictions are herein compared with the data for two, highly-strained, turbulent diffusion flames of the experiments of Masri, Bilger, and Dibble. The principal outcome of this study is that the incorporation of the extinction model enables predictions of good quality to be obtained assuming economical single-step reaction chemistry.

ISSN:0010-2202    

DOI:10.1080/00102200008952126

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Two-dimensional numerical predictions of temperature profiles and pollutants formation in a porous burner are presented and validated through their comparison with available experimental data. The burner under study integrates a heat exchanger where water is heated for household applications. The Navier-Stokes, the energy and the chemical species transport equations are solved and a multislep kinetics mechanism (77 reactions and 26 species) is employed. Thermal nonequilibrium is accounted for and the discrete ordinates method, for the case of isotropic scattering, is used. Centreline temperature predictions are in good agreement with the experimental results. Predicted CO and NO emissions are compared to experimental results for a 5 kW thermal power and several excess air ratios. The model underpredicts the CO emissions and overpredicts the NO emissions. This tendency is stronger for richer mixtures. The effects of the excess air ratio, solid conductivity, convective heat transfer coefficient and radiative properties are investigated.

ISSN:0010-2202    

DOI:10.1080/00102200008952127

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A numerical simulation is completed to analyze the ignition transient in a solid rocket motor with rear ignition system. Time-dependent compressible SIMPLER algorithm for gas phase governing equations and finte volume method (FVM) for radiative transfer equation are employed, respectively. Two dimensional conduction equation for propellant grain is combined as well. While the standard k - ε model with wall function is used for turbulence, the eddy break-up (EBU) model is used for gas phase reaction rate. A detailed development of unsteady flow and temperature fields is obtained. Especially, the radiation is found to play a significant role in igniting the solid propellant by promoting the heat feedback to propellant surface. When the radiation transport was not considered, the predicted ignition and flame spreading sequence was in error, based on a limited experimental data.

ISSN:0010-2202    

DOI:10.1080/00102200008952128

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

This paper reports a laboratory investigation into the role of inherent inorganic matter and additives in the low-lemperatures oxidation and spontaneous combustion of a Victorian brown coal. The raw coal, water-washed coal, acid-washed coal, and acid-washed coal respectively doped with fourteen additives, are prepared. Each of the samples is then tested in a wire-mesh reactor to obtain its critical ambient temperature, above which a thermal runaway occurs. The critical ambient temperatures of the acid-washed sample and water-washed coal are higher than that of the raw coal, indicating that the inherent inorganic matter in the coal catalyses the low-temperature oxidation. The relative effectiveness of the additives is determined by comparing their critical ambient temperatures with that of the acid-washed coal. Magnesium acetate (Mg(Ac)2). calcium acetate (Ca(Ac)2). magnesium carbonate (MgCO3). sodium hydroxide (NaOH). calcium chloride (CaC12), and sodium chloride (NaCI) arc found lo inhibit spontaneous combustion, while copper acetate (Cu(Ac)2), potassium acetate (KAc), sodium acetate(NaAc). copper carbonate (CuCO3), sodium carbonate (Na2CO3), potassium carbonate (K2CO3). calcium carbonate (CaCO3), and calcium hydroxide (Ca(OH)2) promote the spontaneous combustion. The effect of additive loading is also investigated for an inhibition agent (Ca(Ac)2) and a promotion agent (NaAc). Low-temperature oxidation kinetics are estimated by a transient energy balance approach and compared with the spontaneous combustion potential of the samples.

ISSN:0010-2202    

DOI:10.1080/00102200008952129

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A new burner design is presented in this work for highly stabilized partially premixed flames using gaseous fuel. The partially premixed flow is created in a concentric flow tube and the flames are stabilized by a relatively large diverging conical nozzle. The concentric flow conical nozzle burner (CFCN) creates highly stabilized flames at high Reynolds number, up to 60000. Three versions of the burner have been investigated and a maximum load of about 250 kW with 20 mm diameter nozzle has been achieved in partially premixed flame. Higher load is expected for larger burner size. The stability characteristics of the CFCN burner show that it is suitable for industrial applications. The burner turndown ratio is between 15 and 20.

ISSN:0010-2202    

DOI:10.1080/00102200008952130

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A simple theoretical model describing physics of the plasma torch plume is developed in connection with its applications to the arc-plasma waste-treatment system. The theoretical analysis is carried out by making use of Bernoulli's pressure-balance equation, which provides a stable equilibrium solution of the gas density in the plume ejected from the torch into a high-pressure reactor chamber with 4ε < 1. The pressure depression parameter ε is proportional to the gas temperature and inversely proportional to the square of the chamber pressure. In a low-pressure chamber, characterized by 4ε >1, there is no stable equilibrium solution satisfying Bernoulli's equation. Therefore, it is expected that the observable plasma data may change abruptly as the chamber pressure crosses the borderline defined by 4ε = 1. Indeed, most of the plasma data measured in an experiment change abruptly at the pressure borderline of 4ε = 1. The oxygen torch plume is theoretically analyzed for the arc-plasma waste-treatment system. Due to a very high arc-plasma temperature inside the torch, most of the oxygen molecules are atomized when they exit the torch and enter the reactor chamber. The oxidation process of materials by oxygen atoms can be easily achieved at a reaction rate of a million limes faster than that by oxygen molecules. It is therefore essential to evaluate the oxygen atom concentration in the oxygen plume propagating through the waste-treatment system. A numerical example indicates that a high concentration of oxygen atoms exists even at a considerable distance (i.e., 40 cm) from the torch exit in typical torch operation conditions.

ISSN:0010-2202    

DOI:10.1080/00102200008952131

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

NOxemission indices (NOxEI) of laminar high-pressure and turbulent liquid-fueled partially premixed flames arc studied as a function of fuel tube equivalence ratio Ob. In both cases. NOxEI behavior appears to be affected by changes in soot production. Soot levels were visually observed to decrease with increasing levels of partial premixing (decreasing φB). The resulting variation in NOxEI with Ob is vastly different from the variation observed for flames with negligible soot. For the soot containing flames. NOBEI increases continuously with increasing levels of partial premixing. The increase in NOBEI becomes more rapid beyond the point at which soot formation is suppressed. with a subsequent sharp reduction in NO;BEl for φB≤ 1.3. Based on these results, we suggest that optiinuni level of partial premixing can be designed to eliminate soot formation without a sleep NOφBEI penalty in high-pressure flames.

ISSN:0010-2202    

DOI:10.1080/00102200008952132

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Behavior of fire-induced heat and smoke movement in a longitudinally ventilated model tunnel is studied experimentally. A gas burner is used as fire source. Ventilation velocity, heal release rate, temperature distributions arc measured under quasi-steady conditions. Flow visualization using incense smoke as a tracer has been carried out to identify some important characteristics of the flow and heat transfer, such as the upstream layer, thermal stratification, turbulence mixing, etc. Flow patterns under different ventilation velocities are analyzed and discussed. It is found that heat and smoke can be controlled by proper ventilation. Optimum environment for initial evacuation and fire services should be provided at a ventilation velocity close to or slightly less than the critical ventilation velocity, which is a function of the cube root of the heat release rate. The effects of heat release rates and tunnel inclination angles were also investigated.

ISSN:0010-2202    

DOI:10.1080/00102200008952133

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor