摘要:

Radiative heat transfer is of major importance in many large-scale fires. Therefore, a new extinction coefficient algorithm has been developed for the Consolidated Fire Growth and Smoke Transport (CFAST) zone model. The new algorithm estimates extinction coefficient as a function of temperature and absorber concentrations. A developmental version of CFAST (2.2.1) was used, with and without the new algorithm. to simulate a large-scale, shipboard fire. For the fire compartment and the deck (floor) directly above, predictions from both models compared well with experimental results. The improved radiation model gave much better results for the adjacent compartment. Neither model compared well with the experimental results for the remainder of the compartments, suggesting that there is still room for improvement to CFAST.

ISSN:0010-2202    

DOI:10.1080/00102209708935694

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Lean premixed flames at very low equivalence ratios and high mean flow velocities can besustained in a co-axial jet flame burner. The flame shape involves a thin, highly turbulent flame region where most of the lean combustion occurs, and a base flame region which burns at the initial equivalence ratio. Due to the entrainment velocity induced by the high-speed inner jet flow, the flame also has a thin "pinched" region near the flame base. The entrainment of the hot product gas and mixing with the reactant, leading to preheating, along with the fact that the turbulence intensity increases gradually in the presence of the inner jet, are believed to be contributing factors in the stabilization of the flames in the current burner geometry. Addition of the inner jet of always lowers the overall equivalence ratio and enhances the stability limits. The minimum overall equivalence ratio achieved is 0.56 with a mean velocity of 60 m/s for the inner jet. This capability to generate lean premixed flames at high turbulence intensities and mean flow velocities is expected to have useful practical applications. Temperature measurements have been obtained using a point Rayleigh scattering technique, and the temperature profiles show a significant reduction in the flame temperature as the overall equivalence ratio is reduced using the inner jet air. The temperature pdf's show a shift of the cold reactant temperature to a higher value, indicating preheating of the reactant due to the entrainment of hot product gas that surrounds the lean flame. Also, there can be significant departure from flamelet behavior, associated with a bimodal temperature pdf, when the inner jet velocity becomes high. The temperature pdf's are no longer bi-modal at high turbulence intensities caused by the strong inner jet, with temperature pdf's showing a broadened temperature range in the flame zone.

ISSN:0010-2202    

DOI:10.1080/00102209708935695

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The objective of this work was two-fold: to determine the residence time distribution (RTD) in swirling pulverised coal flames and 10 develop a simple configuration of ideal chemical reactors, able to simulate the RTD. The work was performed using the solution of a mathematical model for a 2.2 MWthand a 12 MWthpulverised coal flame. Both flames are type II, resulting in high NOxemissions. From the mathematical solution the RTD was simulated by tracing a number of fluid particles or inert particles. The simulations showed that about 30% (dependent of the flame) of the fluid had a significantly lower residence time compared to the mean residence time. Based on RTD simulations and particle trajectories a simple configuration of ideal chemical reactors, able to simulate the main flow of the gas phase in the furnaces, was developed. The configuration consists of a plug flow reactor representing the jet centre, a well-stirred reactors representing the external recirculation zone, and a combination of well-stirred reactors representing the down stream region of the furnaces. The parameters in the ideal chemical reactor model were shown to berelated to distinct zones in the furnaces. Finally, the ideal chemical reactor model was verified against experimental RTD data of a 2.5 MWthconfined swirling natural gas flame.

ISSN:0010-2202    

DOI:10.1080/00102209708935696

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The oxidation of methyl acetate (MA) has been investigated for the first time in a jet-stirred reactor at high temperature (∼ 800–1230K) and 10atm. Molecular species concentration profiles of O2H2, CO, CO2CH2O, CH4, C2H2, C2H4, C2H6and MA were obtained by probe sampling and GC analysis. MA oxidation in these conditions was modeled using a detailed kinetic reaction mechanism(66 species and 416 reactions, most of them reversible}. The proposed mechanism, also validated for the oxidation of CH4, C2H2, C2H4, C2H6, C3H6, acetaldehyde, ethylene oxide, and natural gas blends in the same conditions, is able to predict experimental results obtained in our high-pressure jet stirred reactor. Sensitivity analyses and reaction path analyses are used to interpret the present results.

ISSN:0010-2202    

DOI:10.1080/00102209708935697

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Results are reported on the thermo-diffusive effects in laminar diffusion flames. The flames studied are those of the Burke-Schumann type, with the exceptions that the axial velocity is uniform in the inlet instead of having uniform mass flux, and that the fuel Lewis number is not equal to unity. The fuel Lewis number was varied using argon and helium dilution of the fuel. Dramatic Lewis number effects were experimentally observed. In some cases a higher degree dilution may cause the measured flame temperature (radiation corrected) to be higher than that with lesser dilution if increasing dilution reduces the Lewis number. The NOxemission level of the flame follows similar trend, consistent with the diffusive-thermal effects. A scaling analysis of NOxemission recently proposed for turbulent jet diffusion flames was examined for the present flames. It was found that as the Damkohler number decreases the normalized NOxemission increases. This further confirms thesuper-equilibrium effects for NOxemission previously found in turbulent jet diffusion flames. Thefuel Lewis number was not found to qualitatively affect the Damkohler number scaling of NOxemission, nor did it quantitatively correlate the value of the exponent of the Damkohler number.

ISSN:0010-2202    

DOI:10.1080/00102209708935698

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

In this paper, the effect of aging on the ignitibility and reproducibility of a composite solid propellant was investigated. Ignition delay times of solid propellant samples undergone different degrees of aging were determined under various levels of incident CO2laser energy fluxes. Micrographs obtained from an Environmental Scanning Electron Microscope (ESEM) showed that the surfaces of the aged samples exhibited fiber-like structure as compared to the heterogeneous structure of the as-machined sample. The porosity of the fiber-like structure increased with the degree of aging. Based upon the results of experiments, it was observed that aged propellant samples require much longer heating time to reach self-sustained combustion condition than the as-machined sample at lower energy fluxes (around 50 W/cm2). However, at higher energy fluxes (around 150 W/cm2), the effect of aging on the ignition delay times became smaller.

ISSN:0010-2202    

DOI:10.1080/00102209708935699

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Exhaust gas sampling was used to understand how spark-ignited internal combustion enginesemit unburned hydrocarbons(HCs) and form non-fuel HCs. A sampling unit collects exhaust gasduring a given 600 microsecond interval of the cycle, from a specific location within the port. Gas chromatography is used to measure individual HC species concentrations; total HC concentrations are in agreement with those measured by a fast flame ionization detector mounted in parallel with the sampling unit. Spatial resolution of port concentrations shows that the gas is well mixed a short distance from the valve, as no radial gradients are apparent. Time resolved measurements during the cycle reveal the distribution of species during the exhaust period, while measurements along the exhaust port axis mark the progress of reaction of each species. The results show that a higher fraction of non-fuel HCs leaves the cylinder during the late period of the exhaust phase, and that a significant fraction of HCs are partially or completely oxidized in transit along the port axis.

ISSN:0010-2202    

DOI:10.1080/00102209708935700

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

We report spatially resolved laser-saturated fluorescence measurements of NO concentration in a pre-heated.lean-direct injection (LDI) spray flame at atmospheric pressure. The spray is produced by a hollow-cone, pressure-atomized nozzle supplied with liquid heptane. NO is excited via the Q2(26.5) transition of the γ(O, 0) band. Detection is performed in a 2-nm region centered on the γ(O, 1) band. Because of the relatively close spectral spacing between the excitation (226 nm) and detection wavelengths (236 nm), the γ(O, 1) band of NO cannot be isolated from the spectral wings of the Mie scattering signal produced by the spray. To account for the resulting superposition of the fluorescence and scattering signals, a background subtraction method has been developed that utilizes a nearby non-resonant wavelength. Excitation scans have been performed to locate the optimum off-line wavelength. Detection scans have been performed at problematic locations in the flame to determine possible fluorescence interferences from UHCs and PAHs at both the on-line and off-line excitation wavelengths. Quantitative radial NO profiles are presented and analyzed so as to better understand the operation of lean-direct injectors for gas turbine combustors.

ISSN:0010-2202    

DOI:10.1080/00102209708935701

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor