摘要:

The experimental study of the thermal degradation of methylethylketone (MEK) in flame conditions is undertaken to provide an experimental data base concerning Volatile Organic Compounds (VOCs) oxidation. The experimental set-up consists of the coupling of microprobe sampling with gas chromatography and mass spectrometry analysis. Temperature measurements are realized by the coated thermocouple technique. The addition of MEK to a reference methane / air flame induces (1) an enhancement of the C2and C3hydrocarbon oxidation pathways which points out the main role of CH3and C2H5radicals, and (2) the formation of oxygenated intermediate compounds such aldehydes (CH2O, CH3CHO. CH3CH2CHO), alcohols (CH3OH, CH3CH2OH) and ketones (CH3COCH3, CH3COCHCH2, CH3CH2COCH2CH3, CH3COCH2CH2CH3). The peak mole fraction of these intermediate species increases with the amount of MEK added to the methane / air flame. The experimental results are discussed to point out the kinetic processes involved in the high temperature oxidation of MEK which may contribute to the development of a detailed chemical mechanism.

ISSN:0010-2202    

DOI:10.1080/00102200008935809

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Acoustic fields interacting with a rectilinear droplet stream flame can increase mixing between fuel and oxidizer. For a droplet stream burning in room temperature air, sufficiently high acoustic intensity levels can cause local flame extinction. The sound pressure levels required to extinguish the flame increase with increasing sound frequency. The key parameter associated with flame quench is the gas displacement produced by the sound field. Quenching occurs when the acoustic displacement distance is approximately the radius of the droplets fueling the droplet stream flame.

ISSN:0010-2202    

DOI:10.1080/00102200008935810

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The paper attempts to obtain an approximate distribution of oxidizer/fuel (O/F) flamelets on the burning surface of a composite solid propellant, mainly of the ammonium perchlorate (AP)-hydrocarbon (HC) binder variety commonly used in rocket propulsion applications today. A computer model is developed to simulate the random packing of oxidizer particles of different size distributions in the propellant. The focus of the present work is on the distinction between pockets of fine AP particles amidst the binder that may bum in a premixed O/F flame and the sufficiently large AP particles that bum with the surrounding vapor flow in an attached diffusion flame. A transition occurs between premixed burning and attached diffusion flamelet-burning over each oxidizer particle as the ambient pressure is varied. A simple criterion evolved earlier to delineate the two regimes of burning in the particle size-pressure domain has been employed to determine the flamelet type that prevails over each exposed particle of the model propellant at a given pressure. Delaunay triangulation is adopted to deal with regions of fine AP-binder corresponding to premixed burning. The results are compared with previously reported experimental observations of burning rate for specific propellant formulations that exhibited distinct jumps in their burning rate with variation in pressure. It was argued that the burning rate jumps corresponded to a concerted shift in the burning regime of a majority of fine particles. The present simulation supports this argument.

ISSN:0010-2202    

DOI:10.1080/00102200008935811

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Previous studies of the non-ideal behavior of condensed explosives with metal particle additives have shown that the explosives’ behavior is different than that predicted by equilibrium codes. Generally lower detonation velocities and pressure are measured, although under many circumstances an increase in performance of metallized explosives is measured. Little to date has been measured regarding the complex kinetics mechanism that is present in these flows under extreme conditions in excess of 30 GPa and 5000 K, respectively. To investigate these phenomena, an unsteady, one-dimensional model is presented that simulates the build-up toward steady detonation of an organic explosive, HMX, containing dispersed aluminum particles. Results indicate that under certain combinations of heat transfer rate and chemical release rate, the measured behavior (data) can be reproduced with a generalized model. The results indicate that these phenomena have a significant effect on die detonation structure, suggesting future models which would include detailed more complex heterogeneous physical chemistry.

ISSN:0010-2202    

DOI:10.1080/00102200008935812

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

This paper reports on an experimental and numerical investigation of the near field and combustion zone of a burner that realizes a FODI (Fuel/Oxidant Direct Injection) strategy for furnace firing. FODI is an non-premixed method of reactants delivery and employs a direct discharge of fuel and oxidant jets into the furnace chamber. The jets entrain significant quantities of furnace gases that have been cooled by furnace heat transfer. The fuel and oxidant streams arrive at the reaction zone diluted by furnace gases, lowering the temperature of the reaction and reducing NOxemissions. FODI involves three-feed mixing processes linked with non-adiabatic reactions at unusually low temperatures and reactant concentrations. The burner investigated here consists of fourteen fuel and air ports arranged in a circle around a central pilot flame. The global performance characteristics of the burner demonstrate the effectiveness of FODI in NOxreduction and its visually flameless oxidation process. The mathematical modelling of the burner using a commercial CFD package was capable of adequately predicting jet trajectories and primary flow structures in the furnace. The predicted temperature and species concentrations depart from measured values thus raising a question of how to effectively model three-feed processes under severe non-adiabatic conditions.

ISSN:0010-2202    

DOI:10.1080/00102200008935813

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

In order to reduce the computational cost of flame simulations, several methods have been developed during the last decades, which simplify the description of the reaction kinetics. Most of these methods are based on partial-equilibrium and steady-state assumptions, assuming that most chemical processes have a much smaller time scale than the flow time scale. These assumptions, however, give poor approximations in the ‘colder’ regions of a flame, where transport processes are also important.

ISSN:0010-2202    

DOI:10.1080/00102200008935814

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

We consider thin unstable premixed flames which are planar on average and evolve spontaneously from weak, random initial conditions. The underlying dynamics is chosen to follow a Michel-son-Sivashinsky equation, and attention is focused on the statistical properties of its solutions.

ISSN:0010-2202    

DOI:10.1080/00102200008935815

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

We report spatially resolved laser-induced fluorescence (LIF) measurements of nitric oxide (NO) in a preheated, two-atmosphere, lean direct-injection (LDI) spray flame. The spray is produced by a hol-low-cone, pressure-atomized nozzle supplied with liquid heptane. NO is excited via the Q2(26.5) transition of the γ(0,0) band. Detection is performed in a 2-nm region centered on the γ (0,1) band. A complete scheme is developed by which quantitative NO concentrations in high-pressure LDI spray flames can be measured by applying linear LIF. Standard excitation and detection scans are performed to assess possible interferences and to verify a non-resonant wavelength for subtracting the influence of oxygen interferences and Mie scattering in the NO detection window. NO is doped into the reactants and convected through the flame with no apparent destruction, thus allowing an NO fluorescence calibration to be taken inside the flame environment. The in-situ calibration scheme is validated by comparisons to a reference flame. Relative axial calibration slopes are utilized in order to obtain radial profiles of absolute NO concentrations. These quantitative 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:10.1080/00102200008935816

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

This paper presents results of the study on the effect of turbulence on droplet dispersion and group behavior in liquid-fuel spray flame. Insertion of grids with different mesh sizes in front of the nozzle resulted in change of turbulence intensity, while the change of turbulence integral scale was negligible. For smaller mesh and lower turbulence intensity total vaporization rate is rapidly increasing, while the droplet size distribution remains practically unchanged. Measurements of combustion group number showed that decrease of average group combustion number is well correlated with increase of vaporization rate. Therefore, the reason for observed vaporization enhancement, could be explained by more uniform spatial distribution and weaker inter-droplet interactions, which usually strongly reduce vaporization rate of droplets in dense sprays. Contrary to observed increase of vaporization rate, flame length is growing. This phenomenon is attributed to reduction of mixing of evaporated fuel and ambient air for lower turbulence intensity and poorer mixing between two gaseous phases compared to mixing between the air and droplets in liquid phase.

ISSN:0010-2202    

DOI:10.1080/00102200008935817

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Though turbulent reacting flows are often encountered in technical applications reliable prediction methods are lacking as a result of the complex nature of the physics. A promising approach to flows of practical interest is Large Eddy Simulation (LES). The philosophy behind LES is to explicitly simulate the large scales of the flow, directly affected by boundary conditions whilst modelling the smaller scales. The effects of the small unresolved scales appear as extra unknown terms in the LES equations that must be modelled. Subgrid models for reacting LES are more difficult to formulate than for non-reacting LES since also filtered reaction rates and other terms resulting from non-linear state equations need to be modelled. With the advent of transported PDF and linear-eddy models the situation has improved; due to the complexity and computational cost of similar models there is, however, still much to be gained from more conventional models. This study focuses on the development and application of a flame-wrinkling LES combustion model in which transport equations for a reaction coordinate, a modelled flame-wrinkling density and the laminar flame speed are derived, modelled and solved for. The unresolved transport terms in the momentum and energy equations are not particular to reacting flows and are modelled by a one-equation eddy-viscosity model. A centred second order accurate finite volume based scheme is used to solve the governing equations. The model is applied to a lean premixed propane air flame stabilised in the wake behind a triangular-shaped flameholder. Besides comparing with experimental data a discussion of different modes of combustion found to occur in this combustor is presented.

ISSN:0010-2202    

DOI:10.1080/00102200008935818

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor