摘要:

Modelling of the structure and the limiting flow turning angles of an oblique detonation wave, established by a two-dimensional wedge, requires the implementation of detailed chemical kinetic models involving a large number of chemical species. In this paper, a method of reducing the computational effort involved in simulating such high-speed reacting flows by implementing a systematically reduced reaction mechanism is presented. For a hydrogen - air mixture, starting with an elementary mechanism having eight species in 12 reactions, three alternate four-step reduced reaction mechanisms are developed by introducing the steady-state approximation for the reaction intermediates HO2, O and OH, respectively. Additional reduction of the computational effort is achieved by introducing simplifications to the thermochemical data evaluations. The influence of the numerical grid used in predicting the induction process behind the shock is also investigated. Comparisons of the induction zone predicted by two-dimensional oblique detonation wave calculations with that of a static reactor model (with initial conditions of the gas mixture specified by those behind the nonreactive oblique shock wave) are also presented. The reasonably good agreement between the three four-step reduced mechanism predictions and the starting mechanism predictions indicates that further reduction to a two-step mechanism is feasible for the physical flow time scales (corresponding to inflow Mach numbers of 8 - 10) considered here, and needs to be pursued in the future.

ISSN:1364-7830    

DOI:10.1080/713665338

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The possibility of a positive synergism among flue gas recirculation, staged combustion and selective non-catalytic reduction technologies to achieve N-containing emission reductions has been investigated by simulating a 320 MW industrial-scale furnace boiler. A detailed chemical kinetic scheme coupled with a simplified fluid dynamic of the system has allowed us to compare the effectiveness of ammonia and isocyanic acid in removing N-containing pollutant emitted (NPE) with hot exhausts. By keeping the same flue gas composition for both cases, the effect of temperature and the impact of different amounts of NH3 and HNCO injected in the final combustion stage has been analysed. Ammonia was the most effective reducing agent for the particular conditions examined. Due to its high reactivity, the maximum effectiveness of the NH3-promoted process occurs at 940 K and an NH3 molar ratio of about 1.25. NH2 dominates the process mainly following two paths: N2 can be produced from direct interaction between NH2 and NO or via intermediate formation of NNH. On the other hand, HNCO is less effective than ammonia, owing to the influence of the particular radical environment within the boiler. HNCO oxidation is influenced by the amine radical pool which partly contributes to N2 formation but is, at the same time, an important source of NOx in the conditions analysed.

ISSN:1364-7830    

DOI:10.1088/1364-7830/1/4/002

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A comparison of several radiative heat transfer models is made for a stagnation-point diffusion flame at low stretch rate, with CO2 and H2O as the participating media. Computed results of the radiative source distribution for wideband, narrowband and SLWSGG show reasonable agreement with each other. Results from the optically thin and grey gas models with Planck mean absorption coefficient are shown to underestimate the self-absorption and overestimate the emission substantially for the low stretch flame. The relative computation times of using the various radiation models are also given.

ISSN:1364-7830    

DOI:10.1080/713665340

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A premixed flame, propagating away from a point ignition source into an unlimited domain displays an increasing flame speed after the flame size has grown beyond a transition radius. Experiments by Gostintsev et alare described by the relation R = R1+ At3/2, where t is the time from ignition and, where SLis the flame burning velocity and is the thermal diffusivity. The non-dimensional function a() is determined from the experimental results to be equal to 0.0022, where is the density ratio across the flame.

ISSN:1364-7830    

DOI:10.1088/1364-7830/1/4/004

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

We investigate how the local burning speed (Un) of laminar premixed flames reacts to weak fluctuating velocity gradients and front distortions, in situations where the latter stimuli have frequencies () comparable to the reciprocal time of transit () across the front itself.

ISSN:1364-7830    

DOI:10.1080/713665342

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor