摘要:

The fluctuating temperature field in a jet stirred flow reactor designed for chemical kinetic studies of hydrocarbon oxidation is investigated. In order 10 address both the question of the degree of micro-mixing and that of the turbulence/chemistry interaction, the present paper analyses and compares the fluctuating temperature structures inside this reactor for various situations. The experimental study is conducted by the technique of fine-wire thermoanemometry. The pdfs. spectra and the relevant time scales of the temperature field are determined. In parallel, the fuel conversion rates of propane oxidation in all the experimental conditions are determined from a simulation work which takes into account a detailed kinetic model previously established. The variation of the unmixedness and the time scales of the temperature field is compared for a wide range of parameters in the reacting and non-reacting cases. The discussion is conducted in terms of the ratio between the time scales of the scalar and dynamic fields and of a Damköhler number.

ISSN:0010-2202    

DOI:10.1080/00102200008947282

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Flame length and CO measurements have been conducted on different geometrical configurations issuing air through the circumferential openings in a reacting cross-flow. The main application of the research is to improve the understanding of jet mixing in a reacting cross-flow in order to optimize the design of combustors used to destroy combustible exhaust gases from steel-melting furnaces. Current combustor designs are characterized by poor mixing with the combustion air entering through a gap (circumferential slit), deflecting the main flow and slowly mixing via turbulent diffusion. Alternate air inlet geometries have been studied by investigating the mixing of various circumferential air jets configurations into a high temperature combusting cross-flow. The experimental results show that the flame length decreases with increasing jet mass flow. The carbon monoxide combustion efficiency does not follow the same trend. All configurations exhibit optimum combustion efficiency at the momentum flux ratio that corresponds to the non-reacting optimum mixing conditions. Jet configurations with higher design momentum flux ratios have improved combustion efficiencies. These results suggest that furnace exhaust gas combustor designs that follow the non-reacting optimum mixing design equations have optimal CO combustion efficiencies.

ISSN:0010-2202    

DOI:10.1080/00102200008947283

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Isothermal physical scale models, employing an equivalent jet radius, are used to simulate combusting flows in furnaces. Computational fluid dynamics is used to assess the isothermal analogues of combustion systems with and without swirl. The accuracy of representation of the flow in the isothermal analogue depends on the swirl number, S, and the ratio of the equivalent jet radius to chamber radius, re/ rc. The representation was good without swirl, S=0, and with swirl for S up to 0.12 with re/ rc>0.16 and for S up to 0.24 with rerc> 0 08. This behaviour was assessed through the normalised recirculation mass flow and the points of separation and reattachment of the main eddy, and should extrapolate to higher swirl numbers as re/rcis reduced. The differences between the combusting and isothermal flows arise from a shifting of the eddies in the enclosure flow.

ISSN:0010-2202    

DOI:10.1080/00102200008947284

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Measurements of the fluctuating liftoff height of turbulent jet flames were made using a linear photo-diode array. A wide range of experimental conditions was investigated, including varying the fuel, nozzle diameter and liftoff height

ISSN:0010-2202    

DOI:10.1080/00102200008947285

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The oxidation of HCN has been conducted in a fused silica jet-stirred reactor (JSR) at atmospheric pressure and from 1 000 to 1400 K. The reduction of nitric oxide (NO) by HCN has also been studied in a JSR in the same operating conditions. A detailed chemical kinetic model for NO-reburning (751 reactions and 102 species) was used to simulate the present experiments. An overall good agreement between the experimental results and the modeling was obtained. According to the proposed kinetic mechanism, in the conditions of this study, the oxidation of HCN proceeds mostly through the following sequence: HCN = O → NCO → NO → N2O → N2. The present modeling also shows that the reduction of NO by HCN proceeds according to the following sequence of reactions HCN = O → NCO; NCO = NO → N20 = CO and C02= NO; N20 = H → N2= OH.

ISSN:0010-2202    

DOI:10.1080/00102200008947286

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The work presented in this paper deals with the synchronous multiwavelength detection of thermal, chemiluminescent and laser-excited (λ0=266nm) emission from spray of a large saturated paraffin (tetradecane) in auto-igniting conditions. Two of these have been selected by varying oxygen molar fraction (0.13 and 0.21) of high pressure (2MPa), high temperature oxidant (900K) stream yielding non-sooting combustion

ISSN:0010-2202    

DOI:10.1080/00102200008947287

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The main purpose is to examine if radiation, considered as the dominant mechanism of fuel bed preheating, can account for experimental results obtained from laboratory fires conducted in no-wind conditions. For this, two one-dimensional radiative models for fire spread in a porous forest fuel bed are derived from Albini's model 1(9S6). The sensitivity of these two models to uncertain input parameters, particularly the emissive powers of the ignition interface and of the flame, are shown. The predictions of spread rates from the two models are then compared against the observed values for different fuel loads and slopes for two kinds of pine litter. In most cases, the observed effects are poorly predicted when fixed emissive powers are used. Thus, in a second step, the necessary values of emissive powers to be used for predicting The observed effects are researched. Although reasonable values of emissive powers are apparently required in most cases, it is suggested that the heat loss due to free convection in the energy balance should be replaced by convective heat transfer depending on the gas temperature profile, in order to give better estimates of the observed effects.

ISSN:0010-2202    

DOI:10.1080/00102200008947288

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A heat release analysis procedure was developed for a two-stroke spark ignition engine. The model was used to calculate instantaneous heat release rates, cumulative heat release and mass fraction burned of base engine and catalytic engine. The combustion chamber of the catalytic engine was coated with a catalyst material by plasma spraying method. The tests were conducted with different air-fuel ratios and heat release analysis was carried out for both base and catalyst coated engines. Engine cylinder pressure traces of 2000 continuous cycles were recorded using a pc based data acquisition system. The average of these traces was calculated and used as input to the heat release model. From the heat release rate various combustion characteristics, such as delay period, start of combustion, end of combustion and combustion duration were calculated for the base and catalytic engines. The results indicate that the heat release model could be used for the calculation of combustion parameters and accurate enough for the present purpose. The calculated combustion parameters indicate that the catalyst induces pre flame reactions of fuel air mixture before combustion, which reduces delay period and increases the combustion rate. The combustion duration of catalytic engine was reduced by 8 degrees at 0.8 equivalence ratio.

ISSN:0010-2202    

DOI:10.1080/00102200008947289

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The turbulent flame structure and flame length of fully-modulated diffusion flames was examined over a range of pulsing frequencies, injection flow rates, and duty-cycles. An injection system employing an electronically-controlled solenoid value was used to discharge puffs of unhealed natural gas and ethylene fuel into still air at one atmosphere pressure. Video imaging of the luminosity from the sooting regions of the flame revealed two distinct types of flame structure. For small injected volumes and short injection times, compact, puff-like structures with a short flame length were generated. More elongated “cigar-shaped” structures, with a longer flame length closer to that of steady-state flames, resulted from longer injection times and larger injected volumes. An injection parameter which characterizes the transition from puff-like to cigar-shaped flame behavior is presented. For puffs, an increase in duty-cycle generally led to an increase in flame length. This increase was less for cigar-shaped flames. The downstream location of the puff-like flame structures increased roughly with time to the 1/2 power, in agreement with buoyant thermals and starting jets.

ISSN:0010-2202    

DOI:10.1080/00102200008947290

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The effect of steam addition on the structure and extinction of hydrogen/air premixed flames is investigated numerically with a detailed kinetic mechanism by adopting both counterflow and stagnation-point flow configurations as model problems. For a specified equivalence ratio of hydrogen/air mixture, the flames in a stagnation-point flow can be maintained to higher steam content compared to those in a counterflow. This can be explained based on the local strain rates defined at the location of maximum heat release rate. The effects of preferential diffusion and reaction incompleteness caused by (lame stretch and the effect of steam addition on flame extinction can be successfully quantified by adopting a local equilibrium temperature, which can be determined from chemical equilibrium calculation using the temperature and concentrations of a local mixture in a flow field. The structure of near-stoichiometric flames with the variation in steam content can be successfully explained by introducing a local equivalence ratio.

ISSN:0010-2202    

DOI:10.1080/00102200008947291

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor