摘要:

Abstract-Non-combusting flow from a bluff-body combustor was studied. The combustor consisted of a cylinder centered in an annular air jet. Water was sprayed downstream from a poppet nozzle mounted in the downstream end of the cylinder. The air flow was seeded with titanium dioxide particles and then illuminated with laser light, as a means of visualizing the flow. Three lighting techniques were used: continuous sheetlighting, pulse sheetlighting, and pulse backlighting. The Reynolds numbers (based on hydraulic diameters) for the water flow ranged from 0 to 12,280; and for the air flow ranged from 0 to 90,400. The effects of varying air and water flow rate on the resulting axisymmetric flow field were recorded on film and videotape.Three general categories of flow structure were observed. In two of these categories, the effect of increasing air flow rate was to widen the dispersion of the spray. In the third category, the momentum flux of the water spray dominated pressure and drag effects of the air, resulting in a spray structure resembling that of a spray in still air. In this case, the air flow is strongly modified by the water spray.

ISSN:0010-2202    

DOI:10.1080/00102208808947088

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Intrinsic instability in the steady, planar deflagration of a homogeneous solid propellant is considered through an asymptotic analysis for large values of nondimensional overall activation energies for the surface pyrolysis and gas-phase combustion processes. It is shown that the previously known pulsating instability is essentially connected with condensed-phase pyrolysis, and that new instability phenomena, which are associated with intrinsic gas-flame instability and which are sensitive to the value of the gas-phase Lewis number and to the distance of the gas flame from the propellant surface, arise. These results are obtained by relaxing the usual assumptions of quasi-steadiness and quasi-planarity for the gas phase, so that the coupling of intrinsic diffusional/thermal instabilities in the gas and solid phases becomes an integral feature of the model. The steady, planar deflagration thus may be unstable not only to pulsating disturbances, but also to (time-independent, nonplanar) cellular perturbations as well. It is shown that the onset of pulsating instability has a dual character which is related to the intrinsic instabilities of both the deflagrating solid and the gas flame. In contrast, the onset of cellular instability, apparently not predicted by previous theories for solid propellants, is clearly related to the stability of the gas flame. Appropriate limiting cases of the model retrieve the well-known pulsating and cellular neutral stability boundaries for strictly gaseous combustions, and the pulsating neutral stability boundary for strictly condensed phase combustion.

ISSN:0010-2202    

DOI:10.1080/00102208808947089

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Simultaneous two-component laser Doppler velocimeter measurements for homogeneous charge combustion in a spark ignition engine are used to calculate ensemble-averaged turbulence stresses. Cyclic variation hias in the data is reduced by conditional sampling. 011 the flame arrival time at the probe volume. Results are presented for engine speeds of 300. 600. and 1200 rpm. The lower speed is believed to be transitional because the general character of the fluid motion is found to he unique. For the two higher engine speeds. the following conclusions can he made: (1) The precombustion turbulence is highly anisotropic. with the component parallel to the piston surface nearly double the component in the direction of piston motion; (2) both the norrnul and shear turbulence stresses scale with mean piston speed; (3) combustion does not have an appreciable effect on either the preflame or postflame normal turbulence stresses. hut compression in front of the flame docs appear to reduce the degree of correlation of the velocity fluctuations: (4) combustion creates strong secondary velocity patterns that persist well after combustion is complete.

ISSN:0010-2202    

DOI:10.1080/00102208808947090

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

A range of aliphatic hydrocarbon fuels have been burned on a porous cylindrical burner which was housed in a duct. The approach flow velocity was adjusted so that the formation of particles was suppressed and the flame turned blue. This defined a critical velocity gradient for the stagnation point flame at which the soot inception chemistry of the flame could not cope with the rate of mixing of reactants imposed by the strain rate of the flow. Measurements of the fluorescence of polyaromatic species with an excimer pumped dye laser indicated that their formation rate in flames of the lightly sooting fuels such as ethane was very sensitive to the flow field. Fluorescence measurements in a heavily sooting fuel such as propene were not as sensitive to the velocity gradient of the flow. Measurements were made of the height to the onset of soot formation in vertical, turbulent diffusion flames of the same fuels. It was found that numerical calculations of the mean scalar dissipation rates at this location in a jet were in reasonably good agreement with the values which were derived from the laminar, counterflow flame experiments.

ISSN:0010-2202    

DOI:10.1080/00102208808947091

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

The role of chemical kinetics in the behavior of near-limit flames at rnicrogravity (μg) was investigated experimentally by comparison of the properties of these flames in mixtures having varying chemistry but similar diffusive transport properties. Conversely, the importance of unequal rates of diffusion of thermal energy and mass was evaluated by comparison of flames in mixtures having similar chemistry but varying Lewis numbers, It was found that the characteristics of near-limit flames at μg were affected much more by Lewis number effects than chemistry. It is concluded that there are at least three regimes of near-limit behavior at μg, depending upon the Lewis number (Le): (1) cellular flames, which are highly resistant to extinguishment, for mixtures with Le≪l, (2) self-extinguishing flames and well-defined flammability limits for mixtures with Le≃ 1, and (3) ignition energy limited flame propagation for Le ≪ 1, Gradual rather than abrupt transitions between regimes were observed.

ISSN:0010-2202    

DOI:10.1080/00102208808947092

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Experiments were performed to clarify the role of metallic fuel additives in relation to soot suppression in a well defined laboratory-scale diffusion flame. Principal emphasis was given to three alkaline-earth metals; namely, Ba, Sr and Ca. The experiments included Cu, Sn, Li, Na and K as well. but only to the extent that the latter contributed to understanding the details of alkaline-earth behavior. The additives were in the form of aqueous solutions of salts of the preceding metals. The solutions were aspirated into the oxidant flow of a nearly two-dimensional laminar C:H/air flame emanating from a symmetric Wolfhard-Parker burner. Soot size, number density and volume fraction were determined from Mie scattering. Metal species concentrations were determined semiempirically by combining H-measurements with known equilibrium constants for the metal/radical reactions occurring in the flame. The flame temperature was measured via sodium line reversal. The alkaline-earth metals were observed to alter the three soot parameters above in accordance with a Ba>Sr>Ca order of effectiveness and, moreover, the effectiveness was a strong function of measurement position. The temperature and species measurements were used to relate this variation to a specific metal combustion product. Following this approach, a conclusion is reached which strongly implicates the charged MOH + (M = Ba, Sr. Ca) species as responsible for soot suppression. In addition, since significant suppression may occur with only a slight size change, the metal principally reduces the soot number density, which suggests that inhihitory intervention is most significant at an early soot formation stage.

ISSN:0010-2202    

DOI:10.1080/00102208808947093

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Combustion measurements are being performed in a laboratory cylindrical pulverised coal fired furnace as part of a continuing research programme, The data are primarily intended to assist the validation of mathematical models ultimately intended for the prediction of full scale plant. In this paper gas-species concentration and temperature data are presented and discussed for a bituminous coal fuel fired at two excess air levels and two swirl numbers.

ISSN:0010-2202    

DOI:10.1080/00102208808947094

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

A direct injection (OI) and an indirect injection (IDI) diesel engine have been used to study the effect of engine type on soot and unburnt liquid hydrocarbons contained in diesel exhausts as a function of the air/fuel mass ratio, α. The impact of the broadening fuel specifications on diesel emissions has been investigated for both engines burning four different fuels in order to provide a relationship between fuel and particulate composition.

ISSN:0010-2202    

DOI:10.1080/00102208808947095

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

The influence of upstream fuel/air mixture stratification on the blowoff behavior of flames behind two-dimensional bluff bodies is investigated theoretically. The analysis identifies two important dimensionless groups through which stratification exerts an influence: a stratification parameter D which characterizes the severity of the stratification, and a dimensionless activation energy ECp/RΔH, which affects the ignitability of the fresh mixture. Results are presented for two possible scenarios. For the kind of stratification which might occur unintentionally in an otherwise homogeneous flow, stratification always reduces the blowoff limits of flows which are entirely lean or entirely rich, but in flows which vary from lean to rich, blowoff limits may be either reduced or improved. For the kind of stratification which might be intentionally introduced, for instance as a thin rich layer in an otherwise lean mixture, blowoff limits are always improved, often drastically.

ISSN:0010-2202    

DOI:10.1080/00102208808947096

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

A numerical study on the ignition behavior of one-dimensional monodispersive sprays is conducted. The effects of key parameters are clearly defined. In particular, the existence of the optimum equivalence ratio and its functional dependence on initial droplet size and fuel volatility are established. Similarly, the existence of the optimum droplet size and its functional dependence on equivalence ratio and fuel volatility are studied. The ignition behavior is strongly nonlinear near fuellean and small initial-droplet mixtures. This causes a substantial improvement in ignitabiliry of fuel-lean mixtures for the heterogeneous sprays as compared with the corresponding homogeneous mixtures. The investigation on ignition sources indicates an Arrhenius type of dependence of the ignition delay time on the source temperature. An attempt is made to compare the numerical results with experimental data. The comparison shows a reasonable agreement despite its qualitative nature due to the limited experimental data.

ISSN:0010-2202    

DOI:10.1080/00102208808947097

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor