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301 results on '"Smallwood, G"'

53. Temporal structure of dense diesel sprays

Author

Gulder, O. L. and Smallwood, G. J.

Subjects
spray structure, diesel spray, drop size profile
Abstract

4t International ICE 99 - Internal Combustion Engines: Experiments and Modeling, September 12-16, Capri-Naples

Published
1999

73. An improved CARS spectgrometer for single-shot measurements in turbulent combustion

Author

Snelling, D. R., Sawchuk, R. A., Smallwood, G. J., and Parameswaran, T.

Subjects
Physics::Optics
Abstract

A broadband coherent anti-Stokes Raman spectroscopy (CARS) system optimized for single shot measurements in turbulent flames is described. The CARS spectrometer incorporates an intensified photodiode array (IPDA) with a P46-phosphor based intensifier that is shown to have an order of magnitude less image persistence than P20-phosphor based IPDAs, and thus largely eliminates the temperature errors that can result from this image persistence. The low and high signal nonlinearity of IPDAs incorporating both P20 and P46 phosphor based intensifiers is described. The CARS signal is dispersed with a single element concave holographic diffraction grating, which is fiber-optically coupled. To provide the necessary dynamic range (approximately 1000:1) to handle CARS spectra whose temperatures can vary from 300 K to adiabatic flame temperatures a fiber-optic splitter was employed and the nonlinearity of the IPDA detectors characterized. A method of determining the nonlinearity was developed that was convenient and the fiber-optic link was shown to provide a stable calibration of this nonlinearity. The problem of dye laser spectral drift, which is particularly severe in a long duration experiment, was addressed by constructing a compact high resolution spectrometer to continuously monitor the dye laser. The dye laser center frequency was maintained constant by manually adjusting an intracavity tuning filter. The accuracy of this technique and its effect on CARS derived temperatues was evaluated. The standard method of determining the instrument function by fitting to 295 K air spectra was compared to other methods and its use was shown to result in an uncertainty of less than 0.5% in CARS derived temperatures. The operation of this CARS instrument was demonstrated in a turbulent diffusion flame. The varying composition of these flames was accounted for by fitting C, tha ratio of the nitrogen mole fraction to the total third order nonlinear susceptibility.

Published
1992

90. Numerical Study of Confined Laminar CH 4 /Air Diffusion Flames Established in an Inverted Burner.

Author

Liu, F. and Smallwood, G. J.

Subjects
NUMERICAL analysis, CONFINED flow, LAMINAR flow, METHANE analysis, DIFFUSION, PARTICLE size determination
Abstract

Several experimental studies have demonstrated that confined laminar diffusion flames established in an inverted burner are very stable and emit soot when the global equivalence ratio exceeds a critical value. An inverted diffusion flame can be used as a stable source of soot particles for development and intercomparison of various particle sizing techniques. Unlike normal coflow diffusion flames fired upward, inverted diffusion flames fired downward experience a negative gravity, the resultant flow fields are very different, and the residence time is significantly prolonged. The different flow fields in normal and inverted diffusion flames mean that the flame structure and soot formation characteristics are significantly different. This study makes a first attempt to numerically investigate the flame properties and soot formation in confined laminar coflow CH4/air diffusion flames established in an inverted axisymmetric burner at atmospheric pressure. A fairly detailed reaction mechanism, GRI Mech 3.0, was used to model combustion chemistry. Soot formation was modeled using a semi-empirical, acetylene-based, two-equation soot model. Radiation heat transfer was calculated using the discrete-ordinates method and a wide-band non-gray gas model. Numerical calculations were conducted over a relatively narrow range of global equivalence ratio of 0.54–0.67 based on a recent experimental study. The heat transfer boundary condition was found to be important to the prediction of soot emission and the velocity distribution. Using measured temperature distribution along the quartz tube, the numerical model successfully predicted the emission of soot under the conditions investigated and revealed the flow, temperature, and species concentration distributions in the inverted coflow diffusion flames for the first time. However, the predicted primary soot particle diameters are significantly smaller than those reported in the literature based on TEM images analysis of sampled soot. The discrepancies between the numerical results and experimental data can be attributed to the deficiency of the simple soot model and the approximate treatment of the heat transfer boundary conditions at the quartz tube. [ABSTRACT FROM PUBLISHER]

Published
2014
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100. A numerical study on the effect of CO addition on extinction limits and NOx formation in lean counterflow CH4/air premixed flames.

Author

Guo, H. and Smallwood, G. J.

Subjects
*NUMERICAL analysis, *FLAME, *SIMULATION methods & models, *EQUIVALENCE principle (Physics), *CARBON monoxide, *NITROGEN oxides
Abstract

The effect of CO addition on extinction and NOx formation in lean premixed counterflow CH4/air flames was investigated by numerical simulation. Detailed chemistry and complex thermal and transport properties were employed. A method that gradually switched off the initial reactions of NO formation from different routes was used to analyse the variation of NO formation mechanism. The results indicate that the addition of certain amount of CO increases the strain extinction limits and reduces the radiation extinction limits. As a result, the lean flammability limit of CH4/air premixed flame is extended to leaner side by the addition of CO. The formation of NO in a flame is increased with the addition of CO at a constant equivalence ratio. For an ultra-lean flame, the increase in the formation of NO is mainly because of the increase in the contribution from the NNH intermediate route, while for a near stoichiometric flame, this increase is mainly attributable to the rise in the contribution from the thermal route. With the fraction of added CO being gradually increased, the formation of NO2 in a flame first decreases and then increases at a given equivalence ratio. The addition of CO reduces the formation N2O in an ultra-lean flame, while affects little on the formation of N2O in a near stoichiometric flame. [ABSTRACT FROM AUTHOR]

Published
2007
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