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Co-Visualization of Flame Structures and Species
Published in Maria da Graça Carvalho, Woodrow A. Fiveland, F. C. Lockwood, Christos Papadopoulos, Combustion Technologies for a Clean Environment, 2021
D. Proctor, I.G. Pearson, M. McLeod
This study uses schlieren and molecular species imaging techniques, to compare largescale structures identified with each, in a laminar diffusion propane-air flame and an oxyacetylene cutting torch. The equipment required is relatively simple and inexpensive. The ability to view and compare transient events in “real-time” leads to a greater underdtanding of the mixing processes. This results in a cost-effective tool to assist in the development of new, more efficient burners. Conditional phase sampling techniques, as described by Pearson (1989), were used to obtain structural images at the same phase in separate cycles of the acoustically forced diffusion flame which has been shown by Pearson et al. (1989) to have a highly reproducible cyclic character. The schlieren technique uses changes of refractive index caused by thermal and/or density gradients to deflect probing light and form light and dark patterns. These patterns represent the large-scale structures in the flame. The NO2 PLIF technique (similar to the OH PLIF technique developed by Dyer and Crosley (1982) and Kychachoff et al. (1982), and recently reviewed by Hanson (1986)) was used in a configuration similar to that used by Muggleton and Proctor (1989), but with a new, novel fluorescence light collection system using part of the schlieren optics.
An Overview
Published in J. David, N. Cheeke, Fundamentals and Applications of Ultrasonic Waves, 2017
In parallel with the technological developments mentioned earlier, there was an increased understanding of acoustic wave propagation, including velocity of sound in air (Paris 1738), iron (Biot 1808), and water (Calladon and Sturm 1826)—the latter a classic experiment carried out in Lake Geneva. The results were reasonably consistent with today’s known values—perhaps understandably so, as the measurement is not challenging because of the low value of the velocity of sound compared with the historical difficulties of measuring the velocity of light. Other notable advances were the standing wave approach for gases (Kundt 1866) and the stroboscopic effect (Toepler 1867), which led to Schlieren imaging.
Improvement of Turbulent Burning Velocity Measurements by Schlieren Technique, for High Pressure Isooctane-Air Premixed Flames
Published in Combustion Science and Technology, 2020
Pierre Brequigny, Charles Endouard, Fabrice Foucher, Christine Mounaïm-Rousselle
Although premixed turbulent combustion has been studied for over 40 years, it remains a significant problem for practical combustion processes such as those found in stationary power gas turbines, spark-ignition (SI) engines, and explosions. The problem is particularly crucial due to the use or future use of premixed turbulent combustion in increasingly drastic conditions in terms of pressure, temperature and diluted environment. As underlined by Verma and Lipatnikov (2016) and Lawes et al. (2012), the notion of turbulent flame speed, or burning velocity, remains unresolved, despite the large amount of data available. Matalon and Creta (2012) consider that represents the mean propagation speed of a premixed flame in a statistical steady state within a turbulent field, similar to the laminar flame speed. In fact, depending on the experimental setup (Bunsen burner, flat burner, spherical vessel) and measurement techniques (Schlieren, Mie or LIF tomography, pressure sensors), the data are more or less sparse. In the case of SI engine applications, the burning speed can be estimated in an optical engine (Aleiferis et al., 2013; Mounaïm-Rousselle et al., 2013). While some studies show good agreement, at least qualitatively, about the evolution of the burning velocity as a function of the thermodynamic and turbulent parameters, it is still challenging to conduct measurements in this kind of experiment due to the strong cyclic variations of the flow and the flame ignition/propagation itself. Therefore, to reach similar conditions to those of an SI engine, a turbulent spherical vessel remains the best apparatus to provide accurate data on turbulent flame speed and thus to validate models. The use of a fan-stirred vessel can allow uniform and isotropic turbulence in the central measurement region with less variability. However, there is currently no consensus on the optimal technique to provide ‘good’ or ‘real’ estimates of the turbulent burning velocity from flame radius measurements (Lipatnikov and Chomiak, 2002). Bradley et al. (2003) did an interesting analysis by comparing turbulent burning velocities estimated from different flame radius definitions. They concluded that Schlieren images remain the most convenient way to provide accurate experimental data. The Schlieren technique is a ‘real’ non-intrusive optical technique, contrary to Mie scattering or LIF tomography that require droplet or tracer seeding. Most recent studies on this kind of setup are based on Schlieren images (Goulier et al., 2017; Lawes et al., 2012; Bagdanavicius et al., 2015; Wu et al., 2015).