Dae-Seok Bae

Effects of Hydrocarbon Addition on Cellular Instabilities in Expanding Syngas-Air Spherical Premixed Flames

Experiments were conducted in a constant-pressure combustion chamber to investigate the effects of hydrocarbon addition on cellular instabilities of syngas-air flames. The measured laminar burning velocities were compared with the predicted results computed using reliable kinetic mechanisms with detailed transport and chemistry. The cellular instabilities that included hydrodynamic and diffusional-thermal instabilities of the hydrocarbon-added syngas-air flames were identified and evaluated. Further, experimentally measured critical Peclet numbers for fuel-lean flames were compared with the predicted results. Experimental results showed that the laminar burning velocities decreased significantly with an increase in the amount of hydrocarbon added in the reactant mixtures. With addition of propane and butane, the propensity for cell formation was significantly diminished whereas the cellular instabilities for methane-added syngas-air flames were not suppressed.

Study of Characteristics of Self-Excitation in Lifted Laminar Free-Jet Propane Flames Diluted with Nitrogen

The characteristics of lifted laminar propane flames diluted with nitrogen have been investigated experimentally to elucidate self-excitation and the effects of flame curvature. Flame oscillation modes are classified as follows: oscillation induced by heat loss, a combination of oscillations induced by heat loss and buoyancy, and a combination of the oscillations induced by heat loss and diffusive thermal instability. It is shown that the oscillation induced only by heat loss is not relevant to the diffusive thermal instability and hydrodynamic instability caused by buoyancy; this oscillation is observed under all lift-off flame conditions irrespective of the fuel Lewis number. These experimental evidences are displayed through the analysis of the power spectrum for the temporal variation of lift-off height. The possible mechanism of the oscillation induced by heat loss is also discussed.

A Visualization of the Spray from Small Liquid-rocket Engine Injector by Dual-mode Phase Doppler Anemometry

Abstract. A focus is given to the breakup behavior of spray droplets issuing from a nonimpinging-typeinjector. The analysis has been carried out experimentally by means of the dual-mode phase Doppler ane-mometry (DPDA). Spray characteristic parameters in terms of axial velocity, mean diameter, velocity fluc-tuation, and span (width of the size distribution) of droplets are measured down the geometric axis ofa nozzle orifice and on the plane normal to the spray stream with the injection pressure variations. Asthe injection pressure increases, the velocity and its fluctuation become higher, whereas the droplet sizesget smaller. It is also shown that the magnitudes of those parameters are smoothed out by dispersion whenthe droplets move downstream as well as outwardly. The atomization process is significantly influencedby the injection pressure rather than the traveling distance in the experimental condition presented. Key Words: Liquid-rocket Engine(액체로켓엔진), Injector(인젝터), Spray Droplet(분무액적), Dual-modePhase Doppler Anemometry(이중모드 위상도플러속도계)

A Study on the Analysis of Temperature Field of Bubbly Flow Using Thermo-sensitive Liquid Crystals

Particle Image Thermometry(PIT) with liquid crystal tracers is used for visualizing and analysis of the bubbly flow in a vertical temperature gradient. Quantitative data of the temperature were obtained by applying the color-image processing to a visualized image, and neural-network was applied to the color-to-temperature calibration. This paper describes the method, and presents the transient mixing temperature patterns of the bubbly flow.

Study on Heat-Loss-Induced Self-Excitation in Laminar Lifted Jet Flames

We experimentally investigated lifted propane jet flames diluted with nitrogen to obtain flame-stability maps based on heat-loss-induced self-excitation. We found that heat-loss-induced self-excitations are caused by conductive heat loss from premixed flame branches to trailing diffusion flames as well as soot radiation. The conductive-heat-loss-induced self-excitation at frequencies less than 0.1 Hz is explained well by a suggested mechanism, whereas the oscillation of the soot region induces a self-excitation of lift-off height of the order of 0.1 Hz. The suggested mechanism is also verified from additive experiments in a room at constant temperature and humidity. The heat-loss-induced self-excitation is explained by the Strouhal numbers as a function of the relevant parameters.