• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2009.11a
• /
• pp.242-245
• /
• 2009

The effect of fuel composition on flame length was studied in a non-premixed turbulent diluted hydrogen jet with coaxial air. The observed flame length was expressed as a function of the ratio of coaxial air to fuel jet velocity and compared with a theoretical prediction based on the velocity ratio. Four cases of fuel mixed by volume were determined. In the present study, we derived a scaling correlation for predicting the flame length in a simple jet with coaxial air using the effective jet diameter in the near-field concept. The experimental results showed that visible flame length had a good relation with the theoretical prediction. The scaling analysis is also valid for diluted hydrogen jet flames with varied fuel composition.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.15 no.1
• /
• pp.355-365
• /
• 1991

New definition for the interaction of flames is introduced and interacting turbulent diffusion flames issuing from two rectangular nozzles are investigated on the basis of the definition. Theoretical study through numerical model is carried out and experiment for validation is conducted. The characteristics of interaction due to the variation of major parameters such as nozzle spacing, Reynolds number and nozzle aspect ratio are studied. Results show that strong interaction occurs for small nozzle spacing, small Reynolds number and large aspect ratio. In order of their magnitude, the intensity of interactions on the individual transport mechanism is momentum, heat and mass. It is also found that interaction makes flames longer, tilted and finally merged. Increase of velocities and temperature, decrease of oxygen concentration and depression of turbulence are occurred in the region between flames.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2011.11a
• /
• pp.595-598
• /
• 2011

Supersonic combustion phenomena in the main combustor of a dual combustion ramjet (DCR) engine are studied numerically. Since the supersonic combustion is affected significantly by the compressibility effects parametric studies have been carried out for the constant are length and the divergence angle. Numerical studies with fixed inflow condition for different geometric configurations reveals that the supersonic combustion in DCR combustor has the characteristics of lifting flame, where the lifting flame is maintained near the injector tip for the case of long combustor length with small divergence angle, but the lifting height is significantly increase for large divergence angle resulting flame blow-out of the combustor. Therefore, it is concluded that flame stability should be considered sufficiently in the design o DCR combustor.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2011.04a
• /
• pp.371-374
• /
• 2011

High-resolution numerical study is carried out to investigate the flame stability of the turbulent supersonic combustion in a Dual-Combustion Ramjet (DCR). The auto-ignition in a shear layer between hydrogen/carbon-monoxide syngas and air was studied at elevated enthalpy condition. Comparison of a constant area combustor and a combustor with a small divergence angle shows that the supersonic combustion has a characteristics of the lifted flame and its stability is influenced significantly by the compressibility.

• 한국연소학회:학술대회논문집
• /
• 2014.11a
• /
• pp.395-396
• /
• 2014

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.36 no.6
• /
• pp.639-646
• /
• 2012

The characteristics of autoignited lifted flames in laminar jets of carbon monoxide/hydrogen fuels have been investigated experimentally in heated coflow air. In result, as the jet velocity increased, the blowoff was directly occurred from the nozzle-attached flame without experiencing a stabilized lifted flame, in the non-autoignited regime. In the autoignited regime, the autoignited lifted flame of carbon monoxide diluted by nitrogen was affected by the water vapor content in the compressed air oxidizer, as evidenced by the variation of the ignition delay time estimated by numerical calculation. In particular, in the autoignition regime at low temperatures with added hydrogen, the liftoff height of the autoignited lifted flames decreased and then increased as the jet velocity increased. Based on the mechanism in which the autoignited laminar lifted flame is stabilized by ignition delay time, the liftoff height can be influenced not only by the heat loss, but also by the preferential diffusion between momentum and mass diffusion in fuel jets during the autoignition process.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.36 no.4
• /
• pp.352-356
• /
• 2008

In this study of lifted hydrogen jet with coaxial air, we have experimentally studied the characteristics of stabilization point in turbulent diffusion flames. The objectives are to present the phenomenon of a liftoff height decreasing as increasing fuel velocity and to analyse the flame structure and behavior including liftoff mechanisms. The fuel jet exit velocity was changed from 100 up to 300 m/s and a coaxial air velocity was fixed at 16 m/s with a coflow air less than 0.1 m/s. For the simultaneous measurement of velocity field and reaction zone, PIV and OH PLIF technique was used with two Nd:Yag lasers and CCD cameras. It has been suggested that the stabilization of lifted hydrogen diffusion flames was correlated with a turbulent intensity, $S_t{\sim}u^{\prime}$, and jet Reynolds number, $S_t{\sim}Re^{0.017}_{jet}$.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.21 no.4
• /
• pp.486-493
• /
• 1997

Experimental investigations on the comparison of developments between transient jets and evolving jet diffusion flames have been made in initial injection period. To achieve this experiment, an ignition technique using a residual flame as the ignition source is devised. High speed Schlieren visualizations, and measurements including jet tip penetration velocities and jet widths of the primary vortex are employed to examine the developing processes for several flow conditions. It is seen that the developing behaviors in the presence of flame are greatly different from those in transient jet, and thus the flow characteristics in the transient part are also modified. The discernible differences are shown to consist of the delay of the rollup of the primary vortex, the faster spreading after the rollup due to exothermic expansion, and the survival of only a primary vortex. The growth of primary vortex in the transient jet is properly explained through an impulsively started laminar vortex prior to the interaction. It is also found that the jet tip penetration velocity varies with elapsed time and an increase in Res gives rise to a higher tip penetration velocity.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.36 no.1
• /
• pp.75-81
• /
• 2012

Autoignited lifted flames in laminar jets with hydrogen-enriched methane fuels have been investigated experimentally in heated coflow air. The results showed that the autoignited lifted flame of the methane/hydrogen mixture, which had an initial temperature over 920 K, the threshold temperature for autoignition in methane jets, exhibited features typical of either a tribrachial edge or mild combustion depending on fuel mole fraction and the liftoff height increased with jet velocity. The liftoff height in the hydrogen-assisted autoignition regime was dependent on the square of the adiabatic ignition delay time for the addition of small amounts of hydrogen, as was the case for pure methane jets. When the initial temperature was below 920 K, where the methane fuel did not show autoignition behavior, the flame was autoignited by the addition of hydrogen, which is an ignition improver. The liftoff height demonstrated a unique feature in that it decreased nonlinearly as the jet velocity increased. The differential diffusion of hydrogen is expected to play a crucial role in the decrease in the liftoff height with increasing jet velocity.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.16 no.3
• /
• pp.578-588
• /
• 1992

In order to predict the effect of swirl on the structure of concentric laminar jet diffusion flame, present study examined the effect of swirl on the flame characteristics by numerical numerical analysis through theoretical model. The theoretical model has been developed for the co-axial laminar jet flame such that the fuel and air are supplying with swirl through inner and outer co-axial tube respectively. For the parametric study, swirl number, Reynolds number of fuel and air and directions of swirl are chosen as important parametes. The results of study show that the flame with width and shorter length is formed by larger swirl number. The important factor of the flame shape is the recirculating zone formed around jet axis near the exit of nozzle. In case of weak swirl, the effect of directions of swirl is not appeared. However, for the strong swirl, the flame with shorter length are appeared in case of counter-swirl compared with the case of co-swirl.