• Journal of the Korean Society of Combustion
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• v.22 no.2
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• pp.19-26
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• 2017

An experimental study investigates the flame response characteristics of jet-diffusion flame and premixed flame. The experiment was conducted while varying the amplitude. Flame lengths were quantified for OH chemiluminescence measurement and compared with the result of the flame transfer function. Flame length and flame velocity perturbation were normalized and compared with the result of the flame transfer function. The comparison results appear that velocity perturbation and flame length oscillation of premixed flame show linear behaviors on the other hand jet-diffusion flame, amplitudes are more thant 0.20, shows nonlinear behaviors of flame velocity perturbation and flame length oscillation.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.4
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• pp.494-502
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• 1997

Experiments on corresponding jet flames with stagnant point diffusion flames have been carried out in initial injection periods. A compensated measurement of maximum flame temperature, which is based on the ion signal, has been employed to inspect flame responses to time-varying strain rates. The flame responses are obtained at two conditions for the slowly time-varying strain rate and the case of flame extinction, and analyzed to confirm similarity between a stagnant point diffusion flame and an evolving jet diffusion flame. Nonsteady effects are addressed via the comparison between several time scales. The time variation with low strain rates, in which illustrates the flame behavior of the upper branch far from extinction in the well-known S-curve, is confirmed to produce a quasi-steady flame response through the nonsteady experiments. The time variation with strain rates in the case of flame extinction indicates an unsteady effect of flame response. It is therefore found that the flame responses near jet tip depend on time histories of characterized strain rates in the developing process.

• Journal of the Korean Society of Combustion
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• v.14 no.4
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• pp.48-53
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• 2009

This paper describes the forced flame response in a turbulent premixed gas turbine combustor. The fuel was premixed with the air upstream of a choked inlet to avoid equivalence ratio fluctuations. To impose the inlet flow velocity, a siren type modulation device was developed using an AC motor, rotating and static plates. Measurements were made of the velocity fluctuation in the nozzle using hot wire anemometry and of the heat release fluctuation in the combustor using chemiluminescence emission. The test results showed that flame length as well as geometry was strongly dependent upon modulation frequency in addition to operating conditions such as inlet velocity. Convection delay time between the velocity perturbation and heat release fluctuations was calculated using phase information of the transfer function, which agreed well with the results of flame length measurements. Also, basic characteristics of the flame nonlinear response shown in the current test conditions were introduced.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.11a
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• pp.415-418
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• 2011

It is critical to assess the characteristics of flame response to pressure perturbations for the understanding of nonlinear combustion instabilities. Previous studies can be grouped into flame response upon perturbed, fresh air and fuel mixture, and flame response directly perturbed from longitudinal waves. The present study presents experimental methodology for the understanding of the flame response exposed to transverse acoustic waves generated by loud speakers.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.32 no.6
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• pp.413-420
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• 2008

The unsteady heat release characteristics play a significant role in combustion instabilities observed in low emissions gas turbine combustors. Such combustion instabilities are often caused by coupling mechanisms between unsteady heat release rates and acoustic perturbations. A generalized model of the turbulent flame response to acoustic perturbations is analytically formulated by considering a distributed heat release along a curved mean flame front and using the flame's kinematic model that incorporates the turbulent flame development. The effects of the development of flame speed on the flame transfer functions are examined by calculating the transfer functions with a constant or developing flame speed. The flame transfer function due to velocity fluctuation shows that, when a developing flame speed is used, the transfer function magnitude decreases faster with Strouhal number than the results with a constant flame speed at low Strouhal numbers. The flame transfer function due to mixture ratio fluctuation, however, exhibits the opposite results: the transfer function magnitude with a developing flame speed increases faster than that with a constant flame speed at low Strouhal numbers. Oscillatory behaviors of both transfer function magnitudes are shown to be damped when a developing flame speed is used. Both transfer functions also show similar behaviors in the phase characteristics: The phases of both transfer functions with a developing flame speed increase more rapidly than those with a constant flame speed.

• Journal of the Korean Society of Combustion
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• v.13 no.2
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• pp.1-6
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• 2008

An experimental study of the flame response in a turbulent premixed combustor has been conducted with room temperature, atmospheric pressure inlet conditions using premixed natural gas. The fuel is premixed with the air upstream of a choked inlet to avoid equivalence ratio fluctuations. Therefore the observed flame response is only the result of the imposed velocity fluctuations, which are produced using a variable speed siren. Measurements are made of the velocity fluctuation in the nozzle using hot wire anemometry and of the heat release fluctuation in the combustor using chemiluminescence emission. The results are analyzed to determine the phase and gain of the flame transfer function as a function of the modulation frequency. Of particular interest is the effect of flame structure on the flame response predictions and measurements. The results show that both the gain and the phase of flame transfer function are closely associated with the flame length and structure, which is dependent upon the upstream flow perturbation as well as equivalence ratio in the current study.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.612-616
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• 2017

An experimental study investigates the flame response characteristics of non-premixed flame and premixed flame. Air was used as the oxidant. Hydrogen($H_2$)/methane($CH_4$) was used as the fuel, and the mixing ratio of the fuel was 50/50%. Flame response characteristics for various velocity perturbations were experimented. The flame images was acquired using the OH fluorescence measurement and the images were digitized using MatLab code. The results of the premixed flame show that flame perturbation increases as the oscillation amplitude increases. As the amplitude increases, the gain value of the flame transfer function is observed to be a linear behavior. The flame length of a nonpremixed flame decreases as the oscillation amplitude increases. Also, it was confirmed that the gain value according to the amplitude behaves nonlinearly.

• Journal of the Korean Society of Combustion
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• v.16 no.1
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• pp.30-35
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• 2011

This study has been mainly motivated to numerically investigate the transient flame response to pressure oscillations in the gaseous hydrogen - liquid oxygen flames at supercritical pressures. The present analysis is based on the real-fluid transient flamlet model and the flame field is acoustically perturbed only by the sinewave oscillations in the frequency range from 1,000 Hz to 5,000 Hz. Based on numerical results, the detailed discussions are made for the flame response characteristics and the transient flamelet response associated with the high-frequency combustion instability in the liquid propellant rocket engines.

• Proceedings of the Korea Institute of Fire Science and Engineering Conference
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• 1997.11a
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• pp.590-597
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• 1997

In this work, a new type of UV flame detection system was developed. In order to measure the performance of UV flame detector, various kinds of experiments was performed. The results show that the maximum response time of the UV flame detector is 0.2 seconds when the detection distance is one meter The advantages of this system include wide area, high speed response and high sensitivity. After testing the W flame detector in engine compartment it detected fire within 0.09 seconds and extinguished within 5 seconds. Hence, the UV flame detector can be applied in automatic fire suppression system for automobiles.

• Journal of Mechanical Science and Technology
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• v.15 no.5
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• pp.623-629
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• 2001

The PSC (Propagation of Surfaces under Curvature) algorithm is adapted to the simulation of a flame propagation in a premixed medium including the effect of volume expansion across the flame front due to exothermicity. The algorithm is further developed to incorporate the flame anchoring scheme. This methodology is successfully applied to numerically simulate the response of an anchored V-flame to two strong free stream vortices, in accord with experimental observations of a passage of Karman vortex street through a flame. The simulation predicts flame cusping when a strong vortex pair interacts with flame front. In other words, this algorithm handles merging and breaking of the flame front and provides an accurate calculation of the flame curvature which is needed for flame propagation computation and estimation of curvature-dependent flame speeds.