• Proceedings of the KSME Conference
• /
• 2007.05b
• /
• pp.2372-2377
• /
• 2007

Characteristics of turbulent lifted flames in coflow jets with the varying initial temperature have recently been investigated about only propane case diluted by nitrogen. The investigation has firstly improved a premixed flame model and a large scale mixing model among competing theories on the stabilization mechanism of turbulent flame to be suitable for a high temperature condition. In this research, about methane with good availability to apply for a practical combustor as clean fuel, its characteristics of turbulent nonpremixed flame have been studied experimentally. The results have shown an effectiveness of the premixed flame model and the large scale mixing model considered initial temperature variation. Additionally, considering the axial distance where the mean fuel concentration falls below the stoichiometric level along the center line of the jet according to diluting nitrogen, the premixed flame model have more accurately been improved.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.32 no.12
• /
• pp.970-976
• /
• 2008

Characteristics of methane turbulent non-premixed flame have been studied experimentally in coflow jets with initial temperature variation. The results showed that the premixed flame model and the large-scale mixing model for turbulent flame stabilization were effective for methane fuel considered initial temperature variation. Especially, the premixed flame model has been improved by considering nitrogen dilution for the liftoff height of turbulent lifted flame. In estimating blowout velocity and the liftoff height at blowout with the premixed flame model and the large-scale mixing model, the two turbulent models were excellently correlated by considering the effect of physical properties and buoyancy for the initial temperature variation.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 1999.04a
• /
• pp.4-4
• /
• 1999

최근 충남대에서는 다양한 추진제와 연소 조건으로 액체로켓 연소 실험이 진행되고 있으며 그에 비례하여 많은 사고들이 발생하고 있다. 한 예로 GO$_2$/kerosene을 추진제로 하는 노즐삭마 시험용 로켓엔진(추력 1001bf, 연소실 압력 600psia) 개발 중에 화염이 인젝터면에 형성되어 인젝터면을 손상시키는 사고를 여러 번 경험하게 되었다. 본 연구는 인젝터 손상의 원인을 규명하여 안정적인 인젝터 설계에 도움을 주기 위한 목적으로 실험용 동축 인젝터를 제작하여 화염 부상 특성을 실험적으로 연구하였다. 사용된 인젝터는 연료인 Kerosene을 접선형 선회기로부터 90$^{\circ}$의 원뿔 각을 가지고 분무되도록 설계하였으며, 그 주위로 산하제인 GO$_2$가 연소실의 축방향에 수평하게 분무되도록 설계하였다. 2-유체 동축 인젝터의 난류 확산 화염에서 연료와 산화제의 혼합은 화염 특성을 결정하는 주요 변수이므로 인젝터로부터 분무되는 추진제간의 유량을 변화시켜 화염 부상 특성을 연구하였다.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.26 no.1
• /
• pp.125-132
• /
• 2002

An experimental study on the characteristics of stability of propane turbulent nonpremixed jet flames discharged normal to air free-streams with uniform velocity profile is conducted. Experimental observations are focused on the flame shape, the stability considering two kinds of flame, lift-off distance, and the flame length according to velocity ratio. In order to investigate the mixing structure of the flame base at the lower limit, we employ the RMS technique and measure the species concentration by a gas chromatography. In the results of the stability curve and lifted flame, it is fecund that the dependency of nozzle diameter is closely related to the large-scale vortical structure representing counter-rotating vortices pair. Also, the detailed discussion on the phenomenon of blowout due to this large vortical motion, is provided.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.38 no.2
• /
• pp.160-168
• /
• 2010

An experimental study has been conducted to investigate the effects of forcing amplitude on the tone-excited non-premixed jet flame of the resonance frequency. Visualization techniques are employed using the laser optic systems, which are RMS tomography, PLIF and PIV system. There are three lift-off histories according to the fuel flow rates and forcing amplitudes; the regime I always has the flame base feature like turbulent flame when the flame lift-off, while the flame easily lift-off in the regime II even if a slight forcing amplitude applied. The other is a transient regime and occurs between the regime I and regime II, which has the flame base like the bunsen flame of partial premixed flame. In the regime I and II, the characteristics of the mixing and velocity profile according to the forcing phase were investigated by the acetone PLIF, PIV system. Particular understanding is focused on the distinction of lift-off history in the regime I and II.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.27 no.10
• /
• pp.1420-1426
• /
• 2003

The stability of turbulent nonpremixed interacting flames is investigated in terms of nozzle configuration shapes and kind of fuels. Four nozzle arrangements - cross 5, matrix 8, matrix 9 and circle 8 nozzles - are used in the experiment. There are many parameters affecting flame stability in multi-nozzle flames such as nozzle separation distance, fuel flowrates and nozzle configuration etc. Key factors to enhance blowout limit are the nozzle configuration and the existence of center nozzle. Even nozzle exit velocity equal 204 m/s, flame is not extinguished when there is not a center nozzle and s/d=15.3∼27.6 in matrix-8 and circular-8 configurations. At these conditions, recirculation of burnt gas is related with stability augmentation. Fuel mole fraction measurements using laser induced fluorescence reveal lifted flame base is not located at the stoichiometric contour.

• 한국가시화정보학회:학술대회논문집
• /
• 2005.04a
• /
• pp.61-83
• /
• 2005

연소현상의 가시화를 위한 몇 가지 레이저 진단기법의 응용 예를 소개한다. 이에는 유동 가시화를 위한 반응성 Mie 산란, 주화학종의 계측을 위한 Rayleigh 및 Raman 산란, 미소화학종 계측을 위한 레이저유도 형광법, 온도계측을 위한coherent anti-Stokes Raman 산란법 및 매연계측을 위한 광 소멸/산란법 등이 포함된다. 이러한 기법들이 확산화염, 층류 및 난류 부상 화염, 비예혼합 와도 내의 화염전파, 매연생성 등의 연구에 적용되어 물리적 메커니즘을 이해하는데 유용하게 적용된 사례를 보고한다.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.26 no.1
• /
• pp.133-140
• /
• 2002

This article presents an application of a large-scale structural mixing model(Broadwell et at. 1984) to the blowout of turbulent reacting cross flow jets. Experimental observations, therefore, aim to identify the existence of large-scale vortical structure exerting an important effect upon the flame stabilization. In the analysis of common stability curve, it is seen that the phenomenon of blowout are only related to the mixing time scale of the two flows. The most notable observation is that the blowout distance is traced at a fixed positions according to the velocity ratio at all times. Measurements of the lower blowout limits in the liftable flame are qualitatively in agreement with the blowout parameter $\xi$, proposed by Broadwell et al. Good agrement between the results calculated by a modified blowout parameter $\xi$'and the present experimental results confirms the important effect of large-scale structure in the stabilization feature of blowout.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.27 no.8
• /
• pp.1089-1096
• /
• 2003

An experiment was performed to investigate lift-off, blow-off and combustion characteristics of a lifted coaxial diffusion flame according to fuel jet and air velocity. A jet diffusion flame which is attached on the nozzle rim begins to be lifted with increase of air velocity, and finally becomes blow-off at higher air velocity. In experiment, blow-off limit increased with increase of fuel jet velocity, however lift-off occurred at lower air velocity. Flame structure and combustion characteristics were examined by schlieren photos, temperature distributions and emission concentration distributions. Flame temperature became higher at midstream and its RMS became larger at up and downstream with increase of air velocity. Local NO concentration decreased but $CO_2$concentration increased with increase of air velocity, which shows combustion reaction becomes close to be stoichiometric at higher air velocity in spite of lift-off.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.22 no.6
• /
• pp.56-63
• /
• 2018

In low swirl combustors the flame is lifted above the nozzle to achieve balance between the flame speed and velocity field at the exit of the nozzle. Characterization of the flame liftoff height is important because it affects the stability of the combustor and degradation of the nozzle material. In experiments, a counter-intuitive trend of flame liftoff heights with respect to inlet velocities was observed. To elucidate the complicated flow field in a low swirl combustor having swirl vanes and a turbulence generator, a series of numerical simulations of non-reacting flows was conducted by varying the inlet velocity. The flow structures at the exit of the nozzle with respect to the inlet velocities are investigated to support the observation in the experiments.