• 한국연소학회:학술대회논문집
• /
• 2002.11a
• /
• pp.25-31
• /
• 2002

For the better understanding of the stability of turbulent combustion, more researches on extinction and re-ignition are needed. Flame interactions in non-premixed flame have also not been greatly researched. We made a hybrid twin jet flame, the combinations of diffusion flame and partially-premixed diffusion flame, in a twin jet counterflow configuration. The extinction limits of a crossed twin jet counterflow have been extended in comparison with those of a one-dimensional counterflow because of flame interactions through heat transfer and joint ownership of various radicals. Besides, we have obtain ignition $Damk\"{o}hler$ number by experimental method without external ignition source using the extinction characteristic in a crossed twin jet counterflow flame. From results, we can identify the hysteresis between extinction and ignition $Damk\"{o}hler$ number in S-curve.

• Journal of the Korean Society of Combustion
• /
• v.23 no.1
• /
• pp.21-27
• /
• 2018

The effect of swirl flow structures on combustion dynamics of two interacting, lean-premixed flames was experimentally investigated, with a particular emphasis on swirl numbers and swirl rotational directions. Our results show that the amplitude of limit cycle oscillations is very sensitive to the combination of swirl numbers and rotational directions, while the instability frequency remains nearly unchanged. The counter-rotating cases show significantly lower pressure perturbations, and this behavior appears to be related to the formation of compact interacting zone with higher heat release rate, indicating the presence of increased flame surface wrinkling caused by intense turbulence.

• 한국연소학회:학술대회논문집
• /
• 2003.12a
• /
• pp.195-200
• /
• 2003

A two-dimensional "twin-jet counterflow" burner has been designed for the better understanding of the stability of turbulent flames. This flow system enables one to systematically investigate various effects on non-premixed flames, including the effects of curvature, negative strain, and non-premixed flame interactions. The objective of this study is comparing characteristics of extinction of non-premixed methane flames with that of non-premixed propane flames investigated previously. The extinction limit of non-premixed methane and propane flames can be extended compare to that for the conventional counterflow non-premixed flame because of the existence of petal shaped flame and have same structure. The hysteresis in transition between the petal shaped flame and the curved two-wing flames could be observed. We could find differences between non-premixed methane flame and non-premixe propane flame such as the position of one wing extinction and the regime of one wing extinction.

• Journal of the Korean Society of Combustion
• /
• v.21 no.1
• /
• pp.8-17
• /
• 2016

Downstream interactions between lean premixed flames with mutually different fuels of syngas and $CH_4$ have been numerically investigated particularly on and near lean extinction limits. The interaction characteristics between lean premixed (50% $H_2$ + 50% CO)-air and $CH_4$-air flames were shown to be quite different from those between the same hydrocarbon flames. The lean extinction boundaries were of slanted shape, thereby implying strong interactions. The weaker flames had negative flame speeds on the upper extinction boundaries, whereas the weaker flame speeds on the lower extinction boundaries were both negative and positive. The results also showed that the flame interaction characteristics did not follow the general tendency with the dependency of Lewis number in downstream interactions between the same hydrocarbon flames. Importance of chemical interaction in flame characteristics is discussed in the downstream interactions between lean premixed (50% $H_2$ + 50% CO)-air and $CH_4$-air flames.

• Journal of the Korean Society of Safety
• /
• v.27 no.6
• /
• pp.70-77
• /
• 2012

Experimental investigations were performed to examine the characteristics of propagating flame fronts around multiple bars within a rectangular chamber. The explosion chamber is 400 mm in height, $700{\times}700mm^2$ in cross-section and has a large top-venting area, $A_v$, of $700{\times}210mm^2$. This results in a value of 0.44 for $A_v/V^{2/3}$ and a L/D value of 0.57. The multiple obstacles of length 700 mm with a blockage ratio of 30 % were placed within the chamber. Temporally resolved flame front images were recorded by a high speed video camera to investigate the interaction between the propagating flame and the obstacles. Results showed that the flame propagation speeds before the flame impinges onto the obstacle almost equal to the laminar burning velocity. As the propagating flame impinged on the obstacle, the central region of flame began to become concave, this resulted in the flame deceleration in the region. As the flame interacted with the modified flow filed generated behind the central obstacle, the probability density functions(PDFs) of the local flame displacement speed were extensively distributed toward higher speeds.

• 한국연소학회:학술대회논문집
• /
• 2000.05a
• /
• pp.1-8
• /
• 2000

The effects of nozzle arrangements, nozzle distances and fuel flowrates on the flame stabilities such as flame length, liftoff height and blowout characteristics are investigated experimentally. Three nozzle arrangements - diamond 4 nozzle, linear 5 nozzle, cross 5 nozzle- are used. Flame interactions result in the increase of the blowout flowrates and constant turbulent liftoff heights. The flames separated about 10 nozzle diameters are sustained as nozzle attached flames to the higher fuel flowrates than the other separation cases. Normally flames are extinguished at the lifted states. Blowout flowrates are affected by the nozzle configuration, nozzle seperation distance. Blowout flowrates for the diamond- or cross- shaped nozzle arrangements are parabolic function of nozzle distances. Maximum blowout flowrates for the 5 nozzle configuration case except linear one is about 2.9 times that of single equivalent nozzle case. Turbulent liftoff heights are not function of flowrates for the interacting flames.

• Journal of the Korean Society of Combustion
• /
• v.15 no.1
• /
• pp.38-42
• /
• 2010

Using a counterflow burner, downstream interactions between $CH_4$-air and $H_2/N_2$-Air premixed flames with various equivalence ratios has been experimentally investigated. Flame stability maps on triple and twin flames are provided in terms of global strain rate and equivalence ratio. Lean and rich flammable limits are examined for methane/air and hydrogen/nitrogen/air mixtures over the entire range of mixture concentrations in the interacting flames. Results show that these flammable limits can be significantly modified in the presence of interaction such that mixture conditions beyond the flammability limit can be still burn if it is supported by stronger flame. The experiment also discusses various oscillatory instabilities in a stability map.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.10 no.2
• /
• pp.232-240
• /
• 1986

Extinction characteristics of the two interacting premixed flames are analyzed for the effects of flame stretch and preferential diffusion using large activation energy asymptotic analysis by adopting counterflow system as a model problem. Results show that the flammable limit of the thermally interacting premixed flames is extended compared to the single flame, and the extinction mechanism is classified into weak and strong interactions. As the lewis number of the deficient species increases, the region of strong interaction diminishes which can explain the different characteristics of the extinction boundaries of the lean (rich) methane/air and butane/air flames. The influence of the flame stretch to the interaction boundaries is also studied.

• Journal of the Korean Institute of Gas
• /
• v.17 no.1
• /
• pp.13-18
• /
• 2013

Experimental studies were carried out to investigate the interactions between the propagating flame fronts and different multiple obstacles within an explosion chamber. The explosion chamber is 600 mm in height, $700{\times}700mm^2$ in cross-section and has a H/L value of 0.86. Three different multiple obstacles with the blockage ratio of 0.43 were replaced within the chamber. The results showed that relatively higher local flame displacement speed was observed with the triangular obstacle while the lower was observed with the circular one. It was found that the local flame displacement speeds behind the obstacle were largely dependent on the obstacle types. It was also found that as the flame interacted with the flow field generated behind the obstacle, the probability density functions(PDFs) of the local flame displacement speed were extensively distributed toward higher speeds.

• Journal of the Korean Society of Combustion
• /
• v.16 no.1
• /
• pp.58-65
• /
• 2011

Thermal spray technology has been used in many industrial application. Especially, thermal spray coating have been employed with the purposes of achieving better resistances in abrasion, heat and corrosion. In the previous studies on the thermal spray coating, thermal spray characteristics from the perspective of combustion engineering have not been investigated sufficiently, while the material characteristics of the coated substrates have been investigated widely. In this study, the effect of spray particles on the flame behavior was experimentally investigated. The amount of the injected particles was measured using the light scattering method and the temperature of the particles was estimated using a two-color method. Various flame-spray interactions were observed and it was found that the high temperature zone near the flame is elongated by particles density. Based on these results, the applicability of the light scattering method and the two-color method was discussed.