• Proceedings of the KSME Conference
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• 2007.05b
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• pp.3264-3269
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• 2007

Combustion instability is a serious obstacle for the lean premixed combustion of gas turbines, and can even cause fatal damage to the combustor and the entire system. Thus, improved understanding of the mechanisms of combustion instability is necessary for designing and operating gas turbine combustors. In this study, in order to understand the instability phenomena, an experimental study was conducted in a rearwardstep dump combustor with LPG and air. The fluctuations of pressure and heat release were measured by piezoelectric pressure sensor and High speed Intensified Charge Coupled Device (ICCD) camera respectively. Various types of combustion modes occurred in accordance with the equivalence ratio and the fuel supplying conditions. The unmixedness of the fuel and air can be controlled by changing the mixing distance ($L_{fuel}$). It is found that the unmixedness of the fuel and air affects the characteristics of flame behavior and pressure fluctuations in a lean premixed flame.

• 한국연소학회:학술대회논문집
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• 2002.06a
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• pp.133-139
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• 2002

The lean premixed technique has been proven very efficient in reducing NOx emissions from gas turbine combustors. However combustion instability is susceptible to occur in lean premixed combustor. So laboratory-scale dump combustor was used to understanding the underlying mechanisms causing combustion instabilities. In this study, tests were conducted at atmospheric pressure and inlet air was up to $360^{\circ}C$ with natural gas. The observed instability was a longitudinal mode with a frequency of ${\sim}341.8Hz$. At selected unstable conditions, phase-resolved OH chemiluminescence images were captured to investigate flame structure with various equivalence ratio. Combustion instability was observed to occur at higher value of equivalence ratio(>0.69). This study was performed to investigate the effects of equivalence ratio and fuel split measuring NOx and acoustic wave. The results reveal the effect of fuel-air unmixedness on lean premixed combustor.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.8 s.239
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• pp.963-970
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• 2005

The combustion instability of turbulent flames is the most important problem of the gas turbine combustor. Thus improved understanding of mechanisms of combustion instability is necessary for the design and operation of gas turbine combustors. In this study, the cause of the combustion instability in a rearward-step dump combustor was investigated with respect to the fuel flow modulation; choked fuel flow, unchoked fuel flow and fully premixed mixture flow. We observed various types of combustion instabilities with respect to the change of equivalence ratio, fuel flow conditions and fuel injection location. Particularly in the unchoked fuel flow condition, it was found that the oscillation time of combustion instability is strongly related to the convection time of the fuel and that the pressure fluctuation in a lab-scale combustor is highly related to the vortex and the equivalence ratio fluctuations due to fuel flow modulation and unmixedness of the fuel and air.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.9
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• pp.658-665
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• 2009

Lean premixed combustors are used for significant NOx reduction which one of issues in current gas turbine combustor. This study was investigated to estimate the effects of the unmixedness of fuel-air, equivalence ratio on the instability mechanism, NOx emission and combustion oscillation in a lean premixed combustor. The experiments were conducted in a dump combustor at atmospheric pressure conditions using methane as fuel. The swirler angle was $45^{\circ}$, the degrees of fuel-air mixing were 0, 50 and 100 and inlet temperature was 650K. The equivalence ratio was ranging from 0.5 to 0.8. This paper shows that NOx emission was increased when the degree of fuel-air mixing is increased in same equivalence ratio and when equivalence ratio is increased. And the range of the combustion instability was enlarged as a function of increasing of the degree of fuel-air mixing.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.10
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• pp.911-918
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• 2013

The combustion characteristics of an EV (Environmental Vortex) burner (double-cone burner) adopted in a gas turbines are numerically investigated. The mixing of fuel and air is analyzed for reduction of NO emission. To predict the correlation between NO emission and fuel-air mixedness, 1-step and 2-step chemistry models are adopted. The results calculated by 1-step chemistry showed that NO emissions increased by 2% in the case of degraded mixedness and by 169% in the case of improved mixedness, where the temperature in the flame zone was overestimated upstream of the cone. However, the corresponding results calculated by 2-step chemistry showed that NO emission increased by 3% and decreased by 5%, where the flame zone was not formed inside the cone. The latter results agree well with the experimental ones indicating an increase of 63% and decrease of 11% in the respective cases. Despite quantitative errors, NO emissions can be predicted reasonably by the application of the 2-step chemistry model adopted here and design modification of burner for NO reduction can be proposed based on the numerical data.