Fuel variability effect on flickering frequency of diffusion flames

• Published in: Frontiers in Energy Vol. 3; no. 2; pp. 134 - 140
• Main Authors: LI, Jizhao, ZHANG, Yang
• Format: Journal Article
• Language: English
• Published: Heidelberg Higher Education Press 01.06.2009; SP Higher Education Press; Springer Nature B.V
• Subjects: Chemistry; Combustion; Data collection; diffusion flames; dynamics of combustion; Energy; Energy efficiency; Energy Systems; Experiments; flickering frequency; Flow rates; Frequencies; fuel variability; Gas turbines; Gases; Gravity; Heat transfer; Measurement techniques; Methane; Propane; Research Article; Reynolds number; Studies; Turbines; Velocity; diffusion flames; fuel variability; flickering frequency; dynamics of combustion
• ISSN: 2095-1701; 1673-7393; 2095-1698; 1673-7504
• DOI: 10.1007/s11708-009-0034-9

It is known that fuel variability of different gas suppliers may cause combustion instability in a gas turbine combustor. Mechanisms that control the time scale of the heat release oscillations and acoustic pressure perturbations are both physical and chemical in nature, and thus can be influenced by changes in fuel composition. The intent of this study is to investigate the fuel variability on the flickering frequency of diffusion flames in the hope of understanding some of the fundamental aspects of fuel variability effect on the dynamics of combustion. Experiments were conducted at atmospheric pressure with a matrix of methane and propane blends. An optical fibre system was applied to capture simultaneously the flame flickering at two different light frequencies (430 nm and 516 nm), which provided a means of comparing the chemistry change. It was found that the low frequency oscillation of flow and flame structures depended only weakly on the exit velocities of the fuel, while ambient conditions had a significant effect on flickering frequencies and spectrum. The results of using CH 4 and C 3H 8 as test fuels at different flow rates showed very little variations, with peak frequencies at 11-13 Hz. When the jet flame was not disturbed, harmonics to at least the third mode were obtained in most of these cases. However, the cases which included CH 4/C 3H 8 splits of 90/10, 85/15 and 80/20 by volume showed that unstable flickering frequencies and flame harmonics were not observed. When a mixture of methane/propane at a ratio of 1:1 was used the peak flickering frequency was around 6 Hz, and slight disturbance in the environment would cause the harmonics to disappear. Mechanisms thought to produce changes in the dynamic response and frequency harmonics were discussed.