Investigating the effect of local addition of hydrogen to acoustically excited ethylene and methane flames

Abstract

While lean combustion in gas turbines is known to reduce NOx, it makes combustors more prone to thermo-acoustic instabilities, which can lead to deterioration in engine performance. The work presented in this study investigates the effectiveness of secondary injection of hydrogen to imperfectly premixed methane and ethylene flames in reducing heat release oscillations. Both acoustically forced and unforced flames were studied, and simultaneous OH and H atom PLIF (planar laser induced fluorescence) was conducted. The tests were carried out on a laboratory scale bluff-body combustor with a central V-shaped bluff body. Two-microphone method was used to estimate velocity perturbations from pressure measurements, flame boundary images were captured using high speed Mie scattering, while global heat release fluctuations were determined from OH* chemiluminescence. The results showed that hydrogen addition considerably reduced heat release oscillations for both methane and ethylene flames at all the forcing frequencies tested, with the exception of methane flames forced at 315 Hz, where oscillations increased with hydrogen addition. The addition of hydrogen reduced the extent of flame roll-up for both methane and ethylene flames, however, this reduction was larger for methane flames. NOx exhaust emissions were observed to increase with hydrogen addition for both methane and ethylene flames, with absolute NOx concentrations higher for ethylene flames, due to higher flame temperatures.

Influence of hydrogen content and injection scheme on the describing function of swirled flames

“…In the second one, designated as PH, a pilot hydrogen jet is used. In this latter case, Hussain et al [32] found that small hydrogen jets injected radially outward at the base of the bluff body where the flame is anchored considerably reduces heat release rate oscillations of a nonswirling methane/air flame at the forcing frequencies 30 and 255 Hz for all perturbation levels tested. In their experiments the heat release rate is deduced from the OH * emission intensity but the level of premixing of hydrogen with the main methane/air combustible mixture is not characterized.…”

Experimental Study of Biogas–Hydrogen Mixtures Combustion in Conventional Natural Gas Systems

“…In recent times, enriched natural gas combustion behavior has been widely studied. Hydrogen injection into conventional gas fuels reduces heat release oscillations and improves flame stability [20][21][22], while enhancing turbulent explosion parameters [21]. It has, indeed, been noticed that with 5% hydrogen, the flame expands greatly, inhibiting combustion instability [23].…”

Experimental investigation of transient ignition dynamics of hydrogen enriched methane diffusion impinging flames

“…al. [10] investigated the secondary injection of hydrogen to imperfectly premixed methane and ethylene flames in a bluff-body combustor under acoustic perturbations. It is found that adding hydrogen can help to reduce the heat release oscillations and thus combustion instability.…”