Experiment study on the combustion performance of hydrogen-enriched natural gas in a DLE burner

The effect of hydrogen enrichment to natural gas swirling flame was experimentally investigated at atmospheric pressure conditions using a radially-staged DLE (Dry Low Emission)burner. The hydrogen volume content was varied as 0%, 5%, 11%, 21% and 26% in the fuel blend to assess that whether it is beneficial or detrimental to combustion characteristics. OH-PLIF (Planar Laser Induced Fluorescence)measurement was performed to examine macro flame topology at both stable combustion conditions. NOx and CO emission was also analyzed. In terms of unstable combustion, pressure fluctuation during combustion instability was monitored by dynamic pressure transducers to characterize the dominant frequency as well as pressure oscillation amplitude. Based on the real time pressure signal, phase-locked PLIF method was utilized to give phase averaged OH images during one thermo-acoustic cycle. The experimental results indicate that the flame shrinks distinctly when the addition of hydrogen is increased to certain content. To be specific, the flame structure changes little as the hydrogen content is lower than 5%, and the flame expanding angle also keeps well. Once the hydrogen concentration is boosted to be over 11%, the flame expands greatly towards the confinement wall. Meanwhile NOx emission increases gradually, but CO emission keeps stable with slightly decrease. The amplitude of the dynamic pressure pulsation reduces with hydrogen addition, but the dominant frequency presents to be irrelevant with hydrogen enrichment during combustion oscillation. It can be concluded that hydrogen addition in the natural gas at this realistic radially staged burner shows potential ability to inhibit combustion instability somehow. The 2D Rayleigh Index distribution then indicates proves that the main circulation zone and flame-wall interaction zone are two regions where local heat release and pressure fluctuation coupled to induce combustion thermo-acoustic problems.