Experimental investigation of the flame characteristics of a fuel mixture with high hydrogen content enriched with oxygen under the externally acoustic enforcement conditions

Abstract

Pollutant emissions are one of the major problems for the World. In this regard, researchers focus on the studies on emission reduction. Hydrogen is an alternative solution for this problem. Hydrogen produces only water as a result of combustion with oxygen. Therefore, this study examines the combustion stability and emissions of a high hydrogen content fuel mixture. The fuel mixture containing 45% H2 by volume was supported with 5% CH4 in order to provide stable combustion. In addition, in order to reduce the instabilities caused by the high laminar burning rate of hydrogen, it was diluted with 50% CO2 which equal volume with the fuel mixture. After the fuel mixture containing 45% H2 - 5% CH4 - 50% CO2 was burned with air containing 21% O2, enrichment was applied at the rates of 24% and 27% O2. The flame that contains different oxygen ratios was acoustically forced through the speakers around the combustion chamber. The stability data, dynamic pressure, and light intensity fluctuation of the flame were recorded under different acoustic resonance frequencies (110 Hz, 190 Hz, 260 Hz). In this way, the oxygen enrichment performance and flame characteristics of hydrogen in a premixed burner, which is promising in zero-emission studies, were investigated. As a result, when the combustion condition of 21% O2 and 24% O2 ratios are compared, the instability increased slightly from 801 Pa to 887 Pa, respectively. However, at 27% O2, the flame could not perform a stable combustion under acoustic enforcement. The flame flashbacked with a dynamic pressure fluctuation of 1577 Pa under an acoustic frequency of 110 Hz. In addition, it was observed that CO emissions have decreased with the increase in oxygen enrichment rate. CO emission measured at 1080 ppm at 21% O2 decreased to 542 ppm and 276 ppm respectively at 24% and 27% oxygen enrichment levels. While NOx emission was measured at 10 ppm in the case of combustion with air, it was observed that decreased to 4 ppm at the rate of 27% O2.