Operational issues in premixed combustion of hydrogen-enriched and syngas fuels

• The stability of different syngas blends was tested and compared with methane.
• H2 and CO addition displaced the stability range towards leaner conditions.
• Results revealed that syngas flames are more prone to flashback.
• Syngas flames with high H2 content displayed higher pressure fluctuations.
• Evidence of coupling mechanism between flashback and instability was found.

The growing interest in the use of syngas, as a means to reduce fossil fuel consumption and CO2 emissions, has promoted many works focused on evaluating their combustion characteristics before their use in existing combustors, generally optimized for conventional fuels. Although the effect of fuel composition on the stability range (flashback and blowout) has been analyzed in a wide number of previous studies, much less attention has been devoted to other issues, such as the relation between flashback and combustion instabilities. The present work is, therefore, focused on analyzing the main concerns in syngas combustion: stability range, combustion instabilities and pollutant emissions, also specifically addressing the relation between pressure fluctuations and flashback appearance.The results obtained revealed that the fuel composition has an important effect on the stability range, especially on flashback appearance. However, different trends were observed not only as a function of composition but also as a function of burner configuration. As a consequence, although some approximations, such as the definition of a critical Damköhler number, seemed to give quite accurate predictions of the stability range for a certain range of fuels or configurations, a thorough analysis should be made for each fuel composition before using it in a given burner configuration. In addition, in fuels with high hydrogen content, under certain circumstances, evidence of the existence of a triggering mechanism between pulsating flashback episodes and thermo-acoustic instabilities was found. This result has a high practical importance since, although thermo-acoustic instabilities had been analyzed in methane flames throughout many previous works, their appearance in syngas flames, where they can be also triggered by flashback events, was clearly less tested. Finally, the effect of fuel composition on pollutant emissions has been also analyzed.