Role of H₂/CO Addition to Flame Instabilities and Their Control in a Stepped Microcombustor

ABSTRACT

The effect of H₂/CO addition on flame dynamics of propane-air mixtures in a stepped microcombustor with heat recirculation was investigated experimentally. Unstable flame propagation regimes and their transition modes were observed for a range of mixture velocities (5–8 m/s) and equivalence ratios (0.6–0.95). Up to 60% H₂ addition to lean propane-air mixtures helps improve the flame stability range in the combustor. The suppression of these flame instabilities with H₂ addition is attributed to the increase in the overall mixture reactivity and burning velocity. The enhancement in OH intensity with H₂ addition indicated a change in the elementary reactions, thereby affecting the flame dynamics. Contrary to H₂ addition, CO addition does not show any noticeable effect on the formation of stable flame modes. The change in mixture properties and burning velocity leads to a change in the flame behavior and alters the heat release rate due to H₂ addition to propane-air mixtures. A higher percentage of H₂ addition led to the reappearance of the unstable (rotating) flames in the microcombustor. Intrinsic flame instabilities appeared at higher H₂ percentages due to differential diffusion and increased thermal-wall coupling effects.

KEYWORDS:

• Oscillating flames
• suppression of flame instabilities
• micro-combustion
• premixed flames
• stepped microcombustor

Nomenclature

FREI	=	Flame repetitive extinction and ignition
b	=	Distance between the combustor and cup, mm
TEG	=	Thermoelectric generator
TPV	=	Thermophotovoltaic
UAV	=	Unmanned aerial vehicle
Vin	=	Inlet mixture velocity, m/s

Greek letters

ϕ	=	Equivalence ratio
ɷ	=	Frequency, Hz

Acknowledgments

This work has been supported by the Science and Engineering Research Council, Department of Science and Technology, Government of India through project SR/S3/COMB-0001/2014. Financial assistance by the Government of India in the form of a fellowship for Senior Research Fellow (SRF) is also sincerely acknowledged.

Supplementary material

Supplemental data for this article can be accessed on the publisher’s website.

Additional information

Funding

This work was supported by the Ministry of Human Resource Development [Senior Research Fellow]; Science and Engineering Research Council [SR/S3/COMB-0001/2014].