Oxygen enrichment effects on CH₄-air turbulent flow characteristics in a coaxial swirl burner

ABSTRACT

This paper reports results on the effect of oxygen enrichment on flow and turbulent flames in a coaxial swirl burner. The investigation was performed by S-PIV in CH₄-air-O₂ non-reacting and reacting flows. This work is the continuation of studies carried out previously by the authors on the same burner, with different new operating conditions. The burner consists of 2 concentric tubes, with a swirler located in the annular part through which the oxidant (air-O₂) is supplied. The CH₄ gas is delivered into the central tube and injected radially into the combustion chamber through small holes. The burner is placed in a parallelepiped combustion chamber with a volume of 120×50×50 cm³. The paper reports detailed results on mean velocity fields, profiles of the three velocity components (U,V,W) and velocity fluctuations (U’,V’,W’) in the case of a 150 Nl/min oxidant flow rate, a swirl number Sn = 1.4 and an equivalence ratio Φ = 1. Three cases of O₂ addition were investigated, 21%, 25%, and 30% (in vol.) corresponding to 9.4 kW, 11.7 kW, and 14.5 kW of combustion power, respectively. In-depth analysis of the field velocity differences between reactive and non-reactive cases was carried out and showed a significant difference in flow velocities between reacting and non-reacting flows. The profiles of the mean velocities, fluctuations and velocity decays differed, and higher values were observed in the reacting case. The enrichment of air with oxygen affected the velocity fields and their fluctuations in both distribution and values. The addition of O₂ increased the flame temperature, leading to a greater radial expansion and a reduction in the size of the recirculation zone. The maximum axial velocity increased significantly as a function of the O₂ rate, whereas the swirling velocity varied only slightly. The velocity fluctuation results also revealed a difference in profiles and values depending on O₂ enrichments and locations along the flow.

KEYWORDS:

• Swirling flame
• turbulent flow
• oxygen enrichment
• S-PIV

Acknowledgments

The authors are grateful for the financial support provided by the French Government’s Investissement d’Avenir program LABEX CAPRYSSES, under GrantANR-11-LABX-0006-01. The financial support given by the Tunisian state to the stay of S. Chakchak in France is gratefully acknowledged.

Disclosure statement

No potential conflict of interest was reported by the authors.