Experimental Study of EGR Dilution and O₂ Enrichment Effects on Turbulent Non-Premixed Swirling Flames

ABSTRACT

This paper presents experimental results of the effects of CO₂ and H₂O dilution on CH₄-air flames enriched by oxygen. The study focuses on pollutant emissions, flame stability through the determination of liftoff heights and flow fields by LDV measurements. Different parameters of the burner are studied such as the swirl number, the global equivalence ratio, and the fractions of O₂, H₂O, and CO₂ in the mixture. The fraction of diluents varies from 0% to 20%, O₂ enrichment from 21% to 30% (in vol.), and the swirl number from 0.8 to 1.4. The experiments are carried out on a coaxial swirled burner placed in a vertical combustion chamber. The flame is visualized by the chemiluminescence technique on OH* in order to locate the flame front. Measurements of combustion products such as NOx, CO, and CO₂ are done using a HORIBA PG250 multi-gas analyzer. Flow fields are measured by LDV measurement for the longitudinal velocity component and its fluctuations. Results show that the CO₂ and H₂O dilution influences significantly the flame characteristics. With dilution the liftoff height increases but the flame remains stabilized. With O₂ enrichment the liftoff height decreases and flame stability is enhanced. If we therefore want to dilute more, we should enrich with oxygen. The increase of dilution rate induces a decrease in NOx emission and exhaust gas temperature and an increase in CO emissions. LDV measurements showed the longitudinal velocity distribution of flow and its fluctuations in reactive and non-reactive conditions. Note that the presence of the flame induces an increase in the longitudinal velocity downstream of the flow due to the expansion of gases.

KEYWORDS:

• Swirling flame
• turbulent flame
• oxygen enrichment
• CO₂ and H₂O dilution
• pollutant emissions

Acknowledgments

The authors are grateful for the financial support of this work provided by the French Government’s Investissement d’Avenir program: LABEX CAPRYSSES, under GrantANR-11-LABX-0006-01