Analysis of Highly CO₂-Diluted Oxy-propane Flames Stabilized over a Multihole Burner of a Model Gas Turbine Combustor

Abstract

Premixed oxy-propane flames are investigated numerically in a multihole model gas turbine combustor at various inlet mixture compositions over a range of equivalence ratios (Ø: 0.241−0.500), oxygen fractions (OF: 32.4−60.0%), and adiabatic flame temperatures (T ad : 1600−1900 K) at a constant bulk throat velocity of 5.2 m/s. The flames in multihole combustors are highly influenced by their corresponding adiabatic flame temperatures. Similar flame shapes are observed at constant T ad , where cases with (Ø = 0.241, OF = 60%) and (Ø = 0.50, OF = 32.4%) both represent lifted flames at T ad = 1600 K, anchored flames in (Ø = 0.276, OF = 60%) and (Ø = 0.50, OF = 36.6%) at T ad = 1750 K, and anchored stronger flames in cases (Ø = 0.313, OF = 60%), (Ø = 0.392, OF = 50%), and (Ø = 0.50, OF = 40.8%) at T ad = 1900 K. Flames in a multihole combustor are characterized by the presence of an outer recirculation zone (ORZ) only. In comparison with a swirlstabilized combustor in identical inlet conditions, flames in a multihole combustor demonstrate a lower Damkoḧler number (Da), higher flame thickness, elevated pattern factor, and increased CO emission. Due to the reduced vorticity level because of the absence of swirl motion, the multihole flames have higher axial temperature than the swirl-stabilized ones.

Stability and Emission Characteristics of a Stratified Hydrogen-Enriched Oxy-Methane Flame on a Multihole Burner: An Experimental Study

“…The cylindrical reaction sheet between them shifts to a blue color and extends axially all the way up to the combustor exit, indicating that the reaction zone is substantially extended. It is important to note here that the bulk flow in micromixer combustors is inherently axial, i.e., these combustors are not designed to induce any swirl motion . Swirl could have been beneficial in this case to stir the flow and enhance the mixing between the core flame and CRZ, thus providing oxygen from the lean core flow to the rich CRZ.…”

“…The poor interaction between the wall region and core flow is evident in Figure a as well. The concentration of CO along the combustor centerline increases gradually as Z / D is increased because slow and insufficient mixing occurs between the CO-rich wall region and the lean core flow . If the bulk flow motion had incorporated any swirl or large-scale vorticity that would stir the flow, the abundant oxygen in the lean core flow could have aided in oxidizing the CO in the rich wall region, leading to an improved overall combustor performance.…”

“…Because of the lower vorticity level of micromixer flames in the absence of any swirl motion, they have greater axial temperatures than swirl-stabilized ones. Moreover, micromixer flames exhibit lower Damköhler number, larger flame thickness, higher pattern factor, and greater CO emissions compared to swirl flames under identical inlet conditions …”

“…Moreover, micromixer flames exhibit lower Damkoḧler number, larger flame thickness, higher pattern factor, and greater CO emissions compared to swirl flames under identical inlet conditions. 24 In a very relevant study, Hussain et al 25 examined the stability and morphology of fully premixed hydrogen-enriched oxymethane flames (CH 4 /H 2 /O 2 /CO 2 ) under high CO 2 dilution conditions in a micromixer-like model gas-turbine combustor. They reported that hydrogen enrichment enhanced flame stability, which allowed for reducing the oxygen fraction (OF � volumetric percentage of O 2 in the O 2 /CO 2 diluted oxidizer) down to a record-low value of 13% at HF = 65%.…”

“… 23 Flames in micromixer combustors are characterized by having a corner recirculation zone (CRZ) only; i.e., the inner recirculation zone typical of swirl-stabilized flames is absent. Because of the lower vorticity level of micromixer flames in the absence of any swirl motion, 24 they have greater axial temperatures than swirl-stabilized ones. Moreover, micromixer flames exhibit lower Damköhler number, larger flame thickness, higher pattern factor, and greater CO emissions compared to swirl flames under identical inlet conditions.…”