Characterization of Additive Layer Manufacturing Swirl Burner Surface Roughness and Its Effects on Flame Stability Using High-Speed Diagnostics

Abstract

In this study, two Inconel 625 swirl nozzle inserts with identical bulk geometry were constructed via additive layer manufacturing (ALM) for use in a generic gas turbine swirl burner. Further postprocessing by grit blasting of one swirl nozzle insert results in a quantifiable change to the surface roughness characteristics when compared with the unprocessed ALM swirl nozzle insert or a third nozzle insert which has been manufactured using traditional machining methods. An evaluation of the influence of variable surface roughness effects from these swirl nozzle inserts is therefore performed under preheated isothermal and combustion conditions for premixed methane-air flames at thermal power of 25 kW. High-speed velocimetry at the swirler exit under isothermal conditions gives evidence of the change in near-wall boundary layer thickness and turbulent fluctuations resulting from the change in nozzle surface roughness. Under atmospheric combustion conditions, this influence is further quantified using a combination of dynamic pressure, high-speed OH* chemiluminescence, and exhaust gas emissions measurements to evaluate the flame stabilization mechanisms at the lean blowoff and rich stability limits. Notable differences in flame stabilization are evident as the surface roughness is varied, and changes in rich stability limit were investigated in relation to changes in the near-wall turbulence intensity. Results show that precise control of in-process or postprocess surface roughness of wetted surfaces can positively influence burner stability limits and NOx emissions and must, therefore, be carefully considered in the ALM burner design process as well as computational fluid dynamics (CFD) models.

Emissions Performance of Staged Premixed and Diffusion Combustor Concepts for an NH3/Air Flame With and Without Reactant Humidification

“…Chemiluminescence measurements were obtained at each experimental condition, targeting electronically excited intermediate chemical radicals within the NH3-air air flames. The species investigated were OH* and NH2*, captured using a combination of Phantom v1212 high-speed CMOS camera, Specialised Imaging SIL40HG50 high-speed image intensifier, UV lens (78 mm, f/11), and narrow bandpass filters selected specifically for each species (further information on this facility is found in other works [22]). OH* chemiluminescence images were taken focusing specifically on the well-known A 2 Σ + -X 2 Π OH* system [23] using a 315 nm (±15 nm FWHM) bandpass filter.…”

“…A complementary trend is evident for change in Φ between the reduction of OH* intensity, an increase in NH2*, and a drop in measured exhaust NO concentrations. Using OH* as a generalized marker for heat release [23], the flame structure appears typical for a swirling premixed configuration [22,31], with the flame stabilized around a conical shear layer of zero axial velocity, with central and outer recirculation zones (CRZ and ORZ respectively). There appears to be increased reacting flow in the ORZ -giving a characteristic 'M' flame, compared to the 'V' observed for near equivalent CH4/air flames with this burner [31].…”

Experimental and Kinetic Evaluation of Pressurized Lean Premixed Hydrogen-Air Flame Stability With Carbon Dioxide and Steam Dilution

“…1. The HPGSB-2 is well-characterized in terms of its stable operating limits, fuel flexibility, and emissions [20][21][22][23]. However, this study presents the first use of LPM pure and diluted H 2 -air in this burner.…”

“…However, this study presents the first use of LPM pure and diluted H 2 -air in this burner. Further information regarding this experimental setup can be found in other works [20][21][22][23]. The air mass flow rate was measured via Coriolis flow meter (Emerson CMF050) and then heated before fuel and diluent were injected upstream of the "Premixed Inlet" in Fig.…”

“…Time-resolved OH* chemiluminescence images were captured for each experimental condition system at 90° relative to the axial flow direction. Measurements focused on the wellknown A 2 Σ + -X 2 Π OH* peak at 309 nm [24] OH* measurements were made with an intensified high-speed CMOS camera system as detailed in [21]. The system was operated at 4000 Hz, with an intensifier gate time of 10 μs and constant gain.…”