Planar Laser-Induced Fluorescence and Chemiluminescence Analyses of CO2-Argon-Steam Oxyfuel (CARSOXY) Combustion

Strict regulations and acts have been imposed to limit NOx and carbon emissions. The power generation industry has resorted to innovative techniques to overcome such a low level of tolerance. Amongst those in the literature, CO2-argon-steam oxyfuel (CARSOXY) gas turbines have theoretically been proven to offer an economically sustainable solution while retaining high efficiency. Although theoretical studies have characterized CARSOXY, no experimental evidence has been provided in the literature. Therefore, this paper attempts to experimentally assess CARSOXY in comparison to a CH4/air flame. OH* chemiluminescence integrated with OH Planar Laser-Induced Fluorescence (PLIF) imaging has been utilized to study flame stability and flame geometry (i.e., the area of highest heat intensity (AOH¯Max center of highest heat intensity (COH¯Max)) over a range of working fluid Reynolds’ numbers and oxidizing equivalence ratios. In addition, the standard deviation of heat release fluctuations (σOH*/OH¯) has been utilized as the base-criteria to compare the stability performance of CARSOXY to CH4/air combustion. Moreover, turbulence-chemistry interactions have been described using Damköhler numbers and by plotting Borghi regime diagrams. This paper suggests a modified numerical approach to estimate Damköhler numbers and plot regime diagrams for non-premixed combustion by utilizing the Buckingham π theorem based on experimental observations and results. CARSOXY flames showed lower flame intensity than that of the CH4/air flame throughout the entire Re interval by approximately 16%, indicating higher heat release. The Damköhler numbers of the CARSOXY flame were also greater than those of the CH4/air flame in all conditions, indicating more uniform CARSOXY flames. It was found that the tendency of the CARSOXY flame of approaching the concentrated reaction zone is greater than that of the CH4/air flame.

Temperature measurements in a swirling impinging flame by planar laser-induced fluorescence

This article presents the results of approbation of the method for registering temperature distributions based on the planar laser-induced fluorescence of a hydroxyl radical (OH) when the band (1-0) of the A2Σ+–X2Π system is excited. The thermometry is based on the recording the ratio of the radiation intensity of the band (2-0) and the bands (0-0), (1-1). Numerical modelling of fluorescence spectra is performed using the LASKIN program for the most frequent excitation lines Q2(7), Q1(8), R1(14), P1(2). The temperature field of a swirling flame, impinging on a flat cold surface, for H/d = 1, 2 and 3 calibres (where H is the distance between the jet nozzle and the surface, d is the outlet diameter of the nozzle) is obtained. The results of the work demonstrate that when the transition Q1(8) is excited, the ratio of the intensity of fluorescence signals for the band (2-0) and the bands (0-0), (1-1) provides a high sensitivity to temperature and is not significantly affected by fluorescence quenching. The report also concludes that this method can be implemented using single pulsed laser illumination and is effective for the detecting the position of flow recirculation zones and registering hot heat release zones with the combustion products.

Investigation of Hydrogen Content and Dilution Effect on Syngas/Air Premixed Turbulent Flame Using OH Planar Laser-Induced Fluorescence

Syngas produced by gasification, which contains a high hydrogen content, has significant potential. The variation in the hydrogen content and dilution combustion are effective means to improve the steady combustion of syngas and reduce NOx emissions. OH planar laser-induced fluorescence technology (OH-PLIF) was applied in the present investigation of the turbulence of a premixed flame of syngas with varied compositions of H2/CO. The flame front structure and turbulent flame velocities of syngas with varied compositions and turbulent intensities were analyzed and calculated. Results showed that the trend in the turbulent flame speed with different hydrogen proportions and dilutions was similar to that of the laminar flame speed of the corresponding syngas. A higher hydrogen proportion induced a higher turbulent flame speed, higher OH concentration, and a smaller flame. Dilution had the opposite effect. Increasing the Reynolds number also increased the turbulent flame speed and OH concentration. In addition, the effect of the turbulence on the combustion of syngas was independent of the composition of syngas after the analysis of the ratio between the turbulent flame speed and the corresponding laminar flame speed, for the turbulent flames under low turbulent intensity. These research results provide a theoretical basis for the practical application of syngas with a complex composition in gas turbine power generation.

Relative Effects of Velocity- and Mixture-Coupling in a Thermoacoustically Unstable, Partially-Premixed Flame

Combustion instability, which is the result of a coupling between combustor acoustic modes and unsteady flame heat release rate, is a severely limiting factor in the operability and performance of modern gas turbine engines. This coupling can occur through different coupling pathways, such as flow field fluctuations or equivalence ratio fluctuations. In realistic combustor systems, there are complex hydrodynamic and thermo-chemical processes involved, which can lead to multiple coupling pathways. In this study, we use a model gas turbine combustor with two concentric swirling nozzles of air, separated by a ring of fuel injectors, operating at an elevated pressure of 5 bar. The flow split between the two streams is systematically varied to observe the impact on the flow and flame dynamics. High-speed stereoscopic particle image velocimetry, OH planar laser-induced fluorescence, and acetone planar laser-induced fluorescence are used to obtain information about the velocity field, flame, and fuel-flow behavior, respectively. Depending on the flow conditions, a thermoacoustic oscillation mode or a hydrodynamic mode, identified as the precessing vortex core, is present. Our results show that, for this combustor system, changing the flow split between the two concentric nozzles can alter the dominant harmonic oscillation modes in the system, which can significantly impact the dispersion of fuel into air, thereby modulating the local equivalence ratio of the flame. This insight can be used to design instability control mechanisms in real gas turbine engines.