Zhiyao Yin

Characterization of a Single-Nozzle FLOX® Model Combustor Using kHz Laser Diagnostics

A single-nozzle FLOX® model combustor was used to produce a confined, premixed CH4-air flame with an equivalence ratio of ϕ = 0.74 and a jet exit velocity of vjet = 150m/s with a preheat temperature of T0=300°C. For the first time for this combustor, surface thermometry was performed on the chamber walls. In addition, particle imaging velocimetry (PIV) and planar laser-induced fluorescence of hydroxyl radical (OH PLIF) were acquired simultaneously in this flame at 5 kHz repetition rate. The interface between burnt and unburnt gas mixture were identified from instantaneous OH PLIF images and were compared with corresponding PIV results for flame-turbulence interaction analysis. Combustion instabilities were analyzed via proper orthogonal decomposition and phase-averaged flow field and OH distribution. A pronounced flapping motion of the jet was identified and its impact on the recirculation of hot burnt gas was characterized.Copyright

Experimental Study Of Transient Mechanisms Of Bi-Stable Flame Shape Transitions In A Swirl Combustor

Sudden changes of flame shape are an undesired, yet poorly understood feature of swirl combustors used in gas turbines. The present work studies flame shape transition mechanisms of a bistable turbulent swirl flame in a gas turbine model combustor, which alternates intermittently between an attached V-form and a lifted M-form. Time-resolved velocity fields and two-dimensional flame structures were measured simultaneously using high-speed stereo-particle image velocimetry (PIV) and planar laser-induced fluorescence of OH (OH-PLIF) at 10 kHz. The data analysis is performed using two novel methods that are well adapted to the study of transient flame shape transitions: First, the linear stability analysis (LSA) of a time-varying mean flow and second, the recently proposed spectral proper orthogonal decomposition (SPOD). The results show that the transitions are governed by two types of instability, namely a hydrodynamic instability in the form of a precessing vortex core (PVC) and a thermoacoustic (TA) instability. The LSA shows that the V-M transition implies the transient formation of a PVC as the result of a self-amplification process. The V-M transition, on the other hand, is induced by the appearance of a TA instability that suppresses the PVC and thereby modifies the flowfield such that the flame re-attaches at the nozzle. In summary, these results provide novel insights into the complex interactions of TA and hydrodynamic instabilities that govern the shape of turbulent swirl-stabilized flames. [DOI: 10.1115/1.4037724]

Wall temperature measurements in gas turbine combustors with thermographic phosphors

Phosphor thermometry has been developed for wall temperature measurements in gas turbines and gas turbine model combustors. An array of phosphors has been examined in detail for spatially and temporally resolved surface temperature measurements. Two examples are provided, one at high pressure (8 bar) and high temperature and one at atmospheric pressure with high

Investigation of confined turbulent jet flames using kHz-rates

An atmospheric, single-jet combustor with rectangular confinement was previously developed based on the FLOX concept. In this study, premixed, preheated H2-air and CH4-air turbulent jet flames were stabilized in this combustor. Self-sustained jet oscillation was observed in both non-reacting and reacting cases. A 3-D and periodic jet flapping is identified via proper orthogonal decomposition (POD) of various 2-D views of the flow field, measured by particle imaging velocimetry (PIV). The frequency of the oscillations and couplings between different Eigenmodes are determined based on results from PIV at 5 kHz repetition rate. The influence of jet flapping on combustion stability is examined in detail using simultaneous PIV/OH chemiluminescence imaging and PIV/planar laserinduced fluorescence of OH radicals (OH PLIF) at 5 kHz repetition rate. The up/down and expand/contract motions of the lateral recirculation zone (LRZ) due to jet flapping is found to modify the flame shape and flame lift-off height. Such variations are traced to the transformation of low-speed regions in the junction of the back flow and the jet. These regions contain counter flows and vortices with relatively long flow residence time and can therefore enhance the mixing between recirculated hot burned gas and fresh fuel-air mixtures. In some cases, the jet flapping is also found to cause temporary local extinction of the flame, due to reduced entrainment of burned gas. However, the flame is able to recover as the jet flaps away from combustor chamber and reopens the back flow channel.

Investigation of Confined Turbulent Jet Flames Using kHz-Rate Diagnostics

An atmospheric, single-jet combustor with rectangular confinement was previously developed based on the FLOX concept. In this study, premixed, preheated H2-air and CH4-air turbulent jet flames were stabilized in this combustor. Self-sustained jet oscillation was observed in both non-reacting and reacting cases. A 3-D and periodic jet flapping is identified via proper orthogonal decomposition (POD) of various 2-D views of the flow field, measured by particle imaging velocimetry (PIV). The frequency of the oscillations and couplings between different Eigenmodes are determined based on results from PIV at 5 kHz repetition rate. The influence of jet flapping on combustion stability is examined in detail using simultaneous PIV/OH chemiluminescence imaging and PIV/planar laserinduced fluorescence of OH radicals (OH PLIF) at 5 kHz repetition rate. The up/down and expand/contract motions of the lateral recirculation zone (LRZ) due to jet flapping is found to modify the flame shape and flame lift-off height. Such variations are traced to the transformation of low-speed regions in the junction of the back flow and the jet. These regions contain counter flows and vortices with relatively long flow residence time and can therefore enhance the mixing between recirculated hot burned gas and fresh fuel-air mixtures. In some cases, the jet flapping is also found to cause temporary local extinction of the flame, due to reduced entrainment of burned gas. However, the flame is able to recover as the jet flaps away from combustor chamber and reopens the back flow channel.