Experimental Investigation of Flame-Wall Interaction by Laser-based Diagnostics

• Main Author: Kosaka, Hidemasa
• Format: Others
• Language: en
• Published: 2018
• Online Access: https://tuprints.ulb.tu-darmstadt.de/8409/8/Dissertation_cover.pdf; Kosaka, Hidemasa <http://tuprints.ulb.tu-darmstadt.de/view/person/Kosaka=3AHidemasa=3A=3A.html> (2018): Experimental Investigation of Flame-Wall Interaction by Laser-based Diagnostics.Darmstadt, Technische Universität, [Ph.D. Thesis]

Flame quenching resulting from flame-wall interactions (FWIs) is important in several thermochemical processes of practical relevance, such as internal combustion engines. Even though FWIs are restricted to regions close to walls of a combustion chamber, they are crucial for wall heat fluxes and unburned hydrocarbon emissions. This experimental work is intended to investigate parametric sensitivities that influence flame quenching at walls and to better understand the influence of non-adiabaticity upon the flame structure. This work uses quantitative and semi-quantitative laser-based diagnostics with high temporal and spatial resolution simultaneously. Experiments are performed on a generic burner with side-wall quenching configurations, where a branch of a V-flame interacts with a laterally oriented wall. Laminar and turbulent boundary conditions are generated for various wall temperatures and two different fuels (methane and dimethyl ether). To investigate the influence of wall heat flux on flame quenching, coherent anti-Stokes Raman spectroscopy (CARS) and phosphor thermometry are combined. From the measurements, gas and wall temperature profiles, wall heat fluxes and quenching distances are deduced and correlated. A further measurement of thermochemical states that provide the opportunity to look at the flame dynamics with flame chemistry. The simultaneous measurement of CARS (for the gas temperature) and laser-induced fluorescence (LIF) of carbon monoxide (CO) (for the CO concentration) are applied. Above all, an influence of the time scales of heat transfer on CO chemistry is shown. Furthermore, simultaneous planar LIF of the formaldehyde molecule and the hydroxyl radical are used to image local heat release rate (HRR) distributions. In the turbulent case, flame fluctuations prevail in the FWI zone and are analyzed statistically regarding flame curvature. The correlation of heat release rate, flame curvature and wall-normal distance is investigated using the instantaneous HRR images for different wall temperatures and equivalence ratios. Finally, the feasibility study of the near-wall Raman spectroscopy is carried out. Raman spectroscopy is a promising technique to quantify combustion-related species simultaneously. However, especially near the wall, scattering and reflections from the wall are even higher than that of the other measurement techniques. The purpose of this feasibility study is to characterize the Raman signal quality near the wall. The resulting signal-to-noise ratio is found to be suitable for further measurements.