High-precision 2D surface phosphor thermometry at kHz-rates during flame-wall interaction in narrow passages

Abstract

This work demonstrates high-speed 2D wall temperature measurements occurring during flame-wall interaction (FWI) within a narrow channel. Such measurements are essential to understand transient wall heat transfer and flame behavior occurring within micro-combustors and designated engine crevices. Wall temperature is measured using the phosphor Bismuth-doped Scandium vanadate (ScVO4:Bi3+). ScVO4:Bi3+ exhibits a short phosphorescence lifetime (2 microseconds at room temperature), enabling kHz measurement rates. ScVO4:Bi3+ also exhibits a high temperature sensitivity, which yields single-shot precision less than 0.5 K within the temperature range of 295 - 335 K. A frequency-doubled Ti:Sapphire laser emitting light at 400 nm is used to excite ScVO4:Bi3+, and wall temperature is measured within a 22 x 22 mm2 region with 380 micrometer spatial resolution. Phosphor thermometry and CH* imaging are combined at 1 kHz to measure the spatiotemporal dynamics of the flame and wall temperature (Twall) within a 2 mm crevice passage in a fixed volume chamber designed for heat transfer studies. Measurements describe Twall signatures associated with transient FWI events, including unique Twall features associated with wrinkled flame fronts. For our operating conditions, Twall associated with flame cusps consistently exhibit temperatures 5 - 20 K lower than flame crest regions. The most extreme difference is seen for large cusp formation, where local wall cooling is noticeable at the trough of the flame cusp. This cooling feature may be caused by intrinsic flame-flow instabilities, which locally and temporally cool the wall.