Heat Flux Temporal Variation and Turbulent Structures on Diesel Flame-Impinged Wall by Comparing High-Speed Infrared Thermography and MEMS Sensor Measurements

For a more detailed understanding of the highly complex mechanism of wall heat transfer during diesel flame impingement, heat flux measurement results obtained using two relatively new approaches—high-speed infrared thermography and a Micro Electro Mechanical Systems (MEMS) heat flux sensor—were compared. Both measurements were conducted on a chamber wall impinged by a diesel flame in a constant-volume combustion vessel under similar experimental conditions.　　High-speed thermography utilizes the world’s fastest infrared camera (TELOPS M3k, 13,000 fps, 128×128 pixels) to capture time-series temperature and heat flux distributions on the wall surface, enabling detailed visualization of near-wall turbulent structures reflected in the heat flux with a spatial resolution of 70 microns (9 mm/128 pixels). The MEMS sensor consists of multiple closely aligned (520-micron spacing) highly sensitive thin-film Resistance Temperature Detectors (RTDs) of 235×235 microns, allowing estimation of near-wall turbulent fluid motion based on cross-correlation analysis of measured heat flux fluctuations.　　Comparing these measurements allows for mutual compensation of their respective limitations: high-speed thermography provides high spatial resolution but limited temporal resolution and quantitative accuracy, while the MEMS sensor offers high temporal accuracy but limited spatial resolution for capturing near-wall turbulence structures.　　The time-series heat flux distribution obtained via high-speed thermography exhibited distinctive radial striped patterns, an increase in their size, and a decrease in their advection velocity, possibly reflecting boundary layer development. Similarly, the heat flux measured by the MEMS sensor showed correlated oscillations between multiple RTDs, a decrease in oscillation frequency, and a reduction in the estimated fluid motion velocity, which correspond well with the trends observed in the high-speed thermography results.