Local instantaneous heat flux measurements in an internal combustion engine using a MEMS sensor

Abstract

• Local instantaneous heat flux was clearly measured using a resistance-type sensor. • Local instantaneous heat flux exhibited a strong cycle-to-cycle variation. • Influence of turbulent eddy on heat flux was detected experimentally. • Local heat transfer coefficient also exhibited a strong cycle-to-cycle variation. Wall heat transfer is one of the most important aspects of internal combustion engines. In this study, the local instantaneous heat transfer characteristics were investigated using an originally developed thin-film resistance-type sensor. The sensor, which was fabricated by micro-electro-mechanical systems (MEMS) technology, had advantages in the sensitivity, the spatial resolution, and the number of measurement points compared with conventional sensors. The MEMS sensor could clearly detect the cycle-by-cycle heat flux. Consequently, it was found that the local instantaneous heat flux had a strong cycle-to-cycle variability, the magnitude of which was in the order of 0.1–1 MW/m 2 , not only in fired operations but also a motored operation. The heat transfer coefficients also exhibited a strong cyclic variability with a magnitude of 0.1–1 kW/(m 2 ⋅K). These results indicated that the heat transfer characteristics could not be properly evaluated only by the conventional analysis based on the ensemble-averaged data. Additionally, it was found that the heat fluxes at the adjacent points exhibited similar but different values, indicating that there were turbulent eddies of sub-millimeter scale and they affected the local heat transfer. Since the local instantaneous heat transfer had quite different characteristics from the average, advanced design and control based on the understandings of the local instantaneous characteristics will be need for the further improvement of the engine’s thermal efficiency.