High-frequency wall heat flux measurement during wall impingement of a diffusion flame

Abstract

The efficiency of internal combustion engines is limited by heat losses to the wall of the combustion chamber. A precise characterization of wall heat flux is therefore needed to optimize engine parameters. However, the existing measurements of wall heat fluxes have significant limitations; time resolution is often higher than the timescales of the physical phenomena of flame–wall interaction. Furthermore, few studies have investigated diesel flame conditions (as opposed to propagation flames). In this study, the heat flux generated by a diffusion flame impinging on a wall was measured with thin-junction thermocouple, with a time resolution of the whole acquisition chain better than 0.1 ms. The effects of variations in ambient gas temperature, injection pressure and injector–wall distance were investigated. Diesel spray impingement on the wall is shown to cause strong gas–wall thermal exchange, with convection coefficients of 6–12 kW/m2/K. Those results suggest the necessity of close-wall aerodynamic measurements to link macroscopic characteristics of the spray (injection pressure, impingement geometry) to turbulence values.