Parasitic heating effects in high frame rate laser imaging experiments

Abstract

The number of applications using high frame rate imaging in combustion research has grown rapidly in recent years. Enabled by continuous improvements in laser power, a wide range of diagnostics have been developed to measure velocity, species concentration, and temperature. Growing attention is focused on measurements near surfaces, e.g., to gain better insight into transient boundary layer flows in internal combustion engines. During such experiments, laser light is used to illuminate the gas phase region above the surface, but often the laser beam is terminated into the surface directly. Thus, laser operation at several kilohertz and power levels in the range of 10–100 W raise concerns about heating the surface and altering the conditions in the gas phase. In other words, the non-intrusive properties of laser diagnostics might not be guaranteed under such conditions. We have investigated the effect of heating by high repetition rate lasers by measuring the temperature of an exposed metal surface with an infrared sensor and by various simulation approaches. The current results show a modest but noticeable influence of laser heating.