Volume-resolved gas velocity and spray measurements in engine applications

Abstract

The ability to visualize in-cylinder phenomena in a three-dimensional (3D) manner is critical to further understand the complex physical and chemical processes within internal-combustion (IC) engines. Recently, plenoptic imaging techniques have been introduced to engine studies because they enable 3D measurements using a promising and simple single-camera setup. The fundamental concept is to record both the origin and direction of each light ray into a single light-field image by inserting a micro-lens array in front of the photosensor. Therefore, a single image contains enough information to reconstruct the 3D volume. In this study, we present the implementation of a plenoptic technique that allows 3D measurements of fuel-spray structure, as well as three-dimensional, three-component (3D3C) particle tracking velocimetry (PTV) of engine in-cylinder air flow. Flow-spray interactions and the impact on the 3D geometry of fuel sprays were investigated with single-shot plenoptic imaging. Volume-illuminated fuel sprays from a multi-hole injector were examined in an optically accessible four-valve gasoline direct-injection engine. The impact of air flows during the intake and compression strokes on the shape of the fuel plumes could readily be observed for individual sprays without averaging. The air flow was measured in a free jet flow and a steady-state engine flow bench employing a 3D3C PTV algorithm that analyzed volume-resolved images taken with a plenoptic camera. Silicone seed oil droplets were added to the air flows and were illuminated by the volume-expanded beam of a double-pulsed laser. Mie scattering from the droplets was recorded by the plenoptic camera, which was operated in double-frame mode. Results from the 3D3C PTV measurements were compared to two-dimensional (2D) planar particle-image velocimetry (PIV) and demonstrate the capability of the 3D velocimetry approach, presently delivering averaged flow fields.