Simultaneous lateral and endwall high-speed visualization of ignition in a circular shock tube

Abstract

High-speed imaging is an excellent methodology to visualize complex features of a transient flow system. This diagnostic has been utilized in visualizing ignition behavior in shock tubes which are otherwise assumed to undergo homogeneous ignition process. In recent works, endwall high-speed imaging was implemented in shock tubes to study the ignition modes of different fuels, and these works have shown the existence of non-homogeneous ignition under specific conditions. Imaging from endwall provides a two-dimensional radial visualization wherein the depth of field is missing, thus making it difficult to detect and diagnose lateral position of non-homogeneous ignition. In this communication, we report the design and implementation of a novel imaging section which enables simultaneous lateral and endwall imaging by using a longitudinal slit window. In contrast to previous works, the new section maintains the circular structure of the shock wave and allows lateral imaging as far as 300 mm from the shock tube endwall. Representative measurements were carried out with ethanol, methanol and n-hexane to illustrate the potential of this three-dimensional diagnostic and its advantages compared to endwall imaging.