Quantitative Ion Probe Measurements for Application in a Rotating Detonation Engine

Abstract

Rotating detonation engines (RDEs) are characterized by extremely high temperatures and pressures, with operating frequencies on the order of several kilohertz. This creates an environment that is challenging to implement research diagnostics. The two most common diagnostics implemented in RDEs operating at speeds capable of defining the detonation wave are dynamic pressure transducers and ion probes. In the case of dynamic pressure transducers, hardware cost and excessive temperatures often dictate remotely coupled transducers, such as a semi-infinite tube pressure configuration in order to improve survivability. Ion probes, on the other hand, are much more robust and can be installed directly within the combustion annulus. However, the information obtained by ion probes in RDEs has been largely qualitative, with their primary use being wave tracking for speed and directionality. This paper presents methodology for determining quantitative ion concentrations from raw ion probe current–voltage data, using known geometry and appropriate electrostatic probe theory. Data are presented from a combustion-driven shock tube, demonstrating applicability of various probe theories and providing comparisons with values determined from a Zeldovich–Neumann–Döring simulation using the Shock and Detonation Toolbox. Results are considered from the perspective of future implementation of a flush-mounted device within the combustion annulus of an RDE.