Application of an optical emission spectroscopy sensor design to a dual-mode scramjet flowpath

Abstract The feasibility of using optical emission spectroscopy (OES) sensors in dual-mode scramjet engines has been demonstrated previously, but the technology is not yet mature. The main weakness in previous studies has been the reliance on sensitivities specific to sensor locations in a flowpath geometry. To address this, this work presents the design of a custom OES sensor and its application in a dual-mode scramjet geometry. Light collection was implemented in an orientation that matches what is achievable in axisymmetric flowpath geometries, viewing into a flameholding cavity as opposed to across it (direct-cavity angle). A multi-anode photomultiplier tube (MAPMT) detector was used in the OES sensor design, which provided increased light sensitivity and the ability to use multiple channels to resolve spatial or spectral information. The OES sensor implemented a transmission grating to disperse OH* and CH* flame chemiluminescence onto discrete anodes of the detector. Experiments in a dual-mode scramjet facility demonstrated that the sensor was sensitive to changes in flowpath conditions from a variety of axial positions. This is the first study to present the design and characterization of an MAPMT-based OES sensor that is sensitive to changes in local reactant composition in a dual-mode scramjet flowpath. Furthermore, to the authors’ knowledge, it is the first study to explore the potential of an OES sensor for dual-mode scramjet flowpath monitoring with a direct-cavity angle.