Development of an Additively-Manufactured Optical Sensor Interface for Rotating Detonation Flows

An additively manufactured, actively cooled optical sensor interface was developed to enable optically based measurements within the extreme environments of next-generation propulsion systems. The modular plug design incorporates an embedded sapphire window, gas film cooling to protect the window surface from in-chamber combustion gases, and liquid cooling via internal channels to regulate temperatures of the optic and housing assembly. Sapphire enables quantitative, mid-wave infrared (mid-IR) sensing methods that are incompatible with conventionally used quartz windows. A prototype was designed, analyzed with conjugate heat transfer (CHT) simulations, and fabricated with stainless steel 316L using the laser powder bed fusion (L-PBF) process. For expected heat fluxes of around 2 MW/m2, simulations show a maximum temperature of 373 K at the optic, reducing propensity for transmission losses and index-of-refraction shifts associated with increased sapphire temperature. A laboratory-scale, actively-cooled chamber was developed to house a methane-oxygen torch and two optical sensor interfaces to demonstrate window thermal management and mid-IR light transmission.