Design and Performance Analysis of an Additively-Manufactured 316L Small-Scale Rocket Engine and Cooling Hardware

A coupled applied and fundamental investigation was conducted on the use of metal additive manufacturing for propulsion applications. The design, manufacturing, and performance analysis of a bench-scale additively-manufactured, water-cooled, bi-propellant gas rocket engine test article is demonstrated. The method of characteristics was employed to design an optimally-expanded diverging nozzle contour for a desired exit Mach number of 1.95, and an active cooling scheme was developed using both numerical heat transfer correlations and computational analysis to optimize channel geometry for both heat transfer performance and additive manufacturing. The integrated additively-manufactured chamber and nozzle are fabricated from stainless steel 316L via selective laser melting on a Renishaw AM400 laser powder bed machine located at The University of Texas at San Antonio. The bi-propellant gas ethylene/oxygen test article was designed for operation with a chamber pressure of 100 psig and an oxidizer-fuel ratio of 2.85. Instrumentation incorporated into the test article include temperature and pressure sensors to assess total heat load experienced during hot firing as well as mass flow rates to determine specific impulse and thrust. The design, manufacturing, and testing process in this project required overcoming several challenges associated with laser powder bed fusion manufacturing for propulsion applications, including mitigating inadvertent heat treatment during the printing process, optimizing the printing parameters to minimize printed material porosity, and minimizing pressure loss in small-diameter channels. Outcomes of this project include improving the quality and functionality of future AM builds, as well as characterization of the effects of thermal management strategies on the degradation and performance of next-generation additively-manufactured test articles, and increasing our understanding of the feasibility and longevity of AM materials when subjected to extreme temperatures.