aerospace Article Numerical Investigation on the Thermal Behaviour of a LOx/LCH 4 Demonstrator Cooling System Daniele Ricci * , Francesco Battista and Manrico Fragiacomo   Citation: Ricci, D.; Battista, F.; Fragiacomo, M. Numerical Investigation on the Thermal Behaviour of a LOx/LCH 4 Demonstrator Cooling System. Aerospace 2021, 8, 151. https://doi.org/10.3390/ aerospace8060151 Academic Editor: Konstantinos Kontis Received: 14 April 2021 Accepted: 24 May 2021 Published: 27 May 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). CIRA, Centro Italiano Ricerche Aerospaziali, Via Maiorise, 81043 Capua, Italy; f.battista@cira.it (F.B.); m.fragiacomo@cira.it (M.F.) * Correspondence: d.ricci@cira.it; Tel.: +39-0823-623096; Fax: +39-0823-623100 Abstract: Reliability of liquid rocket engines is strictly connected with the successful operation of cooling jackets, able to sustain the impressive operative conditions in terms of huge thermal and mechanical loads, generated in thrust chambers. Cryogenic fuels, like methane or hydrogen, are often used as coolants and they may behave as transcritical fluids flowing in the jackets: after injection in a liquid state, a phase pseudo-change occurs along the chamber because of the heat released by combustion gases and coolants exiting as a vapour. Thus, in the development of such subsystems, important issues are focused on numerical methodologies adopted to simulate the fluid thermal behaviour inside the jackets, design procedures as well as manufacturing and technological process topics. The present paper includes the numerical thermal analyses regarding the cooling jacket belonging to the liquid oxygen/liquid methane demonstrator, realized in the framework of the HYPROB (HYdrocarbon PROpulsion test Bench) program. Numerical results considering the nominal operating conditions of cooling jackets in the methane-fuelled mode and the water-fed one are included in the case of the application of electrodeposition process for manufacturing. A comparison with a similar cooling jacket, realized through the conventional brazing process, is addressed to underline the benefits of the application of electrodeposition technology. Keywords: liquid rocket engine; numerical analyses; thermal control; cooling jacket design; regener- ative cooling; methane transcritical behaviour; electrodeposition technology; brazing process 1. Introduction In the last few years, an increasing interest has arisen in the utilization of the LO X /CH 4 propellant combination for space propulsion applications as testified by the efforts spent by several academic and research institutions, international agencies and private companies. The utilization of the LO X /CH 4 combination for space propulsion applications provides many advantages, as indicated by several authors [1–3]: • high specific impulse; • thrust-to-weight ratio performances; • good cooling capability; • engine reusability and throttlability; • fewer storage, handling and insulation concerns; • reduced pollution impact on ground, atmosphere and space; • compatibility with ISRU (in situ resource utilization) purposes for lunar/Martian missions. These capabilities result in a large number of applications and missions enabled by methane-based propulsion systems, from in-space systems (landing or descent ve- hicles, service modules, etc.) to space launchers (main stages or upper stages). In fact, oxygen/methane couple represents a potential candidate to substitute hypergolic and solid propellants in the future. Thus, its versatility makes methane a good candidate for several applications, from in-space propulsion systems (service modules, landing or descent vehicles, and ascent stages) to accessing to space (first stages of launchers or upper Aerospace 2021, 8, 151. https://doi.org/10.3390/aerospace8060151 https://www.mdpi.com/journal/aerospace