The need to refuel future missions to Mars and the Moon via in situ resource utilization (ISRU) requires the development of LOX/LCH4 engines, which are complex and expensive to develop and improve. This paper discusses how the use of digital engineering—specifically physics-based modeling (PBM)—can aid in developing, testing, and validating a LOX/LCH4 engine. The model, which focuses on propulsion performance and heat transfer through the engine walls, was created using Siemens’ STAR-CCM+ CFD tool. Key features of the model include Eulerian multiphase physics (EMP), complex chemistry (CC) using the eddy dissipation concept (EDC), and segregated solid energy (SSE) for heat transfer. A comparison between the complete GRI 3.0 and Lu’s reduced combustion mechanisms was performed, with Lu’s mechanism being chosen for its cost-effectiveness and similar output to the GRI mechanism. The model’s geometry represents 1/8th of the engine’s volume, with a symmetric rotational boundary. The performance of this engine was investigated using NASA’s chemical equilibrium analysis (CEA) and STAR-CCM+ simulations, focusing on thrust levels of 125 lbf and 500 lbf. Discrepancies between theoretical predictions and simulations ranged from 1.4% to 28.5%, largely due to differences in modeling assumptions. While NASA CEA has a zero-dimensional, steady-state approach based on idealized conditions, STAR-CCM+ accounts for real-world factors such as multiphase flow, turbulence, and heat loss. For the 125 lbf case, a 9.2% deviation in combustion chamber temperature and a 15.0% difference in thrust were noted, with simulations yielding 113.48 lbf compared to the CEA’s 133.52 lbf. In the 500 lbf case, thrust reached 488 lbf, showing a 2.4% deviation from the design target and an 8.6% increase over CEA predictions. Temperature and pressure deviations were also observed, with the highest engine wall temperature at the nozzle throat. Monte Carlo simulations revealed that substituting LNG for LCH4 affects combustion dynamics. The findings emphasize the need for advanced modeling approaches to enhance the prediction accuracy of rocket engine performance, aiding in the development of digital twins for the CROME.

This investigation presents the comprehensive thermo-structural analysis of the propellant tanks utilized in the CROME propulsion system, focused on examining the structural effects caused by the storage of liquid nitrogen, liquid oxygen, and liquid methane. These fluids operate at extremely low temperatures and generate large thermal stress gradients in the tanks, significantly influencing their structural properties. For this reason, it is of vital importance to inspect the generation of mechanical and thermal stresses in the tanks to assess the risk of structural failure. To accomplish this effort, this analysis evaluates the tanks containing liquid nitrogen, liquid oxygen, and liquid methane at pressures of 200.0 psi and 400.0 psi. A coupled finite element analysis was performed in Star-CCM+ to compute the resulting Von Mises stresses under steady-state conditions. These stress results were used to determine the factor of safety in each case, enabling a quantitative assessment of structural integrity in the tanks while operating with cryogenic fluids under different pressure loadings.

This study examines the thermal management of the Centennial Restartable Oxygen Methane Engine (CROME) feed system under two propellant tank pressure conditions: 33 psi (227.5 kPa) and 100 psi (689.5 kPa), at a constant liquid methane flow rate of 0.9 lbm/s (0.4 kg/s). Using the Eulerian Single-Phase (ESP) model, the initial test validated experimental data, showing close agreement in total pressure (experimental: 31 psi; CFD: 33 psi) and temperature measurements (experimental: −287.3 °F and −300 °F; CFD: −299 °F and −294 °F) with deviations of 6.4% and ≤4.1%, respectively. For the second test, a simplified Volume of Fluid (VOF) model was used, adjusted for varying liquid-to-gas volume fractions. The best agreement with experimental data was found with 100% GN2, showing a 3.1 psi pressure rise and a 3.3% error. These findings show the importance of improving thermal management and precision control in cryogenic LOX-LCH4 feedline systems for optimal engine performance. Future research will focus on exploring pressures up to the propellant tank’s maximum rated limit of 400 psi.

This paper presents the flow and flame characteristics of a highly turbulent reactive flow over a backward-facing step inside a windowed combustor. Flow and combustion experiments were performed at Re = 15,000 and Re = 30,000 using high-resolution 10 kHz PIV and 10 kHz PLIF diagnostic techniques. Grid turbulators (Grid) with two different hole diameters (HD of 1.5 mm and 3 mm) and blockage ratios (BR of 46%, 48%, 62%, and 63%) were considered for the turbulence study. Grids introduced different turbulent length scales (L_T) in the flow, causing the small eddies and turbulence intensity to increase downstream. The backward-facing step increased the turbulence level in the recirculation zone. This helped to anchor the flame in that zone. The small HD grids (Grids 1 and 3) produced continuous fluid structures (small-scale), whereas the larger HD grids (Grids 2 and 4) produced large-scale fluid structures. Consequently, the velocity fluctuation was lower (~25.6 m/s) under small HD grids and higher (~27.7 m/s) under large HD grids. The flame study was performed at Φ = 0.8, 1.0, and 1.2 using C-X CH PLIF. An Adaptive MATLAB-based flame imaging scheme has been developed for turbulent reacting flows. Grids 1 and 3 induced more wrinkles in the flame due to higher thermal instabilities, pressure fluctuation, and diffusion under those grids. The flamelet breakdown and burnout events were higher under Grids 2 and 4 due to higher thermal diffusivity and a slower diffusion rate. It was observed that the flame wrinkling and flame stretching are higher at Re = 30,000 compared to Re = 15,000. The Borghi–Peters diagram showed that the flames were within the thin reaction zone except for Grid 1 at Re = 15,000, where flames fell in the corrugated zone. It was observed from PIV and PLIF analyses that Re and L_T mostly controlled the flame and flow characteristics.