Cross-consistency of system and characteristic-field models in a coupled liquid-rocket simulation (Merlin 1D–class case study)

Abstract

Coupled liquid-rocket system models and multidimensional nozzle solvers are usually developed separately; when they are made to share a chamber state, the mass-flow consistency between them is easy to leave unmeasured. We describe a transient LOX/RP-1 open-cycle gas-generator engine architecture - capacitance–inertance liquid feed networks, a compressible gas-flow network, shaft dynamics, multi-layer regenerative wall response, offline equilibrium thermochemistry tables, and orifice injector hydraulics- coupled at analysis stop to an axisymmetric method-of-characteristics (MOC) nozzle field evaluated at the shared chamber stagnation state. A headless extraction harness regenerates all tabulated results from frozen inputs and grades two mass residuals: conservation through the marched nozzle field, and agreement between field and system mass flow. The architecture is demonstrated on a Merlin 1D–class case assembled from public data. On the frozen case, field mass conservation closes to +0.92%, the field–system mass-flow residual is -1.78%, sea-level field thrust is ~831 kN, and engine specific impulse on total propellant flow (~305 kg/s) is ~277.7 s, consistent with the public Merlin-class bands that guided case authoring. The result is a documented, reproducible open-cycle composition in which system–field consistency is measured rather than assumed; the case study is a representative reconstruction, and all artefacts are archived on Zenodo.