On Pressures in the Liquid Propellant Rocket Engine Part I: An Alternative Calculation Method

Panu Bieneck

2026.079.0008

DOI https://doi.org/10.59332/jbis-079-01-0008

This paper compares two approaches for evaluating liquid propellant rocket engine (LPRE) performance: the established isentropic flow model and a novel method based on Newtonian mechanics. The traditional method uses chamber pressure as the primary variable and predicts critical velocity, pressure ratio for sonic flow and mass flow rate. In contrast, the novel method treats feed pressure and specific volume as primary variables, deriving a transformation equation between feed (pf) and chamber pressures (pc). A key result is the inequality pc < pf , which holds in steady operation and cannot be derived from the established framework. The novel method offers a quantitative tool for analysing experimental data and, with numerical modelling of thermodynamic properties, may also support LPRE design.

Keywords: Liquid Propellant Rocket Engine, Chamber Pressure, Feed Pressure, Novel Calculation Method, Specific Volume