Thermodynamic performance calculation and test verification of gas–liquid two-phase water ramjet engine

Underwater gas–liquid two-phase propulsion technology is an emerging propulsion method that offers high efficiency and unrestricted navigation speed. The integration of this technology into water ramjet engines can significantly enhance propulsion efficiency and holds substantial potential for broad applications. However, forming a gas–liquid two-phase flow within the nozzle requires introducing a large amount of rammed seawater. At this time, there is a complex phase transition problem of combustion products in the combustion chamber, which makes the thermodynamic calculation for gas–liquid two-phase water ramjet engines particularly challenging. This paper proposes a thermodynamic calculation method for gas–liquid two-phase water ramjet engines, based on the energy equation for gas–liquid two-phase flow and traditional thermodynamic principles, enabling thermodynamic calculations under conditions of ultra-high water-fuel ratios. Additionally, ground ignition tests of the gas–liquid two-phase engine were conducted, yielding critical engine test parameters. The results demonstrate that the gas–liquid two-phase water ramjet engine achieves a high specific impulse, with a theoretical maximum specific impulse of up to 7000 (N·s)/kg. The multiphase flow effects significantly impact engine performance, with specific impulse losses reaching up to 25.86%. The error between the thrust and specific impulse in the ground test and the theoretical values is within 10%, validating the proposed thermodynamic calculation method as a reliable reference for further research on gas–liquid two-phase water ramjet engines.