Abstract <p>This paper discusses a method of increasing the thermodynamic efficiency of a jet engine by modifying the engine nozzle of classic design. The modified engine has a dual-circuit nozzle. Hydrogen is supplied to its outer circuit as an additional heat carrier. Increased thermal efficiency is achieved by utilizing the heat released in the inner circuit of the nozzle. Numerical simulation has shown that the thermal efficiency is enhanced in this case by almost 10%, and the new nozzle design increases thrust as well. The paper compares classic and modified engine designs based on efficiency, thrust, specific impulse, and nozzle weight change.</p>