The objective of work outlined in this paper was to prove experimentally the energy efficiency of Zel'dovich thermodynamic cycle (cycle with detonative combustion of fuel) by direct comparison of thrust performances of liquid-propellant rocket engine (LRE) prototypes operating in continuous-detonation and continuous-combustion modes using gaseous hydrogen as fuel and gaseous oxygen as oxidizer. For this purpose, a test rig and two LEE prototypes were designed and fabricated. It has been proved experimentally that Zel'dovich thermodynamic cycle with continuous-detonation combustion of hydrogen oxygen mixture in two different LEE prototypes is more energy efficient than the cycle with continuous constant-pressure combustion of the same mixture, other conditions being equal. Thus, at predetermined limitations on supply pressures of fuel components and at a fixed mass flow rate of fuel mixture the specific impulse of the LRE prototypes operating in the continuous-detonation mode appeared to be 6-8% higher than the specific impulse of the same LEE prototypes operating in the continuous-combustion mode. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.