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The physical and mathematical model for simulating combustion and detonation of fuel mixture in the semi-confined gas volumes above the free surface of water is applied for modeling the transient two-phase reactive flow in the gas cavity under the bottom of a ship/boat. With the proper organization of the combustion/detonation process in the gas cavity, thermal expansion of combustion products can provide an additional lifting force that reduces the area of contact of the boat bottom with water, as well as a propulsive force caused by the overpressure of combustion/detonation products on redans—vertical sections of the boat bottom. The model is validated on the set of laboratory experiments with pulsed combustion of propane–air mixture in a semi-closed gas cavity. The model is shown to predict satisfactorily the arising lifting and propulsive forces acting on the volumes, the time histories of pressure in the volumes, and the dynamics of flame and gas–water interface motion during combustion in the volumes. For further model validation in terms of its scaling capability, a set of preliminary experiments with a larger-scale (by a factor of at least 5) towed boat with a bottom gas cavity were conducted on open water. In the experiment, the hydrogen–air mixture was ignited and burned in the bottom gas cavity in a pulsed mode. These experiments confirmed that pulsed combustion of fuel–air mixture in a gas cavity under the boat bottom creates positive propulsive and lifting forces acting on the boat. Moreover, in some experiments a considerable increase in the propulsive force was registered due to flame acceleration causing a higher overpressure in the cavity. The elevated values of the propulsive force in these conditions can be treated in favor of a pulsed detonation mode, which will be studied later. [ABSTRACT FROM AUTHOR]

A mathematical model for simulating combustion and detonation of a fuel–air mixture in the gas cavity above the free water surface is developed. The model is based on solving the conservation equations of mass, momentum, and energy for a two-phase reacting gas–water medium with the phases treated as interacting interpenetrating continua having their own values of velocity, temperature, and turbulence characteristics. The model is validated by laboratory experiments. The test rig included a transparent cylindrical tube with one closed-end, a pool with an optically transparent window, as well as power, ignition, control, and measurement systems. The tube was vertically immersed with its open end in water and filled with a gaseous explosive mixture. In the experiments, a stoichiometric propane–air mixture was ignited and burned in the semi-closed 60 mL cylindrical volume above the free surface of water. The model is shown to predict satisfactorily the lift force acting on the tube, the time history of pressure in the volume, and the dynamics of the flame and gas–water interface motion during combustion in the volume. The model is intended to be applied for the design of boats with propulsion solely by combustion/detonation of fuel–air mixture in cavities constructed into a bottom surface of the boat. This propulsion system replaces conventional propellers, thereby reducing hydrodynamic resistance. [ABSTRACT FROM AUTHOR]

A new experimental method for evaluating the detonability of fuel–air mixtures (FAMs) based on measuring the deflagration-to-detonation (DDT) run-up distance and/or time in a standard pulse detonation tube (SDT) is used to rank gaseous premixed and non-premixed FAMs by their detonability under substantially identical thermodynamic and gasdynamic conditions. In the experiments, FAMs based on hydrogen, acetylene, ethylene, propylene, propane–butane, n-pentane, and natural gas of various compositions, as well as FAMs based on the gaseous pyrolysis products of polypropylene (PP), are used: from extremely fuel-lean to extremely fuel-rich at normal temperatures and pressures. The concept of equivalent FAMs exhibiting the same or similar detonability under the same conditions is proposed. Equivalent FAMs can be used for predictive physical modeling of detonation processes involving FAMs of other fuels. The ranking of FAMs in terms of their relative detonability allows choosing a propylene FAM for physical modeling of the operation process in the PP-fueled solid-fuel ramjets operating on detonative combustion. [ABSTRACT FROM AUTHOR]

The possibility of organizing a continuous-detonation combustion of a liquid fuel film in an annular combustor of a detonation liquid-propellant rocket engine has been demonstrated. The near-limit mode of the longitudinally pulsating "film" detonation and the continuous spinning "film" detonation modes with one and two detonation waves circulating in the annular gap of the combustor are recorded in the fire tests. [ABSTRACT FROM AUTHOR]

Combustion tests of a ramjet model 1.05 m long and 0.31 m in diameter with an expanding annular combustor operating in the regime of detonation combustion of hydrogen are described. The tests are performed in a short-duration wind tunnel at free-stream Mach numbers of the incoming air flow from 5 to 8 and stagnation temperature of 290 K. Continuous detonation and longitudinally pulsating regimes of hydrogen combustion with characteristic frequencies of 1250 and 900 Hz, respectively, are observed. The maximum measured values of the fuel-based specific impulse and the thrust generated by the engine are 3600 s and 2200 N, respectively. [ABSTRACT FROM AUTHOR]

First experimental investigations were carried out into the detonation combustion of hydrogen in a demonstrator of an original-design air-breathing ramjet while blowing with an air flow at Mach 4 to 8 in an impulse wind tunnel, and for the first time under these conditions, continuous spin and longitudinal pulsed modes of detonation combustion of hydrogen in an annular combustor were detected. [ABSTRACT FROM AUTHOR]

The article discusses research which proposed and tested approaches for fast diagnostics of continuous- and pulse-detonation combustion based on the phenomena of chemiionization and acoustic emission. Topics discussed include examples of the use chemiionization and acoustic diagnostics in firing tests of continuous-detonation combustors operating on air-hydrogen and oxygen-hydrogen mixtures, the uses of the chemiionization probe, and the possible use for active control of detonation combustion.