F. S. Frolov

Numerical simulation of momentum transfer from a shock wave to a bubbly medium

Based on the system of equations of two-phase compressible viscous flow, we performed a two-dimensional numerical simulation of momentum transfer by a shock wave propagating from a gas to a continuous aqueous medium or an aqueous medium with air bubbles. When a shock wave impinges on a continuous aqueous medium, the incompressible liquid is set in motion by gas overpressure after the reflection of the shock wave from the gas-liquid interface; however, when a shock wave impinges on a bubbly aqueous medium, the compressible liquid is set in motion due to the penetration of a shock wave into it. Parametric calculations have shown that momentum transfer from a shock wave to a bubbly fluid can be accompanied by dynamic effects, which ensure that the momentum transferred to the bubbly liquid for some time by far exceeds the momentum transferred to a continuous liquid, all other things being equal. These dynamic effects can be used to develop energy-efficient hydrojet propulsion units.

Cyclic deflagration-to-detonation transition in the flow-type combustion chamber of a pulse-detonation burner

The possibility of realization of a rapid cyclic deflagration-to-detonation transition (DDT) with a frequency of up to 2 Hz under conditions of high-velocity flow (∼10 m/s) and separate supply of the combustible mixture components (methane and air) in a tube, 5.5 m in length and 150 mm in diameter, with an open end at a low ignition energy (∼1 J) is for the first time demonstrated. It is shown that such a tube with turbulizing obstacles of special shape and placement can ensure reliable DDT at a distance of 3–4 m from the ignition source within ΔτDDT ≤ 20 ms after ignition. The results will be used in the development of a new type of industrial burner—a pulse-detonation burner for high-rate heating and fragmentation, combining thermal and shock-wave (mechanical) impacts on the treated object.

Pulse-detonation burner unit operating on natural gas

The possibility of controlled cyclic deflagration-to-detonation transition within a length of 2.5–3.0 m in an open-end tube (94 mm in diameter) with separate continuous supply of natural gas and air was demonstrated for the first time. Based on experimental studies, a workable pulse detonation burner, a prototype of new generation of industrial burners, was developed. It can produce a combined effect on the objects blown on with combustion products—shock-wave (mechanical) and thermal.

Simulation of the autoignition and combustion of n-heptane droplets using a detailed kinetic mechanism

The autoignition and combustion of n-heptane droplets are simulated using a detailed kinetic mechanism. A mathematical model, based on first principles, contains no adjustable parameters. The burning rate constants for the combustion of droplets are calculated over a wide range of pressures, temperature, fuel-to-oxidizer equivalence ratios of the gas-droplet suspension, and droplet diameters. The calculated and measured delay times of autoignition of droplets are compared. The calculation results agree well with the available experimental data. The detonability of gas-droplet suspensions with partial pre-evaporation of fuel is estimated.

Autoignition and combustion of hydrocarbon-hydrogen-air homogeneous and heterogeneous ternary mixtures

A numerical simulation of the ignition and combustion of hydrocarbon-hydrogen-air homogeneous and heterogeneous (gas-drop) ternary mixtures for three hydrocarbon fuels (n-heptane, n-decane, and n-dodecane) is for the first time performed. The simulation is carried out based on a fully validated detailed kinetic mechanism of the oxidation of n-dodecane, which includes the mechanisms of the oxidation of n-decane, n-heptane, and hydrogen as constituent parts. It is demonstrated that the addition of hydrogen to a homogeneous or heterogeneous hydrocarbon-air mixture increases the total ignition delay time at temperatures below 1050 K, i.e., hydrogen acts as an ignition inhibitor. At low temperatures, even ternary mixtures with a very high hydrogen concentration show multistage ignition, with the temperature dependence of the ignition delay time exhibiting a negative temperature coefficient region. Conversely, the addition of hydrogen to homogeneous and heterogeneous hydrocarbon-air mixtures at temperatures above 1050 K reduces the total ignition delay time, i.e., hydrogen acts as an autoignition promoter. These effects should be kept in mind when discussing the prospects for the practical use of hydrogen-containing fuel mixtures, as well as in solving the problems of fire and explosion safety.

Correlation between Drop Vaporization and Self-Ignition

A parametric analysis of numerical solutions to problems of vaporization and self-ignition of liquid hydrocarbon drops was performed, and a new criterion determining the conditions of drop self-ignition was suggested. According to this criterion, self-ignition at a given reduced distance from the drop begins when the required reduced gas temperature and equivalence ratio are reached. A new model of heating and vaporization of drops in dense gas suspensions was suggested. The model was verified in multidimensional calculations of self-ignition and combustion of drop clouds. Calculations showed that the model correctly described the phenomenology of local formation and anisotropic propagation of self-ignition waves in suspensions of drops in gases.

Momentum transfer from a shock wave to a bubbly liquid

The transfer of momentum from shock waves of various intensities (from 0.05 to 0.5 MPa) to a water column containing air bubbles of a mean diameter of 2.5 mm is studied both experimentally and by numerical simulation. The experiments are performed in a vertical hydrodynamic shock tube with a rectangular cross section of 50 × 100 mm and a length of 1980 mm. The tube consists of a 495-mm-long high-pressure section, 495-mm-long low-pressure section, and 990-mm-long test section filled with water and equipped with a bubble generator. Experiments have demonstrated that, as the gas content in the water increases from 0 to 30 vol %, the momentum transferred from the shock wave to the bubbly water increases smoothly, leveling off at a volumetric gas content of 20–25%. The experimental and 2D-simulation dependences of the shock wave velocity and the velocity of the bubbly liquid behind the shock wave front on the volumetric gas content are in close agreement.

Thermal tests of a pulse-detonation high-speed burner

The steady-state temperatures of the elements of a high-speed pulse-detonation burner (HSPDB) running on a natural gas-air mixture were measured in the course of long-term tests of the burner operating in the pulse-detonation mode without forced cooling at a frequency of 2 Hz. Knowledge of the steady-state temperatures is required for the development of an energy-efficient forced cooling system for the HSPDB. The experiments have shown that the maximum steady-state temperature (∼500°C) is reached after approximately 200 s of operation at internal elements of the HSPDB, more specifically, turbulizing obstacles placed in that part of the burner duct through which the detonation wave travels periodically. The HSPDB wall in this part of the burner duct is heated to 420°C within ∼1000 s. In the part of the burner duct through which the deflagration wave travels periodically, the HSPDB walls and internal elements are heated to a steady-state temperature not exceeding 330°C. The results show that the forced cooling of the HSPDB is generally required only for those parts of the burner duct through which the detonation wave passes periodically.

Formation of nitrogen oxides in detonation waves

Based on detailed kinetic calculations and experimental data, it is demonstrated that the emission of nitrogen oxides from detonation burner units (DBUs) is significantly lower than that from powerful conventional burners with similar characteristics. Under certain conditions, realized largely in DBUs with rotating detonation, the main component of the nitrogen oxides may turn out to be N2O.

Promotion of the self-ignition of fuel–air mixtures with mechanoactivated Al (Mg)–MoO3 particles

The ignition delay times of heptane–air and diesel oil–air mixtures with and without additives of mechanoactivated Mg–MoO3, Al–MoO3, and Mg–fluoroplastic nanopowders are measured using a rapid-mixture-injection setup. At temperatures below a certain threshold value, the metal–MoO3 additives produce practically no effect on the ignition delay time, whereas at higher temperatures, these additives sharply reduce the ignition delay time, down to the resolution time of the experimental method. The promoting efficiency of the small heterogeneous additives tested is many times superior to that of the known homogeneous promoters. Magnesium–fluoroplastic additives are demonstrated to produce no promoting effect on the ignition of the fuel–air mixtures studied. The mechanism of the action of the heterogeneous additives on the gasphase self-ignition of fuels is discussed.