Hydrogen Microjet Research Articles

Взаимодействие круглой микроструи воздуха с коаксиальной (спутной) струей водорода при его горении на сверхзвуковой скорости их истечения

Results of experimental studies of the round air microjet interaction with a coaxial hydrogen jet at its combustion for supersonic speed jets efflux are presented in this work. It is revealed that combustion of the coaxial hydrogen jet with growth of its speed efflux is accompanied by all scenarios, observed at study of the round and plane hydrogen microjets diffusion combustion. However, “bottleneck flame region” undergoes considerable geometrical deformations because of specifics of a flame of a coaxial jet. It is shown that “bottleneck flame region” is transformed from Y-shaped to spherical shape in the activity of growth of a coaxial jet speed efflux. It is found that a round air microjet interaction with a coaxial hydrogen jet at its combustion is accompanied by several new phenomena: existence of cone-shaped area a coaxial jet combustion near a nozzle exit; existence of small-scale supersonic cells on a resultant flame; absence of the hydrogen combustion efflux from combustion region of a coaxial jet near nozzle exit; flame-out from combustion region of a coaxial jet near nozzle exit that leads to hydrogen ignition downstream, its intensive combustion and sharp acoustic noise occurrence; existence of a turbulent flame, to its separation from a nozzle exit and transition to supersonic combustion of a resultant jet.

Diffusion Combustion of a Hydrogen Microjet at Variations of its Velocity Profile and Orientation of the Nozzle in the Field of Gravitation

ABSTRACTExperimental data on diffusion combustion of round hydrogen microjets with a parabolic and a “top-hat” mean velocity profiles at the nozzle exit at different spatial orientation of the microjets are reported. Most of all, we are interested in the behavior of the so-called «bottleneck flame region» of the jet and its contribution to the diffusion combustion. As is found, in the cases of the jet velocity opposite and orthogonal to the direction of the gravitational force, the main features of combustion are practically the same. Otherwise, at the velocity vector matching the direction of the gravitational force, the combustion characteristics become much different. Combustion in the «bottleneck flame region» is found to be more stable at the parabolic profile while the stability of combustion is reduced at the top-hat velocity distribution at the nozzle exit. Then, the flame detachment occurs in the absence of the «bottleneck flame region» and the microjet combustion is terminated at a much higher velocity. An inversion of the dependence l/d = f(U0) is observed at the transition from the parabolic to the top-hat velocity profile of the jet. The ratio of the «bottleneck flame region» size (l) to the nozzle exit diameter (d) is l/d. The nozzle heating is shown to have a profound effect on the microjet combustion.

Micronozzle Chocking under Diffusion Combustion of Hydrogen

The results of experimental investigations of the micronozzle-chocking phenomenon under diffusion combustion of a hydrogen microjet at a high outflow velocity in the case of ignition of hydrogen near the nozzle cut are presented. It is found that the cause of micronozzle chocking is the heating of the nozzle walls from the flame-neck region retained up to transonic velocities and preventing nozzle cooling and the passage of the hydrogen jet to the supersonic-flow velocity. It is shown that hydrogen ignition far from the nozzle cut with a developed hydrogen supersonic flow into the flooded space leads to the disappearance of the flameneck region, flame detachment from the nozzle cut, and, correspondingly, termination of the nozzle heating and the possibility of the microjet coming out at the supersonic-flow velocity for the hydrogen jet. It is established that the flame-neck region is a stabilizing factor for the subsonic combustion of a hydrogen microjet up to transonic velocities. In the second case, the presence of supersonic cells stabilizes the supersonic diffusion combustion of the hydrogen microjet.

Experimental study on diffusion combustion of high-speed hydrogen round microjets

Abstract Experimental data on the phenomenon of nozzle choking at diffusion combustion of a high-speed hydrogen microjet at its ignition close to the nozzle are presented. As is found, such a phenomenon is due to the nozzle heating by the «bottleneck flame region» which is generated at the origin of microjet. This flow region persists up to transonic velocities of the microjet preventing from cooling of the nozzle and the transition to supersonic speed. In the case of hydrogen ignition far from the nozzle exit in supersonic conditions, the «bottleneck flame region» is suppressed, the flame becomes detached from the nozzle which is no longer heated so that the supersonic range is attained. The subsonic combustion of hydrogen microjet is stabilized by the «bottleneck flame region» while the supersonic one becomes more stable at the generation of shock cells. The results of the present study provide new details on the combustion of hydrogen microjets and could by useful for the operation of different burners.

Quasi-monoenergetic proton acceleration from cryogenic hydrogen microjet by ultrashort ultraintense laser pulses

Laser-driven proton acceleration from a micron-sized cryogenic hydrogen microjet target is investigated using multi-dimensional particle-in-cell simulations. With few-cycle (20-fs) ultraintense (2-PW) laser pulses, high-energy quasi-monoenergetic proton acceleration is predicted in a new regime. A collisionless shock-wave acceleration mechanism influenced by Weibel instability results in a maximum proton energy as high as 160 MeV and a quasi-monoenergetic peak at 80 MeV for 1022 W/cm2 laser intensity with controlled prepulses. A self-generated strong quasi-static magnetic field is also observed in the plasma, which modifies the spatial distribution of the proton beam.

Influence of initial and boundary conditions at the nozzle exit upon diffusion combustion of a hydrogen microjet

The objective of this work is an experimental study of the influence of initial and boundary conditions at the nozzle exit upon diffusion combustion of a hydrogen microjet. It is found that the initial mean velocity profile and the presence (or absence) of a material with large heat capacity surrounding the nozzle exit may have a pronounced effect on the flame structure and combustion of the round hydrogen microjet. The rates of fuel consumption (i.e., the efflux velocities of hydrogen) providing diffusion combustion of the round hydrogen microjet, the flame detachment, and the origination of the «bottleneck flame» in the cases of a top-hat and a parabolic mean velocity profiles at the nozzle exit are determined. The variations of the extent of «bottleneck flame» with the hydrogen flow rate are made clear. Also we examine the diminution of the extent of «bottleneck flame» with the growth of hydrogen flow rate in three cases of initial conditions at the nozzle exit.

Experimental Study Of The Diffusion Combustion Of A High-Speed Round Hydrogen Microjet Part 1. Attached Flame, Subsonic Flow

Scenario of subsonic diffusion combustion of a round hydrogen microjet is presented in this work. Stabilization of process of the laminar hydrogen microjet flow and diffusion combustion in region of the «flame bottleneck» is found. The reason of this phenomenon is connected with existence of the toroidal vortex which is promoting as intensification of mixing process of hydrogen with air and at the same time stabilizing a laminar flow of the extended microjet and its laminar diffusion combustion. It is shown that subsonic diffusion combustion of a round hydrogen microjet of is connected with availability of the «flame bottleneck» region in a wide range of a hydrogen consumption, or microjet velocity efflux close to transonic velocity. It is found that heating of a thick-walled micronozzle from «flame bottleneck» region in case of its big thermal capacity has significant effect on characteristics of development of the hydrogen microjet combustion and leads to choked nozzle. It is revealed that the spatial size of the «flame bottleneck» region with growth of a hydrogen consumption at first sharply decreases, and then gradually increases simultaneously with change of the «flame bottleneck» region shape while combustion in this region doesn't stop.

Experimental Study Of The Diffusion Combustion Of A High-Speed Round Hydrogen Microjet Part 2. Lifted Flame, Supersonic Flow

Scenario of supersonic diffusion combustion of a round hydrogen microjet is presented in this work. The main features of supersonic diffusion combustion of a hydrogen round microjet are shown: disappearance of a «bottleneck flame» region, lifted flame from the nozzle exit and existence of supersonic «shock cells» in the lifted turbulent flame. The main reason for this scenario of diffusion combustion connected with a temperature factor is found i.e. with existence of thin-walled micronozzles with a small thermal capacity and a possibility of their quenching that doesn't give the chance to exist of the «bottleneck flame» region at big speeds of a microjet efflux. It is shown that with growth of temperature of a micronozzle heating from the «bottleneck flame» region at the same speed of a microjet efflux growth of its spatial size (l/d) is found.

Особенности диффузионного горения микроструи водорода при различной пространственной ориентации выходного сопла с ударным профилем скорости на его срезе

Особенности диффузионного горения микроструи водорода при различной пространственной ориентации выходного сопла с ударным профилем скорости на его срезе

Экспериментальное исследование диффузионного горения круглой микроструи водорода при ее зажигании вдали от среза сопла

Экспериментальное исследование диффузионного горения круглой микроструи водорода при ее зажигании вдали от среза сопла

Features of diffusion combustion of hydrogen in the round and plane high-speed microjets (part II)

In the second part of the present study, experimental results on the round and plane hydrogen microjets diffusion combustion at various nozzle diameter depending on microjet velocity are shown. Of special interest is the contribution to the combustion process of the so-called «bottleneck flame» region which is observed at diffusion combustion of hydrogen both in the round and plane microjets. The «bottleneck flame» appears as a spherical closed volume of laminar combustion at mixing of the hydrogen microjet with ambient air. This spherical volume is surrounded by a narrow layer of density gradient overcoming which the laminar microjet and its flame become turbulent. A diminution of the «bottleneck flame» with growth of the microjet velocity is revealed.

Influence Of Initial Conditions At The Micro Nozzle Exit On Hydrogen Diffusion Combustion

The purpose of the given work will consist in an experimental study of influence of initial conditions at the micro nozzle exit on hydrogen diffusion combustion. It is shown, that the mean velocity profile and presence/absence of a heatcapacious material at the nozzle exit play an essential role on a flame structure and process of a round hydrogen microjet combustion. Velocity ranges of existence of a round hydrogen microjet diffusion combustion, flame separation and «bottleneck flame» region for a case of a top – hat mean velocity profile at the nozzle and two cases of a parabolic mean velocity profile with presence/absence of a heatcapacious material at the nozzle exit are found. Dependences of the «bottleneck flame» region size from a hydrogen microjet efflux velocity for case of a top – hat mean velocity profile at the nozzle and two cases of a parabolic mean velocity profile with presence/absence of a heatcapacious material at the nozzle exit are shown. Decrements of reduction of the «bottleneck flame» region size with growth of the hydrogen microjet efflux velocity for three situations of changes of initial conditions at the nozzle exit are determined.

Combustion of a high-velocity hydrogen microjet effluxing in air

This study is devoted to experimental investigation of hydrogen-combustion modes and the structure of a diffusion flame formed at a high-velocity efflux of hydrogen in air through round apertures of various diameters. The efflux-velocity range of the hydrogen jet and the diameters of nozzle apertures at which the flame is divided in two zones with laminar and turbulent flow are found. The zone with the laminar flow is a stabilizer of combustion of the flame as a whole, and in the zone with the turbulent flow the intense mixing of fuel with an oxidizer takes place. Combustion in these two zones can occur independently from each other, but the steadiest mode is observed only at the existence of the flame in the laminar-flow zone. The knowledge obtained makes it possible to understand more deeply the features of modes of microjet combustion of hydrogen promising for various combustion devices.

Development of a cryogenic hydrogen microjet for high-intensity, high-repetition rate experiments.

The advent of high-intensity, high-repetition-rate lasers has led to the need for replenishing targets of interest for high energy density sciences. We describe the design and characterization of a cryogenic microjet source, which can deliver a continuous stream of liquid hydrogen with a diameter of a few microns. The jet has been imaged at 1 μm resolution by shadowgraphy with a short pulse laser. The pointing stability has been measured at well below a mrad, for a stable free-standing filament of solid-density hydrogen.

Study on the combustion characteristics of non-premixed hydrogen micro-jet flame and the thermal interaction with solid micro tube

The combustion characteristics of non-premixed hydrogen micro-jet flames in co-flow air were investigated in a wide fuel flow velocity range experimentally and numerically to extend the knowledge on non-premixed micro flame. The direct flame images were captured by a digital reflex camera with long exposure time, and the OH radical distributions in the flames were measured by the laser induced fluorescence technique. The experimental observation shows that the flame height and shape change with the deceasing fuel flow velocity. A detailed chemical reaction mechanism was employed in the numerical computations with considering the heat transfer between gas and solid micro-tube. The computed distributions of OH concentrations agree qualitatively with those obtained by the experiments. The flame structure and thermal interaction between the flame and solid tube were inspected in detail. It was found that the thermal interactions at high, intermediate and low fuel flow velocities are different. The details of the thermal interactions between flames and solid tube are depended on the shape of the micro flame, which essentially affects the temperature distribution.

Diffusion Combustion Of The Round Microjet Mixture Of Hydrogen With Metane, Helium And Nitrogen

The purpose of the given work will consist in an experimental studies of the diffusion combustion features of the hydrogen round microjet mixtures with the metane, helium and nitrogen. It is found, that the mechanism and characteristics of a microjet and a flame evolution at diffusion combustion of the hydrogen mixture with the metane, helium or nitrogen are connected with the «bottleneck» flame area formation, as well as in a situation of a pure hydrogen microjet diffusion combustion. It is revealed, that process of diffusion combustion of a hydrogen / metane mixture in a round microjet is accompanied by stage-by-stage stages of a turbulent flame detachment at preservation of combustion in the «bottleneck» flame area, and, at last extinction of microjet combustion that correlates with combustion process of a similar microjet of pure hydrogen. It is found, that all above-listed stages of a hydrogen / metane mixture combustion are realized in a range considerably smaller speeds of a microjet (200÷500 m/sec), than in a similar situation of a pure hydrogen microjet combustion (600÷800 m/sec). It is shown, that at diffusion combustion of a mixture of hydrogen with metane or helium or nitrogen in a round microjet for stabilization of combustion with growth of a microjet speed it is necessary to increase a portion of hydrogen (or to reduce a portion of an impurity) in a mixture of gases.

Influence of the angle of incident shock wave on mixing of transverse hydrogen micro-jets in supersonic crossflow

A three-dimensional numerical study has been performed to investigate the influence of angle of shock waves on sonic transverse Hydrogen micro-jets subjected to a supersonic crossflow. This study focuses on mixing of the Hydrogen jet in a Mach 4.0 crossflow with a global equivalence ratio of 0.5. Flow structure and fuel/air mixing mechanism were investigated numerically. Parametric studies were conducted on the angle of shock wave by using the Reynolds-averaged Navier–Stokes equations with Menter's Shear Stress Transport turbulence model. Complex jet interactions were found in the downstream region with a variety of flow features depending upon the angle of shock incident. These flow features were found to have subtle effects on the mixing of Hydrogen jets. Results indicate a different flow structure than for a typical micro jet, with the development of shock angle to the flow of the Hydrogen jet. According to the results, without oblique shock, mixing occurs at a low rate. When the intersection of incident shock and the lower surface is at a low angle (15°) of shock incident; significant reduction (up to 30%) occurs in the maximum concentration of the Hydrogen jet at downstream. Moreover, when the angle of shock incident increases, Hydrogen–air mixing rate increase and the concentration of the Hydrogen micro jet is uniformly distributed. Consequently, an enhanced mixing zone occurs downstream of the injection slots which leads to flame-holding.

Numerical study of shock wave interaction on transverse jets through multiport injector arrays in supersonic crossflow

In the present paper, the influence of shock wave position on sonic transverse hydrogen micro-jets in supersonic crossflow is investigated. This study focuses on mixing and shock interaction of the hydrogen jet in a Mach 4.0 crossflow with various jet conditions. Flow structure and fuel/air mixing mechanism were investigated numerically. Parametric studies were conducted on the position of the shock wave by using the Reynolds-averaged Navier–Stokes equations with Menter׳s Shear Stress Transport turbulence model. Complex jet interactions were found in the downstream region with a variety of flow features dependent on the shock position. Results show a different flow structures than for a typical micro jet, with a location of the oblique shock on the flow of the hydrogen jet. According to the results, for oblique shock on the first jet, the mixing performance in high pressure ratio increases more than 20% in downstream. Furthermore, a significant reduction (up to 20%) occurs in the maximum concentration of the hydrogen jet at downstream when the intersection of incident shock is on the top of the last jets. Moreover, hydrogen-air mixing rate increase and the concentration of the hydrogen micro jet are uniformly distributed in the surface close to shock. Thus, an enhanced mixing zone occurs in the vicinity of the intersection of the jet and the shock wave.

Diffusion Hydrogen Microjet Combustion (Round Bevelled Nozzle)

The purpose of this work is experimental study of diffusion combustion of the round hydrogen microjet at the 45° bevelled nozzle. The new phenomenon is revealed during combustion of a given hydrogen microjet, which we have named «bottleneck», as well as in a situation of the round and plane microjet combustion. The special attention has been given to research of characteristics of the «bottleneck» development and its role during of a hydrogen round microjet combustion. It is shown, that «bottleneck» represents the closed spherical area of the hydrogen with air mixture combustion in a jet near-field. The «bottleneck» area is closed by a powerful density gradient. It is found, that the laminar hydrogen jet in this area overcomes a density gradient of gas, becomes turbulent and combustion process is accompanied both a turbulent jet, and a turbulent flame further downstream evolution. It is shown, that the spatial size of a «bottleneck» decreases with growth of a jet velocity. It is found, that shadow patterns of the microjet combustion obtained for two shooting positions (normal and side view to the bevelled nozzle) were identical.

Different Conditions Of The Round Hydrogen Jets Diffusion Combustion In Air

The purpose of this work is experimental study of diffusion combustion of the round hydrogen microjets with different nozzle diameter. The new phenomenon is revealed during combustion of a hydrogen microjet, which we have named «bottleneck». The special attention has been given to research of characteristics of the «bottleneck» development and its role during of a hydrogen round microjet combustion. It is shown, that «bottleneck» represents the closed spherical area of the hydrogen with air mixture combustion in a jet near-field. The «bottleneck» area is closed by a powerful density gradient. It is found, that the laminar hydrogen jet in this area overcomes a density gradient of gas, becomes turbulent and combustion process is accompanied both a turbulent jet, and a turbulent flame further downstream evolution. It is shown, that the spatial size of a «bottleneck» decreases with growth of a jet velocity.