High-pressure Gas Jet Research Articles

An experimental study on the effects of needle dynamics on the penetration of a high-pressure methane jet

The aim of this work was to investigate the needle dynamics of a prototype gas injector under different working conditions. Furthermore, the consequences that these effects would have on the propagation of a high-pressure gas jet in a quiescent environment. To achieve this, two experimental matrices were designed: The first one included variations of the injection pressure, control pressure and injection duration, this was done in order to analyze the movement of the needle. On the second one, the injection and chamber pressure, and consequently the pressure ratio, were changed for the study of the jet penetration. The experiments were carried out in a constant volume cell equipped with optical accesses, This allowed the application of the schlieren technique and therefore the quantification of the propagation of the jet through the ambient gases was possible. The injector used was a single-hole axial injector working with methane as the injection fluid and diesel as the control fluid; different sensors built into the nozzle allowed the needle movement to be recorded as a function of time. The results showed a strong dependency of the needle dynamics on the injection pressure and the control pressure. However, this dependency is less noticeable at higher injection pressures, and in some cases even negligible. The chamber pressure proved to have a small but still noticeable effect on the needle dynamics. For the cases where the conditions seem to have no effect on the needle dynamics, the penetration results showed tendencies which coincided with the theory and literature.

Applicability of high-pressure direct-injected methane jet for a pure compression-ignition engine operation

Natural gas has been suggested as an alternative fuel for compression ignition (CI) engines because it generates significantly less pollutants and has a smaller carbon footprint, while maintaining the cycle efficiency. However, the high auto-ignition temperature of natural gas typically requires the use of a quasi-compression ignition method such as homogenous charge compression ignition (HCCI) or a dual-fuel mode. Yet, methods such as these are unable to realize the full potential of high efficiency and low emissions. This motivated us to evaluate the applicability of a high-pressure direct-injected natural gas jet for a pure CI engine under various engine load, injection timing, and injection pressure conditions using a single cylinder CI engine with a compression ratio of 15.5. The intake temperature was raised to 400 °C to achieve the auto-ignition temperature of methane after compression and a multi-hole GDI injector capable of operating at a pressure of 400 bar was used for fuel injection.As a result, CI operation was possible, but ignition occurred after the end of the injection in the form of a partially premixed flame rather than a diffusion flame for all conditions under which the engine was operated. A sufficient equivalence ratio of 0.8 was achieved at an injection pressure of 300 bar and injection duration of 1.6 ms with the multi-hole GDI injector, and the GMEP value varied from 2 bar to 5.5 bar according to the equivalence ratio. However, at an equivalence ratio of 0.7 or higher, the combustion efficiency decreased drastically because of the limit of the volume fraction of the piston bowl at TDC and the narrow nozzle distribution of the GDI injector. Measurement of the pollutants indicated that the total number of particles from methane CI operation exceeded that of diesel at an equivalence ratio of 0.74 in the same engine setup because of incomplete combustion; however, the total mass of the particulate matter (PM) was approximately 15% of the diesel because the average particle size from methane CI was approximately one third smaller than that of diesel. However, the high post-compression temperature for the auto-ignition of methane gas resulted in a high peak temperature, which resulted in the production of approximately 2000 ppm NOx under all test conditions. The results of the parametric study showed that, as the injection timing retarded, the ignition timing was almost equally retarded, thus the combustion was still observed in the form of a diffusion flame. As the injection pressure increased, the ignition delay became shorter and the emission of PM could be further reduced, but the NOx emission increased.

The Rock-Breaking Mechanism of Directional Fracture Blast Using an Irregular Shape Cartridge and Its Field Application

Abstract The testing system of digital laser dynamic caustics was performed here to examine the super-dynamic fracture mechanics of directional blasting crack, which, using an irregular shape cartridge, revealed the rock breaking mechanism of directional fracture blast. The findings show that the blasting primary crack fracture features—the typical tensile break, the variation trend of the dynamic stress intensity factor (DSIF), crack propagation velocity, and crack length— were more or less the same, the primary crack fracture was finished during 60–200 μs, the limit DSIF scarcely exceeded 1.5 MN/m3/2, and the arrest toughness of the blasting fracture was about 0.3 MN/m3/2. The irregular shape cartridge showed significant detonation wave unloading effects and detonation gas jet effects in the accumulative direction or slotting direction; the “air wedge effect” of the high-pressure detonation gas jet acted as the main drive for further expansion of the compression radial crack in the accumulative direction (or slotting direction), which also held the propagation of the compression radial crack in the nonaccumulative or nonslotting direction). Additionally, the accumulative cartridge and slotted cartridge were applied to the construction field, and it was found that the directional fracture blast was enabled, the good blasting fracture surface was formed, and better economic benefits and less operation time could be achieved using these two cartridges.

Ambient Tracer-LIF for 2-D quantitative measurement of fuel concentration in gas jets

A novel ambient tracer LIF technique with addition of tracer into ambient gas is proposed in this study to quantitatively measure the two dimensional (2-D) fuel concentration distribution in high-pressure gas jets. Firstly, the fundamental principle of the ambient tracer-LIF technique is described, and the equation of fuel concentration in a jet is deduced from the ambient fluorescence intensity. In the ambient tracer-LIF technique, the on-site calibration can be performed, and much more degrees of freedom in selection of tracers or target fuels can be achieved in principle. Then, the experiments are carried out with the high pressure gas injected into the environment doped with acetone in an optical accessible constant volume vessel. The fluorescence in the ambient is induced by using the 266 nm laser, and is recorded by the ICCD camera. The dedicated image processing is implemented to reduce the uncertainty and obtain the quantitative fuel concentration distribution in the jet. The uncertainties of the measurement results are evaluated, including both the systematic and random errors. The uncertainty propagation analysis shows that the measurement uncertainty increases with the local fuel concentration decreasing, and at the boundary regions of the jet, where the mixture is over lean, the relative uncertainty goes up to 26%. Finally, the temporal variations of the fuel concentration distribution in the gas jet are presented, and the effects of injection pressure are discussed. These results are believed to be valuable for development of numerical models and combustion system designs.

Evaluation of the surface profile obtained by abrasive jet machining

The abrasive jet machining is a machining method based on the effects generated by the action of the abrasive particles sent to the workpiece surface to be machined by means of a high pressure gas jet. Essentially, the obtained surface could be considered as constituted by chaining microcraters resulted as a consequence of the abrasive particles action. Taking into consideration the possible influence exerted by some abrasive jet machining process input factors, an experimental research was developed. By mathematical processing of the experimental results, empirical mathematical models were determined to highlight the influence exerted by the average dimension of the abrasive particles, the distance between the nozzle and the flat surface of the test piece and the impact angle on the surface roughness parameter Rz. In order to evaluate the similarities between distinct zones of the machined surface profile, the value of the Pearson’s coefficient was also determined.

Analysis of the stress wave effect during coal breakage by a high-pressure abrasive air jet

In view of the defects of borehole collapse, inhibition of gas desorption and migration of gas existing in hydraulic fracturing and other hydraulic permeability–increasing measures for soft coal seams with low-permeability technology is proposed for coal breakage by a high-pressure abrasive gas jet for relieving pressure and increasing permeability. The comparative analysis of gas jet flow field structure between convergent nozzle and Laval nozzle has been given by numerical simulation. For Laval nozzle, the expansion wave and compression wave alternate and move forward steadily in gas jet and vanish when potential core length reaches maximum. So, the Laval nozzle can form more stable flow filed structure of gas jet and avoid shock wave in gas jet. Furthermore, a high-speed camera is adopted to analyze the jet structure and verify the conclusion of numerical simulation. Based on thermodynamic theory, this article calculates and analyzes the critical local sound velocity and pressure generated from the stress wave during the process of coal breakage by the gas jet. Furthermore, experimental coal breakage by a high-pressure abrasive gas jet is carried out. The high-pressure abrasive gas jet impacts the coal body as a quasi-static load and a dynamic load and forms corrosion pits on the surface of the coal body. Penetrating cracks are formed within the coal in the pattern of the loaded stress wave which leads to coal breakage. The effects of porosity and permeability on the propagation of the stress wave in coal are analyzed by establishing the dispersion equation for the spread of the stress wave in coal. The results show that porosity has a significant effect on wave velocity and that the attenuation of the stress wave is intensified with an increase in porosity. Moreover, the stress wave attenuation is more obvious at high frequency. The effect of permeability on the wave velocity is not significant at low frequencies. In contrast, at high frequency and relatively low permeability, the wave velocity increases with the permeability, and the attenuation of the wave velocity initially increases and then decreases. When the permeability is greater than 10−11 m2, the wave velocity is not affected by the permeability. However, the stress wave is not attenuated.

The Effect of Splitting Timing on Mixing in a Jet with Double Injections

We present large-eddy simulation (LES) of a high-pressure gas jet that is injecting into a quiescent inert environment. The injection is through a nozzle with a diameter of 1.35 mm. Four injection strategies are considered in which the results of a single continuous injection case are compared with those of double injection cases with different injection splitting timing. In all double injection cases, the injection pulsing interval is kept the same, and the total injected mass is equal to that of the single injection case. On the other hand, the splitting timing is varied to investigate the effects of various injection splitting strategies on the mixture formation and the penetration length of the jet. Results show that the jet penetration length is not so sensitive to the splitting timing whereas the mixing quality can significantly change as a result of shifting the onset of injection splitting toward the end of injection. Especially, it is found that by adopting a post-injection strategy where a single injection splits into the main injection and late small injection near the end of injection period the mixing between the injected gas and ambient air is significantly improved. This trend is not as obvious when the injection splitting timing shifts toward the beginning or even in the middle of injection period. The increase of entrainment in the tail of each injection is one of the underlying physics in the mixing improvement in double injection cases. In addition to that, splitting a single injection into two smaller injections increases the surrounding area of the jet and also stretches it along the axial direction. It can potentially increase the mixing of injected gas with the ambient air.

Visualization research on injection characteristics of high-pressure gas jets for natural gas engine

High-pressure gas injection processes with various gas nozzle structures under different nozzle pressure ratio (NPR) were investigated experimentally. Schlieren imaging method was used to investigate macroscopic structure of gas jets. Results showed that increasing the gas injection pressure is unable to improve the jet tip penetration obviously. It is because chocking phenomenon limited gas jet velocity at nozzle exit under high gas injection pressure. The empirical formula for high-pressure gas jet tip penetration was investigated based on the experimental data under various NPRs and orifice diameters. It is found that the experimental data are in good agreement with the empirical formula proposed by Hamzehloo and Aleiferis. The increase of gas injection pressure and orifice diameter could not directly improve the air entrainment effect, nor could it increase the average equivalent ratio of gas jet due to the small gas jet kinetic energy and small density difference between gas jet and the surrounding ambient gas.

Extreme ultraviolet light source at a megahertz repetition rate based on high-harmonic generation inside a mode-locked thin-disk laser oscillator.

We demonstrate a compact extreme ultraviolet (XUV) source based on high-harmonic generation (HHG) driven directly inside the cavity of a mode-locked thin-disk laser oscillator. The laser is directly diode-pumped at a power of only 51 W and operates at a wavelength of 1034 nm and a 17.35 MHz repetition rate. We drive HHG in a high-pressure xenon gas jet with an intracavity peak intensity of 2.8×1013 W/cm2 and 320 W of intracavity average power. Despite the high-pressure gas jet, the laser operates at high stability. We detect harmonics up to the 17th order (60.8 nm, 20.4 eV) and estimate a flux of 2.6×108 photons/s for the 11th harmonic (94 nm, 13.2 eV). Due to the power scalability of the thin-disk concept, this class of compact XUV sources has the potential to become a versatile tool for areas such as attosecond science, XUV spectroscopy, and high-resolution imaging.

Numerical studies of the ignition characteristics of a high-pressure gas jet in compression ignition engines with glow plug ignition assist: Part 2-Effects of multi-opening glow plug shields

The results of a previous study, part 1, showed that use of a shield can improve the thermal performance of a glow plug, and thereby reduce ignition time. However, the part 1 study also found that use of a simple shield with only one circular opening can delay flame propagation out of the shield. The conclusions of that study suggested that there is scope for further improvements of the shield design, especially the shield opening geometry. Accordingly, this article presents the results of computational studies investigating the influence of multi-opening shield designs on natural gas ignition characteristics in glow plug–assisted compression–ignition engines. Two types of multi-opening glow plug shield, consisting of four small circular openings distributed in either diamond-pattern or square-pattern arrangements, were employed. The simulated results demonstrated that both multi-opening shields can not only increase glow plug surface temperature, but also increase the residence time of fuel mixture adjacent to the glow plug surface in the early injection stage, resulting in a faster ignition than the single-opening shield. Furthermore, the diamond-pattern multi-opening glow plug shield provides a faster or comparable flame propagation path back to combustion chamber, compared to single-opening glow plug shield, while the square-pattern multi-opening glow plug shield delays the flame propagation under several specific engine conditions. Compared to the single-opening glow plug shield, the overall natural gas ignition delays are further reduced by 6%–44% when using the diamond-pattern multi-opening glow plug shield, while the square-pattern multi-opening glow plug shield is only able to reduce the natural gas ignition delay under a few specific conditions.

The characteristic analysis of high-pressure gas jets for natural gas engine based on shock wave structure

High gas injection pressure leads to the formation of under-expanded gas jet at nozzle exit. The shock wave structure near the nozzle affects gas jet injection and mixing characteristics, which affects the combustion and emission performance of the engine. Gas jet injection process and shock wave structure evolution law under different nozzle pressure ratio (NPR) and orifice diameter have been investigated with the application of Schlieren imaging and numerical simulation. Results show that long injection duration exists in gas injection process after the end of injection. It is attributed to the slow pressure reduction velocity in the nozzle. This phenomenon is one of the key factors which influence the high HC emission of gas fuel port injection natural gas engines. The change of pressure inside the nozzle also affects the shock wave structure (Mach disk) near the nozzle. It is found that the increase of Mach disk width leads to a large jet near-field angle which promotes the spatial distribution and turbulent mixing of gas jet. In addition to experimental results, numerical simulation is used to analyze the injection characteristics of gas injection system. Increasing gas nozzle flow area and shortening gas nozzle length are regarded as effective ways to improve the responsiveness of gas injection system and reduce gas injection duration. The range of Reynolds number at exit of the nozzle is 0.5–2.5×105 under various gas injection pressures and orifice diameters. This presents that gas jet is easily influenced by air turbulence in intake manifold. Strong air turbulence in intake manifold is needed in a gas fuel port injection natural gas engine in order to obtain homogeneous gas/air mixture.

Numerical studies of the ignition characteristics of a high-pressure gas jet in compression-ignition engines with glow plug ignition assist: Part 1—Operating condition study

This article presents the results of computational studies investigating the ignition of high-pressure natural gas jets in a compression-ignition engine with glow plug ignition assist. The simulation was conducted using a KIVA-3V-based three-dimensional engine model, along with an improved fuel injector model, a detailed cut-off glow plug shield model and a modified two-step methane reaction mechanism, to simulate the natural gas injection and ignition. The simulated results demonstrate the significance of using a shield for the glow plug. Compared to an unshielded (bare) glow plug, the shield not only reduces the heat loss from the hot glow plug surface to the cold intake air charge and the cold injected gas jet but also traps the fuel mixture to increase its residence time adjacent to the hot surface. Over a representative range of heavy-duty diesel engine operating conditions, a shielded glow plug greatly improves the natural gas engine performance and provides reliable ignition, while an unshielded glow plug can only be optimized for specific conditions. The understanding of glow plug shield behavior gained from the simulations suggests avenues for improved shield designs that would yield further reduced ignition delays.

Design and evaluation of high-pressure nozzle assembly for laser cutting of thick carbon steel

Laser cutting of carbon steel is extensively used across a range of industries, due to its advantage of high speed, low kerf and high quality. Currently, a 1-kW carbon dioxide (CO2) laser with its subsonic nozzle assembly can be used only to cut steel plates up to around 10 mm. This paper aims to design and evaluate a high-pressure supersonic laser cutting nozzle assembly, which can enable a 1-kW CO2 laser to cut steel of up to 50 mm thickness. Basic gas dynamic and compressible flow equations were used to design the supersonic nozzle assembly. The flow of the high-pressure gas jet inside the nozzle assembly was investigated using computational fluid dynamics (CFD), and the structural integrity of the high-pressure nozzle assembly was ensured using finite element analysis (FEA). The gas flow pattern at the exit of the nozzle assembly was computed and compared with the experimental observation made through a shadowgraph technique. Laser cutting experiments were performed with the developed supersonic nozzle assembly to demonstrate cutting of 50-mm-thick low carbon steel with 1-kW CO2 laser.

高圧ガスジェットミル法を用いた調和組織制御

高圧ガスジェットミル法を用いた調和組織制御

Air Entrainment and Combustion Process of High-Pressure Gas Jet in Gas Direct Injection Engines

Air Entrainment and Combustion Process of High-Pressure Gas Jet in Gas Direct Injection Engines

The optical measurement of large cluster tracks in a gas jet.

We propose an optical method based on Rayleigh scattering for the direct measurement of cluster tracks produced by a high-pressure gas jet. The tracks of the argon and methane clusters are acquired by a high-speed camera. It is found that the cluster sizes of these tracks are within the range of 7E + 03~1E + 07 for argon and 2E + 06~4E + 08 for methane. Most argon tracks are continuous and their intensity changes gradually, while the majority of the methane tracks are separated into discrete fractions and their intensity alters periodically along the flight path, which may indicate the methane clusters are more unstable and easily to break up. Special methane clusters which may fly at an axial velocity of less than 2.5m/s are also found. This method is very sensitive to large gas cluster and has broad application prospects in cluster physics.

Complex interferometry potential in case of sufficiently stable diagnostic system

Classical interferometry is one of the key methods among active optical diagnostics. Its more advanced version, which allows recording and subsequent reconstruction of up to three sets of data using just one data object —a complex interferogram—was developed in the past and became known as complex interferometry. Employing this diagnostics, not only the usual phase shift, but also the amplitude of the probing beam as well as the fringe contrast (leading directly to the phase shift time derivative) can be reconstructed simultaneously from such a complex interferogram. In this paper it will be demonstrated that even in the case of a not particularly good diagnostic beam quality these three quantities can be reconstructed with a high degree of accuracy provided both the diagnostic beam as well as the corresponding optical line feature a reasonable stability. Such stability requirement is important as in an ideal case four shots need to be gradually recorded (one by one): the signal complex interferogram, the reference interferogram as well as the intensity structures of the signal and reference part of the diagnostic beam. Two examples of complex interferograms obtained in experiments will be analyzed: the laser produced plasma (spark in the air) and the high pressure gas jet. A general ray-tracing based iterative algorithm will be outlined in order to increase a precision of the index of refraction spatial profile taking into account refraction effects (omitted in the Abel inversion) and employing the original reconstructed phase shift and amplitude.

Compact extreme ultraviolet source at megahertz pulse repetition rate with a low-noise ultrafast thin-disk laser oscillator

We present a compact extreme ultraviolet (XUV) source based on high-harmonic generation (HHG) at 2.4 MHz pulse repetition rate driven from the compressed output of a mode-locked thin-disk laser (TDL) oscillator. The system generates very high peak intensities, which enable highly nonlinear frequency conversion reaching VUV/XUV energies. These sources significantly increase the signal-to-noise ratio and reduce measurement durations in many fields such as condensed matter physics. The pulse repetition rate is increased from kilohertz to megahertz with high average photon flux, while keeping the pulse energy sufficiently low to avoid space charge effects. The system uses a semiconductor saturable absorber mirror mode-locked Yb:YAG TDL delivering an average power of up to 70 W with subpicosecond pulses, which are efficiently compressed to sub-100 fs in a simple, single-stage compressor based on a Kagome-type hollow-core photonic crystal fiber. Focusing into a high-pressure xenon gas jet, we generate XUV radiation with up to >5×107 photons/s on the 19th harmonic (23 eV). This HHG system is very compact, has low-noise performance comparable to standard ultrafast low-power laser oscillators, and provides a new tool for the study of attosecond dynamics in condensed matter physics.

In-water injection of high-pressure pulsed gas jet: A simple analytical tool for direct injection of gaseous fuels in automotive engine

Visualizing high pressure pulsed gas jet can be challenging due to its weak scattering of light which requires reliable flow tracer. Complex and costly laser source and high speed camera settings using shadowgraph, Schlieren and Laser Induced Fluorescent (LIF) techniques with seeding of flow tracers such as acetone have been used. In the spirit of simplification, this paper presents a technique to visualize high pressure pulsed gas jet in liquid ambient. It can be used as predictive tool to investigate the structure, dynamic and interaction of gas jet with the environment [1]. A gas injector with square-shaped nozzle was used. High pressure nitrogen gas at 5 and 6MPa with 12ms injection pulse exits the injector through a 1mm2 square nozzle into quiescent water. The injector tip is immersed below water surface in an optically-accessed container and placed inside an extremely low illuminated square chamber. Two small windows on opposite walls of the chamber allow image capturing with injection-flash light synchronization. Images of the gas jets formed from nozzle at various time after the start of the injection (SOI) were captured by a digital camera. During exposure, the flash light was triggered for 1ms at some times after SOI, thus images captured correspond to the flash timing.Results showed that the shape of the gas jet was in agreement with the vortex ball model but with difference in the magnitude of penetration with respect to previous works. Some similarities in the gas injection behavior are found in the liquid and gas ambient. The tip penetration and gas width in water environment are about half of the magnitude in the gas environment. A dimensionless gas dynamic analysis shows a good agreement in the trend of jet development between the gas environment using Planar Laser Induced Fluorescent (PLIF) imaging and in-water imaging techniques. Results indicate that both gas jet length and width are very sensitive to injection pressure.

Carrier-envelope phase dependent high-order harmonic generation with a high-repetition rate OPCPA-system

We study high-order harmonic generation with a high-repetition rate (200 kHz), few-cycle, driving laser, based on optical parametric chirped pulse amplification. The system delivers carrier-envelope phase stable, 8 fs, 10 μJ pulses at a central wavelength of 890 nm. High-order harmonics, generated in a high-pressure Ar gas jet, exhibit a strong CEP-dependence over a large spectral range owing to excellent stability of the driving laser pulses. This range can be divided into three spectral regions with distinct CEP influence. The observed spectral interference structures are explained by an analytical model based upon multiple pulse interferences.