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This paper describes the pulsed injection of hydrogen fuel with an incoming Mach number of 2.5 in a directly connected pulse combustion wind tunnel. The hydrogen pulse injection test with 33 Hz–62hz frequencies was carried out by using a mechanical pulse injector.The effects of different injection frequencies on the ignition delay and combustion performance of the hydrogen fuel are analyzed by means of flame self-luminescence photography and wall pressure measurements, and the results are compared with those of steady injection. The results shows that there is an optimal pulsed injection frequency--39 Hz in the frequency range studied in this paper, at this frequency, the ignition delay of hydrogen is much shorter than that of steady injection.In addition, the study also found that pulsed injection improves the combustion performance of hydrogen, so that the energy released by hydrogen combustion at lower equivalence ratios is equal to that released by steady hydrogen injection at a higher equivalence ratio. For both pulsed and steady injection, the development of the hydrogen flame can be attributed to the propagation theory of diffusion flame. The pulse frequency is not observed to have any significant effects on hydrogen combustion performance. • Effects of steady injection and pulsed injection on ignition and combustion were studied. • The results show that 39 Hz pulsed injection can greatly shorten hydrogen ignition delay. • Penetration depth of pulsed injection is higher than that of steady injection. • Pulsed injection can improve the combustion performance of hydrogen. [ABSTRACT FROM AUTHOR]

Achieving efficient fuel-air mixing is a crucial issue in the design of the scramjet engine due to the compressibility effect on the mixing shear layer growth and the stringent flow residence time limitation induced by the high-speed crossflow, and the potential solution is to enhance mixing between air and fuel by introducing of streamwise vortices in the flow field. In this survey, some mixing enhancement strategies based on the traditional transverse injection technique proposed in recent years, as well as their mixing augmentation mechanisms, were reviewed in detail, namely the pulsed transverse injection scheme, the traditional transverse injection coupled with the vortex generator, and the dual transverse injection system with a front porthole and a rear air porthole arranged in tandem. The streamwise vortices, through the large-scale stirring motion that they introduce, are responsible for the extraction of large amounts of energy from the mean flow that can be converted into turbulence, ultimately leading to increased mixing effectiveness. The streamwise vortices may be obtained by taking advantage of the shear layer between a jet and the cross stream or by employing intrusive physical devices. Finally, a promising mixing enhancement strategy in supersonic flows was proposed, and some remarks were provided. [ABSTRACT FROM AUTHOR]

• Transient cooling of the superheated metal plate by pulsed injection of a liquid jet. • Simultaneous measurement of the liquid film and the plate temperature distribution. • Cooling performance was evaluated from the wetting front and removed heat. • Thermal diffusivity and inertia of the metal affect the cooling performance. Pulse firing is one of the major operation modes of bipropellant thrusters for the attitude control of small-scale spacecrafts. In the pulse-firing mode, the operational range of the thruster depends on the deterioration of liquid film cooling performance. Because cooling performance is determined by the balance of heat removed by the liquid film and transferred to the manifold, the behavior and heat transfer characteristics of liquid films under the intermittent injection of liquid jets must be understood to enable a wider range of operational patterns. We conducted cooling tests on a superheated metal plate via the pulsed injection of a liquid jet for better understanding of the pulsed cooling process. Different injection patterns, including continuous injection, with the same injection quantity were examined on two types of metal plates (aluminum alloy and copper), because the thermal properties of metal plates affect both the heat transfer characteristics of the liquid film and temperature rise of the plate during the inter-pulse duration. The cooling process was evaluated based on the evolution of the liquid film on the metal plate and rear-side temperature of the metal plate. The evolution and temperature were simultaneously visualized using a high-speed camera and infrared camera, respectively. To link the liquid film state to the heat transfer process, the temperature and heat flux on the cooled surface were estimated by solving the inverse problem of three-dimensional transient heat conduction. The results indicate that the wetting front position corresponds to the position of the maximum temperature gradient. Additionally, the residual liquid film is consumed through the evaporation and the droplet dispersion related to the nucleate boiling. The effects of thermal inertia and diffusivity of the metal plate highlight the differences in the amount of heat removed by the liquid film. The heat removed by the liquid film during pulsed cooling exhibited a peak and was higher than that removed by continuous injection on the aluminum alloy plate. Less heat was removed under low-duty-cycle conditions, and the amount of heat removed by the liquid film was lower than that removed by continuous injection on the copper plate. [ABSTRACT FROM AUTHOR]

Shale gas has become an increasingly important source of natural gas ( CH 4 ) in the United States over the last decade. Due to its unconventional characteristics, injecting carbondioxide ( CO 2 ) to enhance shale gas recovery (ESGR) is a potentially feasible method to increase gas-yield while both affording a sink for CO 2 and in reducing the potential for induced seismicity. However, understanding of this issue is limited with few pilot field studies proposed. This study examines CO 2 -ESGR to better understand its feasibility and effectiveness. We explore the roles of important coupled phenomena activated during gas substitution especially vigorous feedbacks between sorptive behavior and permeability evolution. Permeability and porosity evolution models developed for sorptive fractured coal are adapted to the component characteristics of gas shales. These adapted models are used to probe the optimization of CO 2 -ESGR for injection of CO 2 at overpressures of 0 MPa, 4 MPa and 8 MPa to investigate magnitudes of elevated CH 4 production, CO 2 storage rate and capacity, and of CO 2 early-breakthrough and permeability evolution in the reservoir. For the injection pressures selected, CH 4 production was enhanced by 2.3%, 14.3%, 28.5%, respectively, over the case where CO 2 is not injected. Distinctly different evolutions are noted for permeability in both fractures and matrix due to different dominating mechanisms. Fracture permeability increased by ∼1/3 for the injection scenarios due to the dominant influence of CH 4 de-sorption over CO 2 sorption. CO 2 sequestration capacity was only of the order of 10 4 m 3 when supercritical for a net recovery of CH 4 of 10 8 m 3 . We investigated the potential of optimal CO 2 -pulsed injection to enhance CH 4 production (absolute mass recovered)-without the undesirable effects of CO 2 early-breakthrough and also minimum cost on CO 2 injection. This utilizes the competitive sorptive behavior between CH 4 and CO 2 , can also reduce the potential for induced seismicity hence the entire system can be near net neutrality in terms of its carbon and seismic footprint. [ABSTRACT FROM AUTHOR]

A numerical model is built to understand the transport phenomenon during the pulsed MOCVD process. The relations between the transport behavior of the precursors and the pulse duration for III, V, and pure H 2 pulses are studied. The results show that the mass fraction of precursors in the chamber during the III or V pulses becomes stable if they are longer in duration than a certain value. The duration of the pure H 2 pulse has a greater effect on particle generation than the duration of the III or V pulse. On the other hand, the V pulses can easily overtake the III pulses before reaching the substrate because of the lower Pe number of the NH 3. Using an III/V ratio of 1 results in more AlN particles in the high-temperature region during the H 2 pulse after the III pulse. By extending the duration of the H 2 pulse which follows the III pulse, there is a significant reduction in the generation of particles per cycle. When the duration of the H 2 pulse after the III pulse is increased to a certain time, the amount of particles generated after the III pulse becomes equal to that generated after the V pulse. When an even lower particle generation is required, the duration of H 2 pulses after the III and V pulses should be extended at the same time. [ABSTRACT FROM AUTHOR]

Abstract: Tungsten oxide films with various stoichiometries, undoped and hydrogen doped were deposited by heating a W wire at 660°C and at a base pressure of 13Pa set by various gasses (O2, N2, H2) or gas mixtures (N2–O2 10% in O2, forming gas, FG) and pulsed injection of O2 or H2. Using this method and dependent on the deposition conditions four classes of hot-wire (hw) tungsten oxide films were synthesized: i) stoichiometric (hwWO3), ii) oxygen deficient (sub-stoichiometric, hwWOx with x<3), iii) stoichiometric and hydrogen doped (hwWO3:H), and iv) sub-stoichiometric and hydrogen doped (hwWOx:H). Due to the pulsed injection of O2 the W wire re-oxidizes during deposition thus creating WO3 vapors continuously, so films deposited by this method do not suffer by thickness limitations and, moreover, exhibit high porosity. The optical properties of these classes of films, studied with spectroscopic ellipsometry (SE) measurements, differ substantially between them indicating corresponding differences in their electronic structures. So, hwWO3 films were semiconducting exhibiting a band gap near 3eV. Sub-stoichiometric hwWOx deposited with up to 2 injections of O2 were semi-metallic preserving some features of the electronic structure of the pure metal, while further injection of O2 leads to stoichiometric films. Fourier transform infrared spectroscopy and SE measurements indicated that hwWOx films contain H bonded with the O ions while in hwWO3:H and hwWOx:H the H is incorporated in films by direct bonding with the W ions. [Copyright &y& Elsevier]

Abstract: This work is devoted to deposition of alumina–silica films using an innovative pulsed injection metal organic chemical vapour deposition technique and aluminium tri(iso-propoxide) (Al(i-OPr)3) and tetraethoxysilane (TEOS) as precursors. The deposited aluminium silicate films have been characterised by scanning electron microscopy, infrared spectroscopy, X-ray diffractometry and capacitance–voltage (C–V) measurements. The investigation of the deposition at different Si/Al ratios and substrate temperatures has shown that the growth rate increases with the increase of Al(i-OPr)3 proportion in solution and decreases as the proportion of TEOS increases. We have also shown that aluminium content in the film increases at lower deposition temperatures while silicon content increases at higher temperatures. The permittivity of the films determined from C–V measurements decreases with increasing substrate temperature. It was found that films deposited at substrate temperatures of 600 or 700 °C and with the highest Si/Al ratio have the lowest dielectric permittivity. This research should be useful for further development of MOCVD technology for the deposition of aluminosilicate-based dielectric materials with controlled dielectric permittivity. [Copyright &y& Elsevier]

The effects of pH and ionic strength (salt concentration) on transmission of single protein human serum albumin (HSA) and human immunoglobulins (HIgG) through a 100 kDa molecular weight cut-off (MWCO) polyethersulfone membrane have been studied using a pulsed sample injection technique. Experimental results obtained clearly demonstrate the effectiveness of changing solution pH and ionic strength optimisation for selective transmission of HSA or HIgG. These also demonstrate the usefulness of pulsed injection experimental technique for the optimization of ultrafiltration processes. A pulse input carrier phase ultrafiltration (CPUF) was employed to fractionate a binary protein mixture of HSA and HIgG at low NaCl concentration, showing that it is feasible to separate the binary protein at optimised conditions. [Copyright &y& Elsevier]

The design of scramjet engines includes the investigation of minimally intrusive fuel delivery mechanisms which maximize jet fuel penetration and mixing. In subsonic crossflows it has been shown that pulsation of gaseous jets can improve jet penetration and mixing in comparison to unforced (steady) jets. Extensive investigations have already explored subsonic flow regimes for pulsed injection; however, only a limited number of experimental and numerical studies have been performed which investigate pulsed jets in a supersonic crossflow. This study presents fully three-dimensional (3D) scale-resolving simulations of steady and a sinusoidally pulsed jet (f = 16 kHz) using a wall modeled large eddy simulation approach to capture large-scale vortical structures in turbulent jet in supersonic crossflow and pulsed jet in supersonic crossflow. A block-structured, fully 3D turbulent scale resolving finite volume model was used to explore physics simulations of steady and pulsed jets in a supersonic crossflow. The results of the simulations presented show that sinusoidal pulsation of a gaseous hydrogen jet improves penetration and mixing over the steady jet when the momentum flux ratios are equivalent. [ABSTRACT FROM AUTHOR]

• Sensitive determination of nine N -nitrosamines with pulsed injection technique. • Comparative study of seven oxidation processes on N -nitrosamines degradation. • O 3 /H 2 O 2 AOP was the most effective method for N -nitrosamines removal. • NDMA was the most resistant spices which could be monitored as an indicator. • Re-formation of N -nitrosamines from the oxidized solution was negligible. N -nitrosamines are highly toxic disinfection byproducts (DBPs) formed in drinking water treatment process. Moreover, they could permeate reverse osmosis (RO) membrane during water recycling. Herein, an improved detection method for simultaneously determining 9 N- nitrosamines was established, and 7 kinds of oxidation processes were examined for degradation of the 9 N- nitrosamines. Compared with conventional injection mode, pulsed injection technique improved signal to noise ratio (SNR) and peak area of N- nitrosodimethylamine (NDMA) by 2.1 and 3.77 times, respectively. Low method detection limits (MDLs) were achieved ranging from 0.3 to 1.5 ng/L. Based on the improved detection method, simultaneous oxidation of 9 N- nitrosamines with UV irradiation/UV based advanced oxidation processes (AOPs), O 3 /O 3 based AOP, and permanganate and ferrate were comparatively investigated. Among these employed processes, O 3 /H 2 O 2 was the most effective approach for the elimination of N- nitrosamines, and 36.6% (NDMA)-91.4% (NDBA) removal efficiency was achieved. In comparison, ozonation merely removed less than 20% of N- nitrosamines (except NDphA for 29.3%). Compared to UV irradiation, the removal efficiency of N- nitrosamines was improved by almost 10% in UV/Cl 2 process, while the improvement in UV/peroxydisulfate (UV/PDS) process was not obvious. Permanganate and ferrate oxidations on N- nitrosamines removal were not significant. NDMA was found to be one of the most recalcitrant N- nitrosamines, therefore, it could be monitored as an indicator of N -nitrosamines in relevant treatment process. Finally, the risk of N -nitrosamines re-formation was found to be negligible when chloramination was applied after oxidation treatment. [ABSTRACT FROM AUTHOR]

• GC–MS/MS using pulsed split injection was used to determine 1,4-dioxane in cosmetics. • The UAE was used for preparing liquid samples without sample cleanup. • The method was fully validated using a variety of cosmetic matrices. • 1,4-dioxane was detected in 47 out of the 82 products ranged from 0.23 to 15.3 μg/g. 1,4-dioxane is a potential human carcinogen and contaminant produced during the manufacturing process from specific cosmetic ingredients, such as certain detergents and emulsifiers. As such, 1,4-dioxane is not identified on product ingredient labels. To assess the concentration of 1,4-dioxane in cosmetic products, a gas chromatography-tandem mass spectrometry (GC–MS/MS) method using pulsed split injection and electron ionization was developed and validated. For liquid cosmetic products such as shampoo and lotion, test portions were extracted using fast ultrasound-assisted extraction (UAE) procedure without sample cleanup. For solid products (e.g. beauty bars), a C 18 solid phase extraction (SPE) procedure was optimized to reduce potential interferences. The corresponding stable isotopically labeled analogue (1,4-dioxane-d 8) was selected as an internal standard to compensate for matrix effects and sample recovery. Method recovery experiments were performed in lotion, oil gel, hair detangler, bubble bath and beauty bar (solid) sample matrices with recoveries of 84–108% and relative standard deviations less than 5% at three spike concentrations. Method limits of detection (LOD) and quantification (LOQ) for 1,4-dioxane were determined at 0.2 μg/g and 0.5 μg/g, respectively. The method was successfully used to determine 1,4-dioxane in 82 leave-on and rinse-off cosmetic products marketed toward children including bath products, hair treatment, lotions, beauty bars, washes, shampoos, and other products. 1,4-dioxane was detected in 47 of the 82 products with an average concentration of 1.54 μg/g (range: 0.23–15.3 μg/g). The method can increase sample throughput and reduce matrix-induced interferences. [ABSTRACT FROM AUTHOR]

• An optical test rig is built to observe the high-pressure methane gas direct injection in a CVB. • A 3D numerical model of high-pressure methane injection in a CVB is verified by the test data. • The methane jet penetration has a two-stage behavior induced by the dynamic inner flow inside the nozzle. • The methane jet tip penetration and the penetration speed become saturated as the injection pressure rises high enough. • This jet saturation behavior is caused by inner flow saturation of Mach number and gas velocity inside the nozzle. For a direct injection natural gas engine, the fuel jets into the cylinder in cycles, and this gas pulsed injection process causes crucial effects on the combustion. This study presents an experimental investigation on the methane direct injection. An optical test rig is designed to observe the high-pressure methane jet into a constant-volume bomb (CVB), and a numerical model is built to analyze the gas flow. The methane jet has a two-stage feature. The gas jet characteristic parameters (the tip penetration, penetration speed, jet cone cover area) change rapidly in dynamic stage I, and become stable in stable stage II. The dynamic process inside the nozzle induces this two-stage gas jet flow. The inner methane flow experiences a time delay from the inlet to the outlet, and the gas jet undergoes the same time delay to maintain stable. Furthermore, the injection pressure has great effects on the gas jet. As the injection pressure rises high enough, the gas jet saturation behavior occurs, and it is caused by inner flow saturation of Mach number, Reynolds number and gas velocity inside the nozzle. It is not necessary to increase injection pressure as high as possible for improving the gas jet characteristics. [ABSTRACT FROM AUTHOR]