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Due to current and future environmental and safety issues in space propulsion, typical propellants for upper stage or satellite rocket engines such as the toxic hydrazine are going to be replaced by green propellants like the combination of liquid oxygen and hydrogen or methane. The injection of that kind of cryogenic fluids into the vacuum atmosphere of space leads to a superheated state, which results in a sudden and eruptive atomization due to flash boiling. For a detailed experimental investigation of superheated cryogenic fluids, the new cryogenic test bench M3.3 with a temperature controlled injection system was built at DLR Lampoldshausen. After a first test campaign with high-speed shadowgraphy of flash boiling liquid nitrogen sprays, a laser-based Phase Doppler system was set-up to determine the spatial distributions of droplet velocities and diameters in highly superheated sprays. The spatial distributions revealed a core region with high mean velocities close to the injector orifice. With increasing distance from the injector orifice, the sprays develop a more and more monodisperse pattern. These distributions also showed that atomization due to flash boiling generates finer sprays with growing degrees of superheat. In certain spray regions, two droplet populations varying in their direction of motion, velocity and diameter due to possible recirculation zones were observed. The experimental data of flash boiling liquid nitrogen generated within this study provide a comprehensive data base for the validation of numerical models and further numerical investigations., Deutsche Forschungsgemeinschaft, Projekt DEAL

This article is a careful examination of an energy poly-generation unit integrated with an evacuated solar thermal tube collector. A proton exchange membrane (PEM) electrolysis unit is used for hydrogen production, an ejector refrigeration system (ERS) is utilized for cooling demand, and a heater unit is used for heating demand. All sub-systems are validated by considering recent articles. Cooling and heating demand, as well as the net output power are calculated. The modeled poly-generation system's exergy and energy efficiency are maximized by considering the inlet temperature of the heat exchanger and primary pressure of the ejector with the parametric evaluation of the system. The proposed poly-generation set-up can produce cooling load, heating load, and hydrogen with amounts of 5.34 kW, 5.152 kW, and 63 kg/year, respectively. Based on these values, the energy efficiency, and exergy efficiency are computed to be 64.14%, and 49.62%, respectively. Higher energy and exergy efficiencies are obtained by reducing high pressure of the refrigeration cycle or decreasing the temperature outlet of an auxiliary heater. The heat exchanger and thermal energy storage unit have the highest cost rate among all system components with 73,463 $ and 46,357, respectively. Parametric study indicates that the main determinative elements in the total cost rate of the system are the heater, and the solar collector.

In the current work, thermodynamic examination for cogeneration of electricity and cooling based on a polymer exchange membrane (PEM) fuel cell was carried out. To the waste energy in the fuel cell, an absorption refrigeration unit is employed in two modes with ejector and without ejector. This system includes a PEM-FC, an absorption refrigeration unit, a hydrogen storage tank, an ejector, and an air compressor. The produced thermal energy in the fuel cell is received entirely by a working fluid and is given to the absorption chiller generator. The system simulation was carried out from two perspectives of energy and fuel saving. Findings showed that the energy efficiency of the combined cooling and power (CCP) unit and the CCP system equipped with the ejector (CCP-E) was 63.72% and 78.33%, respectively. It indicated that adding the ejector to the system increases the energy efficiency of the system by 23%. The fuel economy percentages of the CCP system and CCP-E were 44.43% and 45.9%, respectively. The results also showed that adding the ejector in the refrigeration system increases the system performance by up to 44%. The presence of the ejector causes the working fluid flow in the evaporator to increase with the suction of the secondary flow, and the cooling capacity increases significantly. Moreover, with increasing generator and evaporator pressure, the suction ratio of the cooling system equipped with the ejector decreases and increases, respectively.

A cylindrical rotating detonation engine (24 mm diameter) with multiple injector holes on the combustor side wall for both propellant injection and cooling by injector gas flow was designed and te...

The paper presents the results of theoretical study for the influence of an additional magnetostatic field applied to the radio-frequency discharge region on the operating parameters of radio-frequency ion injector, taking into account the shape of its discharge chamber. The integral characteristics are calculated for three injector configurations: with a cylindrical, conical, and hemispherical discharge chamber. For calculations, we used a mathematical model, in which the charged particle behavior in plasma is described by relations close to magnetohydrodynamic, while the neutral particle distribution is determined using an approximate analytical solution obtained when considering a one-dimensional problem of gas flow in a tube. Simulation was carried out in the COMSOL Multiphysics software package. According to the calculation results, an additional magnetostatic field can improve the ion injector performance with any discharge chamber configuration. The greatest operation efficiency increase was observed with a cylindrical discharge chamber. However, according to calculations, the best performance can be obtained if a hemispherical chamber is used.

Low fuel regression rate is one of the major drawbacks of hybrid rocket motors. In this study, a novel injector concept is proposed to provide a substantial enhancement in the fuel regression rate....

This paper presents experimental results from a model rocket combustor that uses a gas-centered swirl-coaxial injector element injecting warm oxygen and ambient temperature RP-2 fuel with 900 psia ...

This study provides an experimental analysis of the throttling methods implemented using a throttleable injector that generates a thrust in the range 24–64% on a 50 N monopropellant thruster using ...

The working fluid of the hydrogen recirculation ejector in proton exchange membrane fuel cell (PEMFC) systems is humid hydrogen containing water vapour. However, previous studies on the hydrogen recirculation ejector using computational fluid dynamics (CFD) were based on the single-phase flow model without considering the phase change of water vapour. In this study, the characteristics of the phase change and its effect on the ejector performance are analysed according to a two-phase CFD model. The model is established based on a non-equilibrium condensation phase change. The results show that the average deviation of the entrainment ratio predicted by a single-phase flow model is 25.8% compared with experiments involving a hydrogen recirculation ejector, which is higher than the 15.1% predicted by the two-phase flow model. It can be determined that droplet nucleation occurs at the junction of the primary and secondary flow, with the maximum nucleation rate reaching 4.0 × 1020 m−3s−1 at a primary flow pressure of 5.0 bar. The higher temperature, lower velocity, and higher pressure of the gas phase can be found in the mixing region due to condensation, resulting in a lower entrainment performance. The nucleation rate, droplet number, and liquid mass fraction increase remarkably with an increasing primary flow pressure. This study provides a meaningful reference for understanding phase change characteristics and two-phase flow behaviour in hydrogen recirculation ejectors for PEMFC systems.

The hydrogen recirculation in proton exchange membrane fuel cell (PEMFC) is recommended for the hydrogen supply of PEMFC, and hydrogen ejectors are gradually being used in fuel cell vehicles due to low noise and low energy consumption. However, there is a lack of discussion about the influence of recirculation rate on the stack. Due to passive regulating mechanism of the ejectors, a miniature speed-adjustable peristaltic pump is used to simulate the hydrogen ejector in this study to investigate the effect of hydrogen recirculation on the performance of PEMFC stack. Experiments are conducted under different pump flow rates. The stack with hydrogen recirculation is proven to have better performance, but over high pump flow rate can lead to hydrogen shortage. It is interesting to find that the flow rate fluctuation of hydrogen inlet affects the stability of stack performance, and pressure drop and recovery time during purge process are proposed as effective indicators for performance analysis. Finally, pump flow rates between 60 ml/min and 105 ml/min are defined as “effective area”. Based on the analysis of effective indicators, keeping at “effective area” is further proved to improve the performance of the stack, which is also useful to design hydrogen recirculation.

In this research, steady-state Mixture and Eulerian-Eulerian method for liquid-gas parallel flow ejector have been examined. The simulation demonstrated that the Mixture model simulation represents better and efficient. The Eulerian-Eulerian model needed longer computational time and had a complexity to achieve the optimal convergence. However, both methods' performances were shown slightly similar. The models indicated a difference of about 6% in the flow rate ratio, their pressure diagrams nearly coincide, and their velocity parameter varies by 7% by comparing to the existing experimental data. Additionally, the Mixture model results appropriately conformed much better to the experimental data. So, the Mixture model was chosen for futher parametric study. Simulation results indicated that the flow rate ratio decreases by increasing the throat's cross-sectional area, and the flow rate ratio increases by increasing the nozzle's cross-sectional area. In this regard, e.g., the flow rate ratio of ejector by increasing pressure from 70 to 80 kPa, the air inlet increases up to 94%, and by increasing ejector outlet pressure, the flow rate ratio reduces such that no suction can be observed at 160 kPa. Consequently, in the 150 kPa pressure ratio, the flow rate ratio was reduced by almost 100%.

The development of high-performance static mixers is a critical research topic in process intensification in the process industry. This research combines computational fluid dynamics simulation and experimental testing to design a new type of static micromixer: First, a variable-diameter swirl shear mixer was designed and its structure was optimized. Measured by Malvern laser particle size analyzer, the median particle size decreased from 41 μm to 29 μm in the designed micromixer compared to that of traditional static mixers. Subsequently, the dispersed phase injection method was upgraded to a jet injection method, and the static micromixer was designed with a combination of an ejector and a variable-diameter swirl shear mixer. The median particle size of the dispersed droplets further decreased to 23 μm, achieving a dispersion effect at 2100−2400 rpm of the dynamic high-shear mixer. The micromixer greatly improved the static mixing effect and may replace dynamic high-shear mixers in the future.

Gas-centered swirl coaxial (GCSC) injectors are used in many liquid propellant rocket engines to improve combustion efficiency. In this study, fluctuation of the mass flow rate is analyzed to investigate influence of external excitation in gas feed line on the mass flow rate distribution of sprays. Water and air are used as simulants for the liquid kerosene and gas oxygen, respectively. With external excitation (354 and 1062 Hz), atomization processes changes and periodic breakup phenomenon of a spray occurs. Liquid film thickness at the exit of the injector shows that the width of liquid mass flow rate wave is reserved when the instability mode changes. However, behavior of the liquid droplets captured with a structured laser illumination planar imaging (SLIPI) system for laser diagnostics indicates that time domain concentration of liquid mass becomes more severe with the second instability mode outside the injector. This study can provide a reference for liquid mass distribution with external excitation on gas and imply that resonance in injector feeding systems is one of the important factors in combustion instability.

In the paper, the main results of thermodynamic analysis and optimization of the hybrid two–stage carbon dioxide (СО2) transcritical mechanical compression–ejector cooling cycle are presented. The proposed hybrid cooling cycle contains a two–stage CO2 transcritical mechanical compression refrigeration machine and an ejector cooling machine using refrigerants R245ca, R601b, and R1233zd(E). The operation of the ejector cooling cycle is ensured by using some part of the heat rejected from the compressed superheated CO2 vapor of the mechanical compression refrigeration cycle. The cold obtained in the ejector cooling machine is used for subcooling the high–pressure CO2 vapor after the gas cooler. In addition, the intermediate cooling of the CO2 vapor after the low–pressure stage of the mechanical compression refrigeration cycle is realized by preheating and boiling the refrigerant of the ejector cooling cycle in the additional generator–precooler before entering the main generator–precooler. This paper presents a method for determination of the optimal design parameters and performance of the proposed hybrid cooling cycle. The results showed an increase in efficiency of the two–stage CO2 transcritical mechanical compression refrigeration machine in the proposed cooling system of up to 32.7% compared to the conventional system at transcritical operating conditions with high an environmental temperature.

Liquid atomization is crucial to ensure efficient combustion as it is an inherent part of the injector system. The combustion of fuels relies on effective atomization to increase the surface area of the fuel and consequently achieve high rates of mixing and evaporation. Pressure swirl atomizers are inexpensive and reliable type of atomizer for fuel injection owing to its superior atomization characteristics and relatively simple geometry. The Sauter mean diameter (SMD) of atomizer contributes significantly to the combustion chamber performance. This paper presents a two-step strategy to predict droplet SMD for atomisation model in pressure swirl atomizer through the combination of experimentally validated Computation Fluid Dynamics (CFD) and Optimal Latin Hypercubes (OLHC) Design of Experiments (DoE) techniques. A three-dimensional Eulerian two-phase CFD model is developed to account for liquid and gas phases as a single continuum with high-density variation at large Reynolds and Weber numbers and validated against experimental measurements, before being employed to carry out a parametric study involving operating conditions and fluid properties of the pressure swirl atomizer. The atomizer is then represented in terms of four design variables, namely liquid viscosity, liquid velocity, surface tension and atomizer exit diameter. An 87-point OLHC DoE is constructed within the design variables space using a permutation genetic algorithm resulting in an accurate SMD prediction. Results show the newly developed SMD prediction is found to be superior compared with existing correlations and indicate significant improvement in the droplets SMD.

In the present study, analysis of multi-nozzle ejector systems for aircraft compact heat exchanger applications is performed. CFD procedure is validated with experimental data of a single-nozzle ej...

The effects of submergence ratio and gas flow rate on the performance and hydrodynamic behavior of air–liquid two-phase flow have been investigated during liquid lifting in the developed bubble-generator-type airlift pump system. Here, a mechanistic model was also developed to predict the performance of the bubble-generator-type airlift pump system on the basis of pressure balance with considering the intake angle of the injector, and the suction pipe length. A developed image processing technique was implemented to determine the hydrodynamic behaviors including gas slug velocity, water slug velocity, slug length, and gas hold up under the various submergence ratio and gas flow rate. The submergence ratio is the ratio between the static lift and the sum of static lift and static head. The experimental result was found that the minimum air flow rate for removing water is reduced by 19.17% when the airlift pump is combined with an orifice-type bubble generator. The decrease in submergence ratio causes the lower the efficiency at the critical point of airlift pump-bubble generator. Under the same submergence ratio, an increase in the supplied air superficial velocity increased the hydrodynamic parameter. A mechanistic model from pressure balance and dimensional analysis have a maximum error of 11.97% and 3.33%, respectively.

This paper describes the testing and pulse performance analysis of a 45 N thruster, designated A45, using a 19.78% monomethylhydrazine–80.22% hydrazine fuel blend with mixed oxides of nitrogen cont...

In this work, two representative hybrid rocket injector designs, a single-port and an axial showerhead design, were examined experimentally to determine the comparative influence on the development...

Employing an ejector to recover the expansion work of the auto-cascade refrigeration cycle is a feasible method to improve the system performance. The system operation characteristics are closely relevant to the ejector geometry parameters. In order to obtain the critical structure parameters influencing the freezer's pull-down performance, experimental research was conducted on an ejector-enhanced auto-cascade refrigeration cycle applied in a low-temperature freezer. The impacts of the ejector nozzle throat, mixing chamber diameter and length, and the nozzle exit position on the system's pull-down and steady operation characteristics were explored. The experimental results illustrated that the cooling rate and the attainable freezing temperature were mainly influenced by the nozzle throat and mixing chamber length instead of the nozzle exit position and mixing chamber diameter. The nozzle throat diameter of 0.52 mm and the mixing chamber length of 25 mm was optimal concerning the fastest cool-down rate and lowest freezing temperature of -61.2 °C. At the early phase of the pull-down process, a small mixing chamber diameter would cause the ejector malfunction of the pressure lift. There was a worst nozzle exit position of slowing down the pull-down speed, rising the freezing temperature, and reducing the system COP and exergy efficiency at the given operations. The ejector yielded the maximum pressure lift ratio of 1.196 and the entrainment ratio of 0.523 at the optimal ejector geometries. This work would be helpful to guide the ejector structure optimization for the ejector-enhanced auto-cascade low-temperature freezers.

A comprehensive entrainment performance evaluation system of the ejector was built including four indexes. An ejector's Computational Fluid Dynamics (CFD) model was established, and the sensitivity analysis of the entrainment performance to four key geometry parameters of the ejector, namely, the nozzle diameter (Dn), the primary nozzle exit position (NXP), the mixing tube diameter (Dm), and the secondary flow inlet diameter (Ds) was performed. Based on the quantified boundary conditions obtained by the Simulink simulation, the ejector structure was optimized with a new method. It is found that the total recirculation ratio increases but the hydrogen recirculation ratio decreases with the increase of the relative humidity of the secondary flow. The hydrogen recirculation ratio shows a unidirectional increase tendency with the increase of Ds and the decrease of Dn and NXP. The hydrogen recirculation ratio increases firstly and then decreases with the increase of Dm. High hydrogen recirculation ratio with low primary hydrogen flow rate, corresponding to low current operation point of fuel cell system and low sensitiveness to the changing relative humidity are usually incompatible. The hydrogen recirculation ratio with low primary flow rate degrades significantly when Dn increases and Dm is larger than a certain value. The ejector with smaller Ds shows lower sensitiveness to the changes of relative humidity, while the hydrogen recirculation ratio with low primary hydrogen flow rate is not affected badly. When matching with a specific system, it is necessary to balance the ejection performance at low current density operating points and the sensitiveness to the changes of relative humidity in combination with the anodic gas state at each operating point, so as to find the optimal structural parameters. The optimization sequence of structural parameters should follow: Dn is selected firstly, then NXP and Ds are optimized, and finally Dm is chosen.

Curve diffuser is frequently used in applications such as HVAC, wind- tunnel, gas turbine cycle, aircraft engine etc. as an adapter to join the conduits of different cross-sectional areas or an ejector to decelerate the flow and raise the static pressure before discharging to the atmosphere. The performance of the curve diffuser is greatly affected by the abrupt expansion and inflection introduced, particularly when a sharp 90o curve diffuser is configured with a high area ratio (AR). Therefore, the paper aims to numerically investigate the effect of the expansion direction of AR=1.2 to 4.0 curve diffuser on loss characteristic and flow rectification. 90o curve diffuser operated at inflow Reynolds Number, Rein=5.934 × 104 to 1.783 × 105 was considered. Results show that pressure recovery improves when the area ratio increases from 1.2 to 2.16 for both 2D expansion (z- direction) and 3D expansion (x- and z- direction). On the other hand, the increase of inflow Reynolds number causes the flow uniformity to drop regardless of the expansion directions. 3D expansion (x- and z- direction) curve diffuser with AR=2.16, operated at Rein=8.163 × 104, is opted as the most optimum, producing the best pressure recovery up to 0.380. Meanwhile, 2D expansion (z-direction) curve diffuser of AR=2.16, , operated at Rein= 5.934 × 104, is chosen to provide the best flow uniformity of 2.330 m/s. 2D expansion (x- direction) should be as best avoided as it provides the worst overall performance of 90o curve diffuser.

This paper assesses the exergetic performance inside transcritical CO2 ejector refrigeration system integrated with thermoelectric subcooler (EJE + TES) through conventional and advanced exergy analyses. The results point out that 89.44% of the total exergy destruction is endogenous, which clearly demonstrates that it is not close in the interrelations among the system components. In addition, increasing the efficiency of the different components can decrease the exergy destruction by about 53.36%. The avoidable exergy destructions induced by the compressor is the highest, which indicates that priority should be given to the improvement of the compressor, followed by the thermoelectric subcooler, evaporator, ejector and gas cooler, while the expansion valve has almost no potential for improvement. This conclusion differs from that obtained by the conventional exergy method. The effects of the pinch temperature difference in each heat exchanger, as well as the compressor and ejector efficiencies on cycle theoretically exergetic performance are considered. When the compressor and ejector efficiencies increase from 0.5 to 0.9, the avoidable endogenous exergy destruction taking place in the corresponding system component are reduced by 93.61% and 82.33%, respectively. The performance of the EJE + TES system can be enhanced through reducing the pinch temperature difference.

The ejector driven by the high-pressure gas potential energy from the hydrogen storage tank can reliably recirculate the unconsumed hydrogen in the proton exchange membrane fuel cell (PEMFC) system. However, the fixed-geometry ejector cannot maintain consistently high performance among the whole power output range in the PEMFC system due to its shortage of limited operating range. In this paper, a coaxial two-nozzle ejector, satisfying the requirements of the PEMFC system under different power outputs, is developed for hydrogen recirculation. The proposed ejector is investigated numerically based on an experimentally verified simulation model to reveal the flow distribution and predict its performance. The simulation results show that the proposed ejector can work in a wide power range of 17.90–84.00 kW within a suitable supply hydrogen pressure range of 4–7 bar. More importantly, the ejector can not only maintain a recirculation ratio above 0.9 in the wide output power range but a high recirculation ratio greater than 2.0 in the low power output. The proposed ejector broadens the working range of a single ejector used in the PEMFC system, which significantly promotes the development of fuel cell being widely adopted in automobiles.

Air-assisted fuel injection (AAFI) systems may be installed in aviation piston engines for atomization of heavy fuels. However, there are few studies on the in-cylinder air-assisted spray characteristics, which affects the improvement of AAFI engine performance. In this study, an improved air-assisted spray simulation method based on ANSYS FLUENT was proposed to predict the changes in air-assisted spray characteristics alongside spray development, compared with previous simulations, the simulation in this paper was extended in both temporal and spatial domains and more accurate boundary conditions were given. The Eulerian–Lagrangian approach was used to represent the two-phase spray flow and a dynamic mesh model was used to simulate the movement of injector needle valve. The improved method was validated by comparison against experimental results in terms of spray shape, spray volume, spray penetration, spray droplet size spatial distribution, and overall Sauter mean diameter (SMD). By using the improved method, the average relative errors of the simulation results in spray volume and spray penetration were reduced by 13.5% and 10.2%, respectively. Additionally, some typical spray field parameters (gas phase pressure, gasified fuel mass fraction, etc.) were analyzed. The improved method can be used to study the in-cylinder air-assisted spray characteristics, which is beneficial for the fuel injection parameter optimization and the combustion chamber design of the AAFI engine.

The detailed mechanism of supersonic mixing enhancement by a novel device is investigated computationally based on the Navier-Stokes equations. The device is a wall-mounted three-dimensional cavity, several parts of the rear face of which are cut out, and the lower wall of the cut-out part has a slope directed toward the injector from which the injectant is discharged. The flow structures and behaviors observed in the computational results are confirmed in the experimental results. Experimental information about the high-frequency (several tens of kHz) pressure oscillation in the cut-out part is acquired in this study using a pressure-sensitive paint (PSP) responding to rapid change in pressure. The computational results reveal that a hairpin-like vortex is formed inside the cavity. The vortex works on the shear layer across the cavity to deflect it upward. The deflected shear layer shields the injectant from the primary flow, which causes the injectant to penetrate deep into the primary flow. The computational results also clarify that the expansion and compression waves produced in the rectangular part of the cavity are delivered effectively to the injector along the slope of the cut-out part, which is confirmed in the PSP measurement results. The delivered waves actuate the jet issuing from the injector to fluctuate up and down periodically with a large amplitude.

Ejectors are a kind of pump that does not have any moving components. In certain cases, the motor fluid may be a liquid, steam, or another gas. The research focuses on using nano adsorption combined with a multi ejector to fuel a sophisticated nano adsorption power plant, which is equipped with three shapes of steam boiler generators. The simulation was accomplished by implementing it with the cooperation of the two programs MATLAB A and MATLAB B, together with a solid flow. To raise the temperature of the working fluid before it enters the generator, a jet pump is positioned before the generator. To enhance the mass flow rate of vapor going into the ejector, a two-stage adjustable booster was added after the evaporator, which gives low evaporator temperature. A further experiment in which the two-stage adjustable booster was used before the generator to reduce the amount of work done by the generator. The ejector's cooling unit is powered by steam created from many energy sources powered by advanced hybrid heat and power systems, including solar energy and steam produced by the electric steam generator. The different devices are either directly triggered by a thermal source to achieve heating, cooling, or refrigeration. The steam boiler generator is the core of the cooling unit; in this research, various types of steam boiler generators are linked with adsorption units, such as steam-powered solar boilers, gas boilers, solid fuel steam boilers, and electric boilers. Heat exchangers were utilized to transfer heat from the solar chimney to the ejector cooling unit. The impact of various ejector geometries on the advanced cooling unit was studied and simulated for the single, double, and triple nozzle ejector. There were no issues with the more effective cooling unit. This unit performed better than traditional adsorption cooling units, having a greater efficiency.

The effects of dwell time on the mixture formation and combustion processes of diesel spray are investigated experimentally. A commercial multihole injector with a 0.123 mm hole diameter is used to inject the fuel. The injection procedure is either a single or split injection with different dwell times, whereas the total amount of injected fuel mass is 5.0 mg per hole. Three dwell times are selected, that is, 0.12, 0.32 and 0.54 ms, with a split ratio of 7:3 based on previous findings. The vapour phase is observed, and the mixture formation pertaining to the equivalence ratio is analysed using the tracer laser absorption scattering (LAS) technique. A high-speed video camera is used to visualise the spray combustion flame luminosity, whereas a two-colour pyrometer system is used to evaluate the soot concentrations and flame temperature. An analysis of the mixture formation based on the spray evaporating condition reveals a more concentrated area of the rich mixture within a 0.32 ms dwell time. In the shortest dwell time of 0.12 ms, the equivalence ratio distribution decreases uniformly from the rich mixture region to the lean mixture region. In the case involving a shorter dwell time, a suitable position for the second injection around the boundaries of the first injection is obtained by smoothly growing the lean mixture and avoiding the large zone of the rich mixture. Therefore, the shortest dwell time is acceptable for mixture formation, considering the overall distribution of the equivalence ratios. Spray combustion analysis results show that the soot formation rate of the single injection and 0.32 ms dwell time case is high and decreases quickly, implying a rapid reduction in the high amount of soot. Consequently, 0.12 ms can be considered the optimal dwell time due to the ignition delay and relatively low soot emission afforded.

The transverse injection of rich, premixed natural gas and air (NG-air) and natural gas, hydrogen, and air (NG-H2-air) reacting jets into a high-speed vitiated crossflow was investigated in this work at engine-relevant conditions. The high-speed vitiated crossflow at bulk velocities of approximately 114 and 256 m/s corresponds to crossflow Mach numbers of nominally M a ∞ = 0.15 and 0.35, respectively. For the M a ∞ = 0.15 crossflow, a minimum jet equivalence ratio near ϕ J = 1.4 was required to stabilize the NG-air flame near the elevated injector. Flame stabilization within the viewing window (up to approximately 90 mm downstream of injection) was not observed at M a ∞ = 0.35 for NG-air based on OH∗ chemiluminescence (CL) imaging. Hydrogen was added to the premixed jet and different levels of minimum hydrogen fuel fraction x H 2 were needed to stabilize the flame near the injector, depending on ϕ J . For both NG-air and NG-H2-air jets, flame stabilization near the injector resulted in a significant increase in ΔNOX emissions. The flame position and structure were observed to be different for very rich jets near ϕ J = 2.3 compared to moderately rich jets near ϕ J = 1.4, based on OH∗-CL and OH planar laser-induced fluorescence. For M a ∞ = 0.15, reactions in the windward shear layer were also apparent at x H 2 near 60%. The measurements presented in this paper, to the best of our knowledge, are the first reported measurements in the literature for premixed NG-H2-air reacting jets injected into a vitiated crossflow.

A refined physical model of the jet ejector working process has been compiled. On the basis of the refined physical model, a mathematical model has been developed that takes into account the exchange of work and heat between the ejected and ejected gases. Based on the solution of this mathematical model, it is possible to formulate a method for calculating the optimal geometric dimensions of the jet ejector to obtain the specified thermodynamic parameters and a method for calculating the characteristics of the jet ejector with known geometric dimensions. The effect of viscosity on energy exchange is shown. The agreement between the calculated and experimental data is satisfactory.

The flow dynamics and attrition characteristics of three air reactor designs are investigated using an Eulerian-Eulerian kinetic theory model. The hydrodynamics of these reactor designs are analyzed to identify the flow regimes in which the particles evolve. The investigated designs, which differ in the configuration of the secondary flow ports, exhibit bubbling and turbulent fluidization regimes in similar spatial regions. The most substantial differences in the hydrodynamics was in the turbulent fluidized regions near the secondary inlets. The mechanical stressing environments undergone by the particles were analyzed using the collision energy spectra, reconstructed using the local flow field properties (i.e. granular temperature and particle number density). The spectra show that the increase in the specific collision power is associated with the regions near the secondary injector ports, which are in a turbulent fluidization regime. A simple analysis relying upon a partitioning of the energy spectrum, showed that attrition rate may be reduced by about 34% over the original design.

The present study experimentally investigated the dynamic spray combustion process of a liquid-centered swirl coaxial injector using liquid oxygen/methane in an optically accessible liquid rocket engine. Data were obtained at combustor pressures from 0.4 to 1.8 MPa and the ratio of the oxidizer mass flow rate to the fuel rate between 1.32 and 1.55. Liquid oxygen was injected at 120 K, and the injection temperature of gaseous methane was about 285 K. Based on the obtained spatial distribution and oscillation characteristics of liquid oxygen/methane flame, the combustion process was described by four subprocesses: ignition, low-frequency oscillation combustion, quasi-steady state combustion, and shutdown. In the quasi-steady state combustion subprocess, both the flame length and the normalized flame area are the largest, and the flame expansion angle is the smallest. At the initial stage of combustion, the instability of the liquid oxygen phase state leads to flame instability, which generates low-frequency unstable combustion with a dominant frequency of 93.74 Hz. In addition, the high-frequency (2500-3000 Hz) oscillation of the flame appeared in the whole combustion process. It has been confirmed to be caused by the self-pulsation of spray. Furthermore, with the increase in liquid oxygen manifold pressure, the liquid oxygen phase state changes from a two-phase mixture of liquid and gaseous oxygen to a liquid phase, which increases the mass flow rate of liquid oxygen entering into the combustor, thus generating the increase in the high oscillation frequency of the flame through the whole combustion process.

The purpose of this study was to experimentally investigate a dual evaporator ejector system (DEES) operating with R134a and R456a. In order to see the effect of expansion valves in the system, the...

A well-characterized multi-hole gasoline injector, the Engine Combustion Network’s (ECN) Spray G injector, was investigated in an optically accessible research engine under four motored operating conditions with early injection. The experiments were conducted at intake pressures of [Formula: see text] and [Formula: see text], nearly matching the ECN’s standard early injection operating conditions, Spray G2 (flash boiling) and Spray G3 (early injection), respectively. This was combined with two engine speeds at [Formula: see text] and [Formula: see text]. Using particle image velocimetry and volumetric Mie scatter imaging, the in-cylinder flows were evaluated and the effects on the spray morphology were characterized. The in-cylinder flow was evaluated to understand the spray-flow interaction, including the turbulent kinetic energy. Little effect on turbulent energy was observed in the region examined near the exit of the fuel injector nozzle shortly after injection. Mie scatter imaging was used to characterize the spray morphology and wall wetting was clearly visible on the spark plug. Cyclic variability of the sprays was found to be insignificant; and major differences in spray morphology are attributed to the in-cylinder velocity and intake pressure at the time of injection. Decreasing the bulk gas density by decreasing the intake pressure had a number of effects on the evolution of the spray including faster evaporation, increased axial liquid penetration, and decreased spray angle. Increasing the in-cylinder flow magnitudes by increasing the engine speed had a similar effect on spray morphology by also increasing the evaporation rate, increasing the axial penetration, and decreasing the spray opening angle. Comparison of the motored spray cases with a no-flow case (when the fuel is sprayed into the engine without the piston present) further illustrated the extent to which the intake flow influenced the spray shape.

Air and hydrogen supply systems are key subsystems of polymer electrolyte membrane (PEM) fuel cell systems. This paper reviews the research on the gas (air and hydrogen) supply systems and equipmen...

An increase in gas turbine efficiency is possible by inlet air cooling in chillers converting a heat of exhaust gas into refrigeration. In traditional absorption lithium-bromide chillers of a simple cycle an inlet air can be cooled to 15°С. More decrease of turbine inlet air temperature and greater fuel saving accordingly is possible in refrigerant ejector chiller as a simple in design and cheap. The innovative turbine inlet air cooling (TIC) system with absorption chiller as a high-temperature and ejector chiller as a low-temperature stages for cooling air to 7 or 10 °C is proposed. Its application in temperate climate provides annual fuel saving by 1.5 to 2 times higher compared with traditional air cooling in absorption chiller to 15 °C. A novel universal method of analysing the efficiency of TIC system operation and rational designing has been developed. The method involves the simple numerical simulation based on real input data of site actual climatic conditions. The annual fuel saving is chosen as a primary criterion. The novelty of the methodological approach consists in replacing the current yearly changeable fuel reduction due to TIC by its hour-by-hour summation as an annual fuel saving. The increment of annual fuel saving referred to needed refrigeration capacity of TIC system is used as an indicator to select a design refrigeration capacity. A rational design refrigeration capacity determined by applying the novel methodology allows to decrease the TIC system sizes by 10 to 20% compared with traditional designing issuing from the peaked thermal load during a year. So far as it was developed analytically by introducing quite reasonable criterion indicator and based on the simple summation procedure the method is quite applicable for designing in power and energy.

Sheet-breakup characteristics of a single liquid swirl injector is important for understanding swirling flow characteristics of the swirl coaxial injector. Also, acquirement of a precise breakup length of a swirl injector could be used as a guideline for designing the injector for small thrusters. Theories for obtaining this breakup characteristic have been developed using the waveform instability of a thin liquid sheet. However, these theories could not explain the effect of internal instability of the swirl injector on the breakup characteristic. In the swirl injector, internal instability could be caused by air core fluctuation and this instability could affect the wave and breakup characteristics of the spray sheet. Therefore, in this study, the effect of internal flow instability of the swirl injector on the spray-sheet breakup characteristics was investigated. At first, it was proposed to substitute the new value of the internal growth rate ωint for the existing growth rate, and an empirical formula for the internal growth rate value was presented based on experimental results. Through this equation, it was confirmed that the breakup length could be more accurately calculated using the swirl injector condition in which the internal flow instability of the injector was the dominant influence. Then, a semi-empirical equation for calculating the breakup length more accurately was proposed.

Liquid–gas ejector as a key component of jet loop reactor (JLR), plays an important role in the continuous production of gas–liquid mixing reaction. In this paper, a formula for estimating the gas induction of the ejector is presented. The effects of nozzle radius and mixing length on gas induction of liquid–gas ejector for gas–liquid mixing are simulated, and the formula is verified. Focusing on the efficiency and gas induction, the geometrical parameters are analyzed for the same cases, so that the performance of the ejector can be thoroughly understood. The results show that the optimum mixing section length to diameter ratio (LDR) is about 5–7, and the decrease of nozzle outlet radius can increase the gas induction, which provides a reference for the evaluation of gas induction for liquid–gas ejector and has crucial guiding significance for the design of nozzle and mixing section of liquid–gas ejector in industry.

Understanding the hydraulic and frictional sensitivity of fault to different injection conditions is one of the efficient ways to provide useful implications for fault reactivation potential. Numerical simulations of fractured reservoir have provided information on how fault behaviour varies under changing hydromechanical properties and injection conditions. A coupled hydro-mechanical model which can represent the elastoplastic behaviour of a fault was employed to predict and quantify the effects of varying injection positions and injection rates on permeability response and potential of fault reactivation under isothermal injection. We examine the sensitivity of seismic event magnitude and timing to variations in both pressure perturbation and stress as injection location changes. We generate results for two scenarios: one with changing injection position but with uniform injection rate, and another scenario with increasing injection rate at the same injection position. We observed that the potential of fault reactivation is affected by the hydraulic diffusivity potential of the fluid pressure, and this mechanism is mediated by a function of the injector position and injection rate. As the velocity of fluid transmission increases, increasing fluid pressure impact pore pressure elevation and reduced effective stress. However, an injector position where there is low diffusivity causes low pore pressure build-up rate, incapable of inducing shear failure, and thus, permeability enhancement is retarded in this case. Accordingly, the injection rate variation influences the rate of pore pressure build-up, the timing and magnitude of induced seismic events. This is also reflected in the permeability evolution as a response to the variations in the magnitude of fault openings and cracks. This changing injection conditions however influences the timing required to reach the critical peak friction point as pore pressure build-up rate and sensitivity to loading response change. Hence, with changing position and rate of injection, the evolution of fault permeability appears to be intrinsically controlled by a condition which favours elastoplastic deformation and fracture failure, with slip distance increasing with high injection rates.