Nozzle Outlet Research Articles

Study on the Influence of Nozzle Ablation on the Performance of the Solid Rocket Motor

As a key component of the solid rocket motor, nozzle ablation is very important to the performance of the motor. In order to study the influence of the law of nozzle ablation on motor performance, a two-dimensional axisymmetric model of a ground state nozzle and vacuum state nozzle before and after ablation was constructed on the basis of a reference profile, and the change law of pressure, temperature and velocity with ablation were studied. The comprehensive performance of the nozzle before and after ablation was calculated to evaluate the influence of ablation on motor performance. It was found that the profile ablation changed the shock wave distribution in the flow field of the expansion section, and the appearance of the ablation step also led to a new internal shock wave. The gas was compressed, and the flow direction, velocity, pressure, temperature, etc., were changed. After the ablation, the temperature and pressure of the nozzle outlet location increased, the velocity decreased, and the total thrust and specific impulse decreased.

Conical liquid sheet morphology and 3D droplet distribution of aviation kerosene pressure-swirl spray with digital off-axis holography

In this study, the test performance of high-resolution digital off-axis holography for the non-spherical droplet characteristics and spatial distribution in the primary breakup region of a pressure-swirl nozzle were experimentally investigated, with spatial resolution of 4.5μm and 3.0μm. The field of interest (FOI) was restricted within 9 mm downstream of the nozzle outlet, where the primary and some secondary breakup processes take place. The liquid investigated here is RP-3 kerosene, and the injection pressure and liquid temperature were controlled in the range of 0.5 ∼ 1.0 MPa and 250 ∼ 291 K separately. Clear spray morphology and deformed droplet image were obtained through the holographic reconstruction process. Droplet extraction criteria were proposed to distinguish deformed droplets from ligaments. The overall drop size and ellipticity distribution were quantified and discussed. The results show that the overall drop size distributions near the nozzle are also typical single-peaked curves. The proportions of non-spherical droplet increase as the fuel pressure and temperature increase. The spatial Sauter mean diameter (SMD) distributions of spray at different positions downstream of the nozzle were calculated, with the grid size of 1 × 1 × 1 mm3, showing the doughnut-like annular SMD and droplet number distribution profiles of the hollow conical spray. As the temperature and fuel pressure decrease, SMD distribution becomes uneven and larger. Fine droplets exist in the region where the perforation and primary breakup process occur, and the SMD increases over the axial distance due to the breakup process of ligaments near the nozzle. Results also prove that digital off-axis holography presented here is expected to realize the 3D viewing of the conical liquid sheet and statistical quantification of the droplet where primary and secondary breakup processes mainly occurred.

Numerical Research on the Jet-Mixing Mechanism of Convergent Nozzle Excited by a Fluidic Oscillator and an Air Tab

Unsteady numerical simulations, coupled with the SST (Shear Stress Transport) k-ω turbulence model, were conducted to study the mixing-enhancement characteristics of the excited jet generated by the fluidic oscillator and the air tab in a single channel convergent nozzle with an inlet total pressure of 140–200 kPa. Compared with the steady air-tab jet, the sweeping jet generated by the fluidic oscillator has roughly the same penetration in the main flow, but it can induce streamwise vortices and planar vortices of larger scale and longer duration, which is beneficial to enhance jet mixing efficiency in the range of 1.0 DN (DN represents the diameter of the main nozzle outlet) downstream from the main nozzle. When x > 1.0 DN, the jet mixing is mainly dominated by the shear layer between the main jet and the ambient. As the sweeping jet suppresses the expansion of the main jet, which reduces the contact area between the main jet and the ambient, its mixing efficiency is less than that of the air tab in this region. With the increasing inlet total pressure of the fluidic oscillator, the influence range of the sweeping jet is increased, but its mixing efficiency does not increase significantly. In general, the fluidic oscillator can use a small jet flow (<5%) to achieve a high mixing efficiency (i.e., 60% at x = 2.0 DN) at the expense of low total pressure loss (<2.3%), which indicates that it has good engineering applicability.

Experimental Evaluation of the Influence of the Diameter of the Outlet Nozzle Bore of a Gas Injector on Its Flow Characteristic

Despite the growing share of electrically powered vehicles, internal combustion engines are still one of the primary sources of propulsion in transportation. One way to decarbonize engines is to use alternative fuels, where liquefied petroleum gas (LPG) accounts for a large share. Popular car gas systems are LPG indirect vapor phase injection systems, in which the low-pressure gas-phase injector is the actuator. The purpose of the research and analysis presented in this paper is to determine the flow characteristics of three injectors that are structurally different depending on the diameter of the outlet nozzle bore. The tests are conducted, which is new, with pulsed operation of the injector, which, as it turned out, helps explain the discrepancies found. The obtained characteristics are fitted with a polynomial of the second degree, obtaining high-quality indices. In the group of three tested injectors, the average values of volumetric flow rate decreases relative to the maximum by 19.6 and 35.8%. Differences in opening times of 29.3 and 36.6%, respectively, are cited as one of the main reasons for this. Closing times are similar to each other. In addition, the injector with the highest volumetric flow rate and the shortest opening time obtains 1.8 and 9.94% lower average cycle pressures measured at the outlet of the injector nozzle. The differences in opening times and average cycle pressures are considered as possible reasons for the differences in flow characteristics. The obtained characteristics are applicable to engine conversions and calculations.

A non-axisymmetric temperature field reconstruction method based on the interferometric fringe schlieren method

The typical non-axisymmetric temperature field distribution in the tail nozzle outlet area of the combustion chamber of an aircraft engine can reflect the operating state of the engine. As an effective non-contact method for measuring a non-axisymmetric temperature field, the traditional background-oriented schlieren (BOS) method has the problem that the extraction accuracy of light deflection is not high. In this paper, interference fringes are introduced into the schlieren measurement, and the highly sensitive fringe offset replaces the traditional background speckle offset for measurement, which realizes accurate reconstruction of the non-axisymmetric temperature field. Firstly, through the interferometric fringe schlieren (IFS) method comprising multiple sets of double-slit interferometric systems and imaging sensors, the offset of the interference fringe after passing through the non-axisymmetric temperature field is measured by image processing. The spatial refractive index field is then reconstructed by the filtered back-projection algorithm under the sector model proposed in this paper and the spatial temperature field is obtained. The experimental results show that the temperature field reconstruction error is smaller for the IFS method than the BOS method, the measurement area is accurate from 0.5 mm for the BOS method to 0.2 mm for the IFS method and the temperature error range is reduced from 50 K for the BOS method to 25 K for the IFS method.

DETERMINATION OF ENERGY PARAMETERS OF Ni+Al2O3 POWDER PARTICLES IN A SUPERSONIC NOZZLE DURING COLD GAS-DYNAMIC SPRAYING USING THE ANALYTICAL METHOD

Purpose. To calculate the temperature and velocity of nickel and aluminum oxide particles in the supersonic flow in the low-pressure cold gas-dynamic spraying nozzle. To investigate the effect of gas parameters at the nozzle inlet, in particular temperature and pressure, on the velocity and temperature of particles at the nozzle outlet.
 Research methods. The calculation of the temperature-velocity characteristics of the powder particles is performed after determining the parameters of the gas flow in the supersonic nozzle channel using well known gas-dynamic dependencies. The initial data for the calculation are the following: the geometry of the nozzle, the temperature and pressure of the gas (air) at the nozzle inlet. The density of the material from which particles are obtained, as well as their diameter, were taken into account in the calculation of the energy parameters. Nickel particles with a diameter of 25 µm and aluminum oxide particles with a diameter of 22 µm were used.
 Results. Based on the calculations results, graphs of changes in the velocities and temperatures of the particles of the investigated powders, as well as working gas, in the channel of the low-pressure cold gas-dynamic spraying supersonic nozzle were developed. The dependences of the temperature-velocity parameters of the particles at the nozzle exit in the range of initial values of temperature at the nozzle inlet from 300 to 600 C° and pressure from 0.6 to 1.0 MPa were also developed.
 Scientific novelty. The influence of the initial parameters of the gas at the nozzle inlet in a wide range of values on the temperature and velocity of nickel and aluminum oxide particles during the low-pressure cold gas-dynamic spraying is shown.
 Practical value. The obtained results can be used to determine rational spraying parameters in the development of technological processes of deposition of protective and restorative coatings from Ni+Al2O3 powder mixture.

Double coaxial pipe jet control using DBD-PA and bluff body

In this study, a double-tube burner nozzle with a DBD-PA (dielectric barrier discharge plasma actuator) and flame holder was employed to regulate the lifted flame. The flame holder held the lifted flame and the DBD-PA regulated the lifted flame to suppress the lifted flame’s vertical oscillation. To form a lifted flame, pseudo-biogas, a mixture of CH4 and CO2 in the ratio of 6:4, was jetted out through an inner nozzle and air through an annular nozzle. To control the air jet and prevent the lifted flame’s vertical oscillation, the DBD-PA was installed inside an annular nozzle. The DBD-PA was driven intermittently at regular intervals to produce a tangential flow in the same direction as the jetting gas, and the flame holder was placed above the nozzle outlet on the nozzle center axis. The finding indicated that by driving the DBD-PA at the slightly lower frequency than the frequency of the naturally shedding vortices in the free jet, the lifted flame’s vertical oscillation can be reduced by collapsing the jet’s vortex ring at a steady position and with a steady cycle. By impeding the lifted flame’s vertical oscillation, it is forecasted to reduce the blowout of the lifted flame and combustion noise.

EXPERIMENTAL RESEARCH AND DEVELOPMENT OF A METHOD FOR CALCULATING THE PARAMETERS OF BOREHOLE HYDROMONITOR DISINTEGRATION OF RICH IRON ORE IN PLACE

Purpose. Study and development of a rational methodology for calculating the parameters of the process of downhole hydrodisintegration of martite ore massifs by pressure rotating water jets. Methods. Mine experimental-methodical and experimental-experimental works on: stage-by-stage study of the engineering and geological situation of ore deposits and selection of experimental sites; development of technological schemes for the hydrodisintegration of the ore in place and the creation of appropriate experimental equipment; selection of means for providing hydro-extracting operations; the choice of methods for monitoring and measuring the parameters of the hydrodisintegration process; generalization and analysis of the results of experiments and development of recommendations for the creation of technology and equipment, taking into account the achieved indicators. Results. A technique for calculating the parameters of hydrodisintegration of rich martite ores martite ore in places has been developed based on the study of the features of the formation of rotating compact water jets by borehole hydromonitors. Scientific novelty. Relationships between the structural and morphological characteristics and jointing of martite ores (porosity, the ratio of the grain composition of the ore, the ultimate uniaxial compression strength of ore and lumpiness) and the parameters of the hydromonitoring effect (water pressure, the initial diameter of the jet and the speed of its movement along the exposure of the face), which make it possible to determine rational technological parameters of hydrodisintegration products. Practical implication. Borehole hydromonitor disintegration of martite ores in place is a combined ore preparation process, including enrichment grinding operations and classification of destruction products according to their granulometric composition during their erosion. At the same time, there is a selective opening of ore-forming minerals that improve the quality of the ore by 0.5–1.5% compared to natural, a decrease in the mass fraction of silica from 2.0–1.2 to 0.5–0.3%, which ensures the production of iron ore raw materials of the highest quality – superconcentrates with an iron content of 69.0–69.5%. Control of the granulometric composition of hydrodisintegration products is achieved by adjusting the initial water pressure at the outlet of the jet nozzle, the speed of the jet along the face exposure and the orientation of the jet relative to the elements of occurrence and texture of the ores.

Особенности численного моделирования работы воздушно-тепловой завесы в OpenFOAM

The issues of mathematical modeling of turbulent heat-conductive flow of compressible viscous medium in the internal volume of the body of an air-thermal curtain equipped with a tangential fan are considered. The solution of the problem is constructed on the basis of averaged Reynolds (Favre) Navier-Stokes equations. The solution of the problem is obtained using the MRF (Multiple Reference Frame) approach, which uses a rotating reference frame, and using a transformation of the basic Navier-Stokes equations in the rotation zone. In order to correctly describe the working processes occurring in the internal volume of the air-thermal curtain and in the environment, modular multiblock meshes are applied in the work, including those allowing to separate rotating and stationary areas. The solution of the set tasks is constructed using the tools of the OpenFOAM package. As a result of the work, the peculiarities of the flow structure in the flowing part of the air-heat curtain are described in detail, and the gas velocities achieved at different fan speeds are estimated. The self-similarity of velocity profiles at the air curtain nozzle outlet is shown.

Title Supersonic Condensation and Separation Characteristics of CO2-Rich Natural Gas under Different Pressures

Supersonic separation technology is a new natural gas sweetening method for the treatment of natural gas with high CO2 (carbon dioxide) content. The structures of the Laval nozzle and the supersonic separator were designed, and the mathematical models of supersonic condensation and swirling separation for CO2-CH4 mixture gas were established. The supersonic condensation characteristics of CO2 in natural gas and the separation characteristics of condensed droplets under different inlet pressures were studied. The results show that higher inlet pressure results in a larger droplet radius and higher liquid phase mass fraction; additionally, the influence of centrifugal force is more pronounced, and the separation efficiency and removal efficiency of CO2 are higher. When the inlet pressure is 6 and 9 MPa, the liquefaction efficiency at the Laval nozzle outlet increases from 56.90% to 79.97%, and the outlet droplet radius increases from 0.39 to 0.72 μm, and the removal efficiency is 31.25% and 54.52%, respectively. The effects of inlet pressures on the removal efficiency of the supersonic separator are complicated and are controlled by the combined effects of liquefaction capacity of the nozzle and centrifugal separation capacity of the swirl vane.

NUMERICAL SIMULATION OF THREE-DIMENSIONAL CIRCULAR FREE TURBULENT JET FLOW USING DIFFERENT REYNOLDS AVERAGE NAVIER-STOKES TURBULENCE MODELS

The present research work shows the numerical investigation of free turbulent jet behavior as well as thermal characteristics of the jet being issued from the circular nozzle outlet and it is performed by solving the different Reynolds averaged Navier-Stokes (RANS) equation. In this research work, central jet velocity, and turbulent intensity of the jet along with thermal characteristics are calculated along the jet axis to check the coherency, heat-exchanging capability, and widening of the jet. Simulation results of the jet are first validated with the experimental data of previous literature work. The numerical experiment provides a better potential for future improvements in the field of jet flow and exhibits a great deal of resemblance with experimental data with minimum error. Computational fluid dynamics (CFD) is a capable tool for depicting the various flow behaviors and selecting the suitable turbulence model is always required for an accurate prediction of the jet-flow regime. Most of the turbulence models investigated in this research work show good results for turbulence intensity and predicted the near- and far-field region as per the experimental data. From the thermal analysis of the free turbulent jet, it is seen in the present results utilizing the various turbulence RANS models that <i>Nu</i><sub>x</sub> is rather high near the nozzle exit. The standard <i>k-ε</i> model describes the near field and long field of the free jet very well and it is also easy and inexpensive to execute. Furthermore, for the observed free turbulent jet, the most appropriate model is recommended.

Effects of cryogenic gas jet cooling on milling surface roughness and tool life for GH4169 alloy additive manufacturing parts

Hybrid additive and subtractive manufacturing is development in metal additive manufacturing techniques, wherein the dry cutting cooling method for subtractive cutting is one of the key technologies. To improve the milling performance of GH4169 alloy (namely Inconel 718 nickel-based superalloy) additive manufacturing parts, a dry cutting cooling method with a cryogenic gas jet and its effects on the cutting performance were investigated in this study. The theoretical model of the cryogenic gas jet flow was established, and the geometric characteristics, motion characteristics, and temperature distribution of the jet flow were analyzed. Meanwhile, considering the design of the nozzle outlet, the jet flow core length with a single nozzle and jet flow field envelope effect on the cooling heat transfer process with multiple nozzles were analyzed using a finite element simulation. Then, milling experiments on GH4169 alloy additive manufacturing parts with different cryogenic gas jet flow parameters were carried out. To reduce tool wear and the machined surface roughness of various parts, the jet flow parameters were optimized using the response surface analysis method. The effects of the milling feed direction on the tool wear and machined surface roughness were investigated. Furthermore, the tool wear morphologies were observed under different continuous milling times. The chemical compositions of the worn zone and tool wear mechanism were analyzed. The results show that cryogenic gas jet cooling can significantly improve the tool life and machined surface roughness of parts for GH4169 alloy additive-manufacturing-part milling, and the continuous cutting time within the tool wear allowance can reach approximately 50 min.

Effects of fuel nozzle shape on soot emission of coflow diffusion flames

An experimental study was conducted on the effect of the shape of the fuel nozzle outlet on the suppression of soot emission from a coaxial flow diffusion flame. Three nozzle shapes were used, namely circular, square, and an equilateral triangle. Propane was used as the fuel and air as the oxidizer. The fuel flow rates Qf were 2, 3, and 4 cm3/s. At the maximum Qf of 4 cm3/s, the nozzle shape changed the soot discharge characteristics and the flame structure. The soot discharge was suppressed the most with the triangular nozzle and the least with the circular nozzle. The shape of the soot concentration distribution near the flame tip was similar to the nozzle shape, indicating that the influence of the nozzle shape reached the flame tip. Soot formation started earliest in the triangular nozzle and latest in the circular nozzle. In non-circular nozzles, soot started to form from the downstream regions of the corners of the nozzle rims. This is because the profile of the fuel flow was close to the flame front in these downstream regions. Soot oxidation was fastest in the triangular nozzle and slowest in the circular nozzle. Therefore, the flame was the lowest in the triangular nozzle and the highest in the circular nozzle. The oxidizer flow velocity toward the flame base was high in the downstream region of the flat side of the non-circular nozzles. The velocity was especially high in the triangular nozzle, and the CH radical emission, which is closely related to the heat release rate, was also strong at the flame base. As mentioned above, the fuel concentration distribution, the convective transport of the oxidizer, and the flame structures changed in the non-circular nozzles, and in particular, soot emission was suppressed in the triangular nozzle.

Design of a fixed-pipe cold aerosol spraying system for chemical application in greenhouse

Since the high temperature and humidity in a closed environment, pests and diseases are infecting and spreading seriously in greenhouses. However, the prevention and control of pests and diseases in greenhouses are still dominated by knapsack sprayers. For those reasons, based on twin-fluid atomization, droplet dispersion, and constant pressure transportation technique, a fixed-pipe cold aerosol spraying system composed of the control unit and the fixed-pipe spraying unit comes into being. The indoor pipeline execution unit of the spraying system could be interfaced with the liquid-supply or gas-supply equipment such as the liquid pump, air compressor, and tank of the outdoor master control unit through a quick coupling, which could realize the separation of operator and sprayer in hermetic greenhouse. The atomization of twin-fluid nozzle and the droplet deposition and distribution of the spraying system in greenhouse were tested. Results showed that about 70% of the particle size of the twin-fluid flow nozzle concentrated in the range of 32-65 μm under the spraying air pressure ranged from 0.2 MPa to 0.4 MPa. When the air pressure was 0.2 MPa, 0.3 MPa, and 0.4 MPa, the wind speed at the nozzle outlet reached supersonic speed, as the corresponding VMD of droplets were 45.6 μm, 43.2 μm, and 36.8 μm, respectively. The higher the air pressure is, the more uniform the spray deposition is in the greenhouse. When the air pressure was 0.2 MPa, 0.3 MPa, and 0.4 MPa, the CVs of the liquid deposition in the greenhouse were 109.1%, 62.6%, and 35.4%, respectively. The droplets produced by the spraying system will rapidly disperse into the whole greenhouse. The average deposition was 2.99 μL/cm2 in the front area of the nozzle, the deposition was 1.24 μL/cm2 in the area between two nozzles, and the deposition was 0.58 μL/cm2 in the area behind the nozzles. The spraying system is characterized by the distribution of spraying liquid throughout the entire greenhouse. Keywords: greenhouse, twin-fluid nozzle, spraying system, droplet spectra, distribution, deposition DOI: 10.25165/j.ijabe.20231601.6573 Citation: Wang S L, Lu D P, Li X, Lei X H, Tang Y X, Lyu X L. Design of a fixed-pipe cold aerosol spraying system for chemical application in greenhouse. Int J Agric & Biol Eng, 2023; 16(1): 53–59.

Formation of TiN coatings by air plasma spraying

Titanium nitride (TiN) coatings were obtained on the surface of 12Kh18N10T steel by air plasma spraying (APS) of TiN powders using an arc plasmatron made by the authors. The plasmatron has a node of circular input and gas-dynamic focusing of the powder and the output apertures of the nozzle-anode are made in the form of rectangular narrowing-expanding channels (No.34334 RK: IPC H05H 1/42). A study of operation modes of a plasmatron for spraying of powder coatings was carried out. The structural-phase state, microhardness and wear resistance of TiN coatings were systematically investigated. The optimum APS operating mode for deposition of TiN powder was determined: current 250 A, voltage 68 V, argon gas flow 34 L/min, spraying distance 150 mm. To reduce the oxidation of TiN powder in the APS process, a method of creating a nitrogen environment at the outlet of the anode nozzle, nitrogen flow rate 2.3 bar was used. The results of structural analysis showed that TiN is the main phase of the coating. The mechanism of formation of TiN structures was characterized by analyzing SEM results of TiN coating surface morphology and TiN droplets sprayed on the surface of the sample. The results showed that the TiN(1) coating has better wear resistance than the TiN(2) and TiN(3) coatings. The cross-sectional and longitudinal microhardness of the TiN coating was investigated. The highest cross-sectional hardness of TiN coating is 1250 HV0.1, which is in accordance with mode 1.

Experimental study on pressure oscillation phenomenon of vertical upward bubble submerged jet under heave conditions

With the vigorous progress of nuclear industry under marine environment, the ocean motion will exacerbate the pressure oscillation phenomenon caused by the change of the steam-liquid interface during the jet, causing great harm and challenges to the security and steady operation of device related to steam submerged jets. Therefore, the effects of heave motion on the steam bubble morphology and pressure oscillation phenomenon of jets with vertically upward low mass fluxes were experimentally investigated. The experimental results show that when the heave motion is upward, the steam bubble will be stretched obviously in the necking and detachment stages; while when the heave motion is downward, the steam bubble will accumulate at the nozzle outlet during the growth initial stage. Compared with the land environment, the heave motion increases the dominant frequency and pressure pulses average amplitude, and the dominant frequency and pressure pulses average amplitude have a positive correlation with the heave amplitude and a negative correlation with the heave period. In addition, there is a positive correlation between the Strouhal number and the heave maximum acceleration amplitude. An experimental correlation is proposed to predict the dominant frequency in heave motion, and the error is basically within ±30%.

Numerical analysis of the flow field in a planar nozzle for different divergent angles

In the present work, the flow field is analysed for Mach number, pressure and temperature in 2D computational domains for a planar nozzle of symmetrical geometry as used in the experimental tests for cold (air) flow. The study has been considered for three mean angles of the divergent section: α = 9°, α = 11.01° and α = 13°, and for four pressure ratios: NPR = 2.412, NPR = 3.413, NPR = 5.423 and NPR = 8.78. For the numerical simulation of the turbulence in the presence of shock waves, the RANS model, the Sutherland equation and the Spalart-Allmaras turbulence model were used in the ANSYS-Fluent R16.2 code. The results obtained show fluctuations at the intersections of the internal shocks in the divergent, and the fluctuation decreases as the angle of the divergent increases. For NPR = 3.413, NPR = 5.423 and NPR = 8.78, the Mach number at the nozzle exit is the same, where for α = 11.01° Mach 2.00 was obtained, and based on this reference, for α = 13° there is an increase in velocity of 4.15% and for α = 9° a decrease in velocity of 3.78%. The lowest pressure and temperature drop occurs at the nozzle outlet for α = 13°.

Silesian University of Technology, Gliwice, Poland

An efficient MQL system (Minimal Quantity Lubrification) ensures the proper cooling of the various moving parts, resulting in the cutting process on the machine tools. The introduction of MQL systems responds to the growing demand in the industry with a whole host of real benefits. The geometry of the nozzle influences the flow parameters of the coolant; these parameters can also be influenced by the nature of the fluid or liquids used. The nozzle of the cooling system has a convergent-divergent geometry, the dispersion of the fluid in the areas to be processed being better. A high temperature in the working area above a certain critical value can be harmful to the quality of the surface and can have some negative influences on the life of the cutting tool. MQL-type cooling systems combine different cooling fluids to achieve better cooling and lubrication of the cutting area. Following the simulations performed, the coolant speeds depend on the length of the analyzed nozzle, we can see that the speed has a lower value in the initial section of the nozzle which increases at the nozzle outlet. After exiting the convergence-divergence nozzle, the fluid jet velocity decreases in proportion to the fluid jet length, the simulation of these phenomena can optimize the geometry for the chosen purpose. The present paper aims to analyze the types of coolants and their correct choice, temperature control resulting from the cutting process is achieved due to the correct distribution of cooling fluids in the processing area, optimization can be achieved through computer simulation.

Impact of combustion chamber wall heat loss on the energy, exergy, ecology, NOx emission based performance and multiobjective optimization of the precooled scimitar engine

In this paper, the impact of the combustion chamber wall heat loss on the performance of the hydrogen-fueled precooled combined cycle Scimitar engine is investigated. Overall and exergy efficiencies, coefficient of ecological performance and coefficient of emission based ecological performance (CEEP) are considered as the performance indicators to analyze the effects of wall heat loss flux, chamber length, chamber contraction area ratio, throat area and nozzle convergent half angle. A multiobjective optimization is carried out to find the optimum values of hydrogen and air mass flow rates, cruise speed and altitude and core nozzle outlet area. It is found that a wall heat loss flux of 10 MW/m2 decreases the overall efficiency by 1.1% and causes an increase of 2 kJ/gNOx in CEEP. Multiobjective optimization revealed that increasing the hydrogen mass flow rate, decreasing the cruise speed and air mass flow rate improve the overall performance while the optimum values of cruise altitude and core nozzle outlet area are 23 km and 4.94 m2, respectively. The optimized design has a 20.35% better emission performance than the base design with a compromise of a 3.38% reduction in the overall efficiency.

Experimental and numerical investigation of an innovative non-combustion impulse gas turbine for micro-scale electricity generation

Fulfilling electricity demand in a remote platform has been a great challenge for oil and gas industry. With only pressurized gas line available, the choice of technology that can be implemented is limited; one of it is impulse gas turbine. At the moment, no studies investigating the performance of a compact impulse gas turbine which utilizes pressurized gas line has been reported, hindering the wide adoption of this technology. This study is therefore conducted with the main objective to investigate the performance of small scale impulse gas turbine for electricity generation by using computational fluid dynamics (CFD) approach in tandem with experimental validation. Three-dimensional computational model for the turbine is developed. Concurrently, an experimental set-up, consisting of micro impulse gas turbine, electric generator, flow loop and control system, is prepared to validate the model prediction. The effect of several key parameters, such as working fluid, rotational speed, mass flow rate and input pressure are evaluated to obtain operating envelope of the turbine. Overall, good agreement is achieved between numerical model prediction and experimental measured value. On the effect of working fluid, the results indicate that the impulse gas turbine driven by natural gas at 69 bar produce maximum power output of 1743.81 W at lower speed of 4500 RPM while maximum power of 1084.04 W can be achieved when driven by compressed air at 19 bar at rotational speed of 7000 RPM. In addition, a complete operating envelope for the turbine operating with either compressed air or natural gas has been developed. Furthermore, the effect of distance between nozzle outlet and turbine blade has been evaluated for which the optimum distance within studied range is obtained: 49.62 mm for one with compressed air and 54.62 mm for one with natural gas. The result from this study is expected to serve as a guideline in designing micro impulse gas turbine for electricity generation especially for remote offshore platform.