Injection Orifice Research Articles

Swirled injector modeling for cavitating multiphase flow

The goal of this study is to present a comparison between different approaches to multiphase injection modeling of self-pressurized rocket engine propellant. Swirled, tangential orifice injector of nitrous oxide, for an “N” class hybrid rocket motor is the object of the study. A brief descriptionof the injector purpose and geometry is provided, followed by a description of different approaches for flow modeling. Examined techniques range from 0D, Homogeneous Equilibrium Model (HEM) to 3D multiphase with mass and heat exchange between phases. Results of analyses are provided and compared with experimental data. The discrepancies between results are of significant magnitude but expected nature. Co clusions about most feasible approaches for engineering calculations are drawn.

Experimental Investigation of Reacting Flow Characteristics in a Dual-Mode Scramjet Combustor

Abstract In this work, a hydrogen fueled dual-mode scramjet combustor was investigated experimentally. Clean and dry air was supplied to the combustor through a Mach 2 Nozzle with a total temperature of 800 K and a total pressure of 800 kPa. The high enthalpy air was provided by an electricity resistance heater. Room temperature hydrogen was injected with sonic speed from injector orifices vertically, and downstream the injector a tandem cavity flame holder was mounted. Except wall pressure profiles, velocity and temperature profiles in and at exit of the combustor were also measured using hydroxyl tagging velocimetry (HTV) and tunable diode laser absorption spectroscopy (TDLAS) respectively. Results showed that combustion occurred mainly at the bottom side of the combustor. And there were also an extreme disparity of the velocity and temperature profiles along the Y direction, i.e. the transverse direction.

Emulsion Jet in Crossflow Atomization Characteristics and Dynamics

This work presents the atomization characteristics and dynamics of water-in-heptane (W/H) emulsions injected into a gaseous crossflow. W/H mixtures were tested while varying momentum flux ratios and aerodynamic Weber numbers. Different injector orifice diameters and orifice length-to-diameter ratios were used to test the generality of the results. The atomization properties of W/H mixtures were compared with properties of neat water and neat heptane to evaluate the effect of an emulsion on droplet sizing, cross-sectional stability and dispersion, and jet penetration depth. Liquid dynamics were extracted through analyzing instantaneous spray measurements and dynamic mode decomposition (DMD) on high-speed video recordings of the atomization processes. Correlations were proposed to establish preliminary relationships between fundamental spray processes and test conditions. These correlations allowed for emulsion behavior to be compared with neat liquid behavior. The use of emulsions induces greater spray instability than through using neat liquids, likely due to the difficulty in injecting a stable emulsion. Neat liquid correlations were produced and successfully predicted various spray measurements. These correlations, however, indicate that injector geometry has an effect on spray properties, which need to be addressed independently. The emulsions are unable to adhere to the neat liquid correlations suggesting that an increased number of correlation terms are required to adequately predict emulsion behavior.

Optical Diagnostics in a High-Pressure Combustor with Gaseous Oxygen and Kerosene

This paper presents analysis of results from optical diagnostics in a high-pressure combustor burning gaseous oxygen (GOX) and liquid kerosene RP-2 fuel through a jet-swirl coflow injector. The objectives of the experiment were to measure flame stabilization and position under high-pressure conditions. Data were obtained at pressures from 2 to 16.5 MPa and mixture ratios from 2.9 to 20. High-speed cameras captured side-on chemiluminescence and infrared images of the flame. Results show that the flame-spreading angle from the injector ranges from approximately 3 to 6 deg, varying with pressure and propellant mass flow rate. A novel borescope was used to image the flame from upstream of the GOX post, enabling visualization of the flame near its stabilization location. The flame stabilization characteristics change significantly with the fuel flow velocity (which is proportional to pressure). At low pressures and fuel flow velocities, the flame appears to be distributed azimuthally in a nearly axisymmetric manner. At higher velocities, helical spirals of luminosity develop near the GOX post. In addition, the side-on views reveal concentrated streaks of, presumably, fuel entering the combustion chamber. These results suggest that computations must resolve the individual fuel injection orifices, to capture the flame stabilization.

Drag and heat reduction mechanism of the porous opposing jet for variable blunt hypersonic vehicles

The porous opposing jet strategy which is suitable for the blunt hypersonic vehicle has been proposed and investigated numerically in this study. The numerical method is validated by the wind tunnel experimental data. This work shows that the aerodynamic performance can be improved further by combining the porous opposing jet design with variable blunt methods. When the number of jet orifices (N) is odd, the area of Mach disk and the off-distance of shock wave decrease with the increase in N. When N is even, the high temperature region will decrease with the increase in N. The drag reduction ratio increases with the increase of jet orifices when N is odd. However, the trend is contrary when N is even. Moreover, when N is odd, the influence of drag reduction is better than that when N is even. Considering both factors of the drag reduction and thermal protection, the porous jet design is useful in improving the overall performance of the blunt hypersonic vehicle. The porous jet has three-dimensional effect, and thus the three factors (the number, the spacing and the radius of injection orifices) have the most optimal combination for the porous opposing jet injection to have the best performance for the drag reduction and thermal protection.

Investigation on interphase mixing and flow condensation process in a vertical channel

In this paper, an experimental study is performed on the mixing of superheated gas and subcooled flowing liquid and the subsequent flow condensation process in a vertical visual flow channel using R123 as the working fluid. The flow patterns of the two phase flow in the vertical channel are verified and the flow condensation lengths of the gaseous phase under different operating conditions are obtained. Test results indicate that under the operating conditions in this experiment, the gaseous phase forms a cavity or a film at the gas orifices, and then forms a dispersive bubbly flow in the downstream region. The flow condensation length of the gaseous phase through a single orifice increases approximately linearly with the gas flow rate over a range of 0.35–0.76 m, and it is reduced to a range of 0.27–0.56 m by using multiple gas injection orifices. A computational fluid dynamics (CFD) model is established to simulate the two phase flow and interfacial heat and mass transfer in the channel. The simulation capability and prediction accuracy of the CFD model are validated by comparing numerical results of phase distributions as well as the flow condensation lengths with test data, and satisfying agreements are obtained. This work could be beneficial to the understanding and handling of interphase heat and mass transfer problems in in-tube two phase flows.

Analysis of spray dynamics of urea–water-solution jets in a SCR-DeNOx system: An LES based study

Among various advanced emission control technologies used to reduce NOx emission from diesel engines, the selective catalytic reduction (SCR) technique has proven to be more efficient. However, it is still facing the improvement of low temperature performance and the avoidance of urea deposit formation due to complex spray–wall interaction process.To gain more deep understanding of these processes, a spray module is developed for the first time within a full LES framework based on an Eulerian–Lagrangian approach. It includes especially (1) a primary and a secondary breakup model along with an advanced collision model, both to account for the atomization generated close to the nozzle exit by the multi-hole circular orifice injector used and (2) a multi-component droplet evaporation model along with a two-way coupling between the carrier gaseous phase and the droplet liquid phase throughout the dilute spray region.The suggested model is applied to evaluate the dynamics of the multi-component droplets spray resulting from an adBlue injection into a hot gas cross flow inside a channel mimicking a SCR-DeNOx flow system. First, an assessment of the multi-component droplet evaporation under hot stagnant gas environment is made. Second, the results of the adBlue spray/gas phase cross flow interaction are reported in terms of comparison between experimental data (spray structure, spray angle and penetration depth, droplet size distribution and velocity) with numerical simulations. It turns out that the model designed is able to capture in a satisfactory way the spray properties in a SCR like system.

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

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

Numerical study of choked cavitation in high temperature hydrocarbon liquid jets

A numerical study was conducted on a practical plain orifice injector issuing pressurized high-temperature aviation fuel, in order to simulate injection of fuel after use as a coolant in the active cooling system of a hypersonic vehicle. A three-dimensional unstructured mesh inside the orifice was created using ICEMCFDTM S/W, and the CFD analysis was performed using FLUENTTM S/W. A multiphase mixture model was used to simulate cavitating two-phase flow, and the full cavitation model was activated to predict the mechanism and effects of cavitation induced by the high fuel vapor pressures at elevated temperature conditions. The simulation was performed for fuel heated up to 553 K (280 °C) at an upstream pressure (Pinj) of up to 1.0 MPa, and various ambient pressures (P∞). The results were compared with experimental data, and the simulation was found to predict the discharge coefficient (Cd) with respect to the fuel injection temperature (Tinj) quite well at the given conditions. The CFD analyses for high fuel temperature conditions revealed that the mainstream flow inside the injector separates from the orifice wall at the vena contracta due to the generated fuel vapor cavity, and the attached flow at the end of the cavity separates again to produce a very small recirculation zone. In addition, for a given pressure drop, the sharply decreasing trend of the mass flow rate (or Cd) with increasing Tinj varies depending on P∞, because the mass flow choking is determined by the relationship between P∞ and the vapor pressure (Psat) at Tinj. Finally, Cd with respect to cavitation number was found to follow an almost identical line, even at different P∞. This confirms that choked cavitation at high fuel temperature conditions depends on the downstream pressure of the orifice, and the effect of cavitation on Cd at high Tinj is well represented by the cavitation numbers, regardless of Pinj, P∞, and Tinj.

Spray Characterization of a Slinger Injector Using a High-Speed Imaging Technique

This paper presents the experimental-visualization results of liquid breakup in a slinger injector with high-aspect-ratio radial–axial discharge channels over a range of rotational speeds between 600 and 10,000 rpm to identify detailed breakup pattern and spray characteristics. High-speed images of the jet breakup are captured and processed by a shadowgraph method. The particle/droplet imaging analysis technique is used to obtain the droplet-size distribution. Centripetal/Coriolis-induced stream-mode injection is observed for high-aspect-ratio axially canted discharge channels. The results show that the liquid-breakup process with rotational-speed values up to 4000 rpm corresponds to a subcritical stream-mode breakup. Moreover, a new phenomenon of jet bifurcation is observed at higher rotational speeds (more than 5000 rpm). Liquid-film disintegration is observed at rotational speeds of 10,000 rpm, which constitutes a transitional regime from subcritical to supercritical stream-mode breakup. The results show that the Sauter mean diameter decreases with increasing rotational speed. Furthermore, based on experimental observations, it is concluded that the number of injection orifices and their partitioning in different orientations affect the Sauter-mean-diameter values. Finally, a correlation is obtained between Sauter mean diameter, rotational speed, and volume-flow rate.

Research on the injected effect by the narrow-slit injection orifice in screw compressors

A narrow-slit injection orifice in screw compressors (mainly in single screw compressors) is described in this paper. In contrast to the traditional injection orifice, the section is slit shaped but not circular. Liquid which is injected by the narrow-slit injection orifice appears as a curtain shape. The heat transfer area is increased so that the cooling effect is enhanced and the efficiency of the compressor is improved. The injected effect was simulated through the CFD software, and then the experiments were carried out. The study verified the accuracy of the simulation results and will provide a theoretical foundation for the design of a narrow-slit injection orifice in screw compressors.

Different Injection Strategies to Enhance the Performance of Diesel Engine Powered with Biodiesel Fuels

The compression ignition (CI) engines are most efficient and robust but they rely on depleting fossil fuel. Hence there is a speedy need to use alternative fuels that replaces diesel and at the same time engine should yield better performance. Accordingly, honge oil methyl ester (BHO) and cotton seed oil methyl ester (BCO) were selected as an alternative fuel to power CI engine in the study. In the first part, this paper aims to evaluate best fuel injection timing (IT) and injector opening pressure (IOP) for the biodiesel fuels (BDF). The combustion chamber (CC) used for the study is toriodal re-entrant (TRCC). The experimental tests showed that BHO and BCO yielded overall better performance at IT of 19° before top dead centre (bTDC) and IOP of 240 bar. In the second part, the effect of number of holes on the performance of BDF powered CI engine was studied keeping optimized IT and IOP. The six-hole injector with 0.2 mm injector orifice diameter yielded better performance compared to other injectors of different holes and size tested.

Ducted fuel injection: A new approach for lowering soot emissions from direct-injection engines

Designers of direct-injection compression-ignition engines use a variety of strategies to improve the fuel/charge-gas mixture within the combustion chamber for increased efficiency and reduced pollutant emissions. Strategies include the use of high fuel-injection pressures, multiple injections, small injector orifices, flow swirl, long-ignition-delay conditions, and oxygenated fuels. This is the first journal publication on a new mixing-enhancement strategy for emissions reduction: ducted fuel injection. The concept involves injecting fuel along the axis of a small cylindrical duct within the combustion chamber, to enhance the mixture in the autoignition zone relative to a conventional free-spray configuration (i.e., a fuel spray that is not surrounded by a duct). The results described herein, from initial proof-of-concept experiments conducted in a constant-volume combustion vessel, show dramatically lower soot incandescence from ducted fuel injection than from free sprays over a range of charge-gas conditions that are representative of those in modern direct-injection compression-ignition engines.

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

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

Injecting a Liquid in Weightlessness: Droplet or Geyser Formation

Abstract Injecting a liquid into a gas-filled vessel while in weightlessness can result in at least two conditions–a droplet attached to the wall around the injection orifice and a geyser in which the liquid propagates away from the orifice in a continuous jet. The need to design injection of liquid to accomplish one condition or the other shows up in both zero-g fluids research geometries and spaceflight systems. Previous experiments by others assumed the rim of the injection orifice to be sharp. Liquid flow out of orifices with chamfered and rounded rims during the weightlessness of parabolic aircraft flight are studied in this work. When compared to previous work, results indicate that chamfered and rounded rims have little effect on the value of Weber number dividing the wall-bound droplet and geyser behaviors. Because any manufactured orifice will have finite bluntness, this conclusion is useful for both research and spaceflight systems.

Continuous synthesis of PVP stabilized biocompatible gold nanoparticles with a controlled size using a 3D glass capillary microfluidic device

A reliable glass capillary microfluidic method was developed for a continuous production of well-controlled gold nanoparticles (AuNPs) capped with polyvinylpyrrolidone (PVP) of different molecular weights (PVP K15, PVP K30 and PVP K90). A two-phase co-flow glass capillary microfluidic device with an injection orifice diameter ranging between 100 and 240µm was used to synthesise 100–240µm was used to synthesise AuNPs via the chemical reduction between tetrachloroaurate trihydrate (HAuCl4·3H2O) and ascorbic acid. AuNPs with an average diameter between 48 and 135nm were synthesised, as determined by DLS measurements. Decreasing the injection orifice diameter, increasing the flow rate of ascorbic acid stream and its pH resulted in smaller AuNPs. The polydispersity index (PDI) was found to be independent on the injection orifice diameter or the molecular weight of PVP, but increased with the increase of flow rate and the pH of ascorbic acid stream. The stability study over 6-week period confirmed that PVP K30 with an average Mw of 40000g/mol was the best capping agent to synthesize and stabilise smaller AuNPs. The reactor fouling due to deposition of AuNPs on reactor walls and orifices was mitigated by hydrophobization of reactor/capillary walls with octadecyltrimethoxisilane and the use of ascorbic acid solution of higher pH.

Experimental study of cavitation formation and primary breakup for a biodiesel surrogate fuel (methyl butanoate) using transparent nozzle

The cavitation formation of fuel flow inside an optically transparent nozzle and the dynamics of spray breakup and atomization at the near-nozzle region were captured by a long working distance microscope and a camera with high spatial and temporal resolutions. The images revealed the formation of a variety of complex cavitation and their temporal evolution. The cavitation initially occurred in the valve seat area and then developed in the whole orifice. The increase of injection pressure led to earlier cavitation inception and enlarged cavitation. A new dimensionless number S was proposed to represent the cavitation intensity in a quantitative manner. The S increased about 10% for every 10MPa in injection pressure. Image analysis also revealed the relationship between the spray structure at the near nozzle region and the bubble dynamics in the injector orifice. Spray angle, penetration length and spray area were noticeably affected by the injection pressure (30, 40, 50, 60MPa) as well.

Effects of cavitation flow and stagnant bubbles on the initial temporal evolution of diesel spray

This study focuses on the in-nozzle flow characteristics and the primary spray breakup of diesel at the near-nozzle region under atmospheric conditions. A long working distance microscope and a Canon EOS 700D CCD Camera were employed to study the cavitation flow in the nozzle and the spray structure at near-nozzle region via photographic technique with backlighting. Images were obtained with short exposure time and sufficiently high spatial and temporal resolutions which allowed a detailed observation of the early phase of fuel injection from the nozzle orifice to near nozzle region. The images revealed that the formation of a variety of complex two-phase flow regimes. Stagnant bubbles were present inside the nozzle at the start of injection. The stagnant bubbles may have originated from the last injection because they have not been evacuated from the nozzle or sucked into the nozzle orifice as the needle valve opened. During the opening and closing stages of the needle valve, the cavitation occurred in the valve seat area. Subsequently, free cavitation was observed at the inlet orifice followed by film cavitation, cloud cavitation and string cavitation in the orifice. A dimensionless number S derived from the images of transparent nozzles was adopted to evaluate the cavitation intensity, which increased monotonically with the increase of injection pressure. In addition, mushroom shaped spray head was also found at the nozzle exit. A close inspection revealed that the stagnant bubbles or the fuel trapped in the injector orifice at the end of injection had an appreciable impact on the near nozzle spray structures. The spray angle, penetration length and the spray area also increased for every 10MPa rise by about 20%, 10% and 15% respectively.

The spray characteristics of an open-end swirl injector at ambient pressure

To study the spray characteristics of an open-end swirl injector under ambient pressure, cold flow tests were conducted using a high-speed shadowgraph system. The effects of geometrical parameters (including tangential inlet diameter and injector length) and operating parameters (including injection pressure drop) under high ambient pressure were systematically investigated. The experimental results indicate that spray is suppressed by ambient pressure. With increased ambient pressure, the discharge coefficient increased while the spray cone angle, spray width and breakup length decreased. Under a low injection pressure drop of 0.1 MPa, the maximum deviations of the discharge coefficient and spray cone angle under 5 ambient pressure conditions were 22.6% and 31.2%, respectively. Under a high injection pressure drop of 0.7 MPa, the maximum deviations under 5 ambient pressure conditions were 1% and 18.1%, respectively. A critical pressure value was found at which the spray structure converts from a wide hollow cone to a narrow contracting bell. Increasing the tangential inlet diameter (Dp) or the ratio of the injector length to the injector orifice diameter (L/D) would eventually decrease the swirling intensity. Therefore, the discharge coefficient increases while the spray cone angle decreases. Comprehensively considering the effects of geometrical and operating parameters, empirical formulas for the discharge coefficient and spray cone angle are proposed for engineering applications.

Sub- and supercritical jet disintegration

Shadowgraph visualization and Planar Laser Induced Fluorescence (PLIF) are applied to single orifice injection in the same facility and same fluid conditions to analyze sub- to supercritical jet disintegration and mixing. The comparison includes jet disintegration and lateral spreading angle. The results indicate that the shadowgraph data are in agreement with previous visualization studies but differ from the PLIF results that provided quantitative measurement of central jet plane density and density gradients. The study further evaluated the effect of thermodynamic conditions on droplet production and quantified droplet size and distribution. The results indicate an increase in the normalized drop diameter and a decrease in the droplet population with increasing chamber temperatures. Droplet size and distribution were found to be independent of chamber pressure.