Influence of liquid properties on the characteristics of hollow cone swirl spray (original) (raw)
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International Journal of Heat and Mass Transfer, 2014
The quality of liquid fuel atomization highly affects the formation of gaseous pollutants and particulate matter emissions from combustion processes. Spray characteristics of two geometrically different pressure-swirl atomizers for a turbojet engine in light aircraft were measured on a cold test bench. A spill-return atomizer and its intended replacement simplex atomizer were investigated using Particle Image Velocimetry (PIV) and Phase-Doppler Anemometry (PDA). Single-camera and stereoscopic PIV measurements yielded velocity distributions in the axial cross-section of the spray cone. PDA measurements provided drop-size distribution and axial velocity data. Acquired results reveal significant differences in spray characteristics of the nozzles investigated at the same fuel injection pressures. The simplex nozzle produced spray with Sauter mean diameters lower by 5-20 µm depending on the regime, its spray was more stable but its shape greatly varied with fuel injection pressure. These differences are discussed in detail, their analysis indicate a potential for spray improvement provided by the novel atomizer design and elucidates the possible impact of the nozzle replacement on the combustion process.
2012
This study investigated characteristics of sprays generated with two geometrically different pressure-swirl atomizers for a small-sized aviation turbine engine using Particle Image Velocimetry (PIV) and Phase-Doppler Anemometry (PDA). The former nozzle is a spill-return type; the latter one is the intended upgrade without the spill return. Single-camera and stereoscopic PIV measurements yield distribution of mean velocity measured in an axial cross section of the spray cone. PDA measurements yield drop-size distribution and axial velocity data. Performed measurements revealed significant differences in spray characteristics of the measured nozzles investigated in the same operating regimes on a cold test bench. These differences are discussed in detail. Analysis of differences between the two nozzles elucidates the possible impact of the nozzle replacement on the combustion process. This study provides an extensive database for validation of numerical models of the tested nozzles.
Spray structure of a pressure-swirl atomizer for combustion applications
EPJ Web of Conferences, 2012
In the present work, global as well as spatially resolved parameters of a spray produced by a pressure-swirl atomizer are obtained. Small pressure-swirl atomizer for aircraft combustion chambers was run on a newly designed test bench with Jet A-1 kerosene type aviation fuel. The atomizer was tested in four regimes based on typical operation conditions of the engine. Spray characteristics were studied using two optical measurement systems, Particle Image velocimetry (PIV) and Phase-Doppler Particle Analyzer (P/DPA). The results obtained with P/DPA include information about Sauter Mean Diameter of droplets and spray velocity profiles in one plane perpendicular to the spray axis. Velocity magnitudes of droplets in an axial section of the spray were obtained using PIV. The experimental outputs also show a good confirmation of velocity profiles obtained with both instruments in the test plane. These data together will elucidate impact of the spray quality on the whole combustion process, its efficiency and exhaust gas emissions. Pressure-swirl atomizers as relatively old type of atomizing devices are nowadays often being replaced in many applications by twin-fluid atomizers. But they are still very common parts of present combustion systems mainly for low power demands. Their popularity is based on simple design and operation without additional expensive devices that could lead to unwanted increase of weight in mobile applications and also to reduction of reliability, which are important factors not only in aircraft industry. Research works focused on improvement of atomization characteristics of the pressure-swirl atomizers are persistent despite long-lasting history of their development and utilization in many industrial sectors. Today research effort stems from changes in the legislative, reflects more frequent usage of less refined fuels and answers requirements for more efficient combustion devices. In general, a swirl-flow of the liquid in a pressure-swirl atomizer is induced by feeding the liquid into a swirl chamber through one or several tangential ports, that give it high angular velocity, thereby creating an air-cored vortex. In this manner, the air-core blocks a part of the nozzle outlet orifice. Under both axial and radial forces emerges the fuel through this orifice in the form of a hollow conical sheet. As the sheet expands, its thickness decreases and it soon becomes unstable and disintegrates into ligaments and then drops in the form of a well-defined hollow-cone spray. Disintegration of the sheet depends mainly on the liquid discharge velocity and thus on the liquid injection pressure. Description of the spray development with increasing injection pressure is presented, for
In this work an advanced atomizer concept to control the spray formation for heterogeneous spray combustion is investigated. The objective is to address the spray structure that preserves the flame height and modifies the width of the flame. The atomizer concept for formation of a modified spray combines a swirling liquid film generation that is atomized by an external swirling gas flow. To investigate the main characteristics of the combined atomizer, experiments and numerical simulations of the flow operation with different geometric nozzle parameters (number of gas holes) and process parameters (flow rate of liquid and gas) as well as liquid properties are carried out to produce a modified, enlarged and steady spray of small droplets. In this work, three different liquids (water without and with 40% and 60% weight of glycerol) are used as the liquid phase and air as the gas phase. In the simulations, the multiphase flow is modeled by an Eulerian-Lagrangian approach with two-way c...
Characteristics of spray angle for effervescent-swirl atomizers
Chemical Engineering and Processing: Process Intensification, 2015
This paper draws a link between the liquid viscosity and the spray angle for effervescent and effervescent-swirl atomizers. The spray angle determines the dispersion and coverage area of the resultant sprays. The swirling the gas-liquid mixture in atomizer led to a significant increase of the spray cone angle at low gas to liquid ratio by mass. Additionally, the orifice shape plays an important role in obtaining the spray angle. The highest values of spray angle has occurred during atomization using profiled orifice. Mathematical analysis shows that spray angle depends on the liquid viscosity, the gas and liquid flow rates and the construction of the atomizer. The data obtained are very important from point of view of the design of atomizers and coverage area of spray. 2015 Elsevier B.V. All rights reserved.
The influence of spill-line geometry on a spray generated by a pressure-swirl atomizer
EPJ Web of Conferences, 2016
An experimental investigation of characteristics of spray generated by a pressure-swirl atomizer (spill-return type) was performed using shadowgraphy and Phase-Doppler Anemometry (PDA). Several different geometries of the spill-return orifice were tested in terms of a spray stability and quality on a cold test bench. PDA measurement yields a drop-size distribution and velocity data while the shadowgraphy unveils a break-up process in detail. Performed measurements reveal significant differences in spray characteristics as well as differences in spray stability. The results suggest that the air core, formed inside the swirl chamber, passes through the spill orifice, which causes instability of the inner flow. These instabilities lead to a chaotic state of sheet breakup resulting in shortening of breakup distance. Obtained findings are used to propose possible changes in the atomizer design for improvement of its performance. This is an Open Access article distributed under the terms of the Creative Commons Attribution License 4.0, which permits distribution, and reproduction in any medium, provided the original work is properly cited.
Experimental Investigations on Spray Characteristics in Twin-Fluid Atomizer
Procedia Engineering, 2011
A twin-fluid atomizer was designed and developed for fuel atomization. The droplet characteristic in the spray which was produced with the atomizer was investigated experimentally. Air flow induced in the atomizer causes a pressure reduction, hence the fuel is sucked into the atomizer. The mixture flow of air and liquid caused the atomization downstream due to the turbulence. In the twin-fluid atomizer, atomization is attained by injecting an air stream at tip of the liquid inlet port. In this research, the test liquid supply pressure was kept constant and the air flow rate through the atomizer was varied over a range of air supply pressure to obtain the variation in air liquid mass flow ratio (ALR) from 0.2 to 2.7. The results revealed that the air assisted atomizer had a capability to inject the test liquid in the range of the rates of 0.0019-0.00426 kg/s, with the use of air pressure supplied from 68.9 to 689 kPa. The images of the spray were obtained with a shadowgraph technique and analyzed to obtain the particle size and its distribution. Droplet size from twin-fluid atomizer had various sizes in the range of about 17-200 m. The atomizer can be applied for aerosol and combustion purposes.
In this study performances of sprays from a pressure atomizer (hollow cone) and a twin fluid atomizer are compared using sunflower straight vegetable oil (SVO). The study has been performed at different liquid temperature and pressure to estimate their effects on the spray characteristics. A Mie Scattering optical set-up, employing a laser light sheet and a charge coupled device (CCD) camera, is used to capture the spray images from which the spray cone angles have been evaluated. The liquid distribution from the spray is measured by a mechanical patternator placed at a definite distance below the atomizer. It is observed from the study that, flow number (FN) remains unchanged with the change in the flow rate for both the hollow cone and twin fluid atomizers. In case of hollow cone atomizer, FN increases slightly with the increase in oil temperature thereby consuming less power for delivering the fuel. This phenomenon has not been observed in case of twin fluid atomizer. For pressure atomizers the spray cone angle increases with the increase in the flow rate as well as with the increase in oil temperature. The cone angle of twin fluid atomizer exhibits almost a constant value for the entire operating range of liquid flow rate, but increases with the increase in both air pressure and oil temperature. Symmetrical patternations have been observed in the sprays with more spray areas at higher temperature and liquid pressure for hollow cone atomizer and at higher air pressure for twin fluid atomizer.