ABSTRACT A numerical study of pressure-swirl hollow-cone sprays injected at two different ambient... more ABSTRACT A numerical study of pressure-swirl hollow-cone sprays injected at two different ambient pressures is presented to simulate the gasoline direct-injection process. Only nonreacting sprays are considered, with the focus being on the breakup and atomization processes. Two different breakup models have been evaluated, (1) a hybrid version of a sheet length model combined with the Taylor analogy breakup as a secondary breakup model and (2) the surface wave instability breakup, model. Two test cases, injection into atmospheric and above-atmospheric ambient pressure were computed for the assessment of the breakup models. Comparison of calculations with experimental data reveals sufficient agreement. However, the models' performance was case dependent, which suggested further investigation of their breakup mechanisms.
ABSTRACT The paper describes a combined experimental-theoretical investigation into the intake fl... more ABSTRACT The paper describes a combined experimental-theoretical investigation into the intake flow produced by a port commonly used for both DI diesel and gasoline engines, namely a helical. The study consists of two major parts. Firstly, 3 orthogonal velocity components were measured under steady flow conditions within the valve gap using LDA. Data was obtained around the valve periphery and in different planes between the valve and the cylinder head. This was repeated for a number of different valve lifts. Prior to the second stage, an unsteady gas-dynamics calculation was performed to determine the thermodynamic conditions immediately upstream of the valve and the mass flow rate through the valve opening throughout the intake stroke. Finally, the LDA velocity data and the information from the gas-dynamics calculation were combined to provide ''quasisteady'' velocity profiles which were used as boundary conditions for a 3-dimensional calculation of the in-cylinder flow during the intake period. The paper describes in detail the experimental and theoretical studies and the results obtained therefrom. The main assumptions, approximations and associated sources of error are discussed. Suggestions are made to improve the understanding of this type of calculation and potential application areas are identified.
ABSTRACT Accurate measurements in highly turbulent flows, as they occur in nature, require reliab... more ABSTRACT Accurate measurements in highly turbulent flows, as they occur in nature, require reliable velocity measuring techniques that permit instantaneous velocity components to be locally recorded. Hot-element techniques and optical methods are available for local measurements of instantaneous velocity and the present paper summarizes the advantages and disadvantages of different techniques when applied to flow fields in the environment of vegetation.The paper points out the advantages of laser-Doppler anemometry for velocity measurements in highly turbulent flows under laboratory conditions and stresses the reliability of the technique for measurements in polluted air and water flows. The basic principles of the method are explained and developments are described that have yielded optical anemometer systems for measurements of the magnitudes and signs of the instantaneous velocity components. Both quantities have to be known if accurate measurements of the mean flow properties and turbulence characteristics in flow fields with unknown flow directions are required. Electronic data-processing systems for laser-Doppler anemometer measurements are surveyed, embracing frequency analysers, automatic filter banks, frequency trackers, photon correlators and frequency counters. Photon-correlation and counting techniques are introduced as the methods most likely to be employed for the laser-Doppler anemometer.Laser-Doppler anemometer investigations are described in boundary-layer flows along bean leaves and a metal model of plant leaves. These measurements formed the basis of heat and mass transfer predictions near leaves for a specific leaf position relative to the free stream and with different turbulence properties imposed onto the oncoming flow. These data are presented and discussed in some detail. Measurements are also presented that were carried out to investigate the velocity fields in different flow regimes around a square obstacle in a water flow. These flow properties were needed to understand the different growth rates of sea-weed observed in differing flow regimes.
This work describes the systematic approach adopted to establish the LDA/PDA experimental techniq... more This work describes the systematic approach adopted to establish the LDA/PDA experimental technique that would allow measurements to be made over a wide dropsize range with confidence. The analysis considers the sprays generated by different gasoline direct injection (GDI) systems injecting into air under atmospheric conditions. The upper limit to the dropsize measurement range in the fuel sprays was confirmed using Oxford Lasers' VisiSizer and droplets of a known size produced by a mono-dispersed droplet generator. GDI fuel sprays are highly transient, optically dense and provide a high degree of penetration and atomization. The measurement problem is therefore one of the detection of small, high speed droplets inside a dense cloud of surrounding droplets. Furthermore, under the transients found at the start and end of injection and at high fuel loads, fuel elements in the form of sheets, ligaments and filaments can also be injected. These liquid fuel elements subsequently bre...
Laser anemometry instrumentation and techniques have been developed for the investigation of swir... more Laser anemometry instrumentation and techniques have been developed for the investigation of swirling air motion in production diesel engines. Swirl measurements were taken in a Perkins 4.236 diesel engine operating under both motoring and firing conditions. Data were collected over many engine cycles to produce velocity histograms at 1000 and 1600 rpm for 50% of full fuel loading. Swirl velocity profiles under motoring conditions were found to be very close to the profiles obtained prior to injection in the firing case. After injection, a stratification in the flow appears relative to the motoring velocities with a marked reduction in the flow velocity in the region between the cylinder head and the spray. After combustion, the swirl velocity is always less than in the motoring case. The onset of turbulence causes a sharp increase in the measured turbulence intensity. Problems encountered in the use of the laser anemometry are also discussed.
ABSTRACT To comply with the worldwide regulations on automotive exhaust gas standards, modern com... more ABSTRACT To comply with the worldwide regulations on automotive exhaust gas standards, modern combustion methods rely on sophisticated injection systems to deliver highly reproducible spray patterns with precise control of the injected volume. The outward-opening, piezo-driven pintle injector, designed for spray guided direct injection gasoline engines, is an injector which fulfills these boundary condi- tions. The outward opening pintle produces a hollow cone spray formed by a dense array of distinct streaks of fuel systematically ordered around the circumference of the cone. The most significant ad- vantage of the piezo drive is its ability for precision control of the needle. In combination with a direct injection control unit it allows a high degree of flexibility of the needle lift and lift profile. To date, the exact needle lift and its influences on spray propagation and spray shape are not yet fully un- derstood. In this work different aspects of needle lift and the injection of an outwardly opening piezo injector have been studied: Under a microscope the needle lift of the dry injector has been measured with the help of a highspeed camera. With an Injection Analyzer the mass flow through the injector for the corresponding needle lifts has been determined. It was shown that earlier analytical investi- gations on the discharge coefficient for the hollow cone injector (Gavaises, M., Tonini, S., Marchi, S., Theodorakakos, A., and Bouris, D., Int. J. Engine Res., vol. 7, p. 17, 2006) are close to the experi- mental investigations. Furthermore, the shape of the hollow cone spray as well as the vapor phase has been investigated with the help of the shadowgraphy technique. The shadowgraphy measurements under nonevaporating conditions showed that spray shape is heavily influenced by the needle lift. The streaklike structure diminishes toward higher needle lift. The investigations under evaporating conditions showed that the vapor phase is also influenced by the needle lift, as the high local mass fraction of liquid fuel leads to a retardation in evaporation with increasing needle lift.
The traditional goal in engine development is to minimise the fuel consumption while maintaining ... more The traditional goal in engine development is to minimise the fuel consumption while maintaining or improving performance combined to lowering of the primary emissions [1]. One strategy to achieve this goal for spark igni-tion engines is gasoline direct injection. The injector technology has evolved rapidly and the recent introduction of the piezo hollow cone injector promises a very wide flexibility to cover many different engine requirements such as cold start, full load or stop and go driving. Due to its piezo activated needle, different needle lifts can be applied easily and with an extremely high reproducibility. This work demonstrates the results of the spray ana-lysis for a piezo hollow cone injector operating with two different injection strategies which result in the same injected mass. One strategy works with a reduced lift and a long injection duration while the other is a multiple injection strategy consisting of a medium lift and five short, independent injections. To c...
During certain stages of GDI engine operation there is a high probability of fuel being injected ... more During certain stages of GDI engine operation there is a high probability of fuel being injected into the cylinder in a superheated state. Upon injection into the cylinder the fuel will then undergo flash boiling which leads to many drastic changes to the spray including changes to the overall morphology and a reduction in mean drop size. Test conditions were chosen to range from a non-flash boiling condition to a flare flashing condition, complete degradation of the spray shape, with intermediate conditions in which the spray was in a partial flashing state. An imaging study showed that as the superheat degree was increased from a non-superheated case through to a flare flashing case there were a number of different spray morphologies exhibited. Under non-flashing conditions there were the original six spray plumes from this injector. As superheat was increased these plumes were shown to widen and eventually interact with one another. With sufficient superheat for flare flashing th...
GDI multi-hole injector spray dynamics are investigated numerically and experimentally to determi... more GDI multi-hole injector spray dynamics are investigated numerically and experimentally to determine the secon-dary atomization regimes and jet to jet interactions. Parameters which affect the global penetration are analysed and local velocity and droplet size fields are obtained from the experimental and numerical results to illustrate the spray structures.
The research presented is based on the application of optical diagnostics to determine the qualit... more The research presented is based on the application of optical diagnostics to determine the quality of a liquid fuel spray generated by a Y-type nozzle designed according to the works of Mullinger (1974) and Madsen (2006). Two non-intrusive optical measurement techniques were used to characterize the spray in terms of droplet velocity and size, PDA (Phase Doppler Anemometry), and flow structure, PIV (Particle Image Velocimetry). PDA measurements were made in the downstream region of the fully atomized spray, where uniform spherical droplets were expected. The velocity and drop size profiles were measured by PDA in a plane at a distance of 100 mm downstream from the nozzle. These velocity measurements were assumed as a reference for later comparison with the PIV flow measurements. The main application of the PIV technique was to determine the velocity field of the spray in the near nozzle region where the presence of the ligaments and large non-spherical droplets were expected. The si...
Steady state measurements on engine cylinder heads have been performed for many decades as a simp... more Steady state measurements on engine cylinder heads have been performed for many decades as a simple and early design tool in an effort to predict the performance of an engine. These integral techniques have proved very successful for swirl based engines but have failed to show the same success for tumble flow, where the absence of the piston in steady state work is believed to have a big impact. Modern spark ignition engine design, particularly with direct injection, is finding the tumble flow in the cylinder to be a critical part, for both guiding of the fuel for stratified operation and as an aid to the combustion speed and stability under all operating conditions. This had led to laser diagnostics being applied in place of the simpler integral methods, but with the assumption of a close correspondence between the steady state flow and that in a running engine. This paper looks at a comparison between in-cylinder flows under steady state and motored engine conditions to test the a...
The in-cylinder flow field during the latter half of the intake stroke in a single cylinder optic... more The in-cylinder flow field during the latter half of the intake stroke in a single cylinder optical engine operating at 750, 2000 and 3500 rpm has been quantified by PIV. This was complemented by a Mie imaging study of the structure of multi-stream GDI sprays with injection timings of 90 120 and 150 0 CA. The vector fields and spray images at specific crankangles have been used to demonstrate the effect of inlet air velocity on the disruption and transport of the fuel spray. The study has shown that it is the early airflow through the valve gap that is more responsible for fuel disruption than the latter air motion.
Internal combustion engine development has come to rely heavily on the Phase Doppler technique to... more Internal combustion engine development has come to rely heavily on the Phase Doppler technique to characterise fuel injector performance and in-cylinder air-fuel mixing. However, fuel injectors produce sprays that are optically dense, highly transient and with fuel break up and primary atomisation occurring on a similar scale as to the cylinder dimensions. Additional diagnostics have to be introduced to interpret the PDA data in a robust and unique manner. Two such diagnostics are demonstrated on a pressure swirl GDI injector operating at 100 bar fuel pressure. Imaging of the interaction between the spray cone and input laser beams is combined with monitoring of the scattered light intensity and the directly transmitted light intensity during the passage of the spray through the PDA measurement volume. The images, light intensity signatures and PDA data are evaluated for two measurement planes, the first, at 1 mm, below the nozzle orifice where the conical liquid sheet appears be br...
ABSTRACT A numerical study of pressure-swirl hollow-cone sprays injected at two different ambient... more ABSTRACT A numerical study of pressure-swirl hollow-cone sprays injected at two different ambient pressures is presented to simulate the gasoline direct-injection process. Only nonreacting sprays are considered, with the focus being on the breakup and atomization processes. Two different breakup models have been evaluated, (1) a hybrid version of a sheet length model combined with the Taylor analogy breakup as a secondary breakup model and (2) the surface wave instability breakup, model. Two test cases, injection into atmospheric and above-atmospheric ambient pressure were computed for the assessment of the breakup models. Comparison of calculations with experimental data reveals sufficient agreement. However, the models' performance was case dependent, which suggested further investigation of their breakup mechanisms.
ABSTRACT The paper describes a combined experimental-theoretical investigation into the intake fl... more ABSTRACT The paper describes a combined experimental-theoretical investigation into the intake flow produced by a port commonly used for both DI diesel and gasoline engines, namely a helical. The study consists of two major parts. Firstly, 3 orthogonal velocity components were measured under steady flow conditions within the valve gap using LDA. Data was obtained around the valve periphery and in different planes between the valve and the cylinder head. This was repeated for a number of different valve lifts. Prior to the second stage, an unsteady gas-dynamics calculation was performed to determine the thermodynamic conditions immediately upstream of the valve and the mass flow rate through the valve opening throughout the intake stroke. Finally, the LDA velocity data and the information from the gas-dynamics calculation were combined to provide ''quasisteady'' velocity profiles which were used as boundary conditions for a 3-dimensional calculation of the in-cylinder flow during the intake period. The paper describes in detail the experimental and theoretical studies and the results obtained therefrom. The main assumptions, approximations and associated sources of error are discussed. Suggestions are made to improve the understanding of this type of calculation and potential application areas are identified.
ABSTRACT Accurate measurements in highly turbulent flows, as they occur in nature, require reliab... more ABSTRACT Accurate measurements in highly turbulent flows, as they occur in nature, require reliable velocity measuring techniques that permit instantaneous velocity components to be locally recorded. Hot-element techniques and optical methods are available for local measurements of instantaneous velocity and the present paper summarizes the advantages and disadvantages of different techniques when applied to flow fields in the environment of vegetation.The paper points out the advantages of laser-Doppler anemometry for velocity measurements in highly turbulent flows under laboratory conditions and stresses the reliability of the technique for measurements in polluted air and water flows. The basic principles of the method are explained and developments are described that have yielded optical anemometer systems for measurements of the magnitudes and signs of the instantaneous velocity components. Both quantities have to be known if accurate measurements of the mean flow properties and turbulence characteristics in flow fields with unknown flow directions are required. Electronic data-processing systems for laser-Doppler anemometer measurements are surveyed, embracing frequency analysers, automatic filter banks, frequency trackers, photon correlators and frequency counters. Photon-correlation and counting techniques are introduced as the methods most likely to be employed for the laser-Doppler anemometer.Laser-Doppler anemometer investigations are described in boundary-layer flows along bean leaves and a metal model of plant leaves. These measurements formed the basis of heat and mass transfer predictions near leaves for a specific leaf position relative to the free stream and with different turbulence properties imposed onto the oncoming flow. These data are presented and discussed in some detail. Measurements are also presented that were carried out to investigate the velocity fields in different flow regimes around a square obstacle in a water flow. These flow properties were needed to understand the different growth rates of sea-weed observed in differing flow regimes.
This work describes the systematic approach adopted to establish the LDA/PDA experimental techniq... more This work describes the systematic approach adopted to establish the LDA/PDA experimental technique that would allow measurements to be made over a wide dropsize range with confidence. The analysis considers the sprays generated by different gasoline direct injection (GDI) systems injecting into air under atmospheric conditions. The upper limit to the dropsize measurement range in the fuel sprays was confirmed using Oxford Lasers' VisiSizer and droplets of a known size produced by a mono-dispersed droplet generator. GDI fuel sprays are highly transient, optically dense and provide a high degree of penetration and atomization. The measurement problem is therefore one of the detection of small, high speed droplets inside a dense cloud of surrounding droplets. Furthermore, under the transients found at the start and end of injection and at high fuel loads, fuel elements in the form of sheets, ligaments and filaments can also be injected. These liquid fuel elements subsequently bre...
Laser anemometry instrumentation and techniques have been developed for the investigation of swir... more Laser anemometry instrumentation and techniques have been developed for the investigation of swirling air motion in production diesel engines. Swirl measurements were taken in a Perkins 4.236 diesel engine operating under both motoring and firing conditions. Data were collected over many engine cycles to produce velocity histograms at 1000 and 1600 rpm for 50% of full fuel loading. Swirl velocity profiles under motoring conditions were found to be very close to the profiles obtained prior to injection in the firing case. After injection, a stratification in the flow appears relative to the motoring velocities with a marked reduction in the flow velocity in the region between the cylinder head and the spray. After combustion, the swirl velocity is always less than in the motoring case. The onset of turbulence causes a sharp increase in the measured turbulence intensity. Problems encountered in the use of the laser anemometry are also discussed.
ABSTRACT To comply with the worldwide regulations on automotive exhaust gas standards, modern com... more ABSTRACT To comply with the worldwide regulations on automotive exhaust gas standards, modern combustion methods rely on sophisticated injection systems to deliver highly reproducible spray patterns with precise control of the injected volume. The outward-opening, piezo-driven pintle injector, designed for spray guided direct injection gasoline engines, is an injector which fulfills these boundary condi- tions. The outward opening pintle produces a hollow cone spray formed by a dense array of distinct streaks of fuel systematically ordered around the circumference of the cone. The most significant ad- vantage of the piezo drive is its ability for precision control of the needle. In combination with a direct injection control unit it allows a high degree of flexibility of the needle lift and lift profile. To date, the exact needle lift and its influences on spray propagation and spray shape are not yet fully un- derstood. In this work different aspects of needle lift and the injection of an outwardly opening piezo injector have been studied: Under a microscope the needle lift of the dry injector has been measured with the help of a highspeed camera. With an Injection Analyzer the mass flow through the injector for the corresponding needle lifts has been determined. It was shown that earlier analytical investi- gations on the discharge coefficient for the hollow cone injector (Gavaises, M., Tonini, S., Marchi, S., Theodorakakos, A., and Bouris, D., Int. J. Engine Res., vol. 7, p. 17, 2006) are close to the experi- mental investigations. Furthermore, the shape of the hollow cone spray as well as the vapor phase has been investigated with the help of the shadowgraphy technique. The shadowgraphy measurements under nonevaporating conditions showed that spray shape is heavily influenced by the needle lift. The streaklike structure diminishes toward higher needle lift. The investigations under evaporating conditions showed that the vapor phase is also influenced by the needle lift, as the high local mass fraction of liquid fuel leads to a retardation in evaporation with increasing needle lift.
The traditional goal in engine development is to minimise the fuel consumption while maintaining ... more The traditional goal in engine development is to minimise the fuel consumption while maintaining or improving performance combined to lowering of the primary emissions [1]. One strategy to achieve this goal for spark igni-tion engines is gasoline direct injection. The injector technology has evolved rapidly and the recent introduction of the piezo hollow cone injector promises a very wide flexibility to cover many different engine requirements such as cold start, full load or stop and go driving. Due to its piezo activated needle, different needle lifts can be applied easily and with an extremely high reproducibility. This work demonstrates the results of the spray ana-lysis for a piezo hollow cone injector operating with two different injection strategies which result in the same injected mass. One strategy works with a reduced lift and a long injection duration while the other is a multiple injection strategy consisting of a medium lift and five short, independent injections. To c...
During certain stages of GDI engine operation there is a high probability of fuel being injected ... more During certain stages of GDI engine operation there is a high probability of fuel being injected into the cylinder in a superheated state. Upon injection into the cylinder the fuel will then undergo flash boiling which leads to many drastic changes to the spray including changes to the overall morphology and a reduction in mean drop size. Test conditions were chosen to range from a non-flash boiling condition to a flare flashing condition, complete degradation of the spray shape, with intermediate conditions in which the spray was in a partial flashing state. An imaging study showed that as the superheat degree was increased from a non-superheated case through to a flare flashing case there were a number of different spray morphologies exhibited. Under non-flashing conditions there were the original six spray plumes from this injector. As superheat was increased these plumes were shown to widen and eventually interact with one another. With sufficient superheat for flare flashing th...
GDI multi-hole injector spray dynamics are investigated numerically and experimentally to determi... more GDI multi-hole injector spray dynamics are investigated numerically and experimentally to determine the secon-dary atomization regimes and jet to jet interactions. Parameters which affect the global penetration are analysed and local velocity and droplet size fields are obtained from the experimental and numerical results to illustrate the spray structures.
The research presented is based on the application of optical diagnostics to determine the qualit... more The research presented is based on the application of optical diagnostics to determine the quality of a liquid fuel spray generated by a Y-type nozzle designed according to the works of Mullinger (1974) and Madsen (2006). Two non-intrusive optical measurement techniques were used to characterize the spray in terms of droplet velocity and size, PDA (Phase Doppler Anemometry), and flow structure, PIV (Particle Image Velocimetry). PDA measurements were made in the downstream region of the fully atomized spray, where uniform spherical droplets were expected. The velocity and drop size profiles were measured by PDA in a plane at a distance of 100 mm downstream from the nozzle. These velocity measurements were assumed as a reference for later comparison with the PIV flow measurements. The main application of the PIV technique was to determine the velocity field of the spray in the near nozzle region where the presence of the ligaments and large non-spherical droplets were expected. The si...
Steady state measurements on engine cylinder heads have been performed for many decades as a simp... more Steady state measurements on engine cylinder heads have been performed for many decades as a simple and early design tool in an effort to predict the performance of an engine. These integral techniques have proved very successful for swirl based engines but have failed to show the same success for tumble flow, where the absence of the piston in steady state work is believed to have a big impact. Modern spark ignition engine design, particularly with direct injection, is finding the tumble flow in the cylinder to be a critical part, for both guiding of the fuel for stratified operation and as an aid to the combustion speed and stability under all operating conditions. This had led to laser diagnostics being applied in place of the simpler integral methods, but with the assumption of a close correspondence between the steady state flow and that in a running engine. This paper looks at a comparison between in-cylinder flows under steady state and motored engine conditions to test the a...
The in-cylinder flow field during the latter half of the intake stroke in a single cylinder optic... more The in-cylinder flow field during the latter half of the intake stroke in a single cylinder optical engine operating at 750, 2000 and 3500 rpm has been quantified by PIV. This was complemented by a Mie imaging study of the structure of multi-stream GDI sprays with injection timings of 90 120 and 150 0 CA. The vector fields and spray images at specific crankangles have been used to demonstrate the effect of inlet air velocity on the disruption and transport of the fuel spray. The study has shown that it is the early airflow through the valve gap that is more responsible for fuel disruption than the latter air motion.
Internal combustion engine development has come to rely heavily on the Phase Doppler technique to... more Internal combustion engine development has come to rely heavily on the Phase Doppler technique to characterise fuel injector performance and in-cylinder air-fuel mixing. However, fuel injectors produce sprays that are optically dense, highly transient and with fuel break up and primary atomisation occurring on a similar scale as to the cylinder dimensions. Additional diagnostics have to be introduced to interpret the PDA data in a robust and unique manner. Two such diagnostics are demonstrated on a pressure swirl GDI injector operating at 100 bar fuel pressure. Imaging of the interaction between the spray cone and input laser beams is combined with monitoring of the scattered light intensity and the directly transmitted light intensity during the passage of the spray through the PDA measurement volume. The images, light intensity signatures and PDA data are evaluated for two measurement planes, the first, at 1 mm, below the nozzle orifice where the conical liquid sheet appears be br...
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