Andreas Cronhjort - Publications

In order to include something about my professional career, I have here added a list covering the scientific publications to which I have contributed so far, all linked to the corresponding abstracts. In this way you can see what I have been working with through the years. The first publication goes back to my master thesis work, which I finished in 1992. Thereafter follow eleven publications, which I was involved in during my postgraduate studies, and a few more papers published after my dissertation.

	Wåhlin, F. and Cronhjort, A., "Impinging Diesel Sprays", Atomization and Sprays, Volume 18, Issue 2, pp. 97-127, March 2008.
	Desantes, J. M., Arrègle, J., López, J. J. and Cronhjort, A., "Scaling Laws for Free Turbulent Gas Jets and Diesel-Like Sprays", Atomization and Sprays, Volume 16, Issue 4, pp. 443-474, June 2006.
	Cronhjort, A., "Optical Studies in a Direct Injected Diesel Engine", Fifth Symposium "Towards Clean Diesel Engines", Lund, June 2005.
	Cronhjort, A. and Dahlén, L., Diesel Flame Studies in an Optical Engine, Seminar on "Optisches Indizieren", Haus der Technik, Munich, December 7, 2004.
	Cronhjort, A. and Wåhlin, F., Segmentation Algorithm for Diesel Spray Image Analysis, Applied Optics, Volume 43, Issue 32, pp. 5971-5980, November 2004.
	Wåhlin, F. Cronhjort, A., Olofsson, U. and Ångström, H. E., Effect of Injection Pressure and Engine Speed on Air/Fuel Mixing and Emissions in a Pre-Mixed Compression Ignited (PCI) Engine using Diesel Fuel, Society of Automotive Engineers, Paper 2004-01-2989, Tampa, October 2004.
	Wåhlin, F. and Cronhjort, A., Fuel Sprays for Premixed Compression Ignited Combustion - Characteristics of Impinging Sprays, Society of Automotive Engineers, Paper 2004-01-1776, Detroit, March 2004.
	Cronhjort, A., Droplet Velocities in a Liquid Spray, Doctoral Thesis, ISRN KTH/MMK/R--02/1--SE, February 2002.
	Cronhjort, A., Droplet Velocities in a Sliced Diesel Spray, 17th Annual Conference of ILASS-Europe, Zurich, September 2001.
	Cronhjort, A. and Konstanzer, D., Analysis of a Diesel Spray Using a Mechanical Slicing Device, Society of Automotive Engineers, Paper 2001-01-2009, Orlando, May 2001.
	Cronhjort, A., Spray Visualization Using a Mechanical Slicing Device, Eighth International Conference on Liquid Atomization and Spray Systems, Pasadena, July 2000.
	Rantanen, P., Valkonen, A. and Cronhjort, A., Measurements of a Diesel Spray with a Normal Size Nozzle and a Large-Scale Model, International Journal of Heat and Fluid Flow, Volume 20, pp. 545-551, 1999.
	Rantanen, P., Valkonen, A. and Cronhjort, A., Measurements of a Diesel Spray with a Normal Size Nozzle and a Large Scale Model, 14th Annual Conference of ILASS-Europe, Manchester, July 1998.
	Cronhjort, A., Development of a System for Diesel Spray Analysis, Licentiate Thesis, ISRN KTH/MMK/R--97/18--SE, January 1998.
	Gåsste, J., Cronhjort, A. and Konstanzer, D., Photographic Investigation of a Sliced Diesel Spray, 13th Annual Conference of ILASS-Europe, Florence, July 1997.
	Cronhjort, A., Gåsste, J. and Konstanzer, D., Advanced Control System for Optical Diesel Spray Analysis in a Pressurized Vessel, 13th Annual Conference of ILASS-Europe, Florence, July 1997.
	Konstanzer, D. and Cronhjort, A., Spray Analysis using FIRE, Third International FIRE User Meeting, Graz, June 1997.
	Sjöberg, H., Manneberg, G. and Cronhjort, A., Long working-distance microscope used for diesel injection spray imaging, Optical Engineering, December 1996.
	Cronhjort, A. and Sjöberg, H., Diesel Spray Droplet Analysis using a Long Distance Microscope, 12th Annual Conference of ILASS-Europe, Lund, June 1996.
	Cronhjort, A., A computer-controlled bowing machine (MUMS), STL-QPSR 2-3/1992, pp. 61-66, 1992.

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Impinging Diesel Sprays
Fredrik Wåhlin and Andreas Cronhjort
Scania CV AB, Advanced Combustion
SE - 151 87 Södertälje, Sweden

Abstract

Diesel fuel sprays from a common-rail injector have been optically investigated with respect to their macroscale characteristics. The tested nozzle designs were of standard plain orifice type, as well as the impinging-spray type, in which two orifices intersect at a specific angle at the exit. Testing was conducted using a pressurized vessel at room temperature. The impinging sprays were found to be low penetrating and widely dispersed compared to the nonimpinging sprays. The shape of the impinging sprays was as one homogeneous spray with no trace of individual sprays. It was found that impinging diesel sprays can be predicted in a manner similar to standard nonimpinging sprays, using a dimensionless penetration correlation. The cone angle of the impinging sprays increases with the impingement angle, and in contrast to nonimpinging sprays, appears insensitive to ambient density. The results indicate that the impinging spray has a larger spray volume at lower ambient densities. However, at higher ambient densities, the volume of the nonimpinging sprays is larger.

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Scaling Laws for Free Turbulent Gas Jets and Diesel-Like Sprays
José M. Desantes, Jean Arrègle and J. Javier López
CMT-Motores Térmicos, Universidad Politécnica de Valencia
Spain, Camino de Vera, s/n. 46022 Valencia, Spain
Andreas Cronhjort
Scania CV AB, Advanced Combustion
SE - 151 87 Södertälje, Sweden

Abstract

Scaling laws for free turbulent gas jets and diesel-like sprays are deduced and experimentally validated. The analysis is based on basic conservation equations and experimental evidence. As a new contribution, the effect of the Schmidt number on the scaling laws is analyzed and included, which leads to a more general set of normalized parameters. By analyzing the scaling laws, it is possible to obtain a clear comprehension of gas-jet or diesel-spray behavior, as well as an understanding of the relationship between input and output parameters. Two new parameters are introduced that characterize mass and momentum transfer in the radial direction of the gas jet or diesel spray, thus providing valuable information about the mixing process.

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Optical Studies in a Direct Injected Diesel Engine
Andreas Cronhjort
Scania CV AB, Advanced Combustion
SE - 151 87 Södertälje, Sweden

Abstract

A heavy-duty diesel engine with optical access through an extended piston has been used to study diesel spray combustion. Conventional photography using a solid-state camera was adopted to image the flames. The images were parameterized using image processing software. Due to extended crevices and reduced stiffness as compared to the original engine, the effective compression ratio was slightly lower in the optical cylinder. To compensate for the lowered compression ratio, the inlet pressure as well as the inlet temperature were increased. As top dead center conditions regarding gas density and temperature were desired to be maintained, this approach resulted in an increased overall air to fuel ratio. However, despite these drawbacks, the engine allows for spray combustion studies under realistic diesel engine conditions regarding pressure and temperature. The inlet pressure was kept at 400 kPa absolute and the temperature was 325 K. To predict the air mass in the cylinder as accurately as possible, the exhaust back pressure was always kept equal to the inlet pressure. To minimize the thermal load on the piston, fuel was injected only when an image was to be exposed. This was also beneficial when estimating the air mass in the cylinder, as the temperature of the rest gas was quite low. A nozzle with eight orifices fitted to a common-rail injector was used to generate the sprays. The rail pressures used were 160 MPa and 220 MPa, the injected amount of fuel was varied between 80 mg and 240 mg.

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Diesel Flame Studies in an Optical Engine
Andreas Cronhjort and Lars Dahlén
Scania CV AB, Advanced Combustion
SE - 151 87 Södertälje, Sweden

Abstract

A diesel engine with optical access through an extended piston has been developed. It is based on a heavy duty truck engine and the purpose is to generate calibration data for computer simulation of spray combustion, hereby facilitating reliable combustion prediction using Computational Fluid Dynamics (CFD). Conventional photography using a solid-state camera was adopted to image the combustion. As the upper surface of the glass window in the piston is flat, the compression ratio of the engine is reduced to 12:1, in order to avoid that the spray plumes hit the glass surface. To compensate for the lowered compression ratio, the inlet pressure as well as the inlet temperature were increased. As top dead center conditions regarding gas density and temperature are desired to be maintained, this approach results in an increased overall air-to-fuel ratio. Additionally, the cylinder pressure decay due to the piston movement becomes slower than it should be at the present engine speed. However, despite these drawbacks, the engine allows for spray combustion studies under realistic diesel engine conditions regarding pressure and temperature. In the preliminary study the inlet pressure was 400 kPa absolute and the temperature was 450 K, resulting in a compression pressure of about 8.6 MPa at top dead center when the engine runs at 1200 rpm. To predict the air mass in the cylinder as accurately as possible, the exhaust back pressure is always kept equal to the inlet pressure. To minimize the thermal load on the piston, fuel is injected only during cycles when an image is exposed. This is also beneficial when estimating the air mass in the cylinder, as the temperature of the rest gas from the preceding cycle is quite low. In the preliminary study a nozzle with eight orifices fitted to a common-rail injector was used to generate the sprays. The orifice diameter was 190 µm. The rail pressure was 160 MPa and the injected amount of fuel was 80 mg. The resulting combustion was dominated by diffusion flames.

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Segmentation Algorithm for Diesel Spray Image Analysis
Andreas Cronhjort and Fredrik Wåhlin
Scania CV AB, Advanced Combustion
SE - 151 87 Södertälje, Sweden

Abstract

An algorithm for segmentation of diesel spray images has been developed. Its most important feature is robustness against experimental setups that fail to guarantee images whose histograms show two distinct peaks. According to the approach presented, only the peak from the background is used, and it is assumed that the background peak is narrow enough not to include too much of the spray. The algorithm has proved successful for evaluation of images from a pressurized vessel as well as from an engine with optical access, with no need for adjusting the tuning parameters. By adjusting them, one may tune the noise sensitivity.

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Effect of Injection Pressure and Engine Speed on Air/Fuel Mixing and Emissions in a Pre-Mixed Compression Ignited (PCI) Engine using Diesel Fuel
Fredrik Wåhlin and Andreas Cronhjort
Scania CV AB, Advanced Combustion
SE - 151 87 Södertälje, Sweden
Ulf Olofsson
Royal Institute of Technology, Machine Elements
SE - 100 44 Stockholm, Sweden
Hans-Erik Ångström
Royal Institute of Technology, Internal Combustion Engines
SE - 100 44 Stockholm, Sweden

Abstract

PCI combustion of diesel fuel was accomplished in a direct-injected heavy-duty single-cylinder research engine. An impinging spray nozzle combined with a shallow bowl piston design offered a short air/fuel mixing time. Low HC and CO emissions were observed compared to fully premixed operation using n-heptane. A method for evaluating the air/fuel mixing process has been established by quantifying the in-cylinder air/fuel heterogeneity with the NOx emission. The results indicate that high injection pressure and engine speed are favorable for a fast mixing process. The injection pressure had a small impact on HC and CO emissions, while the engine speed had a larger impact. There were no correlation between air/fuel mixing time and HC and CO emissions.

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Fuel Sprays for Premixed Compression Ignited Combustion -
Characteristics of Impinging Sprays
Fredrik Wåhlin and Andreas Cronhjort
Scania CV AB
Advanced Combustion
SE - 151 87 Södertälje, Sweden

Abstract

For homogeneous charge compression ignition (HCCI) engines with direct-injected fuel (also called PCI, Premixed Compression Ignition), it is important to achieve a lean and homogeneous mixture before ignition. For this purpose, impinging diesel sprays have proven to be useful. In this study, an evaluation of the overall air/fuel ratio of such sprays was made in a test rig. The test rig consists of a pressurized vessel with optical access and a Common Rail (CR) fuel injection system. The investigation was made for impinging spray nozzles with different impingement angles and orifice diameters. Three gas back pressures and three injection pressures were evaluated. The evaluation was based on images of the fuel sprays taken in the test rig. The fuel spray images were automatically processed using in-house developed software. The results of the investigation point out some important factors to obtain a lean spray, (a high air/fuel ratio). The investigation also points out some factors that give a low spray penetration for a certain injected mass of fuel.

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Droplet Velocities in a Liquid Spray
Andreas Cronhjort
Royal Institute of Technology
Internal Combustion Engines
SE - 100 44 Stockholm, Sweden

Abstract

A method to look into a dense liquid spray has been evaluated. The spray was mechanically sliced to remove the obscuring parts of it, thus gaining optical access to the internal regions and thereby allowing for visualization of previously unavailable parts of the spray. The width of the mechanical slit was 100 µm, which was significantly smaller than earlier experiments performed by other researchers. The approach was applied to a diesel fuel spray, and velocities were measured by means of image analysis applied to double-exposed images of droplets in the spray. To perform the evaluation a test rig was developed, where liquid sprays could be optically studied under controlled conditions. In the test rig diesel fuel was injected into a pressurized vessel with optical access, which was achieved using two glass windows, one for the light from the flash, and the other for the camera. The necessary optics and the camera were fitted on a rail, to allow for easy adjustment of the focus. Personal computers controlled the injection sequence and the image acquisition. The injector used was a prototype with an internal hydraulic pressure booster, which delivers approximately 100 MPa peak injection pressure. The nozzle used was a specially manufactured one with an axial orifice, in order to fit into the available vessel. The diameter of the nozzle orifice was 110 µm, and the orifice length was 700 µm. The temperature in the vessel was 300 K and the gas pressure 3 MPa. The gas in the vessel was air, and consequently the gas density was about 35 kg/m³. Enlarging optics in conjunction with a solid-state camera was used to acquire the images. The magnification of the optics was about ten times, the useful resolution 10 µm, and the depth of field approximately 100 µm. The double-exposures were achieved in two different ways, in the beginning by means of a spark discharge flash unit able to deliver multiple sparks, with a flash duration of approximately 300 ns, but later with the shutter of the camera in combination with a xenon discharge flash lamp, to achieve shorter exposure times. The spray was lighted up from behind by the flashlight, and consequently the droplets were visible as dark regions against a bright background. It was considered convenient to work with an image velocimetry software for which the source code was accessible, and for that reason primarily in-house developed codes were used. Three different velocimetry approaches were evaluated, namely cepstrum, cepstrum with the low frequency pedestal removed from the intermediate spectrum, and finally auto-correlation. It was concluded that the most powerful algorithm was the cepstrum with pedestal removal. However, this method showed significant sensitivity to variations in input data, and was therefore rejected. Auto-correlation was considered the most rugged algorithm, and as the images were to be processed in an automated manner, it was decided that auto-correlation was to be used. In order to make the final algorithm able to discard images from which it failed to get correct velocity data, a number of filters and thresholds were used. The filter parameters and the threshold levels were adjusted manually to treat a small reference group of images correctly before they were applied to the real data.

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Droplet Velocities in a Sliced Diesel Spray,
Andreas Cronhjort
Royal Institute of Technology,
Internal Combustion Engines,
SE - 100 44 Stockholm, Sweden

Abstract

This paper gives a summary of particle image velocimetry (PIV) measurements performed in a sliced diesel spray. The slicing of the spray was necessary to achieve good image quality in the more dense regions of the spray. The images were double exposed to allow auto-correlation based velocimetry. The exposure time of each exposure was 100 ns, as that was the shortest possible exposure with the camera used. The illumination was achieved with a flashlight located at the opposite side of the spray, consequently the droplets were visible as dark shadows. The long exposure time limited the possibilities to measure high velocities, and therefore the velocities in the very rapidly moving spray core could not be measured, as the images were smeared out in the direction of the velocity. The resulting velocities were compared to velocities in the corresponding unsliced spray in the points where both sprays gave velocity data. The results were also compared with computer simulations. Some disagreements were found, and possible reasons for these are discussed.

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Analysis of a Diesel Spray Using a Mechanical Slicing Device,
Andreas Cronhjort and Dennis Konstanzer
Royal Institute of Technology,
Internal Combustion Engines,
SE - 100 44 Stockholm, Sweden

Abstract

This paper gives a summary of image velocimetry measurements performed in a sliced diesel spray. The slicing of the spray was necessary to achieve sufficient image quality in the more dense regions of the spray. The images were double exposed to allow auto-correlation based velocimetry. The illumination was achieved with a xenon flashlight behind the spray and consequently the droplets were visible as dark shadows. Images were acquired from different points downstream from the nozzle, and a number of different radii were employed at every position. In the images the smaller droplets seem to be spherical, while the larger ones are distorted due to high weber numbers. Computer simulations indicate that large droplets may reach high weber numbers when passing through the slit, and that some of these large droplets break up. Simulations were also used to estimate how much the velocity of the droplets was affected by the slicing device, and accordingly the expected reduction in velocity does not exceed 30 % for the smallest droplets. Considering this, an acceptable agreement was found between velocities measured with the slicing device and velocity data found in the literature. Therefore, it is concluded that the slicing device used in this paper gives new valuable information about the internal structures in dense diesel sprays.

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Spray Visualization Using a Mechanical Slicing Device
Andreas Cronhjort
Royal Institute of Technology,
Internal Combustion Engines,
SE - 100 44 Stockholm, Sweden

Abstract

This paper describes a concept for gaining photographic access, at a high magnification level, to quite dense regions in liquid sprays, aiming primarily at photographic investigations of the spray and studies of the trailing edge with its associated large droplets. The slicing of the spray is achieved with two sharp edges, which cut out a thin sheet of the spray. The sheet of droplets is visualized with conventional shadow photography. The images acquired with the slicer are compared with images acquired without it, and even though some ligaments are identified as originating from the edges of the slit, the method is still considered as being beneficial, as the quality of the images is significantly enhanced.

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Measurements of a Diesel Spray with a Normal Size Nozzle and a Large-Scale Model
Pekka Rantanen and Antti Valkonen
Helsinki University of Technology
p.O. Box 4300, FIN-02015 HUT, Finland
Andreas Cronhjort
Royal Institute of Technology
Internal Combustion Engines
SE - 100 44 Stockholm, Sweden

Abstract

Advantages of the large-scale modeling of diesel sprays based on dimensional analysis were studied. Measurements of the spray tip penetration, spray angle, droplet size and velocity in a diesel spray have been made with a small nozzle and a large-scale model of the same nozzle. Measurements were made with image analysis, diffraction drop size analyzer and laser Doppler anemometer. Results show that scaling might give us new possibilities to research diesel sprays.

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Measurements of a Diesel Spray with a Normal Size Nozzle and a Large Scale Model
Pekka Rantanen and Antti Valkonen
Helsinki University of Technology
p.O. Box 4300, FIN-02015 HUT, Finland
Andreas Cronhjort
Royal Institute of Technology
Internal Combustion Engines
SE - 100 44 Stockholm, Sweden

Abstract

Advantages of the large scale modeling of diesel sprays based on dimensional analysis were studied. Measurements of the spray tip penetration, opening angle, droplet size and velocity in a diesel spray have been made with a small nozzle and a large scale model of the same nozzle. Measurements were made with image analysis, diffraction drop size analyzer and laser Doppler anemometer. Results show that scaling might give us new possibilities to research diesel sprays.

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Development of a System for Diesel Spray Analysis
Andreas Cronhjort
Royal Institute of Technology
Internal Combustion Engines
SE - 100 44 Stockholm, Sweden

Abstract

A system to visualize diesel sprays in a pressurized vessel has been developed. The system consists of a rigid steel bench with an injection vessel and the necessary optics fitted. A personal computer controls the injection sequence and the image acquisition. The injector uses an internal hydraulic pressure booster and allows injection pressures up to 200 MPa to be used. The spray is lighted up from behind with a fast flashlight and photographed with a conventional camera. The exposure time is 250 ns and up to four separate flashes can be used to achieve multiple exposures of the film. The four flashes can also be fired simultaneously in order to increase the optical energy in the flash. The optics used allow continuously variable magnification between unity and 50 times magnification at the image plane. The resolution of the optics is approximately 5 µm when using the largest magnification, but is drastically reduced if diesel droplets reach the window located between the optics and the spray. The depth of field varies with the selected magnification, at largest magnification it is approximately 800 µm. The computer manages the entire system and thereby allows systematic photographic studies at predefined ambient conditions to be performed. The temperature in the vessel can be varied between 30 °C and 100 °C and the gas pressure between 0.1 MPa and 5 MPa. The computer first adjusts temperatures and pressures in the system according to the predefined values. Then the injector is activated and the picture exposed. Between each picture the vessel is purged with hot air and the film is advanced one frame. As each picture is exposed, the computer stores the corresponding actual values for the regulated parameters together with the injection sequence. A series of photos has been taken in order to test the system behavior. The spray penetration into air at 60 °C and 4.2 MPa has been studied. The air density corresponds to full load conditions in a direct injected two-liter per cylinder heavy duty diesel engine. The peak injection pressure was 140 MPa. The fuel used was diesel fuel and the opening pressure of the injector was set to 30 MPa. The nozzle was a specially developed nozzle with four orifices, one pointing forward and three larger pointing backwards, in order not to interfere with the optical path. The one pointing into the optical path was 210 µm diameter and the length of the orifice was 700 µm. The photos were compared with CFD-calculated spray outlines. The CFD-code tended to over predict the penetration of the spray and under predict the opening cone angle of the spray.

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Photographic Investigation of a Sliced Diesel Spray
Jan Gåsste, Andreas Cronhjort and Dennis Konstanzer
Royal Institute of Technology
Internal Combustion Engines
SE - 100 44 Stockholm, Sweden

Abstract

Due to the high density of a diesel spray, normally no visualization of the spray core can be done by backlightning. By slicing the spray into a spray-sheet, the phenomena inside the spray can be optically studied in the same way as the outer regions of the spray. Special spray slicers with very thin gaps have been designed and tested. By taking photos of the sliced sprays, the geometry and structure of the spray in the center of the spray have been studied. Comparisons with unsliced sprays and with FIRE^® CFD simulations have been done to study if the results of a sliced spray are representative of an ordinary diesel spray. The tests have been performed in an injection test rig equipped with an optical system which enables high resolution. Measurements were performed with the diesel spray injected into a pressurized vessel. The peak injection pressure was 140 MPa. The vessel pressure was set to 4.2 MPa and the vessel temperature to 60 °C Photos of the spray tip just leaving the slicer have been taken to study the structure of the spray tip. Studies whether the spray-sheet remains unaffected downstream from the slicer, or if it turns into a more normal spray shape, have been done. Prestudies have been made to investigate the internal spray structure.

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Advanced Control System for Optical Diesel Spray Analysis in a Pressurized Vessel
Andreas Cronhjort, Jan Gåsste and Dennis Konstanzer
Royal Institute of Technology
Internal Combustion Engines
SE - 100 44 Stockholm, Sweden

Abstract

An advanced control system to enable systematic photographic studies of diesel injections has been developed. The system automatically generates series of photos under predefined conditions. The injections are made in a pressurized vessel. The temperature in the vessel can be varied between 30 °C and 100 °C and the gas pressure between 0.1 MPa and 5 MPa. The entire system is controlled by a computer, and therefore the safety level is very high when performing experiments under extreme conditions. During the injection sequence the system can be remote controlled and monitored from another computer. The timing of the image acquisition is adjustable with an accuracy of 1 µs. Up to four separate flashes can be used to achieve multiple exposures of the film. The four flashes can also be fired simultaneously in order to increase the optical energy in the flash. When using double exposure at a low level of optical magnification the spray tip velocity can be determined. If the double exposure facility is used in conjunction with a high magnification the droplet speed can be measured. The system has been used to study the spray penetration into air at 60 °C and 4.2 MPa. The air density corresponds to full load conditions in a direct injected 2 liter per cylinder heavy duty diesel engine. The peak injection pressure was 140 MPa. To minimize the influence of cycle to cycle variations the median values of several images have been used. The results have been compared with computer simulations.

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Spray Analysis using FIRE
Dennis Konstanzer and Andreas Cronhjort
Royal Institute of Technology
Internal Combustion Engines
SE - 100 44 Stockholm, Sweden

Abstract

This paper focuses on numerical studies and experimental investigations of diesel sprays. The commercial CFD-software package FIRE^® has been used to describe dynamic flow properties of the fluid in a pressurized vessel with optical access. The temperature in the vessel can be varied in the interval 300 - 370 K and the pressure can be set to between 0.1 MPa and 5 MPa. An advanced control system, which automatically generates systematic series ofphotographs under predefined conditions has been used. In addition a long distance microscope was employed, which allows magnifications up to 50 times at the image plane. The maximum resolution is 5 mm and depth of focus is approximately 800 mm. Local droplet size distributions can be measured with these pictures. The timing of the image acquisition is adjustable with an accuracy of 1 ms and the flash duration is 250 ns. Four separate flashes can be used to achieve multiple exposures of the film, or be fired simultaneously to increase the intensity of the light. Using double exposure at low level magnification provides means to determine the spray tip velocity, whereas at high magnification the velocity of single droplets can be determined. This way the control system is able to provide powerful help to verify and validate calculated CFD-data. The system has been used to study diesel spray injections into air at 330 K and 4.2 MPa (i.e. gas density equivalent to full load conditions in a heavy duty direct injected diesel engine with a displacement of 2 litre per cylinder). The peak injection pressure was 140 MPa. Since the dense diesel spray core cannot be visualized by the employed back lighting method, special mechanical spray slicers have been designed and tested. The slicer extracts a thin sheet from the spray, which can then be studied. Calculations using the default settings of FIRE^® have been carried out and compared with the experimental data. Ordinary sprays as well as horizontally and vertically sliced sprays have been studied. The spray contour and penetration length have been compared at different stages of the first 200 ms of the injection. The results show a small over-prediction of the penetration length. However, it should be emphasized that it is difficult to estimate the amount of liquid fuel required to ensure detection on a photograph, which render a uncertainty in the experimentally determined penetration lengths. Thus the algorithm used for automatic evaluation of penetration length may need modification to become compatible with calculated CFD-data. In order to eliminate some of the cycle-to-cycle variations, the average value of 16 pictures have been calculated and compared with FIRE^® calculations.

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Long working-distance microscope used for diesel injection spray imaging
Henrik Sjöberg, Göran Manneberg and Andreas Cronhjort
Royal Institute of Technology
SE - 100 44 Stockholm, Sweden

Abstract

An optical system for analysis of diesel spray penetration and atomization has been developed. The basic system is based on a microscope with a long working distance (230 mm) and a modest resolution. The magnification is variable between 1:1 and 50:1. On the camera plane. This enables the study of individual droplets with a diameter of 5 µm. A number of different techniques have been used together with the basic system to study different parts of the spray. They include the dark-ground technique, double exposure, and ordinary magnification. The size, speed, and direction of propagation of the individual droplets have been calculated using the elongation of the droplet image caused by the duration time of the flash.

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Diesel Spray Droplet Analysis using a Long Distance Microscope
Andreas Cronhjort and Henrik Sjöberg
Royal Institute of Technology
Internal Combustion Engines
SE - 100 44 Stockholm, Sweden

Abstract

An injection test rig suitable for optical analysis of diesel fuel injections has been developed. The system is based upon an injector with an internal hydraulic pressure booster. The system has been tested at a temperature of 300 K and a peak injection pressure of 98 MPa. The ambient pressure was 100 kPa. The entire system is controlled by a computer. The spray is backlighted with a flashlight. A long distance microscope magnifies the image of the injection. The distance between the object and the first lens is approximately 230 mm. The magnification is continuously variable between unity and 50 times magnification. The resolution of the system is approximately 5 µm when using the largest magnification. The depth of focus depends on the selected magnification. With the largest magnification engaged the depth of focus is 800 µm. The pictures were analyzed using commercially available software. The droplet size distribution as well as the concentration of droplets were calculated. The system was also used to study the early breakup of the spray.

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A Computer-Controlled Bowing Machine (MUMS)
Andreas Cronhjort
Department of Speech, Music and Hearing
Royal Institute of Technology
SE - 100 44 Stockholm, Sweden

Abstract

MUMS is a bowing machine, i.e., a machine that bows (plays) a violin in a controlled and repeatable manner by mechanical means. Traditionally, the main application of bowing machines has been in studying string vibrations and violins under reproducible conditions. MUMS uses a normal bow to excite the violin, which also allows a comparison of different bows and their influence on the string vibrations. The position and velocity of the bow and the force between bow and string ("bow pressure") can be specified and controlled within close limits. MUMS consists of two parts; a converted printer which contains the mechanical support of the bow and motors for bow motion and force, and a PC-computer which controls the motion by software servos.

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