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SAE TECHNICALPAPER SERIES 1999-01-0498

Spray Formation of High Pressure Swirl GasolineInjectors Investigated by Two-Dimensional Mie

and LIEF Techniques

Wolfgang Ipp, Volker Wagner, Hanno Krmer, Michael Wensing and Alfred

LeipertzUniversitt Erlangen-Nrnberg

Stefan ArndtRobert Bosch GmbH

Amar K. JainIndian Institute of Petroleum

Reprinted From: Direct Injection SI Engine Technology 1999(SP-1416)

International Congress and ExpositionDetroit, Michigan

March 1-4, 1999

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1999-01-0498

Spray Formation of High Pressure Swirl Gasoline Injectors

Investigated by Two-Dimensional Mie and LIEF Techniques

Wolfgang Ipp, Volker Wagner, Hanno Krmer, Michael Wensing and Alfred LeipertzUniversitt Erlangen-Nrnberg

Stefan ArndtRobert Bosch GmbH

Amar K. JainIndian Institute of Petroleum

Copyright 1999 Society of Automotive Engineers, Inc.

ABSTRACT

Two-dimensional Mie and LIEF techniques were appliedto investigate the spray formation of a high pressure gas-oline swirl injector in a constant volume chamber. Theresults obtained provide information on the propagationof liquid fuel and fuel vapor for different fuel pressuresand ambient conditions. Spray parameters like tip pene-tration, cone angles and two new defined parametersdescribing the radial fuel distribution were used to quan-tify the fuel distributions measured. Simultaneous detec-tion of liquid and vapor fuel was applied to study theinfluence of ambient temperature, injector temperature

and ambient pressure on the evaporating spray.

INTRODUCTION

In the last years a variety of direct injection strategies forSI engines has been presented and some gasoline directinjection (GDI) engines are already available on the mar-ket [1-8]. Nearly all of the strategies and the GDI enginespresented so far, use high pressure swirl injectors. Highpressure swirl injectors offer the advantage to combine awell atomized spray with relatively low penetration atmoderate injection pressure levels [9]. But, at the same

time the spray formation of this type of injectors is to ahigh extent dependent on the ambient conditions, injec-tion parameters and details of the injectors design [9-12].Most direct injection strategies require a wide operatingrange of the injectors from low ambient temperatures andpressures in case of early injection to high temperaturesand pressures at late injection, different rail pressure lev-els and even secondary injection. All this has contributedto an increasing demand of measurement techniques forthe investigation of GDI sprays. Especially optical tech-niques offer the required temporal and spatial resolutionand are non-intrusive as well. Consequently, a large num-

ber of the publications on gasoline direct injection includeoptical spray investigations: The optical measurementechniques commonly used are integral and two-dimen-sional Mie scattering techniques [13,14], Laser andPhase Doppler Analysis (LDV/PDA) [15, 16] and laser-induced (exciplex) fluorescence [17-19]. Examples ofundamental spray investigations of high pressure swirinjection can be found in [9,11,12,20,21], measurementsinside injection chambers and optical accessible enginesin [1-3,5,7,8,21-27].

This work presents two-dimensional Mie scattering andLIEF techniques optimized for the investigation of spray

structures and spray formation (liquid and vapor phase)of high pressure swirl injectors. The results obtainedshow the spray formation and spray evaporation at different ambient conditions providing very high resolution inspace, time and measured intensity. The two-dimensionaMie measurements give information on the distribution oliquid fuel in an axial and in a radial cut of the spraysImage processing routines were developed to automati-cally extract spray parameters out of the Mie images. Bymeans of LIEF measurements the liquid fuel phase andthe fuel vapor were simultaneously acquired onto twoseparate images, so that the influence of ambient condi-tions on the fuel vapor phase and spray evaporation was

visualized.

EXPERIMENTAL SETUP

In spite of the fact that laser sheet investigations of fuesprays and mixture formation in combustion engineshave become quite common in the last years, the experi-mental setup and details of the technique applied have tobe carefully chosen for each spray type not only to getthe best possible result, but also to ensure a realisticimage of the spray process. Fig. 1 illustrates the experi-mental setup used for the investigation of the GDI sprays

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The injector tested in a constant volume injection cham-ber is a typical swirl injector used for gasoline direct injec-tion with nominal 90 cone angle and a static flow of 15cm/s. The injector was fitted to a high pressure/high tem-perature injection chamber. The chamber is electricallyheated by means of a continuous air flow through thechamber. The velocity of the air flow is less than 0.1m/sinside the spray region. The maximum possible tempera-ture is 800K, the maximum air pressure 5.0MPa. Theinjector is cooled by water. A constant pressure dia-phragm system supplied by pressurized nitrogen wasused to create the fuel pressure in order to avoid pres-sure fluctuations in the fuel rail.

Figure 1. Experimental setup

SETUP FOR MIE MEASUREMENTS The laser beamof a frequency doubled Nd:YAG laser was formed to athin light sheet of 80mm height and less than 200mthickness (FWHM). Two different light sheet positionswere used. First the light sheet illuminated one centralplane of the spray including the spray axis. Secondly, aplane normal to the first one and in 15mm distance to theinjector orifice was used. For the second position thelaser beam was separated into two beams and the mea-surement plane was illuminated from two sides to mini-mize extinction effects in the dense spray. Due to therelatively large cone angle of 90, it was not necessary to

illuminate the spray from two sides, when the first lightsheet position was used. In the present study light sheet1 was introduced from the spray tip and directed towardsthe injector orifice. The images given e.g. in Fig. 3 dem-onstrate, that the attenuation of the laser light is small.However, for sprays with narrower cone angles as well asfor light sheet 2, it is necessary to use illumination fromtwo sides.The signal strength of the Mie scattering pro-cess makes it possible to use non-intensified CCD cam-eras which offer a better dynamic range than intensifiedones. The physical dynamic range of the detector isessential for spray investigations since strong signalsfrom dense spray regions coexist in the same spray

image with weak signals in other parts of the spray. Theimages were stored in a 12bit format (which should notbe mixed up with the physical dynamic range) which issufficient to represent spray structures at high signal lev-els in dense spray regions as well as structures at lowsignal levels in thinner parts of the spray. An extensiontube was put in between camera body and lens to adjust

the image magnification and reduce the focal depthAdditionally, an interference filter was used to reduce theinfluence of daylight. The exposure time of the camerawas set to be 0.1s while the time resolution of the mea-surement is defined by the laser pulse duration of abou10ns. A dimension of 0.05mm was imaged on each pixedue to the size of the measurement plane of 60mm x50mm and the 1280 x 1024 camera pixels.

SETUP FOR LIEF MEASUREMENTS AND CHOICE OFSEED LIEF measurements are a challenging task indense sprays like GDI sprays with the aim to distinguishbetween liquid fuel and fuel vapor. For a couple of rea-sons no multi-component fuels like customized or stan-dard gasoline can be used for such investigations. Majorreasons are the fluorescence spectra of the liquid fuephase and that the vapor phase of a multi-componentfuel may change during the evaporation process, eachcomponent is affected by quenching in a different wayand absorbtion of the irradiating laser occurs in the liquidand in the vapor phase. Additionally, it is nearly impossi-ble to correct for absorption in a completely instanta-

neous spray and (since the fluorescence spectra fromfuel vapor and the by far stronger signal from the liquidfuel at least overlap) it is very hard to distinguish betweenthe two phases. Therefore, a non-fluorescing base fuewas doped with a suitable combination of seeds. Thechoice of seeds is an important point for the techniqueFor spray investigations the physical properties of theseeds have to be close to that of the base fuel since onlythe seeds are detected and both, base fuel and seedsshould represent a mid-range component of gasolineSecondly, the fluorescence of the seeds has to be suffi-ciently characterized even for qualitative investigations inorder to make sure that a strong signal always indicates a

comparatively high fuel concentration. Thirdly, since fluo-rescence is a mass proportional signal the fluorescenceof the liquid phase is by far stronger than the signal fromthe fuel vapor due to the higher densities and therefore, awide spectral shift between the fluorescence of the twophases is required or at lest very helpful. We have cho-sen the exciplex seed system of benzene and triethy-lamine found and characterized by Frba et. al. [18] fothe non-fluorescing base fuel isooctane. The fluorescence spectra of the seed combination that forms anexciplex with a red shifted fluorescence spectrum in theliquid phase is shown in Fig. 2.

The experimental setup used in the LIEF measurements issimilar to that one shown in Fig. 1 while only the first lighsheet position (axial) was investigated. A KrF-excime

laser at 248nm and two intensified CCD cameras (752 x580 Pixel, images stored in 8 bit format) were used. The fil

ters applied to separate liquid fuel and fuel vapor are30725nm (vapor phase) and 360-400nm (liquid).

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Figure 2. Fluorescence spectra of the mixture benzene-TEA [18]

RESULTS - MIE LIGHT SHEET MEASUREMENTS

The first series of spray images in Fig. 3 represent thespray formation process at atmospheric conditions. Thedifferent parts of the spray (leading edge, trailing edgebody, vortex region) described by Evers [21] can clearlybe identified in the image series. The swirl injector pro-duces a hollow cone spray structure, which is precededby a pre-jet. The acquisition times given in the figure

represent the time delay to the electrical opening signaof the injector and not to actual injection start. This starof injection is 0.34ms delayed to the electrical signalAfter start of injection first a pre-jet is formed and after-wards the main spray cone builds up (0.55ms). The pre-jet structure is compact near injection start at 0.55ms andbreaks up at 0.75ms while the intensity distribution indi-cates relatively large drops in the pre-jet. The main spraybody forms a hollow cone (0.75ms). At 1.15ms a vortex isvisible resulting from the interaction between the injectedfuel and the quiescent air. The vortex grows by movingdownstream. It is clearly visible that liquid fuel is trans-ported upstream again into the spray region by the vor-

tex. This is believed to enhance the transport of mainlysmall droplets into the spray center evoked by a lowerpressure in the center of the spray cone. A large numberof small droplets in the spray center can simulade a filledcone structure in Mie measurements because the intensity of Mie scattered light is - depending on the polariza-tion [28] - in a first approximation proportional to the liquidsurface. Later in this paper a comparison between Mieand LIF images of the same sprays will be shown. How-ever, in the image series shown, clearly a hollow conestructure can be recognized by the Mie measurements.

Figure 3. Spray formation at atmospheric conditions (axial light sheet position; pChamber=0.1MPa; TChamber=293K;pRail=10MPa; tinjection=2.5ms)

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Figure 4. Spray formation at atmospheric conditions (radial light sheet position in 15mm distance from the injector orifice;pChamber=0.1MPa; TChamber=293K; pRail=10MPa; tinjection=2.5ms)

After the end of the main injection three bouncers of theneedle were detected and two are shown in the figure.The first of these needle bouncers creates a second hol-low cone spray. At about 5.0ms the injection generatedflow in the chamber is visible in the liquid fuel distribution.The highest droplet concentration is at that time found atthe spray tip. Please note again, that the intensity distri-bution measured by means of the Mie-technique in a first

approximation corresponds to the distribution of the totalsurface area and not to the mass distribution.

The images plotted in Fig. 4 represent the evolution ofthe liquid fuel distribution in the second light sheet plane,which is perpendicular to the propagation direction.Angular irregularities are visible in the spray patterns andthese irregularities explain that, depending on the posi-tion (orientation), different results could be obtainedwhen the first light sheet position is used. At 0.65ms (Fig.4) parts of the pre-jet can be observed followed by thehollow cone of the main spray body. The contour of thehollow cone is highly irregular (0.75ms and 0.85ms) with

steep gradients. When the vortex starts to grow up thecontour gets blurred, and afterwards a second ring is vis-ible covering the hollow cone spray. This r ing grows whilethe diameter of the hollow cone stays approximately con-stant. After injection end the spray pattern shows a nearlyregularly filled cone. Please note that the position of theangular irregularities stays constant although the imagesshown were acquired in different injection events. Later inthis paper we will present a definition for two new sprayparameters that describe the measured angular andradial fuel distributions.

AMBIENT PRESSURE The influence of the ambienpressure on the spray formation is given in Fig. 5. Withincreasing pressure the spray becomes increasinglycompact. All images have been taken at 1.15ms. At veryhigh pressures pre-jet and main spray body do not sepa-rate. For pressure levels of and above 0.65MPa (notincluded in the figure) vortex formations were found evenin the pre-jet region. The lower signal intensities near the

injector orifice occur due to extinction of the laser lightBut the dynamic range of the measurement is sufficiento represent the fuel distribution in that part of the spraytoo. Note that the rail-pressure and not the pressure dif-ference was kept constant in this variation. The influenceof the ambient pressure is quantified by the spray parameters plotted in the next section.

AMBIENT TEMPERATURE The influence of the ambi-ent temperature on the liquid fuel distribution is given inFig. 6 in the range from 293K to 523K. Due to thedecrease in ambient density the spray tip penetrationincreases up to temperatures of about 373K. For a fur-ther increase the reduced density is compensated by anenhanced evaporation so that a constant tip penetrationwas measured. At times later in the injection process anincrease of the tip penetration was found in the LIEFinvestigations up to about 450K. The spray cone anglestays approximately constant in this variation. The intensity distribution inside the main spray body is only slightlychanged while the significant changes of the fuel distribu-tion in the pre-jet region are cyclic fluctuations. The effecof the ambient temperature on the fuel vapor phase isvisible in the LIEF results.

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Figure 5. Spray formation under ambient pressure variation (axial light sheet position; TChamber=393K; pRail=10MPa;tinjection=1.0ms; tacquisition=1.15ms)

Figure 6. Spray formation under ambient temperature variation (axial light sheet position; pChamber=0.46MPa; pRail=10MPa;tinjection=1.0ms; tacquisition=1.15ms)

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Figure 7. Spray formation for rail pressure variations (radial light sheet position; pChamber=0.46MPa; TChamber=393K;tinjection=1.0ms; tacquisition=1.15ms)

RAIL PRESSURE A change of the fuel pressure in therail significantly affects the spray formation. The effect ofthe variation of the rail pressure is shown for an elevatedambient pressure of 0.46MPa in Fig. 7. For high rail pres-sure a regular filled cone structure of the spray is foundwhich changes to a hollow cone structure with decreas-ing fuel pressure. It is obvious in the measurements, thatthe spray is well atomized at high rail pressures while theatomization is significantly reduced at the lower pressurelevels.

RESULTS - SPRAY PARAMETERS EXTRACTEDFROM THE MIE LIGHT SHEET MEASUREMENTS

For a more quantitative description of the spray formationand also for a reduction of the enormous amount of datathe spray parameters tip penetration, cone angle and twonewly defined parameters describing the radial fuel distr i-bution (e.g. that ones given in Fig. 4) were extracted outof the acquired spray images. Every single shot was eval-uated while each measurement was repeated 15 times.Consequently, mean values and standard deviation from

15 measurements are given. 15 repetitions is a verysmall sample for estimating mean values and even lessfor quantifying fluctuations. On the other hand it was notpossible for us to increase the number of repetitions inthis investigation since the total amount of data alreadyexceeded 60GB using the high resolution in space andintensity, which we wanted to keep. Therefore, we ask the

reader to keep the small sample size in mind. The sprayparameters were evaluated automatically using imageprocessing routines. The spray contour is automaticallyfound by means of a threshold in the background cor-rected images. The tip penetration is separately evalu-ated for pre-jet and main spray. The cone angle is derivedfrom the measurements using the axial light sheet posi-tion including 20% of the main spray from the orifice to20% of the main body penetration in the determinationTwo regressions are fitted on this part of the spray and

the cone angle is defined as the angle between the tworegressions on the spray contour.

Fig. 8 gives the time history of tip penetration and coneangle evaluated from the spray images in Fig. 3. Thespray tip penetration of the main spray can well be repre-sented by a square-root fit. This tip penetration was eval-uated separately for the upper and lower half of the sprayThe values measured for the two halfs are nearly thesame and only one was plotted. The pre-jet shows afaster and larger penetration with significantly highecyclic fluctuations than the main spray. The spray coneangle shows a decrease vs. time which is also known

from PFI and Diesel injection processes. For the swirinjector tested here, the decrease is superimposed byfluctuations which can be interpreted to be caused bypressure fluctuations inside the injector (although a constant pressure supply was used).

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Figure 8. Time history of spray tip penetration and spraycone angle (images in Fig. 3; axial light sheetposition; pChamber=0.1MPa; TChamber=293K;pRail=10MPa; tinjection=2.5ms)

The influence of ambient pressure and of ambient tem-perature on the spray parameters is given in Fig. 9 andFig. 10, respectively. An increase of the ambient pressurenaturally reduces tip penetration and cone angle. Themeasured spray parameters are only slightly effected bythe ambient temperature. The tip penetration shows avery weak increase in the region up to ca. 373K and isconstant afterwards. For the cone angle a significantchange was only found for the highest temperature tested(523K).

Figure 9. Influence of ambient pressure on spray tippenetration and spray cone angle (images inFig. 5; TChamber=393K; pRail=10MPa;tinjection=1.0ms; tacquisition=1.15ms)

The rail pressure variation that was performed for anambient pressure of 0.46MPa has not only a strong effecton the spray pattern (Fig. 7), but also changes the sprayparameters extracted (Fig. 11). As it could be expectedthe tip penetration increases with the fuel injection pres-sure, while the cone angle is reduced with increasing rail-pressure.

Figure 10. Influence of ambient temperature on spray tippenetration and spray cone angle (images inFig. 6; pChamber=0.46MPa; pRail=10MPa;tinjection=1.0ms; tacquisition=1.15ms)

(a)

(b)

Figure 11. Influence of rail pressure on (a) spray tippenetration and (b) spray cone angle (imagesin Fig. 7; pChamber=0.46MPa; TChamber=393K;

tinjection= 1.0ms; tacquisition=1.15ms)

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Figure 12. Functions R and describing the radial fuel distribution in polar coordinates

PARAMETERS DESCRIBING THE RADIAL FUELDISTRIBUTION The images given in Fig. 4 can verywell be used to get a quick impression on the spray struc-ture, but it is difficult to quantify differences in the spraypattern from these images. Therefore, it is difficult to

compare different injectors. We have tried to representthe distributions in polar coordinates by two curves, thefunction R giving the fuel distribution versus the distanceto the spray axis and the function which gives theangular distribution of the spray. These functions aregiven by:

F: intensity of the measured light signal

Fig. 12 illustrates these functions for a typical hollow conespray. The function R represents the average intensitymeasured on a ring with radius r. The function givesthe accumulated intensity acquired in each direction j.The functions are given in arbitrary units and depend onthe experimental setup and the laser intensity used.

Therefore, comparisons are valid only for constant mea-surement conditions.

Fig. 13 represents the temporal development of the radiafuel distribution. The curves show the building up of thehollow cone structure and the vortex formation. Slight dif-

ferences in the distributions can easier be identified in thecurves than in the images in Fig. 4. Fig. 14 exhibits theradial fuel distribution for the variation of the ambienpressure. The curves illustrate the change from the hol-low cone spray with the visible vortex ring to a filled conestructure at larger pressures. In Fig. 15 and Fig. 16 theangular fuel distribution is given for five identical measurements and in its temporal evolution, respectivelyStrong oscillations of the curves can be seen in the plotBoth diagrams indicate by the uniformity of the angulastructures measured, that the angular fuel distribution isa characteristic of the (probably individual) injector. Thestructures in the angular distribution are a consequenceof the injector`s internal geometry and surface rough-ness. For the high pressure swirl injector investigatedhere, the angular fuel distribution is (in spite of the skein-ness detected) more uniform than e.g., distributions pro-duced by pintle type injectors used in port fuel injection Sengines [14].

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Figure 13. Temporal development of the radial distributionfunction R (images in Fig. 4; radial light sheetposition in 15mm distance to the injectororifice; pChamber=0.1MPa; TChamber=293K;pRail=10MPa; tinjection=2.5ms)

Figure 14. Change of the radial distribution function R fora ambient pressure variation (images in Fig. 7;pRail=10MPa; tinjection=1.0ms;tacquisition=1.15ms)

Figure 15.Angular fuel distribution (pChamber=0.1MPa;TChamberr=293K; pRail=10MPa;tinjection=2.5ms; tacquisition=1.15ms)

Figure 16. Temporal development of the angulardistribution (pChamber=0.1MPa;TChamber=293K; pRail=10MPa; tinjection=2.5ms)

SIMULTANEOUS AND SEPARATE IMAGING OFTHE LIQUID AND THE VAPOR FUEL PHASE

The LIEF technique explained above was used to simul

taneously acquire the liquid and the vapor fuel phaseonto two separate images for three different conditionsAt first, a time history of the evaporation process isshown for relatively high temperature (Fig. 17). Secondlya variation of the ambient temperature has been usedcomparing the resulting fuel distribution after end of theinjection process (Fig. 18). In the last image series acomparison between measurements performed with andwithout injector cooling has been performed (Fig.19).

It can be seen in the images that the separation of thetwo phases, liquid and vapor phase, is not complete. Theinfluence of the vapor phase on the image of the liquidphase can be neglected, but the vapor phase image issuperimposed by the signal from the liquid phase. Thiscan well be seen in the second pair of the images in Fig17. The fuel injected because of the needle bounce canbe assumed to consist nearly completely of liquid fuel inthis case. But this fuel is, although strongly reduced in itssignal intensity, also visible on the vapor phase image.

However, strong signals in the vapor phase image are toa significant part caused by fuel vapor. Additionally, weaksignals in parts of the spray with weak liquid phase signals (like the pre-jet region in the same image) are alsocaused from the fuel vapor phase. Therefore, it can beconcluded that the vapor phase image is interfered by the

liquid phase signal, but with respect to the degree of thainterference, the vapor phase images can well be inter-preted, when the superimposition is kept in mind. Thefactors x and y given in the images are magnification fac-tors of the intensity scaling. This means the plotted inten-sity in every series of images was raised from the firstimage to the last image of the series by the given factorsand with respect to the first image of the series while theimage of the liquid series and the vapor series wereamplified in the same way.

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Figure 17. Time history of the spray evaporation (TChamber= 523K; pChamber=0.46MPa; pRail=10MPa; tinjection=1.0ms)

Figure 18. Spray evaporation for different ambient temperatures (pChamber=0.46MPa; pRail=10MPa; tinjection=1.0ms;tacquisition=4.0ms)

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Figure 19. Effect of injector body and fuel temperature (TChamber= 523K; pChamber=0.46MPa; pRail=10MPa; tinjection=1.0ms;tacquisition=4.0ms

Figure 20. Comparison of Mie and LIEF images of the liquid fuel phase T Chamber= 453K; pChamber=0.46MPa;tinjection=1.0ms; tacquisition=1.0ms

50

m

m

signalin

tensity:

p =4 M PaR

p = 2 M P aR

p = 10 M PaR

M

IE

LIEF

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In the time history plotted in Fig. 17 it can be seen thatthe fuel vapor follows the path of the evaporating liquidfuel. Both phases are found at the leading edge of thespray. At 1ms vaporized fuel was already detected. Fromthe raise of the vapor signal, compared to the nearly con-stant signal level of the liquid phase, it can be derivedthat evaporation starts in a distance of approximately10mm to the orifice. But further investigations are neces-sary to get a better separation between the two phases toverify this result. Even 4ms after the electrical start of theinjection no clear separation in the flow path of the twophases was found. Due to the continuous evaporationprocess, the liquid signal decreases more rapidly thanthe vapor phase.

Fig. 18 shows that the temperature enhancement in therange from 353K to 523K enhances the spray evapora-tion while spray structure is changed mainly by the variedambient density.

Fig. 19 shows the influence of the an elevated injectorbody and fuel temperature on spray formation and sprayevaporation by switching of the injector cooling. For this

test the water cooling of the injector which was used in allother tests was switched off. The effects measured canbe compared to the flash boiling described by Hochgrebet. al. [29]. Hochgreb et. al. found strong changes in thespray formation of high pressure swirl injectors when thefuel was superheated relative to the boiling point about20K and injected into subatmospheric pressure. Due tothe higher ambient pressure in our test no dramaticchange of the spray evaporation was found and due tothe already compact spray structure caused by the ele-vated air pressure, no strong change in the spray struc-ture is detected. But, both the liquid fuel and the fuelvapor show a slightly more compact structure. This can

reduce the fuel air mixing, and although the evaporationprocess is enhanced by the fhigher fuel temperature theoverall mixture formation can appear to be slower. On theother hand much less single large drops are detected,when the injector cooling is switched off.

COMPARISON OF MIE AND LIEFMEASUREMENTS OF THE LIQUID FUELDISTRIBUTION

As already mentioned above it is not easy to decidewhich of the two experimental techniques applied is best

suited to visualize the formation of the liquid fuel phase ina GDI spray process. The LIEF technique offers theadvantage to have a mass proportional signal. On theother hand for Mie scattering experiments it is possible touse non-intensified cameras with a significant advantagein the dynamic range. A comparison between images ofthe liquid fuel phase acquired using the LIEF and the Mietechnique is given in Fig. 20.

CONCLUSIONS

Two-dimensional Mie and LIEF techniques were used toinvestigate the spray formation (liquid and vapor phase)of a high pressure swirl gasoline injector in a constantvolume injection chamber.

The formation of the liquid fuel phase was visualizedin two measurement planes by means of a Mie tech-nique with high spatial and temporal resolution. The

results show a strong influence of the ambient condi-tions and of the fuel rail pressure on the spray formation. The influence of ambient pressure, temperatureand rail pressure was quantified in spray parametersdescribing the axial (cone angle, tip penetration) andradial (radial and angular distribution curves) fuel dis-tribution (Mie-intensity distribution). The measurements using the radial light sheet position visualizethe fuel distribution in the spray in a better way thanthe distribution measured in the axial plane. Largeangular irregularities were found in the fuel distribu-tions. These irregularities stayed constant in repeti-tions of the measurements and throughout the sprayprocess. We conclude, that the irregularities in thefuel distribution are a peculiarity of the (individual)injector. Further investigation will have to show towhat extend these irregularities vary for differeninjectors especially of the same type.

The LIEF technique was used to simultaneouslyacquire the liquid fuel phase and fuel vapor onto twoseparate images while the separation at present isnot 100%, but sufficient for the evaluation. Theresults show that the fuel vapor phase follows the liq-uid fuel phase throughout the injection process andeven more than 2ms after injection end. A higher

injector body and fuel temperature causes for an ele-vated ambient pressure level of 0.46MPa a morecompact distribution of both, liquid and vapor fuelaccompanied by a visible reduction of large drops.

The comparison of the Mie and LIEF technique hasshown that both techniques are well suitable to visu-alize the liquid fuel phase in GDI sprays.

ACKNOWLEDGMENTS

The authors gratefully acknowledge financial support foparts of the work by the German Federal Ministry of Edu-cation, Science, Research and Technology (BMBF) undeconduct of the VDI-TZ Physical Technologies in the frameof project 13N7179.

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