Droplets Size and Velocity Measurements in a Spray from a Common Rail System for DI Diesel Engines L. Allocca, S.Alfuso, M.Auriemma, G. Valentino Istituto

Droplets Size and Velocity Measurements in a Spray from a

Common Rail System for DI Diesel Engines

L. Allocca, S.Alfuso, M.Auriemma, G. ValentinoIstituto Motori – CNR, Napoli - ITALY

ISTITUTO MOTORI

Istanbul - Nov. 13th-14th

Investigation of Diesel jet from a common rail injection system for engines applications

Motivation and target of investigation

Experimental apparatus for imaging

Spray morphology and time evolution

Experimental setup for PDA Tests

Discussion of Size and Velocity Results

Conclusions and Future Work

PRESENTATION OUTLINE

X [mm]

Y[m

m]

-30 -20 -10 0 10 20 30

-20

-10

0

10

2050474340373330272320171310730

sp

eed

m/s

X [mm]

Y[m

m]

-30 -20 -10 0 10 20 30

-20

-10

0

10

20

The fundamental mechanism of atomization has been under extensive experimental

and theoretical study for many years and reviews have been provided by many

researchers that also have developed different sub-models to compute the diesel

spray combustion in internal combustion engines

MOTIVATION AND TARGET OF SPRAY INVESTIGATION

In spite of the importance of atomization of diesel jet for engines the mechanism

still needs deeper understanding because of the difficulty to provide the

necessary drop size, velocity and trajectory data at the injector nozzle exit. The

atomization process has a strong influence on the spray vaporization rates

because it increases the total surface area of liquid fuel

The application of optical diagnostics (2D Image, PIV, PDA, LIF/LII) can provide velocity distributions, droplets size, fuel trajectories and spray morphology, as well vapor distribution to supply the experimental database for air motion and turbulence for advanced spray modeling development

AIM OF THE PRESENT PAPER

Describe the structure of a fuel spray generated by a common rail injection system equipped with a 5-hole injector

Characterize the spray evolution by imaging technique:- non evaporative conditions in a quiescent optically accessible vessel- evaporative conditions in a single-cylinder 2-stroke direct injection

diesel engine provided of optical accesses to the combustion chamber

Estimate liquid droplets size and axial velocity distribution on a multiple injection strategy in an optically accessible vessel at ambient temperature and atmospheric backpressure under quiescent conditions

The common rail injection system has been equipped by:

electro-hydraulic controlled injector micro-sac nozzle 5 hole, 0.13 mm diameter 150° spray angle flow rate of 270 cm3/30s@10 MPa

EXPERIMENTAL SET-UP & OPERATIVE CONDITIONS

High PressurePump

RailPECU

Pulse/DelayGenerator

Oscilloscope

Fuel Tank

Filter

ElectricalMotor

Injector

ChargeAmplifier19

Injector

CCD(1376x1024)

FlashH. P. Vessel

Flash

SF6 gas (6.2 kg/m3)rch=16.15 kg/m3

13° BTDC


The fuel has been injected into a optically accessible single-cylinder 2-stroke direct injection Diesel engine with the air velocity in the combustion chamber low enough to assume it as quiescent ambient



Single cylinder 2 stroke, loop scavenged

Bore 150 mm

Stroke 170 mm

Connecting rod 360 mm

Displacement 3000 cm3

Combustion chamber quiescent

Air supply roots blower engine

Compression ratio 10.1:1

ENGINE SPECIFICATIONS

Injector type: micro-sac nozzle

5 holes, F=0.130 mm, L=1.0 mm 150° spray angle

Injection strategies: low and medium, with a triple injection

high, with a single injection

INJECTION STRATEGIES

Pilot Pre Main dw1 [s]

dw2 [s]

Injection Pressure

[MPa]

Solenoid exciting time [s]

375 375 480 Low Load Fuel

injected [mg/str]

0.66 1.15 1.5

200 240 28.0


270 275 515 Medium

Load Fuel injected [mg/str]

1.65 2.06 8.51

230 230 71.0


- - 685 High Load Fuel

injected [mg/str]

- - 26.7

- - 140.0

Ambient conditions: Three gas densities

evaporative and non evaporative conditions

TEST CONDITIONS

Non evaporative conditions

Evaporative conditions

Gas density [kg/m3]

Gas temperature

[K]

Gas density [kg/m3]

Gas temperature

[K] 12.50 294 12.50 716 16.15 294 16.15 785 20.62 294 20.62 858



In-cylinder pressure signal for motored engine condition at 500 rpm. Tests have been made at the same gas density estimated from the perfect gas law. The injection timings have been set at 20°, 13° and 5° crank angle BTDC corresponding to the gas density of 12.50, 16.15, and 20.62 Kg/m3

Jets dispersion measurements

SPRAY CHARACTERIZATION: MORPHOLOGY & EVOLUTION

1 2 3 4 50

5

10

15

20

25

30

35

1 2 3 4 5 1 2 3 4 5

100 s 200 s 150 s 250 s

Pilot

Tip

Pen

etr

ati

on

[m

m]

Main Pre

Jets dispersion in non evaporating conditions for the medium load strategy


Jets dispersion for pre and main injection: medium load strategy and 16.15 Kg/m3 gas density

Non evaporating spray Evaporating spray


0 100 200 300 4000

5

10

15

20

25

30

35

0 100 200 300 400 0 100 200 300 400

Medium Load Strategy

Pilot

Ave

rag

ed

Tip

Pen

etr

ati

on

[m

m]

g=20.62 kg/m3

g=16.15 kg/m3

g=12.50 kg/m3

Pre

Time after SOI [s]

Non-evaporating spray

Main

0 100 200 300 4000

5

10

15

20

25

30

35

0 100 200 300 400 0 100 200 300 400

Medium Load Strategy

Pilot

Ave

rag

ed

Tip

Pen

etr

ati

on

[m

m] g=20.62 kg/m3

g=16.15 kg/m3

g=12.50 kg/m3

Pre

Time after SOI [s]

Evaporating spray

Main

Liquid jet penetration at medium load injection strategy


At early stage the gas density do not affected the tip penetration with a linear behavior in time. The tip penetration shows the same slope for the pilot, pre and main injection. At injection time later than 0.2 ms the gas density starts affecting the spray penetration producing a change in the slope. Highest penetrations are observed as the gas density decreases

0 100 200 300 4000

5

10

15

20

25

30

35Non-evaporating spray

High Load Strategy

g=20.62 kg/m3

g=16.15 kg/m3

g=12.50 kg/m3

Ave

raged T

ip P

enetr

atio

n [m

m]

Time after SOI [s]

0 100 200 300 4000

5

10

15

20

25

30

35Evaporating spray

High Load Strategy

g=20.62 kg/m3

g=16.15 kg/m3

g=12.50 kg/m3

Ave

raged T

ip P

enetr

atio

n [m

m]

Time after SOI [s]

Liquid jet penetration at high load injection strategy


0 200 400 600 800 1000 1200 1400 16000

10

20

30

40

50

60

70

80

High Load Strategy

Non-evaporating spray

g = 20.62 kg/m3

g= 16.15 kg/m3

g= 12.50 kg/m3

Tip Pe

netrat

ion [m

m]

Time after SOI [s]

Main

0 200 400 600 800 1000 1200 1400 16000

40

80

120

160

200Non-evaporating spray

High Load Strategy

g=20.62 kg/m3

g=16.15 kg/m3

g=12.50 kg/m3

Mean

Tip

Sp

eed

[m

/s]

Time after SOI [s]

Tip penetration at high load strategy – non evaporative

Mean tip speed at high load strategy – non evaporative

To provide a full tip penetration profile a 28 mm lens has been used with a 5.4 pixel/mm spatial resolution


Droplet size and velocity measurements

SPRAY CHARACTERIZATION: SIZE & VELOCITY RESULTS

ECU

H/P PUMP

SPECTRUM ANALYZER PHOTOMULTIPLIERS

EXTERNAL INPUT

ARGON-ION LASER

30°

SYNCHRONIZER

ENCODER

TRANSMITTER

RECEIVER

PDA System:Argon-ion laser operating at 514.5 nm.A 310 mm focal length transmitting optics with a beam separation of 65mmA modular collecting optics working in forward scattering mode at an off-axis of 30°.A synchro-unit device, driven by an optical encoder connected to the pump shaft, to trigger the ECU of the injection system and the PDA processorTests have been taken over 300 injection cycles with a time resolution of 20 s.

A two channel phase Doppler analyzer system is used to acquire, simultaneously, droplets size and the axial component of droplets velocity



0 250 500 750 1000 1250 1500 1750 2000 2250 2500

0.0

0.5

1.0

1.5

2.0

Time (s)

inst

. gauge p

ress

ure

[M

Pa]

INJECTION STRATEGY

Pinj=71 [MPa]

Pilot [ms]

Pre [ms]

Main [ms]

Dwell [ms]

dt [s] 270 275 515 230

Injected fuel

[mg/str]

1.65 2.06 8.51

Total fuel 12.22 mg

2.55.07.510.012.5

20.0

30.0

40.0

50.0

PDA Test grid

PDA Measurements:Different locations from the nozzle and along the spray axis up to the borderThe radial step was r=0.5 mm

r

z

0 500 1000 1500 2000 2500 3000

-0,5

0,0

0,5

1,0

1,5

2,0

0,0

0,1

0,2

0,3

0,4

0,5

8.38mg/str1.99mg/str1.65mg/str

in

st. g

au

ge p

ressu

re [M

Pa]

time [s]

515 s275s270 s

230 s230 s

medium load total inj. fuel12.02 mg/strP

inj=71 MPa

so

len

oid

co

rren

t

t=0

utente

The injector has been mounted tilted in order to investigate a single iet set with its axis along the vertical axis as it is shown in this figure that depicts the grid points where PDA measurements have been performed

utente

The injection strategy conditions are shown in the table where the single amount of fuel inejcted for each injection are shown. The total amount of fuel of 12.22 mg is injected during the triple strategy pilot - pre and main with a flow rate experimentally estimated by the Bosch tube procedure.


0 300 600 900 1200 1500 1800 2100 24000

20

40

60

80

100

120r=0.0 mm

Time [s]

z= 5.0 mm z= 7.5 mm

Axia

l velo

city

[m/s

]

0 300 600 900 1200 1500 1800 2100 24000

5

10

15

20

25

30

Time [s] Main startsPre startsPilot starts

r=0.0 mm

z= 5.0 mm z= 7.5 mm

Dia

mete

r [m

]

Main results:At 5 mm from the nozzle the jet is already atomized with small droplets of about 1-2 micron that travels up to 100 m/s Profiles of diameter and axial velocity have a flat behavior during the needle steady phase and a rapid increase of the axial velocity during the transient needle opening phase. During the transient phase of the needle lift larger droplets are produced.

Droplets size and velocity at the spray axis [R=0 mm]


0 200 400 600 800 1000 1200 1400 1600 1800 2000 22000

5

10

15

20

25

30r=0.0 mm

Time [s]

z= 5.0 mm z= 7.5 mm z=10.0 mm

Dia

mete

r [m

]

0 200 400 600 800 1000 1200 1400 1600 1800 2000 22000

5

10

15

20

25

30r=0.0 mm

Time (s)

z=12.5 mm z=20.0 mm z=30.0 mm z=40.0 mm

Dia

mete

r (m

)

Main results:Along the spray axis, in the near field region (up to 10 mm from the nozzle), the droplets diameter shows a slight decreasing trend. This behavior may be due to the occurrence of the atomization process that is still proceeding. Moving away from the nozzle the bigger droplets disappear so confirming that they are confined at the spray border

Near and far field droplets size at the spray axis [R=0 mm]

SPRAY CHARACTERIZATION: SIZE & VELOCITY RESULTSAxial velocity at the spray axis [R=0 mm]

0 200 400 600 800 1000 1200 1400 1600 1800 2000 22000

20

40

60

80

100

120r=0.0 mm

Time [s]

z= 5.0 mm z= 7.5 mm z=10.0 mm

Axia

l velo

city

[m/s

]

Main results:Along the spray axis the axial velocity shows an uniform field both in the near as well in the far field of the spray.

0 200 400 600 800 1000 1200 1400 1600 1800 2000 22000

20

40

60

80

100

120r=0.0 mm

Time [s]

z=12.5 mm z=20.0 mm z=30.0 mm z=40.0 mm

Axia

l velo

city

[m/s

]

SPRAY CHARACTERIZATION: SIZE & VELOCITY RESULTSZ=10 mm from the nozzle

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.40

5

10

15

20

25

30

35

Time (ms)

r,z(0.0;10) r,z(0.5;10) r,z(1.0;10)

Dia

mete

r (m

)

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.40

20

40

60

80

100

120

Time (ms)

r,z(0.0;10) r,z(0.5;10) r,z(1.0;10)

Axia

l velo

city

(m/s

)

Main results:Locations farther from the spray axis give bigger droplets during the transient needle lift phase with mean diameter up to 20 microns at r=1mmThis behavior is confirmed for the pilot, the pre, as well the main injection.During the opening transient stage of pilot injection the larger droplets travel at lower axial velocity pushed to the spray periphery by the jet momentum

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.40

20

40

60

80

100

120

r,z(0.0;20) r,z(0.5;20) r,z(1.0;20) r,z(1.5;20)

Axia

l velo

cit

y (

m/s

)

Time (ms)

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4

0

5

10

15

20

25

30

35 r,z(0.0;20) r,z(0.5;20) r,z(1.0;20) r,z(1.5;20)

Dia

mete

r (m

)

Time (ms)


Main results:Same trend as that observed at 20 mm from the nozzle with bigger droplets during the transient needle lift phase increasing along the spray axis An opposite trend was observed for the axial velocity that shows the highest values close to the spray axis.

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6

0

5

10

15

20

25

30

35 r,z(0.0;30) r,z(0.5;30) r,z(1.0;30) r,z(1.5;30)

Dia

mete

r (m

)

Time (ms)

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.60

20

40

60

80

100

120

r,z(0.0;30) r,z(0.5;30) r,z(1.0;30) r,z(1.5;30)

Axia

l velo

cit

y (

m/s

)

Time (ms)


Main results:Locations at higher distances from the nozzle produce the same behavior for droplets diameter and axial velocity Droplets diameter collected during the steady state stage of the mean injection exhibits an increasing trend along the spray axis ranging from about 1 micron to 2.5 micron. Droplets size results also give the same trend as that observed at 10 mm from the nozzle, with bigger droplets produced during the transient needle lift phase with an increasing trend along the spray axis

1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.40

1

2

3

4

5

6

main injection

r,z(0.0;30) r,z(0.5;30) r,z(1.0;30) r,z(1.5;30)

Dia

mete

r (m

)

Time (ms)


Z=40 mm from the nozzle

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.60

20

40

60

80

100

120

r,z(0.0;40) r,z(1.5;40) r,z(2.0;40) r,z(2.5;40) r,z(3.0;40) r,z(3.5;40)

Axia

l velo

cit

y (

m/s

)

Time (ms)

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6

0

5

10

15

20

25

30

35 r,z(1.5;40) r,z(2.0;40) r,z(2.5;40) r,z(3.0;40) r,z(3.5;40)

Dia

mete

r (m

)

Time (ms)

Main results:Locations at higher distances from the nozzle produces the same behavior for droplets diameter and axial velocity although a higher fluctuation of the diameter profiles is observedDroplets diameter, collected during the steady state stage of the mean injection, exhibits an increasing trend along the spray axis ranging from about 4 micron to 7 micron.The axial velocity profile starts to reduce its value with a more rapid trend along the spray axis also during the steady state part of injection

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.60

20

40

60

80

100

120 r,z (0.0;50) r,z (0.5;50) r,z (1.0;50) r,z (1.5;50) r,z (3.0;50) r,z (3.5;50)

Axia

l velo

cit

y (

m/s

)

Time (ms)

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6

0

5

10

15

20

25

30

35 r,z(0.0;50) r,z(0.5;50) r,z(1.0;50) r,z(1.5;50)

Dia

mete

r (m

)

Time (ms)


Main results:Locations at higher distances from the nozzle produces the same behavior for droplets diameter and axial velocity although a higher fluctuation of the droplets size profiles is observedDroplets size diameter collected during the steady state stage of the mean injection exhibits an increasing trend along the spray axis ranging from about 2 micron to about 10 micron. The axial velocity profile starts to assume a decreasing trend along the radial location also during the steady state part of injection


0 200 400 600 800 1000 1200 1400 1600 1800 2000 22000

20

40

60

80

100

120r=0.0 mm - z=7.5 mm

Time [s]

Axia

l velo

city

[m/s

]

0 200 400 600 800 1000 1200 1400 1600 1800 2000 22000

5

10

15

20

25

30

Time [s]

r=0.0 mm - z=7.5 mm

Dia

mete

r [m

]

Data scattering:Data collection has shown a very narrow dispersion during the steady-state stage of injection During the transient working phase of the nozzle a wide scattering of data has been provided

0 200 400 600 800 1000 1200 1400 1600 1800 2000 22000

5

10

15

20

25

30r=0.0 mm - Z=30.0 mm

time (s)

Dia

mete

r (m

)

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.50

5

10

15

20

25

30Pilot

Distance from the spray axis [mm]

tinj

=0.55 ms tinj

=0.65 ms t

inj=0.60 ms t

inj=0.70 ms

Mea

n di

amet

er

D10

[m

]

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.50

5

10

15

20

25

30

Pre-Inj


tinj

=1.05 ms tinj

=1.15 ms t

inj=1.10 ms t

inj=1.20 ms

Dia

met

er D

10 [

m]

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.50

5

10

15

20

25

30

Main Inj

tinj

=1.55 ms tinj

=1.85 ms t

inj=1.65 ms t

inj=1.95 ms

tinj

=1.75 ms tinj

=2.10 ms

Dia

met

er D

10 [

m]



D10 versus spray radial distance at 20 mm fromthe nozzle for the pilot, pre and main injection

CONCLUSIONS

An experimental investigation of the fuel spray characteristics, generated by a common rail injection system for light duty diesel engines, in terms of droplets size and axial component of velocity has been carried out.2D imaging techniques for studying the spray morphology and the spatial and temporal evolution in quiescent ambient has been applied.

The main results can be summarized as follows:• visualization of the spray, both under non evaporative and evaporative

conditions, has shown a good jet stability with a slight cycle to cycle shape variation;

• the gas density does not affect the spray penetration in the early stage of injection suggesting that the fuel momentum is the main controlling parameter for the jet evolution;

• the central region of the spray shows a mean diameter profile with a decreasing trend during the transient needle opening phase, a flat zone characterized by droplets diameter of few microns (1 to 7 microns) during the steady-state stage and an increasing trend during the non-stationary needle closure phase;

CONCLUSIONS• during the transient needle opening the diameter profiles show a decreasing

trend with an early production of large droplets, up to 25 microns, located mainly around the spray periphery and traveling at a lower axial velocity;

• close to the jet axis, time-resolved axial velocity profiles show maximum values of about 100 m/s with a flat zone during the steady state part of the pilot, pre and main injections. Lower values, with more fluctuating profiles, have been observed moving toward the spray periphery because of the interaction with the air that produces wide fluctuations;

• during the steady state part of each injection, the jet shows an uniform velocity field with a good atomization level in the central region of the spray both in the near and far field. Droplets diameter ranges between 1÷7µm presenting higher values in the far field (up to 40 mm from the nozzle). Moving farther from the nozzle (Z=50 mm) bigger droplets have been found also during the steady period of the main injection that might be due to a coalescence process;

• the spray periphery, instead, is characterized by bigger droplets, up to 25-30mm formed mainly during the transient opening phase of the needle with high velocity gradients due to its interaction with the surrounding air.

Droplets Size and Velocity Measurements in a Spray from a Common Rail System for DI Diesel Engines

L. Allocca, S. Alfuso, M. Auriemma, G. ValentinoIstituto Motori – CNR, Napoli - ITALY

Istanbul - Nov. 13th-14th

THANK YOU FORYOUR ATTENTION

ISTITUTO MOTORI

INTRODUCTION

Key role in i.c. engines of fuel injection systems for meeting high power, reduced fuel consumption and emission requirements

Droplet atomization and dispersion, vapour distribution and stoichiomentric air/fuel mixture burning affect the combustion stability, efficiency and pollutant formation

Droplet atomization and dispersion, vapour distribution and stoichiomentric air/fuel mixture burning affect the combustion stability, efficiency and pollutant formation

Non intrusive optical techniques for investigationg on spray development for understanding the mixture preparation (imaging, PDA, LIF, LII, …)

Common rail: injection modulation in terms of rate shaping, multiple injection, injection pressure

SPRAY IMAGING AND TIP PENETRATION RESULTS

0 100 200 300 400 5000

10

20

30

40

50

60 pilot pre main

Mea

n tip

pen

etra

tion

(mm

)

Time [s]

pilot

pre

main

50 μs 100 μs

150 μs 250 μs 300 μs 350 μs

400 μs 500 μs 600 μs 200 μs

INJECTION STRATEGY

Pinj=71 [MPa]

Pilot [ms]

Pre [ms]

Main [ms]

Dwell [ms]

dt [s] 270 275 515 230

Injected fuel

[mg/str]

1.65 2.06 8.51

Total fuel 12.22 mg

utente

Single shot images of the spray have been also acquired to provide the spray evolution and locate correctely the PDA grid points.Images have been collected by a CCD camera 1280x1024 pixel resolution setting an exposure time of 1 microsec. The illumination was provided by a photographic flsag triggered by a pulse generated that also set the CCD camera and the injection system

utente

The spray travels mainly as a compact column at the early stage of injection showing a well defined conical profile whereas at later time the air drag effects deform the tip with some radial dispersion and detached layers from the main jet. Also some wave perturbation can be observed on the peryphery of the liquid jet

Documents

Droplets Size and Velocity Measurements in a Spray from a Common Rail System for DI Diesel Engines L. Allocca, S.Alfuso, M.Auriemma, G. Valentino Istituto