Content uploaded by Michael Wensing
Author content
All content in this area was uploaded by Michael Wensing on Jul 18, 2023
Content may be subject to copyright.
The Japan Society of Mechanical Engineers
NII-Electronic Library Service
TheJapanSociety oE Mechanical Engineeis
FLI-4 The Eighth International
Conference
on Modeling
and Diagnostics
for
Advanced
Engine Systems (COMODIA
2012), July
23-26, 2012, Fukuoka, Japan
Effects
of fuelcomposition on spray ignit
relevant conditionsion
under engine
"Thomas Nlogel,
Michael Wensing
Institute ofEngineering Thermodynamics (I:TT),
F
Am Weichselgarten 8, 91058 Erlangen, Gerrnanyriedrich-Alexander-UniversityofErlangen-Nuremberg
Kley Pfo,ttsr Diesel, CI, RME, FAME, OH, Ignition, Fuel, Cetane number, CN
ABSTRACT
The knowledge about fuel composition efTects on the combustion behavior becomes more and more important due to
strict
legislative exhaust emission restrictions on the one hand and modified fuel compositions on the other hand. In
diesel combustion the addition of new fuel components, such as fatty acid methyl ester and pure
alkanes from the
Fischer-Tropsch-synthesis, have significant effect on the thermo physical
properties
of the diesel fuel mixture and
therefore infiuence the irijection and the evaporation process.
These processes
have a strong impact on the fo11owing
ignition and combustion process
and therefbre on the power generation,
engine noise and emissions. This can be seen in
gasoline
and diesel iniection. In the present
investigation the focus was set on the ignition phase.
Using a typical
piezo-type
diesel iajector and iajection pressures
up to 200 MPa different diesel fuels were iniected into a stationary
high temperature (up
to 1OOO K) and high pressure
(up
to 10 MPa) atmosphere. By means oftwo different cameras
the spray formation and the appearance (time
and location) of prernixed
and diflUsion controlled combustion were
acquired, separately.
It was found that the timing ofthe ignition processes
(premixed
and diffiisien controrled combustion) was dominated by
the ambient gas temperature while the location of ignition is defined by the pressure
ratio between gas and fuel. The
time delay between the first appearance ofthe lean combustion and appearance ofthe clifftision controlled fiame was
consequently also dominated by the gas temperature. At part
load conditions the UV-flame appeared at 800 ps after the
visible start ofiajection while at fu11 load conditions the ignition delay was reduced to 250 ps.
Cetane-number was not
found to have big effect on ignition timing under the conditions applied. The start ofcombustion was found on the fi'ont
or the side ofthe spray cone tip for all operating conditions investigated.
INTRODUCTION
The discussion
about C02 emissions and the
limited
resources of fossil fuels led to new approaches in intemal
combustion development and fuels from different basic
materials. While the compression ignition engine
development brought out the common rail iajection,
which gave various new parameters
that can be
eontrolled by the OEM in development and operation ef
the engine, additional parameters
that cannot be
controlled are given by new types of diesel fuels that
were brought to market. Throughout the years
fatty acid
methyl ester (FAME)
became rnore important and with
legislative regulations an additional FAME-fraction is
provision.
Moreover several new premium diesel fuels
with increased
cetane-number or additions from
synthetically diesel fuels, like those pure alkanes from
Fischer-Tropsch synthesis, became commercially
available.
These new diesel fuels differ in their thermo-physical
and chemical properties
which can have effbct on all
stages in
the combustion, like spray forrnation,
evaporation, mixture distribution, ignition and
cornbustion and therefore on specific fuel consumption,
power development and pollutant
formation.
In earlier investigations the effect of low volatile fuel
components on spray formation
was examined [1,
2].
Also the effect of the fuel quantity
on ignition behavior
used to be
in the focus
[3].
Now the
effect of fuel
on the
ignition phase,
especially the ignition delay and position
ofthe first flame, is under investigation.
TESTED FUELS
Three different, but common fuels were investigated
(Table
1). The CEC RF-06-03 is the European legislative
fuel for automotive testing and therefore a common
referenee fbr fuel investigations. It is defined by the
Coordinating European Council in the normative EN 590
[4]
but with narrower tolerances in order to provide
a
good repeatability in engine testing.
As second fuel a rapeseed fatty acid methyl ester (RME)
was chosen [S].
This type of fuel uses rapeseed oil as
basic
material. Through a few steps of chemical
processing
the glycerin
is separated from the fatty acids
which are transforrned into
esters via the
addition of a
methyl group.
However, the fatty acids from rapeseeds
Copyright @ 2012 by
theJapan Society of Mechanical Engineers
- 317
-
NII-Electionic
The Japan Society of Mechanical Engineers
NII-Electronic Library Service
TheJapanSociety oE Mechanical Engineeis
vary in their molecule-structure and therefore
in their
thermo-physical propenies.
For this reason the
EN 142
14
[6]
defines the limits ofthese properties
thus the fuel can
be used in the diesel process.
The third fuel is the market available premium diesel fuel
`CUItimate
Diesel" from AraVBP. This fuel
is
produced
without the
addition of RME and shows an increased
cetane number of 60.
The remaining thermo physical
properties
are cornpliant to the normative EN 590.
Table 1:
Fuel
Overview
value
CECRF-06-03
(EN590)[4]
RME(EN14214)
[5,6]
ArallBP
c`Ultimate
DieseP'
(EN590)
density(150C)[kgfm3]833-837860-900820-845
cetanenumber[-]52-54min.51 60
boiringcurve[eC]245-370245-370245-370
kin.viscosity
(400C)[mm2fs]2.3-3.43.5-5.02.3-3.4
FAME-fraction
[vol-O/o] omin96.5 o
THE INJECTION CHAMBER
Both measurement techniques, Mie-scattering and the
flame luminosity measurements, were perfbrmed in
a
high-pressure and high-temperature iajection chamber
presented
in Figure 1.
Figure 1: The irpection chamber
With an inner volume of 1O liters the chamber (Figure
1)
is permanently scavenged with gas
adjustable from air to
pure
nitrogen. The gas
flows through the chamber from
the top corners, where electrical heaters are installed, to
the bottom comers inte water coolers. The gas
temperature and pressure
can be varied independently
from 298K to 1OOOK in the area of investigation and
from
30 kPa to
10 MPa. The gas
flow has an average
velocity of approx. 30 mmfs thus the spray formatiQn is
not infiuenced by the air movement. This makes
investigation repetition rates of3 Hz possible.
Table2:Technicaldataofthein'ectionchamber
asressure 30kPato10MPa
'maxlmumtemerature 1000K
maximumscavengingflowrate 11Om3N･h'
scavengingmedium N2airormixtures
,
clearanceoftheoticalaccesses 125mm
Innervesselvolume 1OIiters
maximumfuelpressure 250MPa(dieEel)
28MPa(gasolme)
fueltemperature 243Kto383K
in'ectionrepetitionrate O.1Hzto3Hz
The diesel fuel system allows pressures
up to 250 MPa.
The iniector itself is mountecl on the
bottom
side into
the
chamber, The iniector housing contains an intercooler
which is connected to temperature control device
which
allows ibjector temperatures from 243 K to 383 K.
OPTICAL SETUP
The optical setup is
displayed in Figure 2 and was
chosen after former measurements [3].
Figure 2: The measurement setup
The sprayjets and the combustion is recorded from the
top side. For the Mie images only the Sensicam, a
sensitive CCD-camera with a eooled CCD element (1),
is
in use. The spray is illuminated via fbur flashlights on
each side of the cell. For the combustion measurements
an additional intensified camera (Dicam,
2) was installed.
The optical signal is
divided
by a dichroic beam splitter
(3)
reflecting the wavelength from 260 nm to 320 nm. In
order to eliminate background noise a filter
set,
consisting of a Schott
UG 11
and a BR 350-505, was
attached to the Dicam. This fiIter set made it possible
to
record mainly the signal from
OH-radicals
at --308
nm.
The Sensicam recorded the visible spectral range of the
whole flame including the intensive diffUsion flame
signal. To prevent
the top-mounted camera from
overheating a heatshield and coeling air supply were
installed (4).
- 318
-
The Japan Society of Mechanical Engineers
NII-Electronic Library Service
TheJapanSociety oE Mechanical Engineeis
MEASUREMENT PROGRAM
A measurement program
was defined
to cover the engine
operating peint
range from the cold start to fu11 load,
However not all
thermodynamic conditions work also for
combustion measurement. When it comes to iniection in
real diesel engine this can be in case ofa pre-iniection
at
a crank angle far before top dead cente: The temperature
and the pressure
increase afterwards and ignition
conditions are reached. The rise of temperature and
pressure
is not given
in a stationary iajection chamber
and therefore in general
different conditions have to be
applied different to the
`real'
engine operation and
different
for the investigation of spray propagation
and
ignition. A condition which was used in this study fbr
both,
spray propagation
and ignition is given in Table 3.
Table3:Oeratinoint
name
pG[MPa]TG[K]pF[Mpa]TF[K]tinj[ps]
partialload4f1606873160363550
All measurements were performed with a Bosch CRI 3.0
8-hole piezo-iniector
from a BMW 3.0 ltr, six-cylinder
engine from 2006. The iniector itself is driven with 160
MPa fuel pressure
in serial production
but for the test
bench use 200 MPa iniection pressure
is also possible.
Unlike in
the
car the
iajector
is
driven
by a fu11y
programmable electronic drive unit from Genotec. The
iniection timing was kept constant for all operating
points.
A total iajection time of 450ps represents a
panial
load fuel mass.
IMAGE PROCESSING AND EVALUTION
The image processing
and evaluation is done
automatically to provide
a good comprehensibility and
reproducibility which is mandatory in order to compare
results ofdifferent measurement campaigns. The process
is displayed is described in [1,
3].
Out of the spray images a mean image, an outline plot
and a frequency scale image are produced.
In addition to
the images for the spray measurement the penetration
depth, the spray cone angle and the area within spray are
evaluated. The penetration
depth ef every spray cone
represents the
far
most point
ofthe spray from
the
nozzle
in any direction. The spray cone angle is calculated via a
point
on each side ofthe spray in
the same distance (i.e.
the center ofgravity ofthe spray). The area within spray
is a qualitative
value in order to compare the progress
of
sprayfflame propagation.
It is calculated out ef the
integral signal ofthe sprayffiame projected
on the image
plane,
RESULTS - SPRAY PHASE
First
the spray formation
was determined in order to plot
the penetration
depth and the cone angle of the liquid
fuel phase
vs. time.
In Figure 4 a typical plot
of penetration
depth and cone
angles at part
load condition is
given
and in
Figure 3 the
corresponding frequency scale images are presented.
The
spray propagation
can be divided into
three stages. The
first stage, the propagation
phase
describes the evolution
of the liquid spray phase.
In this
stage the evaporation
effects are minor while the influencing parameters
are
the delta pressure
and the fuel
density
itself
according to
the law of Bernoulli. Due to the very similar density of
alL
fuels
and the
same thermodynamic conditions the
propagation
is neariy the same until the end ofthis phase
at approx. 175 ps
after vSOI,
tsS･s8t..-
tsf5t9R
tsi5g?;
tsEs,am.co
PEas
= 6 MPa/ T,s. = 873 Kl
PfueL
= 160 MPat Tfues = 363 Kt tinj = 550 ps
AraVBP
CECRF-06-03 Ultimate
RME
Figure 3: Spray images ofthe different fuels
The second stage is the stationary spray state. In this
state iajected fuel mass and evaporated fuel mass are
nearly the same which results in a constant maximum
liquid fuel penetration
depth. The parameters affecting
this stage are temperature and the evaporation behavior
ofthe fuel. A higher gas temperature and a high volatile
fuel lead to an increased evaporation and therefore to a
decreased maximum penetration
depth. Here, the fuel
behavior is clearly different. While the CEC reference
fuel
and the "Ultimate Diesel"
fuel
behave
the same, the
liquid phase
of the RME is clearly more present
and
shows an increase in the penetration
depth which is
more
than 30% higher than for the standard fuel, In the time
between 50 ps
and 600 ps the rapeseed fuel shows a
slight tendency tewards higher cone angles. After 600 ps
in all curves for both parameters
a kink can be seen
- 319
-
The Japan Society of Mechanical Engineers
NII-Electronic Library Service
TheJapanSociety oE Mechanical Engineeis
caused by the end of injection afier approx. 550 ps.
The
length
of the stationary spray state depends on the
iniection duration in the case that the thermodynamic
conditions do not change.
V35fi-30eg25:･e-
2og'
15glo
5
o
25
E.2o:.ge1588
loRX5
o
Psas
= 6 MPal Tgns = 873 KI
Pfuel
=: 160 MPa/ Tfoe] = 363 KI tioi =
550 PS
tirne after vSOI [ps]
200 400 600 8001000
o
o 2oo
4oo 6oe goo looo
Figure 4: Penetration depth and spray cone angle vs. time
The end ofiTijection leads the spray to enter the last stage
of complete evaporation. For short iTijection durations it
became clear that evaporation starts from the spray tip in
direction to the nozzle tip [3].
RESUIJI]S
- IGNITION PHASE
Except the inert nitrogen gas,
which has been changed to
normal air, all the thermo dynamical are the same like in
the spray investigation. Afterwards the same operating
point
like for the spray measurement series is presented
here for the ignition behavior determination,
In Figure 6 the flame intensity images are presented
on
the left side, Each fiame intensity signal image censists
ofthe picture
acquired frorn
the OH* signal on the left
side and the integral flame signal, dominated by the
diffusion flame, ofthe same flame regimes mirrored on
the right hand side and can be compared directly. The
image is
a mean image out of 32 single images in false
colors, In addition an intensity distribution of both
spectra of a single fuel jet
flame is plotted
vs. the
distance to the nozzle. In this case the graph represents
the horizontal flame jet
of both images and the intensity
is
measured on the centerline ofthese flames.
At 600 ps
after vSOI the RME ignites first, At a distance
in between 20 and 30 mm to the nozzle first spots were
recorded in the UV spectra only slightly represented in
the images and the intensity graphs.
At 700 ps a part
of
the fuel jets
is ignited whi]e others aren't.
This
can be
caused either by slight differences in the thermal field or
by slight diffbrences
in the nozzle hole geometry,
This
effect is much more pronouncecl
in constant pressure
vessel conditions. In the intensity plet
the first flame
development
is
at about 40 mm while the UV spectra is
located
slightly more outside than the visible spectra.
The CEC reference fuel and the "Ultimate Diesel" ignite
at about 800 ps.
At the beginning the ignition behavior of
both fiames is nearly even in intensity and location, The
fuel jets
that ignite first
are the
same as for
the
RME, For
the RME all fueljets show a big area for
the
OH' while
the diffusion flame is just
about te start. The wide area
for the OH" radical and the sLightly developed
diffusion
flame refers to a wide area ofa locally lean combustion.
100 ps later the first signals of the diffUsion flame are
recorded fbr
the
CEC and the "Ultimate Diesel".
In
contrast to these two, the diffusion
flame ofthe rapeseed
fuel isjust slightly more established which can be seen in
their spatial intensity curves in Figure 6 on the right hand
side. The intensity distribution ef the OH'-flame of the
RME has a homogenous intensity distributien ever the
entire flame area. There is no intensity maximum neither
on the
outside, towards the vessel walls, or on the inside,
towards the nozzle tip.
If the fiame propagation
at 1000 ps and 1100 ps is
compared, the CEC reference fuel
and the
"Ultimate
DieseP' behave the same until the flame propagation,
represented by the area covered by the flame and the
spatial intensity distribution, of the "Ultimate Diesel" is
dramatically increased at 11OO ps
which can be observed
by the nearly doubled intensity in the intensity graph and
the color change in the flame images,
300"2SOug2oogts150oEq100
¢
50
o1,O
O,8T:O,6;;R
o,4D9no2o,o
Pgss
= 6 MPat TgA, = 873 Kl
Pfuet
= 160 MPal TftveL = 363 Kt ti.j z 550 ps
time after vSOI [ps]
600 700 800 900 1000 11001200
600 700 800 900 1000 1100 t200
Figure 5: FIame area and probability
vs, time
- 320 -
The Japan Society of Mechanical Engineers
NII-Electronic Library Service
TheJapanSociety oEMechanicalEngineeis
CEC RF-e603
UV VIS
P!as
= 6 MPal TEas = 873 KI Pfuel
= 160 MPal Tfuel = 363 K/ tini = 550 PS
AraVBP UItimate
RME Spatiat flame intensity distribution
UV VIS UY VIS
110
20distance
to nozzle [mm]
30 40 50 60
O,5
o1
Aral
Uttimate
Diesel
UV
CEC RF-06t03
UV
RMEUV
- - Aral Ultimate Diesel VIS
- -
CEC RF-06-03
VTS
- -･ RMEVIS
O,5
o1 -tt-
O,5
-.-r#
N
oITI
1
o,s
Fua'U'mm
o1 --
.--
5vetsceto2-
O,5
o
Figure 6:UV- an
o1"Ldig1
O,5,::2
o
1
-t
10 20 30 40
distance to nozzle [mm]
1
d visible mean flame images and their spatial intensity distribution
50 60
For the other fuels a second peak
can be found on the
nozzle-near side which is not present
at the
"Ultimate
Diesel".
Also the diffusion flame is clearly more present
fbr the
premium fuel. At 1200ps the UV fiame is fu11y
established. The peak
intensity is about 50% higher than
the others and also the size ofthe high intensity flame is
clearly increased. The diffusion flame is clearly
established and the highest in intensity. The RME and the
CEC fuel behave similar in both, the UV- and visible
spectra, although the RME is slightly more established.
If the area covered by the UVLflarne and the ignition
probability
are considered (Figure
5) it becomes clear
that the rapeseed flame ignites earlier, at about 600 ps,
and with a higher probability,
The ignition probability
is
calculated in
a way that for each single OH" image, 32
- 321
-
NII-Electionic
The Japan Society of Mechanical Engineers
NII-Electronic Library Service
TheJapanSociety oE Mechanical Engineeis
per point
in time, and each single nozzle hole,
8 per
iniector,
is
counted whether a signal could be detected
and normalized to the maximum possible
ignitions. For
this
investigation
more points
in time have been taken
into account to
be
more accurate and therefore the
ignition
delay
is
represented indirectly. The area covered
by the
flarne
represents the integral
fiame propagation
detected
in
the irnages
and is calculated in the same way
like
the area within spray and from the
same amount of
irnages
like
the probability
determination.
The area covered by
the
rapeseed fuel flame is nearly
constant between 800ps and 1050ps. Afterwards the
flame
is
developing
again. The flame propagation
of the
other two fuels is nearly even. Both ignite at
about
750 ps and are trailing
the RME-flame. They are nearly
stationary frem 900 ps to 1000 ps.
At this point
the
values split and increase
dramaticalry for the "Ultimate
Diesel"' fuel. It overtakes also the earlier ignited
flame
of
the RME at about 1050 ps.
At the end this flame is the
most present
flame.
The ignition
probability
of the
non-RME fuels
is
nearly the same except at 925 ps
which is a measuring inaccuracy.
CONCLUSIONS
The aim ofthis investigation was to point
out the
impact
of fuel composition on the ignition behavior, especially
ignition
delay and flame propagation.
Foregoing spray
measurements were perfbrmed to gain
information
about
the propagation
ofthe liquid phase.
In the Mie scattering measurement at every operating
point
a total of 16 points
in tirne and 32 images per
point
of time were acquired. The spray propagation,
reflected
by the penetration
depth and the spray cone angle vs.
time, was determined. It became clear that
RME, made
of rape seeds, is more present
in the liquid phase than
standard diesel
and
"Ultimate
Diesel". The liquid
penetration
length is 30% higher at the presented
operating point.
The spray cone angle is clearly affected
by the fuel composition, too. After reaching a maximum
value the RME difTers
and has slight higher values up to
600 ps.
These results difTer from the results measured by
Desantes [7]
because
ofthe high temperature conditions
which increases
the effect ofevaporation dramatically. A
difilerence in the spray formation
between
the
CEC
reference fuel
and the
"AralfBP UItirnate
Diesel"
was not
noticeable recorded.
However, the behavior in spray fbrmation cannot be
linked to the ignition behavior.
The RME was the
first
to
ignite under air atmosphere. These results approve
indicated
pressure
measurements at CI engines [8,
9].
Under stationary conditions the .ignition delay
for
the
presented
conditions is approx. 200ps shorter. The
"Ultimate
Diesel" has about the same ignition delay than
the reference although the cetane number is increased to
60 which difTers from earlier investigations [10].
The
cembustion behavior changes dramatically at about 1 rns,
represented in the fiame images and the corresponding
graphs,
which should affe ¢t the untreated engine
ernissions like
it
was described for fuels with higher
cetane number [11,
12]. These
effects can be
seen in
both
spectra. In contrast the ignition
probability
vs, time is not
affbcted by the
cetane nurnber.
By considering the intensity of the flame in
distance
to
the
nozzle it
can be
also determined
where the reaction
takes place,
The UVLflame has very homogeneous spatial
intensity
distribution
in a period
early after the start of
cornbustion, Later on two peaks can be identified. The
intensity distribution rines
of the
non-RME fuels
show
two peaks
at later times with higher intensity.
Although the RME fuel
has
the
same cetane number than
the CEC reference fuel, the ignition
delay
is
shortened
and the ignition
probability
is higher and closer to the
start of ibjection. Also the flame
structure is
different
which and can be linked to the fuel-bound oxygen.
Considering these facts it becomes clear that
the
increased
cetane number has no effect on the ignition
delay
but
on the flame
propagation
in the late stages.
Acknowletigements
The authors gratefu11y
acknowledge funding of the
Erlangen Graduate School in Advanced Optical
Technologies (SAOT)
by the
German National
Science
Foundation (DFG)
in the framework of the excellence
lnltlatlve.
Furthermore the authors gratefuIIy
acknowledge the
financial
support of the European Community and the
Federal
State
of Bavaria for
the prQject
"Optical
high
pressure
combustion bench test".
REFERENCES
[1]
T. Vbgel, M. Lutz, M. Wensing, A. Leipertz, 23rd
International
Conference on Liquid Atomization and
Spray Systems, (201O).
[2]
L.
Zigan,
I.
Schmitz, A. FIUgel, T, Knorsch, M,
Wensing,A. Leipertz, Fuel, (201O).
[3]
T.
Xbgel,
M. Lutz, S. Iannuzzi, M. Wensing, A.
Leipertz, Powertrains, Fuels and Lubricants,
2011-Ol-1928(2011).
[4]
EN 590:2009, Automotive fuels.
Diesel.
Requirements and test methods, 2009.
[5]
Mahne, Certificate of Analysis RME, Louis
Dreyfus Commodities GmbH, Wittenberg, 201O,
[6]
EN 14214:2009, Automotive fuels -
Fatty acid methyl
esters (FAME)
for diesel engines, 2009.
[7]
J.M. Desantes, R.1. Payri, A. Garcia, J,
Manin,
Energy & Fuels, 23 (2009)
3227-3235.
[8]
P. Soltic, D. Edenhauser, T. Thumheer, D. Schreiber,
A. Sankowski, FUEL, 88 (2009)
1-8.
[9]
A. Tsolakis, Energy & Fuels. 20 (2006)
1418-1424.
[10]
N. Laclommatos, M. Parsi,
A.
Knowles,
FUEL, 75
(1996)8-14.
[11]
P.
Rounce, A, Tsolakis, J. Rodriguez-Fernandez, A.
Ybrk, R. Cracknell, R. Clark, SAE Paper, 1999-Ol-0200
(2009).[12]
S.S. GM, A. Tsolakis, K,D, Dearn,
J.
Rodriguez-Fernandez, Progress in Energy and
Combustion Science, 37 (2011)
503-523.
- 322
-
