A computational investigation of theA computational investigation of theA computational investigation of the A computational investigation of the effects of swirl ratio and injection effects of swirl ratio and injection pressure on mixture preparationpressure on mixture preparationpressure on mixture preparation pressure on mixture preparation
in a lightin a light--duty diesel engineduty diesel engine
F. Perinia, A. Dempseya, R. Reitza
D. Sahoob, B. Petersenc, P. MilesbD. Sahoo , B. Petersen , P. MilesaUniversity of Wisconsin Engine Research Center
bSandia National LaboratoriescFord Motor CompanycFord Motor Company
ERC Student Seminar – 01/22/2013
University of Wisconsin -- Engine Research CenterERC Seminar – 01/22/2013
slide 1
OutlineOutlineOutlineOutline Experimental vs. Numerical study details
Motivation and problem setup
Model improvementp Compressible connecting rod assembly
Local mixture preparation study Local mixture preparation study Non-reacting conditions
Model accuracy impact on fired operation Wall heat transfer sensitivity to swirl ratio and injection pressure
University of Wisconsin -- Engine Research CenterERC Seminar – 01/22/2013
slide 2
OpticalOptical engineengine experimentalexperimental setupsetupf ASME ICES2012 81234 Engine specifications
Bore x stroke [mm] 82.0 x 90.4 Unit displacement [cm3] 477.2 Compression ratio 16 4 : 1
cf. ASME ICES2012-81234
P1 = Half of squish regionP1 = Half of squish regionCompression ratio 16.4 : 1Squish height at TDC [mm] 0.88
Bosch CRIP 2.2 Injector
P1 Half of squish region
P2 = Piston bowl rim
P3 = Inner bowl region
P1 Half of squish region
P2 = Piston bowl rim
P3 = Inner bowl regionBosch CRIP 2.2 InjectorSac volume [mm3] 0.23 Number of holes 7 Included angle [deg] 149
rede
ck [c
m]
CA = -15 deg ATDC
-0.5
0.0
0.5
P1P2
rede
ck [c
m]
CA = -15 deg ATDC
-0.5
0.0
0.5
P1P2
Hole diameter [mm] 0.14 Hole protrusion [mm] 0.3 Fuel properties r axis [cm]
dist
ance
from
fir
0 1 2 3 4
-2.0
-1.5
-1.0
0.5
P3
r axis [cm]
dist
ance
from
fir
0 1 2 3 4
-2.0
-1.5
-1.0
0.5
P3
p pComposition [mole fractions] 75% nC7H16 25% iC8H18 Fluorescent tracer [mass fraction] 0.5% C7H8
266 nm UV horizontal laser sheet Images at (degrees ATDC):
r axis [cm]
0 0.5 1 1.5 2 2.5 3 3.5 4
r axis [cm]
0 0.5 1 1.5 2 2.5 3 3.5 4
University of Wisconsin -- Engine Research CenterERC Seminar – 01/22/2013
slide 3
Equivalent Cetane Number 47
CA = [-17.5:2.5:-5.0]
OpticalOptical engineengine experimentalexperimental setupsetup IIIIi l N ti R ti 7 Diesel PPCI cases
(ASME ICES2012-81234)
Low-load
Non-reacting mixture
Reacting mixture
Intake charge composition [mole 100% N2
10% O2 81% N2 Low load
Highly dilute Slightly boosted
R d
fractions] 9% CO2 Intake pressure [bar] 1.5 Intake temperature [K] 300 372
Rs and pinj sweeps
Very low PM and NOx
Si ifi t UHC d CO
Engine speed [rpm] 1500IMEP [bar] --- 3.0 Global equiv. ratio [-] --- 0.3 I j t d f l [ ] 0 0088 0 0088 Significant UHC and CO
incomplete oxidationof bulk gas mixtures
Injected fuel mass [g] 0.0088 0.0088
Start of Injection [deg] -23.0 0.1, -23.3 0.1 Parameter sweeps: *Rs = 1.55,
*Rs = 2.20,*pinj = 860 bar *pinj = 860 barswirl ratio R [ ]g
comb. efficiency Crucial role of mixing
and chemical kinetics
Rs 2.20, *Rs = 3.50, *Rs = 4.50, *Rs = 2.20, *R = 2 20
pinj 860 bar*pinj = 860 bar *pinj = 860 bar *pinj = 500 bar * 1220 b
- swirl ratio, Rs [-] - injection pressure, - pinj [bar]
*baseline case
University of Wisconsin -- Engine Research CenterERC Seminar – 01/22/2013
slide 4
and chemical kinetics *Rs = 2.20, *pinj = 1220 barbaseline case
ComputationalComputational modelmodel setupsetup The ERC version of KIVA3v-R2 is employed Improvements to:
Phenomenon Submodel
Spray breakup KH-RT instability, Beale and Reitz
Near-nozzle flow Gas-jet theory, Abani et al. Spray j y
Droplet collision O’Rourke model with ROI (radius-of-influence)
Wall film O’Rourke and Amsden
p y
Evaporation Discrete multi-component fuel, Ra and Reitz
Turbulence RNG k- ε, Han and Reitz
C b ti Detailed chemical kinetics with sparse
Fuel
G id f l ti t d (SAE 2012 01 0143)
Combustion panalytical Jacobian, Perini et al.
Reaction kinetics Reduced PRF mechanism, Ra and Reitz
Chemistry
University of Wisconsin -- Engine Research CenterERC Seminar – 01/22/2013
slide 5
Grid from resolution study (SAE 2012-01-0143)
CompressibleCompressible connectingconnecting rodrod modelmodel IIMotivation Motoring pressure trace match requires
model calibration
over-predictionaround TDCmodel calibration
Incomplete piston/head geometry modeling Charge blow-by to the crankcase Compressibility in silica piston assemblies
around TDC
under-predictionis not negligible (Aronsson et al., SAE2012-01-1604)
Using Geometrical CR leads to significantdi ti i th d l
under predictionduring expansion
pressure overprediction in the model
Engine grid’s CR typically reducedb tifi i ll i i i lby artificially increasing crevice volume Affects trapped mass, wall heat transfer, pollutants Still difficult to match pressure trace shape
University of Wisconsin -- Engine Research CenterERC Seminar – 01/22/2013
slide 6
CompressibleCompressible connectingconnecting rodrod modelmodel IIII*figure not in scale
Target squish = 0.88 mm
C ld l 1 04 Th l i 0 31
Measured thermalexpansion
Cold clearance = 1.04 mm
Compression 0.15 mm (TDC)
Thermal expansion 0.31 mm
TARGET POS.
SETTINGSETTINGMeasured extended
piston assemblycompliance
Experimental setup accounts for deviations from rigid slider-crank does not consider bearing and crankshaft clearances
compliance
does not consider bearing and crankshaft clearances Thermal expansion less affected by engine operation
Ring friction is dominant scarcely reached by hot gases Dynamic squish height can improve modelling pollutants
University of Wisconsin -- Engine Research CenterERC Seminar – 01/22/2013
slide 7
Dynamic squish height can improve modelling pollutants
CompressibleCompressible connectingconnecting rodrod modelmodel IIIIII
MODEL DETAILS Static intertial forces are
Ap
dtd
2sr c
b
||F
F
neglected Global compliance is modeled
as an effective connecting rod length, c
F
z
tan1i dcsdzP
g g ,
Extended piston + bearings + crankshaft
MODEL CALIBRATION
.costan
1sin2
dtdtP
6 x 106 motored trace match
Need to reduce CR:Wall heat transfer
modeling inaccuracy?MODEL CALIBRATION “Rigid” grid: CR= 16.7,
squish = 0.73 mm (cold height+thermo) very low compliance (k = 4.5e4 N/mm)
5
6
[Pa]
y p ( / )(5 times lower than measured)
“Calibrated” grid: CR=16.3, sq = 0.73 mm k = 1.0e5 N/mm (half than measured) 3
4
pres
sure
CR = 15.7, rigidCR = 16.7, k = 4.5e07 N/m
University of Wisconsin -- Engine Research CenterERC Seminar – 01/22/2013
slide 8 -30 -20 -10 0 10 20 302
crank angle [degrees ATDC]
CR = 16.3, k = 1.0e08 N/mexperiment
LocalLocal equivalenceequivalence ratioratiopredictionprediction
University of Wisconsin -- Engine Research CenterERC Seminar – 01/22/2013
slide 9
SwirlSwirl ratioratio effectseffects I I –– CA = CA = --17.5 17.5 degdeg
KIVA, -17.5 CA
m]
Experiment, -17.5 CA
KIVA, -17.5 CA
m]
Experiment, -17.5 CA
2
Rs = 1.55, pinj = 860 bar Rs = 4.5, pinj = 860 bar
P1, y
axi
s [cm
-2
0
2
-2
0
2
1
2
P1, y
axi
s [cm
-2
0
2
-2
0
2
1
2
P
-2 0 2
s [cm
]
2
-2 0 2
2
0
2
3
P
-2 0 2
s [cm
]
2
-2 0 2
2
0
2
3
Jet deflection very well predicted at high Rs
P2, y
axi
s
-2 0 2
-2
0
-2 0 2
-2
0
0
1
P2, y
axi
s
-2 0 2
-2
0
-2 0 2
-2
0
0
1
2Jet deflection very well predicted at high RsExcessive distortion at Rs = 1.55 lack of
penetration into the squish region2 0 2
axi
s [cm
]0
2
2 0 2
0
2
2
4
y ax
is [c
m]
0
2
0
2
2
4
6penetration into the squish region
University of Wisconsin -- Engine Research CenterERC Seminar – 01/22/2013
slide 10
x axis [cm]
P3, y
-2 0 2
-2
x axis [cm]
-2 0 2
-2
0x axis [cm]
P3, y
-2 0 2
-2
x axis [cm]
-2 0 2
-2
0
2
SwirlSwirl ratioratio effectseffects II II –– CA = CA = --5.0 5.0 degdegRs = 1.55, pinj = 860 bar Rs = 4.5, pinj = 860 bar
KIVA, -5.0 CA Experiment, -5.0 CA 1.5
KIVA, -5.0 CA Experiment, -5.0 CA1L k f i i l l i t f i f
1, y
axi
s [cm
]
-2
0
2
-2
0
2
0.5
1
1, y
axi
s [cm
]
2
0
2
2
0
2
0.5
1Lack of mixing no overly lean mixture forming fromthe jets and remaining near the center
P
-2 0 2
[cm
]
2
-2 0 2
2
0
1
P1
-2 0 2
-2
[cm
]
2
-2 0 2
-2
2
0
1
Spray penetration very well captured
P2, y
axi
s
2 0 2
-2
0
2 0 2
-2
0
0
0.5
P2, y
axi
s [
2 0 2
-2
0
2 0 2
-2
0
0
0.5Spray penetration very well captured
Squish region and central inner bowl plane
-2 0 2
axis
[cm
]0
2
-2 0 2
0
2
0.5
1-2 0 2
axis
[cm
]
0
2
-2 0 2
0
21
1.5
University of Wisconsin -- Engine Research CenterERC Seminar – 01/22/2013
slide 11
x axis [cm]
P3, y
-2 0 2
-2
x axis [cm]
-2 0 2
-2
0
x axis [cm]
P3, y
-2 0 2
-2
x axis [cm]
-2 0 2
-2
0
0.5
SwirlingSwirling flow flow structurestructureC i i h PIV b P (SAE 2011 01 1285)
25
Rs = 2.20Rs = 3 50 12
14
Comparison with PIV measurements by Petersen (SAE 2011-01-1285)
tangential velocities [m/s], CA = -50.013
tangential velocities [m/s], CA = -35.0 tangential velocities [m/s], CA = -25.0
15
20
eloc
ity [m
/s]
Rs 3.50 Rs = 4.50
8
10
12
eloc
ity [m
/s]
[cm
]
11
12
13
5
10
tang
entia
l v
( k ) i f [2 ] 2
4
6
tang
entia
l v
CA = -50.0 CA = -35.0 CA = -25.0
( k ) i f [25]CA = -35° ATDC
z ax
is
9
10
0 5 10
0 1 2 3 4 50
radius [cm] from cylinder axis
(marks) experiments from [25](lines) KIVA, Bessel fit = 2.20
0 1 2 3 4 50
2
radius [cm] from cylinder axis
(marks) experiments from [25](lines) KIVA, Bessel fit = 2.20
r axis [cm]
0 1 2 3 4 5
8
r axis [cm]
0 1 2 3 4 5
r axis [cm]
0 1 2 3 4 5
Predicted velocity profile accuracy deteriorates when approaching TDC high angular momentum from the squish volume forced inward OK with the model’s geometry but not seen in the experiments
University of Wisconsin -- Engine Research CenterERC Seminar – 01/22/2013
slide 12
g y p- impact of valve recesses in the head and cut-outs on the piston
InjectionInjection pressurepressure effectseffects I I –– CA=CA=--5.05.0
KIVA, -5.0 CA Experiment, -5.0 CA 1
KIVA, -5.0 CA Experiment, -5.0 CA 1.5
Rs = 2.2, pinj = 500 bar Rs = 2.2, pinj = 1220 bar
Fuel does not reach back
P1, y
axi
s [cm
]
-2
0
2
-2
0
2
0.5
P1, y
axi
s [cm
]
-2
0
2
-2
0
2
0.5
1into plane P2
P
-2 0 2
[cm
]
2
-2 0 2
2
0
1
P
-2 0 2
[cm
]
2
-2 0 2
2
0
1pinj far from typical valuesfor validation of diesel
P2, y
axi
s
2 0 2
-2
0
2 0 2
-2
0
0
0.5
P2, y
axi
s
2 0 2
-2
0
2 0 2
-2
0
0
0.5spray models
I ffi i t t ti-2 0 2
axis
[cm
]
0
2
-2 0 2
0
21
1.5-2 0 2
axis
[cm
]
0
2
-2 0 2
0
2
0.5
1Insufficient penetrationBetter mixing in P1
University of Wisconsin -- Engine Research CenterERC Seminar – 01/22/2013
slide 13
x axis [cm]
P3, y
-2 0 2
-2
x axis [cm]
-2 0 2
-2
0
0.5
x axis [cm]
P3, y
-2 0 2
-2
x axis [cm]
-2 0 2
-2
0
InjectionInjection pressurepressure, , mixturemixture stratificationstratification Cumulative azimuthal equivalence ratio distributions
100 %KIVA, Rs = 2.2, pinj = 500 bar
100 %Experiment, Rs = 2.2, pinj = 500 bar
Histograms at fixed distances from cylinder axisRs = 2.2, pinj = 500 bar Rs = 2.2, pinj = 1220 bar
100 %
]
j 100 %
0 %
20 %
40 %
60 %
80 %
dist
ribu
tion
of
[-]
P10 %
20 %
40 %
60 %
80 % P1
0 %
20 %
40 %
60 %
80 %
dist
ribu
tion
of
[-]
P10 %
20 %
40 %
60 %
80 %
P1
Most deviations are in the central region impact on ignition and pollutants!
0.1 0.9 1.6 2.4 3.1 0 %
radius [cm]
60 %
80 %
100 %
ion
of
[-]
j
60 %
80 %
100 %
0.1 0.9 1.6 2.4 3.1 0 %
radius [cm]
0.1 0.9 1.6 2.4 3.1 0 %
radius [cm]
60 %
80 %
100 %
tion
of
[-]
j
60 %
80 %
100 %j
0.1 0.9 1.6 2.4 3.1 0 %
radius [cm]
Close match at the squish plane OK for emissions
0.0 0.5 0.9 1.4 1.9 0 %
20 %
40 %
radius [cm]
dist
ribu
t
P2
100 %j
100 %j
0.0 0.5 0.9 1.4 1.9 0 %
20 %
40 %
radius [cm]
P2 0.0 0.5 0.9 1.4 1.9
0 %
20 %
40 %
radius [cm]
dist
ribu
t
P2
100 %j
100 %
0.0 0.5 0.9 1.4 1.9 0 %
20 %
40 %
radius [cm]
P2
20 %
40 %
60 %
80 %
dist
ribu
tion
of
[-]
P3 20 %
40 %
60 %
80 %
P3 20 %
40 %
60 %
80 %
dist
ribu
tion
of
[-]
P320 %
40 %
60 %
80 % P3
University of Wisconsin -- Engine Research CenterERC Seminar – 01/22/2013
slide 14
0.9 1.2 1.6 1.9 2.2 0 %
radius [cm]
0.9 1.2 1.6 1.9 2.2
0 %
radius [cm]
0.1 0.25 0.25 0.5 0.5 0.75 0.75 1.01.0 1.25 1.25 1.5 1.5
0.9 1.2 1.6 1.9 2.2 0 %
radius [cm]
0.9 1.2 1.6 1.9 2.2
0 %
radius [cm]
FiredFired engineengine operationoperation I I –– RRss sweepsweep
40AHRR, pinj = 860 bar, Rs sweep
/deg
]
KIVA, Rs = 1.55Exp, Rs = 1.55
Experiment: ignitionadvances at Rs = 1.55
i h i t i th
20
30
t rel
ease
[J/
KIVA, Rs = 2.20Exp, Rs = 2.20KIVA, Rs = 3.50Exp, Rs = 3.50
richer mixtures in the squish region
At higher Rs richer
10
pare
nt h
eat At higher Rs, richer
mixtures are due to fuelmore strongly confined to
the bowl
-15 -10 -5 0 5 10 15 200
crank angle [degrees ATDC]
app
the bowl
KIVA: - similar ignition timings good average match- inverse ignition behavior at Rs under investigation:
1) Wall heat transfer
University of Wisconsin -- Engine Research CenterERC Seminar – 01/22/2013
slide 15
1) Wall heat transfer. 2) over-predicted jet deflection more homogeneous and
leaner mixtures longer ignition delay
FiredFired engineengine operationoperation II II –– ppinjinj sweepsweep
40AHRR, Rs = 2.20, pinj sweep
deg]
KIVA, pinj = 500 bar
exp, pinj = 500 bar
LT HR timing well captured at the experimental pressures
20
30
rele
ase
[J/d KIVA, pinj = 860 bar
exp, pinj = 860 bar
KIVA, pinj = 1220 bar
exp, pinj = 1220 barHT HRR peaks well captured Wall heat transfer
10
20
aren
t hea
t
Lower and delayed AHRR peak at pinj=500 bar in
-15 -10 -5 0 5 10 15 200
crank angle [degrees ATDC]
appa
injKIVA lack of penetration in
the central region6.5
7 x 106pressure trace, Rs = 2.20, pinj sweep
pinj = 500 bar
pinj = 860 bar
p = 1220 barg [ g ]
Computational Investigation at higherinjection pressures Misfiring conditions at pinj 1500 bar
5.5
6
pres
sure
[Pa]
pinj = 1220 bar
pinj = 1500 bar
pinj = 1750 bar
pinj = 2000 bar
University of Wisconsin -- Engine Research CenterERC Seminar – 01/22/2013
slide 16
Misfiring conditions at pinj 1500 bar Wall heat transfer
-20 -10 0 10 204.5
5
crank angle [degrees ATDC]
ConcludingConcluding RemarksRemarks II
Aim: assess+improve the accuracy of KIVA modelling of anoptical light duty diesel engine operated in LTC (PPC) mode, withrespect to:p quantitative equivalence ratio distributions provided by the experiments at three in-cylinder planes understanding and exploring the role of mixing and wall understanding and exploring the role of mixing and wallheat transfer on combustion development
Non-reacting operation and equivalence ratio distribution Elastic extended piston – connecting rod assembly model
Significantly improved motored pressure curve match Need to lower geometrical CR wall heat transfer?
University of Wisconsin -- Engine Research CenterERC Seminar – 01/22/2013
slide 17
ConcludingConcluding RemarksRemarks IIII
Non-reacting operation and equivalence ratio distribution Mixture dynamics and equivalence ratio stratification before ignition
Very accurate penetration is predicted with a refined grid Very accurate penetration is predicted with a refined grid Over-predicted swirl when approaching TDC jet deflection and under-predicted penetration at pinj
Under predicted turbulent mixing crucial to emissions Under-predicted turbulent mixing, crucial to emissions
Fired engine operation At increasing Rs: predicted HTHR timing delays
measured HTHR timing advances
The model responds to wall heat transfer and over-predicted spray deflection
the experiments instead show that mixing rules over ignition timing
University of Wisconsin -- Engine Research CenterERC Seminar – 01/22/2013
slide 18
the experiments instead show that mixing rules over ignition timing
ConcludingConcluding RemarksRemarks IIIIIIFi d i iFired engine operation Injection pressure plays a major role on combustion development
Increased impact area + greater spray jet momentum Delayed ignition timing can lead to misfire at very high pressures
F W kF W kCFD model impact on mixing and ignition
Future WorkFuture Work
Turbulent transport generalized RNG k- model
Fluid flow solver accuracy solution tolerances and numerics Fluid flow solver accuracy solution tolerances and numerics
Wall heat transfer Impact of wall temperatures C j t h t t f
University of Wisconsin -- Engine Research CenterERC Seminar – 01/22/2013
slide 19
Conjugate heat-transfer
Future WorkFuture Work
UHC and CO emissions Investigate impact of the reaction mechanism on predicted emissions
160
180
200
220
[g/k
g f]
UHC, CA=35.0
100
120
140
160
CO
@ E
VO
125k cells grid48k cells gridexperiment
1 2 3 4 580
100
swirl ratio, Rs [-]
CO, CA=35.0
Identif and alidate
Simulation
Identify and validatein-cylinder emissionsources
University of Wisconsin -- Engine Research CenterERC Seminar – 01/22/2013
slide 20
Simulation
ThanksThanks forfor youryour attentionattention!!QuestionsQuestions??
University of Wisconsin -- Engine Research CenterERC Seminar – 01/22/2013
slide 21
BackBack--upup slidesslidesBackBack--up up slidesslides
University of Wisconsin -- Engine Research CenterERC Seminar – 01/22/2013
slide 22
Laser Laser sheetsheet imagingimaging –– missingmissing zoneszones
Laser sheet
distortion whenpassing throughcomplex surfaces
(266nm, UV)
injector tip “shade”
LLens
Mirror CameraMirror
University of Wisconsin -- Engine Research CenterERC Seminar – 01/22/2013
slide 23
KIVA KIVA planeplane slicesslices reconstructionreconstruction
Generate a plane representation:
kjikjiPPP vvvuuuzyxplane
O
z
P v
x
y u
Compute intersectingpoints of KIVA mesh 3
4
points of KIVA mesh with plane
1
2
University of Wisconsin -- Engine Research CenterERC Seminar – 01/22/2013
slide 24-2 -1 0 1 2
0
KIVA KIVA planeplane slicesslices reconstructionreconstruction
Reconstruct data at those values using Delaunay Triangulation (left)
Pursue cubic spline interpolation at a more refined grid, p p g ,using point positions from the laser sheet images (right)
4
4.5
4
2.5
3
3.5
cm]
3
4
1
1.5
2
y ax
is [c
1
2
-2 -1 0 1 2-0.5
0
0.5
x axis [cm]-2 -1 0 1 2
0
University of Wisconsin -- Engine Research CenterERC Seminar – 01/22/2013
slide 25
x axis [cm]
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