Cepheid calibrations of_modern_type_ia_supernovae_implications_for_the_hubble_constant
Progress towards understanding combustion ine˜ciencies… · • Contrast to emissions sources...
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Transcript of Progress towards understanding combustion ine˜ciencies… · • Contrast to emissions sources...
Progress towards understanding combustionine�ciencies:
In-cylinder sources of CO and UHC
Paul MilesSandia National Laboratories
Acknowledgements: Isaac Ekoto (SNL), UW-ERC, Lund UniversitySponsors: US Department of Energy, EERE-OVT Gurpreet Singh, Program Manager General Motors Corporation Russell Durrett, Project Technical Lead
University of Wisconsin Engine Research Center Symposium“Reducing fuel consumption: solutions and prospects”
June 10-11, Madison WI
M OF
E YDPAR T
ENTNE ER G
E
A
UNI
DOF
MR
C
T
S T S
E
TA
I
A
E
Factors a�ecting brake fuel e�ciencyFactors a�ecting brake fuel e�ciency
ηb = ηm ηt ηc
• Pumping work• Friction - Downspeeding - Downsizing - Materials - Lubricants - Additives
• Accessories
Factors a�ecting brake fuel e�ciencyFactors a�ecting brake fuel e�ciency
ηb = ηm ηt ηc
In�uenced by:• Compression ratio (Expansion ratio)• Specific heat ratio• Combustion phasing and rate of heat release• Heat transfer losses
Net chemical energy released
p dV∫
-
-?
+
Factors a�ecting brake fuel e�ciencyFactors a�ecting brake fuel e�ciency
ηb = ηm ηt ηc
• Low ηc manifested by “fuel” in the exhaust gases (CO, UHC, H2 ... )• Normally high > 0.98 diesels > 0.95 spark
• Can drop drastically for low- temperature diesel or HCCI
Net chemical energy released
mf QLHV
OverviewOverview
• Description of UHC and CO sources from early-injection (PCI-like) low temperature combustion systems
- Understanding developed from homogeneous reactor simulations
- Experimental images of in-cylinder UHC and CO
• Description of UHC and CO sources from late-injection (MK-like) low temperature combustion systems
- Understanding developed from homogeneous reactor simulations
- Experimental images of in-cylinder UHC and CO
• Contrast to emissions sources from conventional (Euro 5) calibrations
• Implications for combustion chamber design and operating condi-tion selection
Emissions behavior of early-injection, PCI-likecombustionEmissions behavior of early-injection, PCI-likecombustion
Pint=1.5 bar, 3 bar load, 1500 rpm
NO
x [g
/kg-
fuel
], S
oot x
10 [F
SN]
CO
, UH
C [%
of f
uel e
nerg
y]
MPR
R [bar/°C
A]
CO
UHC
Soot
NOx
dPdθ
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
0
5
10
15
20
ExcessiveCO
ExcessiveNOx
8 10 12 14 16 18
0.20.250.30.350.40.5
O2 Concentration [%]
Global equivalence ratio
• Within a range of intake charge O2 concentrations, early injec-tion low-temperature combus-tion schemes can provide low soot, low NOx, and acceptable noise
• At high dilution levels, CO and UHC emissions rise and com-bustion efficiency deteriorates
• We will examine UHC and CO sources for a 10% oxygen con-centration in the intake charge, which provides a combustion efficiency of ≈ 98%
Impact of equivalence ratio on early-injection,PCI-like combustion Impact of equivalence ratio on early-injection,PCI-like combustion
0
0.005
0.010
0.015
0.020
CO COUHC UHC
CO
[Mol
e Fr
actio
n]
Equivalence Ratio
UH
C [M
ole Fraction]
10% O2
IncreasingO2
15% O2
0
20
40
60
80
-40 -20 0 20 40 60Crank Angle [ ° ]
Cyl
inde
r Pre
ssur
e [ b
ar ]
Homogeneous reactor simulations, following real-istic pressure and temperature histories, help us understand the impact of equivalence ratio on CO and UHC emissions.
3 bar IMEP1500 RPM
10% O2
0
0.02
0.04
0.06
0.08
0.1
0 0.5 1 1.5 2
Increasing O2
Impact of equivalence ratio on early-injection,PCI-like combustion Impact of equivalence ratio on early-injection,PCI-like combustion
Crank Angle [ ° ]
Hea
t Rel
ease
Rat
e [ J
/ cm
3 -s
] Other than ignition timing and temperature re-lated di�erences in peak rate, the heat release rate characteristics of rich mixtures are similar to those of clean-burning mixtures
Rich mixture emissions are mixing-limited
0
0.005
0.010
0.015
0.020
CO COUHC UHC
CO
[Mol
e Fr
actio
n]
Equivalence Ratio
UH
C [M
ole Fraction]
10% O2 15% O2
0
0.02
0.04
0.06
0.08
0.1
0 0.5 1 1.5 2
0
2 104
4 104
6 104
8 104
1 105
1.2 105
-15 -10 -5 0 5
φ = 1.4
φ = 0.8
Impact of equivalence ratio on early-injection,PCI-like combustion Impact of equivalence ratio on early-injection,PCI-like combustion
Crank Angle [ ° ]
For lean mixtures, the heat release is retarded and slowed compared with clean-burning mixtures
Lean mixture emissions are kinetically-limited
CO oxidation is impeded �rst, then UHC for very lean mixtures
φ = 0.8
φ = 0.6
φ = 0.4Hea
t Rel
ease
Rat
e [ J
/ cm
3 -s
]
0
0.005
0.010
0.015
0.020
CO COUHC UHC
CO
[Mol
e Fr
actio
n]
Equivalence Ratio
UH
C [M
ole Fraction]
10% O2 15% O2
0
0.02
0.04
0.06
0.08
0.1
0 0.5 1 1.5 2
0
2 104
4 104
6 104
8 104
1 105
1.2 105
-5 0 5 10 15
For PCI-like combustion, the CO and UHC are notco-located within the clearance volume For PCI-like combustion, the CO and UHC are notco-located within the clearance volume Data at 30°CA
0 10 20 30 40r (mm)
Mole Fraction
5.0 x 10-3
0.0
white isotherm = 1200K
Modeled UHC(CO is similar)
Measured CO and UHC
• CO is broadly distributed throughout the squish volume, with greater concentrations near the piston
• Unburned fuel is observed near the injector, and to a lesser extent near the bore wall
• Partially-burned fuel is generally found between fuel and CO—showing the direction of reaction progress
• Simulations (and exp. parameter sweeps) show that squish volume mixture is over-all fuel-lean
Reaction progress
0
0.5
1
0
0.5
1
0
0.5
1
0 10 20 30 40r (mm)
0 10 20 30 40r (mm)
0 10 20 30 40r (mm)
CO C2 (partially-burned)
PAH (fuel)
By 50°CA, it is clear that the near-injector andsquish regions dominate CO and UHC emissions By 50°CA, it is clear that the near-injector andsquish regions dominate CO and UHC emissions
Data at 50°CA
Mole Fraction
CO
5.0 x 10-3
0.0
white isotherm = 1200K
Measured CO and UHC
• At 50° CA, 83% of the cylinder volume is within the clearance volume
• Distributions of CO and UHC components are similar to those seen at 30°CA—just stretched axially
The flow exiting the bowl is clean
Mean �ow structures and squish volume emissions are well predicted, even if CO and UHC emissions are not
C2 (partially-burned)
PAH (fuel)
0
0.5
1
0
0.5
1
0
0.5
1
Modeled UHC (CO is similar)
Mole Fraction
5.0 x 10-3
0.0
Single-cycle images reveal UHC within the bowl and better characterize squish volume UHC Single-cycle images reveal UHC within the bowl and better characterize squish volume UHC
UHC within the bowl: - Observed infrequently - More frequent with retarded SOI - Absent with advanced SOI - More pronounced at higher load
Simulations capture the general fuel distribution,but mixing is underpredicted
30°CA
Within the squish volume, UHC �uores-cence is observed from:
• Diffuse (fuel lean) bulk gas UHC
• Apparent liquid films on the piston top
• Crevice flows
The near-injector UHC is made up of both liquidand gaseous fuelThe near-injector UHC is made up of both liquidand gaseous fuel
Di�use �uorescence also seen near the cylinder center is characteristic of gaseous UHC
Intense, spherical regions show liquid fuel near the injector...
...that are also seen in elastic scatter images
End-of-injection over-leaning is one possible source of this di�use �uorescence
0 mm 5-5
Dis
tanc
e fr
omIn
ject
or [m
m]
Equivalence Ratio Contours from fuel tracer LIF
Musculus, et al. SAE 2007-01-0907
30°CA
30°CA
Emissions seen in both the squish volume andnear-injector regions drop signi�cantly with loadEmissions seen in both the squish volume andnear-injector regions drop signi�cantly with load
0
0.2
0.4
0
0.25
0.5
0
0.5
1
0
0.4
0.8
0
0.75
1.5
0
0.75
1.5
C2(partially burned)
CO
1.5 barIMEP
3.0 barIMEP
4.5 barIMEP
CO
[ppm
]
UH
C [p
pm]
Bas
elin
e
Hig
h Lo
ad
Low
Loa
d
Bas
elin
e
Hig
h Lo
ad
Low
Loa
d
0
1000
2000
3000
4000
5000
6000
7000
8000
0
200
400
600
800
1000
1200
1400
1600
• Both near-injector and squish volume emissions decrease signi�-cantly with load
• Central cylinder CO at higher loads is consistent with better oxidation of near-injector UHC
• Optical data correlate closely with engine-out emissions
High Load (30°CA)
0 10 20 30 40r (mm)
x10
Higher resolution, cycle-averaged images showimpact of load on squish volume UHC sourcesHigher resolution, cycle-averaged images showimpact of load on squish volume UHC sources
Baseline (30°CA)
0 10 20 30 40r (mm)
x40
Image GainLow Load (30°CA)
0 10 20 30 40r (mm)
x20
• As load increases: 1) bulk gas UHC from the near-injector and central cylinder region decreases 2) the diffuse, bulk gas signal within the squish volume decreases 3) the UHC associated with crevice flows and piston top films increases The 1st and 2nd factors dominate
• Note also the predicted fuel-lean UHC in the bowl periphery is clearly observed, and vanishes at the highest load
30°
CA
Development of counter-rotating
vortex pair
Squish volume emissions are minimized bysmall squish heights and low spray targeting Squish volume emissions are minimized bysmall squish heights and low spray targeting
22
24
26
28
30
32
0.6 0.8 1 1.2 1.4 1.6Squish Height [mm]
CO
[g/k
W-h
r]
SPT = 0.0
SPT = -0.5
SPT = 0.5
CO
1.2
1.4
1.6
1.8
2
2.2
2.4
2.6
2.8
0.6 0.8 1 1.2 1.4 1.6Squish Height [mm]
SPT = 0.0
SPT = -0.5
SPT = 0.5
UHC
UH
C [g
/kW
-hr]
-SPT
+SPT
Statistically signi�cant set of experiments, incorporating repeated engine builds at each condition
Conventional diesel design guidelines still apply when PCI-like combustion is em-ployed in typical diesel hardware geom-etries:
A large k-factor and spray targeting within the bowl is desirable
Emissions behavior of late-injection, MK-likecombustionEmissions behavior of late-injection, MK-likecombustion
Pint=1.5 bar, 3 bar load, 1500 rpm• Like early injection schemes,
late-injection LTC can provide low soot, low NOx, and accept-able noise
• At retarded timings, CO and UHC emissions rise and com-bustion efficiency deteriorates, just as noise levels become ac-ceptable
• We will examine UHC and CO sources for a late injection case which provides a combustion efficiency of ≈ 97%
0.0
0.5
1.0
1.5
2.0
CO
, UH
C [%
of f
uel e
nerg
y]N
Ox
[g/k
g-fu
el],
Soo
t x10
[FSN
]
0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
16.0
MPR
R [bar/°C
A]
CO
UHC Soot
NOx
dPdθ
ExcessiveNOx
-25 -20 -15 -10 -5 0SOI
15% O2
COCO
UHCUHC
Equivalence RatioEquivalence Ratio
CO
[Mol
e Fr
actio
n]C
O [M
ole
Frac
tion]
UH
C [M
ole Fraction]U
HC
[Mole Fraction]
For rich mixtures, the emissions characteristics do not change as injection is retardedFor rich mixtures, the emissions characteristics do not change as injection is retarded
Impact of equivalence ratio on late-injection,MK-like combustion Impact of equivalence ratio on late-injection,MK-like combustion
0
10
20
30
40
50
60
70
-40 -20 0 20 40 60
SOIc = -2.3°
SOIc = -2.3°
SOIc = -0.5°
SOIc= -0.5°
Crank Angle [ ° ]
Cyl
inde
r Pre
ssur
e [ b
ar ]
3 bar IMEP1500 RPM
15% O2
0
0.02
0.04
0.06
0.08
0.1
0
0.005
0.010
0.015
0.020
0.025
0.030
0 0.5 1 1.5 2
CO
UHC
Equivalence Ratio
CO
[Mol
e Fr
actio
n]
Impact of equivalence ratio on late-injection,MK-like combustion - lean mixtures Impact of equivalence ratio on late-injection,MK-like combustion - lean mixtures
UH
C [M
ole Fraction]
0.030
0
5000
1 104
1.5 104
2 104
2.5 104
3 104
10 15 20 25 30Crank Angle
0
0.02
0.04
0.06
0.08
0.1
0
0.005
0.010
0.015
0.020
0.025
0 0.5 1 1.5 2
φ = 0.7
φ = 0.65φ = 0.6
Hea
t Rel
ease
Rat
e [ J
/ cm
3 -s
]
For lean mixtures, higher equivalence ratios are required to complete oxidation at retarded timing
Oxidation is limited by the failure to transition into strong high temperature combustion – leading to similar limiting equivalence ratios for CO & UHC
With late injection, there is evidence of CO, PAH,and C2 exiting the bowl at 30°CA (as predicted) With late injection, there is evidence of CO, PAH,and C2 exiting the bowl at 30°CA (as predicted) SOIC = -2.3° (Data at 30°CA)
0 10 20 30 40r (mm)
Mole Fraction
5.0 x 10-3
0.0
white isotherm = 1200K
CO C2 (partially-burned)
PAH (fuel)
Modeled UHC(CO is similar)
Measured CO and UHC
• The (fuel-lean) squish volume is again a dominant source of UHC and CO, despite spray targeting deep within the bowl
• Fuel is again observed near the injector, with small amounts of CO
• Experiments appear to support model predictions of fuel-rich UHC leaving the bowl
0 10 20 30 40r (mm)
0 10 20 30 40r (mm)
0 10 20 30 40r (mm)
0
0.25
0.5
0
10
20
0
0.35
0.7
By 50 °CA, however, the rich-mixture sourcefrom the bowl has vanished By 50 °CA, however, the rich-mixture sourcefrom the bowl has vanished
Modeled UHC (CO is similar)
At this crank angle, the �ow exiting the bowl, as was seen with early injection timing, is very clean
0
0.25
0.5
0
5
10
0
0.35
0.7
SOIC = -2.3° (Data at 50°CA)
CO C2 (partially-burned)
PAH (fuel)
Measured CO and UHC
Mole Fraction
5.0 x 10-3
0.0
white isotherm = 1200K
With more retarded SOI, the squish volume UHCand CO emissions completely dominate With more retarded SOI, the squish volume UHCand CO emissions completely dominate
0
0.25
0.5
0
5
10
0
0.35
0.7
CO
C2 (partially-burned)
PAH (fuel)
CO
C2 (partially-burned)
PAH (fuel)
0
0.25
0.5
0
5
10
0
0.35
0.7
Baseline late-injection1.8° additional retard
0
500
CO
[ppm
]
UH
C [p
pm]
1000
1500
2000
2500
3000
3500
Bas
elin
e
Ret
arde
d
Bas
elin
e
Ret
arde
d
0
500
1000
1500
2000
2500
3000
50°CA
• Notable increases in squish volume concentrations are observed for both UHC and CO
• Larger increase in engine-out UHC than CO is consistent with homogeneous reactor simulations of lean mixtures
How do conventional (Euro 5) combustion UHCand CO distributions compare? How do conventional (Euro 5) combustion UHCand CO distributions compare?
35
40
45
50
55
60
65
70C
ylin
der p
ress
ure
[ bar
] H
eat R
elea
se [
J/°C
A ]
0
10
20
30
40
50
60
70
-10 0 10 20 30Crank Angle [ ° ]
Late-injection
Late-injection
Euro 5
Euro 5
InjectorEnergizingCommand }
The Euro 5 calibration features a main injection timing very similar to our late-injection, low temperature condition
Euro 5 emissions are low CO and UHC, but relatively high soot and NOx
1500 rpm3.0 bar gIMEP 15% O2
0
500
CO
[ppm
]
UH
C [p
pm]
1000
1500
2000
2500
3000
3500
Euro
5
Late
inje
ctio
n
Euro
5
Late
inje
ctio
n
0
500
1000
1500
2000
2500
3000
NO
x [p
pm]
FSN
[-]
Euro
5
Late
inje
ctio
n
Late
inje
ctio
n
0
10
20
30
40
50
60
70
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Euro
5
With conventional combustion, UHC and CO arepredominantly found in the near-injector regionWith conventional combustion, UHC and CO arepredominantly found in the near-injector region
0 10 20 30 40r (mm)
0
0.5
1
0 10 20 30 40r (mm)
0
10
20
0 10 20 30 40r (mm)
0
0.3
0.6
0
0.3
0.6
0
5
10
0
0.5
1CO C2 (partially-burned)
PAH (fuel)
CO C2 (partially-burned)
PAH (fuel)
30°CA
50°CA
• Very intense “UHC” signals may have a soot component
• CO observed in the squish volume at 30°CA appears to fully oxidize by 50°CA
Summary & implications for operating conditionselection and combustion chamber designSummary & implications for operating conditionselection and combustion chamber design• Fuel dribble from the nozzle sac volume is a significant (though not a dominant)
source of UHC and CO emissions (≈ 15-30% ?)
• Significant gaseous UHC in fuel-lean mixture is seen in the near-injector region. Under some operating conditions, this may dominate engine-out UHC
• Fuel-lean mixture within the squish volume is the dominant source of CO emissions from both early- and late-injection LTC strategies at low loads. It is also a significant, and likely dominant, source of UHC
Strategies to reduce squish volume CO and UHC include:
- Minimize squish height, target spray well within the bowl (generally prevent lean mixture formation within the squish volume)
- Attack combustion noise by means other than increased dilution or SOI retard Reduce ignition delay through pilot injections? (lean mixture is the problem) Disrupt/split heat release with an appropriately timed post injection?
- Increased Tin (high pressure EGR? VVA?)
- Adopt a more open chamber, lower swirl design?
Better BSFC; with part-load LTC, no part-load soot catastrophe!