The Importance of Intermediate-Temperature Reactions in ... · John E. Dec Sandia National...
Transcript of The Importance of Intermediate-Temperature Reactions in ... · John E. Dec Sandia National...
John E. DecSandia National Laboratories
The Importance of Intermediate-Temperature Reactions in HCCI and HCCI-like Engines
MACCCR – 5th Annual Fuels Research ReviewSandia National Labs, CRF, Sept. 17 - 20, 2012
Sponsors:U.S. DOE, Office of Vehicle Technologies
Program Manager: Gurpreet SinghChevron USA, Inc.
Program Manager: William Cannella
Acknowledge: Yi Yang and Nicolas Dronniou
Motivation Global demand for transportation fuels is increasing rapidly.
– New discoveries of petroleum are not keeping pace.
Global temperatures are rising.– CO2 from transportation is a major contributor to GHG.
Strong motivation to reduce petroleum consumption.
Engine-efficiency improvements offer a huge potential!– Could be implemented in
a relatively short time.
Biofuels or other renewable fuels also important part of solution.– Progress is being made.– Full discussion is beyond the
scope of this presentation.
Improving Vehicle-Fleet Efficiency Diesel engine is the most efficient transportation engine ever developed.
– Potential fuel savings of ~30% over spark-ignition (SI) engines.
Drawbacks to diesel engines:– Diesel emissions control is challenging expensive aftertreatment.– Cost of the engine alone can be significantly higher than SI.– Increased demand is driving up diesel fuel prices.
US, ~ equal taxes, diesel 8% higher. Spread will increase if diesel demand increases.
Total cost can be > gasoline.
For high-efficiency vehicles to have a large impact, it is important thatthe technology be economical. Particularly for the developing world.
For full utilization of crude oil stocks need a high-efficiency engine fueled with “light” distillates (e.g. gasoline), as well as diesel.
Looking to the future, the vast majority of new vehicles added will be in the developing world. 0.0
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Advanced engines using HCCI or partially stratified “HCCI-like” combustion can provide diesel-like or higher efficiencies & ultra-low emiss. NOX & soot.– Potential for significantly lower cost than an emissions-compliant diesel.– More-volatile, light-end fuels are well suited for HCCI.– HCCI can also work well with biofuels and biofuel/gasoline blends.
HCCI dilute premixed charge and compression ignition.– Volumetric flameless combustion.– Never truly homogeneous due to natural thermal stratification (TS).– Also advantages to adding controlled mixture stratification at some conditions
partial fuel stratification (PFS).
Advanced High-Efficiency Engines
Other low-T, HCCI-like concepts also show promise (PCCI or RCCI).
Challenges for HCCI:– Controlling start of combustion.– Extending operation to higher
loads.
Fuel autoignition chemistry is critical for both.
HCCI is the most fundamental low-temperature combustion process and the first to be widely investigated.– High Efficiencies Relatively high CR = 12 – 16, no throttle, and low
combustion temperatures less heat-transfer loss and higher .– Ultra-low NOx & soot Lean or dilute with EGR for low Tcombst , and Well mixed
HCCI is relatively well developed.– GM demonstrated prototype cars operating in HCCI mode from idle 70 mph,
using regular pump gasoline.– Strong potential to extend operating range substantially with intake boost & PFS.
Other low-T combustion modes rely on these same principles.– PCCI or PPCI developed to achieve HCCI-like combustion in diesel engines.
DI fueling ~60° bTDC for diesel-fuel vaporization and “premixed enough.”> Widely used with diesel fuel for low emissions at light load in production.> Also efforts to use gasoline for longer ignition delay more premixing for higher
loads, but difficulties with smoke & NOX low-octane gasoline, RON ~70.
– RCCI more recent concept introduced by Reitz et al. at UW shows promise, but requires two fuels (gasoline and diesel).
Low-Temperature Combustion Modes
Active research on these low-T modes & Autoig. chemistry important for all.
Sandia Dual-Engine HCCI Engine Laboratory
All-Metal Engine
Optical Engine
Optics Table
Dynamometer
Intake Plenum
Exhaust Plenum
Water & Oil Pumps & Heaters
Flame Arrestor
Matching all-metal & optical HCCI research engines.– Single-cylinder conversion from Cummins B-series diesel.– Open combustion chamber.
Optical EngineAll-Metal Engine
Bore x Stroke = 102 x 120 mm 0.98 liters, CR=14
PTDC-motored = 30 – 100 bar
Thermal-stratification image at TDC
Side View
Nature of HCCI Combustion Ignition timing is mainly controlled by fuel autoignition chemistry.
– Heat release prior to hot autoignition is kinetically controlled (LTHR, and ITHR).– Adjustment of operating parameters required to control ignition timing.
High-T combustion kinetics are very rapid. Main combustion HRR is controlled mostly by thermal stratification (TS).
– TS occurs naturally due to heat transfer and imperfect mixing with hot residuals.– TS causes sequential autoignition & combustion of the in-cylinder charge.
> Crucial for controlling HCCI HRR for fully premixed combustion.
-50
50
50
50
335 345 355 365 375 385 395Crank Angle
Hea
t Rel
ease
Rat
e
AUTOIGNITION
Fuel autoignition kinetics control ignition timing, and pre-igntion heat release, i.e. LTHR & ITHR.
Thermal stratification usually controls HRR of main combustion.
KINETICALLY CONTROLLED THERMALLY CONTROLLED
LTHR ITHR
(Dronniou and Dec, SAE 2012-01-1111)
Thermal-stratification image at TDC
Side View
Chemiluminescence of HCCI (iso-octane, = 0.24, fully premixed)
Nature of HCCI Combustion Ignition timing is mainly controlled by fuel autoignition chemistry.
– Heat release prior to hot autoignition is kinetically controlled (LTHR, and ITHR).– Adjustment of operating parameters required to control ignition timing.
High-T combustion kinetics are very rapid. Main combustion HRR is controlled mostly by thermal stratification (TS).
– TS occurs naturally due to heat transfer and imperfect mixing with hot residuals.– TS causes sequential autoignition & combustion of the in-cylinder charge.
> Crucial for controlling HCCI HRR for fully premixed combustion.
-50
50
50
50
335 345 355 365 375 385 395Crank Angle
Hea
t Rel
ease
Rat
e
AUTOIGNITION
Fuel autoignition kinetics control ignition timing, and pre-igntion heat release, i.e. LTHR & ITHR.
Thermal stratification usually controls HRR of main combustion.
KINETICALLY CONTROLLED THERMALLY CONTROLLED
LTHR ITHR
(Dec et al., SAE 2006-01-1518)
Ignition Chemistry Changes with Fuel-Type
CA50 = TDC, Premixed, Pin = 1 bar, 1200 rpm Intake temperature (Tin) required for a given combustion phasing varies substantially with fuel type.– Representative real-fuel
constituents and gasoline.
Hot-ignition temperature also varies, but proportionally less than Tin.
One main reason is that low-temp. heat release (LTHR, or “cool flame”) raises temperature for PRF80.– 80% iso-octane + 20% n-heptane
However, for single-stage ignition fuels, early reactions also important. – “Intermediate temp. heat release”
(ITHR) reactions.– Raise temperature to thermal
runaway (hot-ignition point CA10).
600
800
1000
1200
1400
1600
1800
300 320 340 360 380Crank Angle [°CA]
Mas
s-A
vg. T
empe
ratu
re [K
] Tolueneiso-OctaneGasolineMCH-methylcyclohexaneDIB-diisobutlyenePRF80
CA
10
020406080
100120140160180200
Toluene Iso-Oct. Gasoline DIB MCH PRF80
Inta
ke T
empe
ratu
re [°
C]
50°C
107°C
(Hwang et al., C&F 154(3), 2008)
800
900
1000
1100
1200
1300
348 350 352 354 356 358 360 362Crank Angle [°CA]
Mas
s-A
vg. T
empe
ratu
re [K
]
Motored
iso-Octane
CA
10
-2000
200400600800
10001200140016001800
335 340 345 350 355 360 365 370 375 380Crank Angle [°CA]
Mas
s-A
vg. T
empe
ratu
re [K
]
04080120160200240280320360400
Hea
t-Rel
ease
Rat
e [J
/°CA
]Tolueneiso-OctaneMCHDIBPRF80
Intermediate Temp. Heat Release (ITHR)
For all fuels, slower ITHR reactions precede hot ignition ( CA10).– 900 < T < 1050 K
For many single-stage fuels, trends are self-similar, Tig. varies with Tin. – Tig varies significantly with fuel-type.
However, DIB (diisobutylene) has more intense ITHR reactions.
Also, for two-stage PRF80, ITHR reactions more intense after LTHR.– Note that HRR never goes to zero
after LTHR ends.
Examine the effects of ITHR in more detail for iso-octane (single-stage) and PRF80 (two-stage)
(Hwang et al., C&F 154(3), 2008)
800
900
1000
1100
1200
1300
348 350 352 354 356 358 360 362Crank Angle [°CA]
Mas
s-A
vg. T
empe
ratu
re [K
]
Motored
iso-Octane
CA
10
800
900
1000
1100
1200
1300
348 350 352 354 356 358 360 362Crank Angle [°CA]
Mas
s-A
vg. T
empe
ratu
re [K
] Tolueneiso-OctaneGasolineDIBMCHPRF80
CA
10
800
900
1000
1100
1200
1300
348 350 352 354 356 358 360 362Crank Angle [°CA]
Mas
s-A
vg. T
empe
ratu
re [K
] Toluene
iso-Octane
Gasoline
MCH
CA
10
800
900
1000
1100
1200
1300
348 350 352 354 356 358 360 362Crank Angle [°CA]
Mas
s-A
vg. T
empe
ratu
re [K
] Tolueneiso-OctaneGasolineDIBMCH
CA
10
800
900
1000
1100
1200
1300
348 350 352 354 356 358 360 362Crank Angle [°CA]
Mas
s-A
vg. T
empe
ratu
re [K
] Tolueneiso-OctaneGasolineDIBMCHPRF80
CA
10
-2000
200400600800
10001200140016001800
335 340 345 350 355 360 365 370 375 380Crank Angle [°CA]
Mas
s-A
vg. T
empe
ratu
re [K
]
04080120160200240280320360400
Hea
t-Rel
ease
Rat
e [J
/°CA
]Tolueneiso-OctaneMCHDIBPRF80
Intermediate Temp. Heat Release (ITHR)
For all fuels, slower ITHR reactions precede hot ignition ( CA10).– 900 < T < 1050 K
For many single-stage fuels, trends are self-similar, Tig. varies with Tin. – Tig varies significantly with fuel-type.
However, DIB (diisobutylene) has more intense ITHR reactions.
Also, for two-stage PRF80, ITHR reactions more intense after LTHR.– Note that HRR never goes to zero
after LTHR ends.
Examine the effects of ITHR in more detail for iso-octane (single-stage) and PRF80 (two-stage)
(Hwang et al., C&F 154(3), 2008)
800
900
1000
1100
1200
1300
348 350 352 354 356 358 360 362Crank Angle [°CA]
Mas
s-A
vg. T
empe
ratu
re [K
]
Motored
iso-Octane
CA
10
800
900
1000
1100
1200
1300
348 350 352 354 356 358 360 362Crank Angle [°CA]
Mas
s-A
vg. T
empe
ratu
re [K
] Tolueneiso-OctaneGasolineDIBMCHPRF80
CA
10
800
900
1000
1100
1200
1300
348 350 352 354 356 358 360 362Crank Angle [°CA]
Mas
s-A
vg. T
empe
ratu
re [K
] Toluene
iso-Octane
Gasoline
MCH
CA
10
800
900
1000
1100
1200
1300
348 350 352 354 356 358 360 362Crank Angle [°CA]
Mas
s-A
vg. T
empe
ratu
re [K
] Tolueneiso-OctaneGasolineDIBMCH
CA
10
800
900
1000
1100
1200
1300
348 350 352 354 356 358 360 362Crank Angle [°CA]
Mas
s-A
vg. T
empe
ratu
re [K
] Tolueneiso-OctaneGasolineDIBMCHPRF80
CA
10
800
900
1000
1100
1200
1300
348 350 352 354 356 358 360 362Crank Angle [°CA]
Mas
s-A
vg. T
empe
ratu
re [K
]
iso-Octane
PRF80
CA
10
-2000
200400600800
10001200140016001800
335 340 345 350 355 360 365 370 375 380Crank Angle [°CA]
Mas
s-A
vg. T
empe
ratu
re [K
]
04080120160200240280320360400
Hea
t-Rel
ease
Rat
e [J
/°CA
]Tolueneiso-OctaneMCHDIBPRF80
-2000
200400600800
10001200140016001800
335 340 345 350 355 360 365 370 375 380Crank Angle [°CA]
Mas
s-A
vg. T
empe
ratu
re [K
]
04080120160200240280320360400
Hea
t-Rel
ease
Rat
e [J
/°CA
]iso-Octane
PRF80
Intermediate Temp. Heat Release (ITHR)
For all fuels, slower ITHR reactions precede hot ignition ( CA10).– 900 < T < 1050 K
For many single-stage fuels, trends are self-similar, Tig. varies with Tin. – Tig varies significantly with fuel-type.
However, DIB (diisobutylene) has more intense ITHR reactions.
Also, for two-stage PRF80, ITHR reactions more intense after LTHR.– Note that HRR never goes to zero
after LTHR ends.
Examine the effects of ITHR in more detail for iso-octane (single-stage) and PRF80 (two-stage)
(Hwang et al., C&F 154(3), 2008)
Why does timing retard slow PRR?
10
20
30
40
50
60
70
80
90
350 355 360 365 370 375 380Crank Angle [° aTDC Intake]
Cyl
inde
r Pre
ssur
e [b
ar]
Experiment, Phi=0.3, 360°CAExperiment, 365°CAExperiment, 369°CA
0
2
4
6
8
10
12
14
358 360 362 364 366 368 370 372 374 376 37850% Burn Point [°CA aTDC]
Rin
ging
Inte
nsity
[MW
/m2]
Phi = 0.30
Ringing limit
0
2
4
6
8
10
12
14
358 360 362 364 366 368 370 372 374 376 37850% Burn Point [°CA aTDC]
Rin
ging
Inte
nsity
[MW
/m2] Phi = 0.30
Phi = 0.34Phi = 0.38Phi = 0.40Phi = 0.42
Ringing limit
Nat. TS in the bulk gas significantly slows the combustion rate.
High-load op. still limited by knock. Retarding combustion phasing
reduces PRR & ringing intensity. Allows higher fueling stab. limit
Retarded Combustion Allows Higher Loads
0
10
20
30
40
50
60
70
80
345 350 355 360 365 370 375Crank Angle [°] aTDC
Cyl
inde
r Pre
ssur
e [b
ar]
Phi = 0.3
Phi = 0.26
Phi = 0.22
Phi = 0.18
= 0.3
Decrease Tin
0
10
20
30
40
50
60
70
80
345 350 355 360 365 370 375Crank Angle [°] aTDC
Cyl
inde
r Pre
ssur
e [b
ar]
Phi = 0.3Phi = 0.26Phi = 0.22Phi = 0.18CHEMKIN, Phi = 0.3CR = 18
Const. CA50 = 360°CA (TDC)
Timing retard amplifies the benefit of a given thermal stratification.
(Sjöberg et al., SAE 2004-01-2994, and Dec et al., SAE 2006-01-1518)
700
750
800
850
900
950
1000
1050
1100
335 340 345 350 355 360 365 370Crank Angle [°CA]
Mas
s-A
vera
ged
Tem
p. [K
] ISO-OCTANEPRF80 TDC
700
750
800
850
900
950
1000
1050
1100
335 340 345 350 355 360 365 370Crank Angle [°CA]
Mas
s-A
vera
ged
Tem
p. [K
] ISO-OCTANEPRF80
LTHR
TDC
Strong ITHR causes high TRR
850
900
950
1000
1050
1100
1150
345 350 355 360 365 370 375 380Crank Angle [°CA]
Mas
s-A
vg. T
empe
ratu
re, O
ffset
(to m
atch
T34
5 of
the
160k
Pa
case
)
Pin = 100 kPa
Pin = 100 kPa, motored
900
950
1000
1050
1100
1150
1200
1250
1300
345 350 355 360 365 370 375Crank Angle [°CA]
Tem
pera
ture
[K]
T350 = 987.5 K + 1.9 KT350 = 987.5 KT350 = 987.5 K - 1.9 KRun-Away TemperatureT350 = 974.3 K + 1.9 KT350 = 974.3 KT350 = 974.3 K - 1.9 K
Model, = 0.38
-0.005
0
0.005
0.01
0.015
0.02
335 340 345 350 355 360 365 370Crank Angle [°CA]
HR
R /
tot H
R [J
/°CA
]
PRF80
ISOOCTANE
Pre-Ignition Heat Release
Allowable CA50 retard limited by combustion stability.– Must maintain positive temperature
rise rate (TRR) before hot ignition.– Lack of sufficient TRR causes
combustion to become unstable and eventually misfire.
Fuels with stronger ITHR, e.g. PRF80, produce higher TRR.– Can sustain more CA50 retard.
Combustion Retard Relies on ITHR
(Sjöberg and Dec, Proc. Combust. Inst. 2007)
Strong ITHRHigh TRRMore retarded CA50 with Good
StabilityReduced HRRHigher loads without knock
900
950
1000
1050
1100
1150
1200
1250
1300
345 350 355 360 365 370 375Crank Angle [°CA]
Tem
pera
ture
[K]
T350 = 987.5 K + 1.9 KT350 = 987.5 KT350 = 987.5 K - 1.9 KRun-Away TemperatureT350 = 974.3 K + 1.9 KT350 = 974.3 KT350 = 974.3 K - 1.9 K
Model, = 0.38
700
750
800
850
900
950
1000
1050
1100
335 340 345 350 355 360 365 370Crank Angle [°CA]
Mas
s-A
vera
ged
Tem
p. [K
] ISO-OCTANEPRF80 TDC
700
750
800
850
900
950
1000
1050
1100
335 340 345 350 355 360 365 370Crank Angle [°CA]
Mas
s-A
vera
ged
Tem
p. [K
] ISO-OCTANEPRF80
LTHR
TDC
Strong ITHR causes high TRR
-0.005
0
0.005
0.01
0.015
0.02
335 340 345 350 355 360 365 370Crank Angle [°CA]
HR
R /
tot H
R [J
/°CA
]
PRF80
ISOOCTANE
Pre-Ignition Heat Release
Combustion Retard Relies on ITHR
(Sjöberg and Dec, Proc. Combust. Inst. 2007)
0
2
4
6
8
10
12
365 367 369 371 373 375 37750% Burned (CA50) [°CA]
Std.
Dev
. of I
MEP
g [%
] iso-OctanePRF80Acceptable Limit
0
2
4
6
8
10
12
14
366 368 370 372 374 376 378 380
CA50 [°CA]
IMEP
g [b
ar]
Pin = 200 kPa
Pin = 100 kPa
1.6 bar6ºCA
Intake Boosting Enhances ITHR of Gasoline For dilute combst. like HCCI, intake-
press. boost required for high loads. Enhances ITHR of gasoline.– Remains as single-stage ignition.– Allows considerable CA50 retard
with good stability.
For Pin = 200 kPa, CA50 retard can be > 379°CA. – 6°CA more than for Pin = 100 kPa.– Allows significantly higher IMEPg.
As a result, very high loads can be reached with boosted gasoline HCCI.– IMEPg = 16.3 bar at Pin = 3.25 bar.– E10, IMEPg = 18.1 bar at Pin = 3.4 bar.– Approaching loads of conventional
diesel engines.
Enhanced ITHR with boost is the key to high-load operation with premixed fueling, using gasoline.
-0.002
0
0.002
0.004
0.006
0.008
0.01
-35 -30 -25 -20 -15 -10 -5 0 5 10Crank Angle relative to Peak HRR [°CA]
HR
R /
tota
l HR
[1/°C
A]
Pin = 200 kPa, Tin = 60°CPin = 160 kPa, Tin = 74°CPin = 130 kPa, Tin = 105°C Pin = 100 kPa, Tin = 130°C
TDC Range
(Dec and Yang, SAE 2010-01-1086)
0
2
4
6
8
10
12
14
366 368 370 372 374 376 378 380
CA50 [°CA]
IMEP
g [b
ar]
Pin = 200 kPa
Pin = 100 kPa
1.6 bar6ºCA
Intake Boosting Enhances ITHR of Gasoline For dilute combst. like HCCI, intake-
press. boost required for high loads. Enhances ITHR of gasoline.– Remains as single-stage ignition.– Allows considerable CA50 retard
with good stability.
For Pin = 200 kPa, CA50 retard can be > 379°CA. – 6°CA more than for Pin = 100 kPa.– Allows significantly higher IMEPg.
As a result, very high loads can be reached with boosted gasoline HCCI.– IMEPg = 16.3 bar at Pin = 3.25 bar.– E10, IMEPg = 18.1 bar at Pin = 3.4 bar.– Approaching loads of conventional
diesel engines.
Enhanced ITHR with boost is the key to high-load operation with premixed fueling, using gasoline.
-0.002
0
0.002
0.004
0.006
0.008
0.01
-35 -30 -25 -20 -15 -10 -5 0 5 10Crank Angle relative to Peak HRR [°CA]
HR
R /
tota
l HR
[1/°C
A]
Pin = 200 kPa, Tin = 60°CPin = 160 kPa, Tin = 74°CPin = 130 kPa, Tin = 105°C Pin = 100 kPa, Tin = 130°C
TDC Range
(Dec and Yang, SAE 2012-01-01107)
2
4
6
8
10
12
14
16
18
20
0.8 1.2 1.6 2.0 2.4 2.8 3.2 3.6Intake Pressure [bar]
Max
imum
IMEP
g [b
ar]
Gasoline, PM
Gasoline, PM, no EGR
2
4
6
8
10
12
14
16
18
20
0.8 1.2 1.6 2.0 2.4 2.8 3.2 3.6Intake Pressure [bar]
Max
imum
IMEP
g [b
ar]
Gasoline, PM
Gasoline, PM, no EGR
E10, PM
-0.002
0
0.002
0.004
0.006
0.008
0.01
-30 -25 -20 -15 -10 -5 0Crank Angle offset by CA10 [°CA]
HR
R /
tot H
R [1
/°CA
]
Gasoline, Pin = 200 kPa, 31% EGRiso-Pentanol, Pin = 200 kPa, 37% EGRGasoline, Pin = 100 kPa, Tin = 141°CIso-Pentanol, Pin = 100 kPa, Tin = 132°C
TDC
TDC
Can Biofuels Give Similar Performance?
Iso-pentanol is a next-generation biofuel process developed by JBEI.
Iso-pentanol shows gasoline-like ITHR, naturally aspirated.– Greater than ethanol.
ITHR of iso-pentanol is significantly enhanced by boost, similar to gasoline.– Provides good stability with significant
timing retard.
Allows a substantial increase in load with boost like gasoline.
Ethanol shows no enhancement in ITHR with boost.– Not as good for high-load HCCI.– Likely more knock resistance for
boosted SI operation.
-0.04
0
0.04
0.08
0.12
0.16
-20 -15 -10 -5 0 5 10 15 20 25Crank Angle relative to CA10 [°CA]
HR
R /
tota
l HR
[1/°C
A]
Iso-PentanolGasolineEthanol
-0.002
0
0.002
0.004
0.006
0.008
0.01
-30 -25 -20 -15 -10 -5 0Crank Angle relative to CA10 [°CA]
HR
R /
tota
l HR
[1/°C
A]
Iso-PentanolGasolineEthanol
TDC
Naturally Aspirated
Engine compatibility must be considered in developing new biofuels/blends.
Iso-Pentanol and Ethanol Isopentanol
Iso-pentanol closely matches gasoline performance good compatibility.
(Yang et al., SAE 2010-01-2164)
-0.002
0
0.002
0.004
0.006
0.008
0.01
-30 -25 -20 -15 -10 -5 0Crank Angle offset by CA10 [°CA]
HR
R /
tot H
R [1
/°CA
]
Gasoline, Pin = 200 kPa, 31% EGRiso-Pentanol, Pin = 200 kPa, 37% EGRGasoline, Pin = 100 kPa, Tin = 141°CIso-Pentanol, Pin = 100 kPa, Tin = 132°C
TDC
TDC
-0.002
0
0.002
0.004
0.006
0.008
0.01
-30 -25 -20 -15 -10 -5 0 5 10Crank Angle relative to CA10 [°CA]
Hea
t Rel
ease
Rat
e / T
otal
HR
[1/°C
A]
Pin = 247 kPa, Tin = 94°C, Phi=0.355Pin = 181 kPa, Tin = 108°CPin = 146 kPa, Tin = 119°CPin = 124 kPa, Tin = 129°CPin = 100 kPa, Tin = 141°C
Ethanol
Can Biofuels Give Similar Performance?
Iso-pentanol is a next-generation biofuel process developed by JBEI.
Iso-pentanol shows gasoline-like ITHR, naturally aspirated.– Greater than ethanol.
ITHR of iso-pentanol is significantly enhanced by boost, similar to gasoline.– Provides good stability with significant
timing retard.
Allows a substantial increase in load with boost like gasoline.
Ethanol shows no enhancement in ITHR with boost.– Not as good for high-load HCCI.– Likely more knock resistance for
boosted SI operation.
-0.04
0
0.04
0.08
0.12
0.16
-20 -15 -10 -5 0 5 10 15 20 25Crank Angle relative to CA10 [°CA]
HR
R /
tota
l HR
[1/°C
A]
Iso-PentanolGasolineEthanol
-0.002
0
0.002
0.004
0.006
0.008
0.01
-30 -25 -20 -15 -10 -5 0Crank Angle relative to CA10 [°CA]
HR
R /
tota
l HR
[1/°C
A]
Iso-PentanolGasolineEthanol
TDC
Naturally Aspirated
Engine compatibility must be considered in developing new biofuels/blends.
Iso-Pentanol and Ethanol Isopentanol
Iso-pentanol closely matches gasoline performance good compatibility.
(Dec and Yang, SAE 2010-01-1086)
363
364
365
366
367
368
369
370
371
0.3 0.32 0.34 0.36 0.38 0.4 0.42 0.44 0.46 0.48 0.5Charge Mass Equivalence Ratio [m]
CA
10 [°
CA
]
368
369
370
371
372
373
374
375
376
CA
10 [°
CA
]
PRF73, Pin = 1 bar, base-phi = 0.42
Gasoline, Pin = 1 bar, base-phi = 0.42
Pin varies
363
364
365
366
367
368
369
370
371
0.3 0.32 0.34 0.36 0.38 0.4 0.42 0.44 0.46 0.48 0.5Charge Mass Equivalence Ratio [m]
CA
10 [°
CA
]
368
369
370
371
372
373
374
375
376
CA
10 [°
CA
]
PRF73, Pin = 1 bar, base-phi = 0.42
Gasoline, Pin = 1 bar, base-phi = 0.42
Gasoline, Pin = 2 bar, base-phi = 0.42
Pin varies
-Sensitivity of Gasoline and ITHR
363
364
365
366
367
368
369
370
371
0.3 0.32 0.34 0.36 0.38 0.4 0.42 0.44 0.46 0.48 0.5Charge Mass Equivalence Ratio [m]
CA
10 [°
CA
]
368
369
370
371
372
373
374
375
376
CA
10 [°
CA
]
PRF73, Pin = 1 bar, base-phi = 0.42Gasoline, Pin = 1 bar, base-phi = 0.42Gasoline, Pin = 1.6 bar, base-phi = 0.367Gasoline, Pin = 2 bar, base-phi = 0.345Gasoline, Pin = 2 bar, base-phi = 0.42
Pin varies
High -sensitivity of gasoline with boost offers the possibility of using mixture stratification to reduce the HRR and allow higher loads.
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21
Cycle #
Pres
sure
= variable = 0.42Fire 19/1
Acquired cycle ITHR correlates with -sensitivity over
a range of fuels & operating conditions.(Dec et al., SAE 2011-01-0897)
Isolate fuel-chemistry effects from thermal effects, use Fire19/1 technique.– Dec & Sjöberg SAE 2004-01-0557.
PRF73, ↑ ITHR strong -sensitivity– Autoignition timing significantly
advanced by higher .– Chemical reaction rates promoted by
higher fuel concentration.
Gas. Pin = 1 bar, ↓ ITHR not -sensitive– Retards due to cooling effect of .
ITHR of gasoline increases greatly from Pin = 1 to 2 bar.
Corresponding incr. in -sensitivity.
Fully Premixed
Equivalence ratio
Prob
abili
ty
Fully Stratified
Premixed
DI
Partially Stratified
356
357
358
359
360
361
362
363
364
365
0.04 0.08 0.12 0.16 0.2 0.24 0.28 0.32Equivalence Ratio [ ]
50%
Bur
n Po
int [
°CA
aTD
C]
PRF80iso-Octane
Fire F19/1-ExperimentConst. Wall and Residual Temp.
356
357
358
359
360
361
362
363
364
365
0.04 0.08 0.12 0.16 0.2 0.24 0.28 0.32Equivalence Ratio [ ]
50%
Bur
n Po
int [
°CA
aTD
C]
PRF80iso-Octane
Fire F19/1-ExperimentConst. Wall and Residual Temp.
Controlling the HRR with Mixture Stratification Potential to reduce HRR beyond TS Higher loads & Higher efficiency.
Two requirements must be met for mixture stratification to be effective:1) -Sensitive Fuel 2) Appropriate -Distribution
Dec and Sjöberg, SAE 2004-01-0557
PRF80 is strongly -sensitive (high ITHR), iso-octane is not (weak ITHR)
Partial fuel stratification (PFS) most fuel premixed, up to 20% late DI.1. Provides sufficient stratification.2. Good air utilization with leanest regions burning hot enough for good comb.
Sjöberg and Dec, SAE 2006-01-0629
5
6
7
8
9
10
11
12
13
14
0.25 0.3 0.35 0.4 0.45 0.5 0.55 0.6Charge-Mass Equiv. Ratio [m]
IMEP
g [b
ar]
42
43
44
45
46
47
48
49
50
51
Indi
cate
d Th
erm
al E
ff. [%
]
IMEPg, PFSIMEPg, PreMixedT-E, PFST-E, PreMixed
Advantages of PFS for Boosted Gasoline, Pin = 2 bar
Increase PFS by increasing the DI%.– Greatly reduces HRR, PRR and ringing.
PFS allows significantly higher loads.– Premixed IMEPg = 11.7 bar, m = 0.47– PFS IMEPg = 13.0 bar, m = 0.54– Approaching O2 availability limit (0.9%).
Thermal Eff. is higher for the same load.– More advanced CA50.
Ultra-low NOX and soot.
Using PFS to exploit -sensitivity provides substantial advantages.
Important to understand the I-T chemistry that allows this operation.
50
60
70
80
90
100
110
340 350 360 370 380 390Crank Angle [°CA]
Pres
sure
[bar
]
3% DI @ 300°CA6% DI @ 300°CA9% DI @ 300°CA13% DI @ 300°CA17% DI @ 300°CA20% DI @ 300°CA
-1000
100200300400500600700
340 350 360 370 380 390Crank Angle [°CA]
HR
R [J
/°CA
]
3% DI @ 300°CA6% DI @ 300°CA9% DI @ 300°CA13% DI @ 300°CA17% DI @ 300°CA20% DI @ 300°CA
CA50 = 374°CA, m = 0.44
(Dec et al., SAE 2011-01-0897)
Summary and Conclusions Advanced low-temperature compression-ignition engines such as HCCI
offer substantial advantages for high-efficiency, low emiss. & moderate cost.
Early autoignition chemistry is critical for the operation of these engines. – LTHR 760 < T < 870 K– ITHR 900 < T < 1050 K
ITHR varies significantly with fuel type even when no LTHR is present.
Magnitude of the ITHR is critical for allowing sufficient combustion-phasing retard to prevent engine knock.– ITHR must be sufficient to keep a positive TRR during the early expansion.
Intake boosting greatly increases the ITHR of gasoline allowing very high loads without knock and with good stability up to IMEPg = 16.3 & 18.1 bar– Enhanced ITHR also found with the biofuel iso-pentanol, but not with ethanol.
Amount of ITHR also correlates with the -sensitivity of the fuel. – -Sensitivity allows the use of PFS to significantly reduce the HRR & PRR.– Provides higher loads and higher efficiencies.
A more complete understanding of I-T chemistry at engine conds. is needed.