an enabling study of diesel low-temperautre combustion via
TRANSCRIPT
1Zheng
An Enabling Study of Diesel Low-Temperature Combustion via Adaptive Control
Ming Zheng, Graham T Reader, Usman
Asad,Yuyu
Tan, Xiaoye
Han, Kelvin Xie, and Meiping
Wang
Clean Diesel Engine Research LaboratoryUniversity of Windsor
Technical Session 1: Advanced Combustion Technologies, Part 14:00–4:20pm Monday August 4 2008, Grand Foyer
U.S. Department of Energy 14th
Diesel Engine-Efficiency and Emissions Research (DEER) ConferenceHyatt Regency Dearborn Hotel, August 4-7, 2008
Dearborn, Michigan
Contact: [email protected]
2Zheng
LTC Enabling Prospects1.
Optimize control by separating the time scales of fuel air mixing and ignition
2.
Stabilizing LTC operations –
on cliff operation of ultra low NOx emissions and acceptable fuel efficiency
3.
Guide transient combustion control within LTC mode when major engine operating parameters such as boost, EGR, and engine speed varies
4.
Raise engine Load level in LTC5.
Mode shifts between conventional and LTC
6.
Multi-cylinder EGR, fuel, and air distributions7.
Biodiesel Impact –
Cetane, oxygen content, volatility,
viscosity, biodegradation, high pressure compressed solid
3Zheng
Diesel LTC Challenges1.
The fuel efficiency of the LTC cycles is commonly mired by the high levels of hydrocarbon (HC) and carbon monoxide (CO) emissions. The fuel-efficiency of HCCI engines is often compromised by the high levels of HC and CO emissions that may drain substantial amount of fuel energy (5~15% in low-load cases) from the engine cycle.
2.
Moreover, the combustion process becomes less robust and enters into narrower operating ranges and with higher instabilities compared to conventional high temperature combustion (HTC) operations –
LTC is closer to the flame-out limits than HTC.
3.
The scheduling of early fuel delivery in HCCI engines has lesser
leverage on the exact timing of auto-ignition that may even occur before the compression stroke completes when a high compression ratio of conventional diesel cycles is applied, which may cause excessive efficiency reduction and combustion roughness.
4.
The high HC and CO emissions are attributed to the relatively low volatility of diesel fuels, the lowered combustion efficiency of
the lean and/or EGR weakened cylinder charge, the non-homogeneity of the cylinder charge, and the fuel condensation and flame quenching on the surfaces of the combustion chamber.
4Zheng
5Zheng
Research Platform –
non compromised for control performance
The research platform consists of an advanced common- rail diesel engine modified for the intensified single
cylinder research and a set of embedded real-time (RT) controllers, field programmable gate array (FPGA) devices, and a synchronized personal computer (PC) control and measurement system. Up to 12 fuel injection pulses per cylinder per cycle have been applied to modulate the homogeneity history of the cylinder charge in mixed mode combustion in order to improve the phasing and completeness of combustion under independently controlled exhaust gas recirculation (EGR), intake boost, and exhaust backpressure.
6Zheng
Experimental Setup -
Capable of multiple parallel 1st
priority control tasks
Engine Type 4 Cylinder, Ford “Puma” Displacement [cm3] 1998 Bore x Stroke [mm] 86 x 86 Compression Ratio 18.2:1 Combustion System Direct Injection Injection System Common-rail; PRail ≤ 160 MPa
7Zheng
Adaptive Combustion Control Platform
-2 0
1 1 5
2 5 0
2 7 0 .5 2 8 3 .3 2 9 6 .1 3 0 8 .9 3 2 1 .7 3 3 4 .5 3 4 7 .3
2
High speed network
Fast Communication
-1
0
1
2
3
4
280 290 300 310 320 330
1
Power DriveReconfigurable
-8
0
8
278 288 298 308 318 328 338
3
Signal Conditioning
Engine Control Parameters
Prompt Communication
Cylinder Pressure EncoderZ & A Signals, 0.1°CA Resolution
Common Rail Diesel Engine
Injector
Data Flow Legend: ControlFeedback
Host & RT-FPGA Controller
RT-FPGA Controller
Cycle-by-CycleCA50 Estimation
Common Rail HP Pump Pressure Control
Combustion Pattern Recognition and Characterization
RT Controller
t ~ after each combustion cycle
Decision Making for FPGA
t ~ after a number of combustion cycles
Programming & Control Platform
Host PCs/Data Storage
Local Decision Making
Reconfigurable I/O
t ~ within one combustion cycle
FPGA VI, 96 sync DI/O8 16bit A/I, 8 16bit A/O3 million gates, 40MHz
ADAPTIVE FUELING CONTROL SYSTEM INTEGRATION
COMBUSTION CHARACTERIZATION
Power DrivesEV Driving Cycle Reconfigurable
Output upto 20A 200VMin. Dwell 10 s b/w EVs PCs: Boost & Exhaust
Back-pressure Control
CLEAN DIESEL ENGINE LAB: COMBUSTION CONTROL PLATFORM III
IMEP Estimation for within Cycle Control
Smart NOx & dual λ Sensors
EGR Estimation and Application StrategiesNOx conformation etc.
Prompt Communication
8Zheng
Fuel Injection Scheduling1.
Up to 12 fuel injection pulses per cylinder per cycle have been applied to modulate the homogeneity history of the HCCI operations in order to better phasing and completing the combustion process.
2.
Empirical studies have been conducted under independently controlled exhaust gas recirculation (EGR), intake boost, and exhaust backpressure.
9Zheng
Challenges in Digital Combustion Control
1.
Adaptation step relaxation versus prompt performance modulation
2.
Cylinder pressure noise filtration versus signal sharpness
3.
Simplex feedback control versus model based forward control
4.
Fuel injection pulse numbers versus total injection time window of the least condensation
10Zheng
Experimental Case Outline
1.
Single shot with heavy EGR to separate the time domains between injection and combustion
2.
Multiple early shots with moderate EGR to improve homogeneity
3.
Multiple early plus main to gain power output4.
Speed and boost transients
11Zheng
DIESEL LTC CHALLENGES•
Prolonged Ignition Delay to enable LTC
0
0.05
0.1
0.15
0.2
0.25
30 40 50 60 70 80EGR Ratio [%]
Indi
cate
d So
ot [g
/kW
-h]
0
1
2
3
4
IME
P [b
ar] &
Ind
NO
x,TH
C
SootNOxIMEPTHC
IncreasedCycle-to-Cycle
Variation toUnstable Operation
Decreased Thermal Efficiency
LTCSlope 2
HTCSlope 1
Free NOx Reductionwithout Soot Penalty
Single Shot Experiments (EGR Sweep)Engine Speed: 1400 RPM
Pintake: 1 bar (abs)Tintake: 30°C
[g/k
W-h
]
Ignition delayprolonged by >50%
12Zheng
New LTC Emission Trade-off
10
100
1000
10000
0 1 2 3 4 5 6Smoke [FSN]
log
(TH
CC
1 )
60MPa & 45kPa90MPa & 45kPa90MPa & 75kPa120MPa & 45kPa150MPa & 45kPa150MPa & 75kPa
HTC
LTC
Single Shot Experiments (EGR Sweep)CA50% HR: ~365°CASpeed: 1500 RPM IMEP: ~8 barEGR Rate: 0 ~ 66%
Increasing EGR Increasinginjectionpressure
0
1
2
3
4
5
6
0 50 100 150 200 250 300NOx [ppm]
Smok
e [F
SN] 60MPa & 45kPa
90MPa & 45kPa90MPa & 75kPa150MPa & 45kPa150MPa & 75kPa
High injection pressure effectiveto reduce smoke in HTC
Increasing EGR
Single Shot Experiments (EGR Sweep)CA50% HR: ~365°CASpeed: 1500 RPM IMEP: ~8 barEGR Rate: 0 ~ 66%
LTC Regime
13Zheng
Diesel LTC vs. Engine Load
Relatively high CO & HC penalty due to large injection quantity/shot; Use of heavy EGR to improve combustion
phasing
0
20
40
60
80
100
120
320 340 360 380 400Crank Angle [°CA]
Cyl
inde
r Pre
ssur
e [b
ar]
0
0.2
0.4
0.6
0.8
Nor
mal
ized
HR
R [1
/°C
A]
Multi-pulse HCCI - 3 Injections/cycleSpeed: 1200 RPM Injection Pressure: 120 MPaFuelling: 45 mg/cycle Pintake: 1.5 bar absTintake: ~45°C
IMEP: 7 barEGR: 45 %CA50%: 350.1°CAO2exh: 4.7%Indicated (g/kWh)NOx: 1.02Soot: 0.1CO: 12.9THCC1: 7.2
IMEP: 7.5 barEGR: 61 %CA50%: 361.3°CAO2exh: 0.65%Indicated (g/kWh)NOx: 0.07Soot: 0.01 CO: 14.4THCC1: 3.9
Injection Scheduling#1: 450 μs@260°CA#2: 600 μs@280°CA#3: 200 μs@335°CA
Smok
eles
sR
ich
Com
bust
ion
0
40
80
120
160
200
320 340 360 380 400Crank Angle [°CA]
Cyl
inde
r Pre
ssur
e [b
ar]
0
0.2
0.4
0.6
0.8
Nor
mal
ized
HR
R [1
/°C
A]
Multi-pulse HCCI - 8 Injections/cycleSpeed: 1200 RPM Injection Pressure: 120 MPaFuelling: 53.7 mg/cycle Pintake: 2.2 bar absTintake: ~45°C
IMEP: 9.1 barEGR: 52 %CA50%: 348.9°CAO2exh: 2.8%Indicated (g/kWh)NOx: 0.1Soot: 0.002CO: 10.3THCC1: 3.2
IMEP: 9.7 barEGR: 58 %CA50%: 353.7°CAO2exh: 0.3%Indicated (g/kWh)NOx: 0.02Soot: 0.002CO: 10.7THCC1: 3.7
Injection Scheduling# 1,3,5,7: 290 μs@260°,274°,288°,302°CA# 2,4,6: 280 μs@267°,281°,295°CA#8: 200 μs@335°CA
Smok
eles
sR
ich
Com
bust
ion
Reducing CO & HC penalty with 8 Injections/ cycle; Higher boost and heavy
EGR to improve LTC
14Zheng
Combustion Cycle Efficiency Calculations•
Exhaust hydrocarbon energy with respect to fuel input at different engine loads
0
2
4
6
8
10
0 1000 2000 3000 4000 5000Exhaust THCC1 [ppm]
Exh
aust
TH
C w
rt Fu
el [%
]
2
4
2012
86
Lines ofConstant IMEP
AssumptionsPintake: 1 bar absLHV: 42.9 MJ/kgη ind : 45%EGR: 0 %
15Zheng
Engine Cycle Simulation•
Heat release rates used as input for simulations
320 330 340 350 360 370 380 390 400CA50 [°CA]
Hea
t Rel
ease
Rat
e [1
/°C
A]
Duration variation
Phase variation
(TDC)
Shape variation
Splitting
16Zheng
Engine Cycle Simulation ResultsEffect of CA50 and combustion duration on ηind
, pmax
& (dp/dθ)max
(1500 RPM, IMEP: 6 bar, Pint
: 1.15 bar abs)
Conventional DieselTypical HCCI Conventional DieselTypical HCCI Conventional DieselConventional DieselTypical HCCI
17Zheng
Engine Cycle Simulation Results•
ηind
comparison between –
Upper: different heat release shapes; Lower: single hump and split combustion
CA50 [°CA]
Single hump Double hump Long tail
Split combustion
Hea
t Rel
ease
Dur
atio
n [°
CA]
Split combustion340 350 360 370 380 390 400 410 420
20
40
60
8
020
4
0
60
80
Single hump Double hump Long tail
CA50 [°CA]
Single hump Double hump Long tail
Split combustion
Hea
t Rel
ease
Dur
atio
n [°
CA]
Split combustionSplit combustion340 350 360 370 380 390 400 410 420
20
40
60
8
020
4
0
60
80
Single hump Double hump Long tailSingle hump Double hump Long tail
18Zheng
Equivalent Combustion Cycle Deficiency Calculations
•
Equivalent THC penalty with CA50 off-phasing
-20
-15
-10
-5
0
5
10
15
0 1000 2000 3000 4000 5000Equivalent Exhaust THCC1 [ppm]
Off-
phas
ing
from
CA
ηm
ax [°
CA
]
2 4
2086
Lines ofConstant IMEP
AssumptionsPintake: 1 bar absEGR: 0 %LHV: 42.9 MJ/kgCAη max : ~365°CA
12
Per
cent
age
Dec
reas
e in
ηm
ax [%
]
27
0
5
15
1
5
12
20
RetardedTiming
AdvancedTiming
19Zheng
Cycle Based Adaptive Control to Improve LTC Transients
1.
SOI synchronized at optimized HR phasing via dPmax
timing modulation
2.
dPmax
ceiling limitation via pilot quantity modulation
3.
IMEP compensation via pilot and main modulations
4.
IMEP top-up control via post quantity modulation
20Zheng
Transient Peak Pressure Rise Timing Modulation after Entering LTC with High EGR (single shot)
Injection Timing Control
348
352
356
360
364
368
372
0 1000 2000 3000 4000Engine Cycle # [-]
SOI,
CA
(dp/
d θ) m
ax [°
CA]
0
5
10
15
20
25
IMEP
& (d
p/d θ
) max
[bar
]
Adaptive Control Tests - EGR, Speed & Boost Transients1000 rpm/50kPa → 1500/100 →1000/50
CA (dPmax) ModulationPinj: 90MPa
High EGR ON
1000 rpm50 kPa
1500 rpm100 kPa
1000 rpm50 kPa
CA dPmax
IMEPStart of Combustion
dPmax
21Zheng
Emission Result when Entering LTC with High EGR under Peak Pressure Rise Timing Modulation
Injection Timing Control
0
100
200
300
400
8580 9080 9580Time [sec]
NO
x &
TH
C [p
pm],
EG
R [%
]
0
1000
2000
3000
CO
[ppm
], S
peed
[RPM
]
Adaptive Control Tests - EGR, Speed & Boost Transients1000 rpm/50kPa → 1500/100 →1000/50
CA (dPmax) ModulationPinj: 90MPa
NOx < 20 ppm
Sharp EGR Increase
1000 rpm50 kPa
1500 rpm100 kPa
1000 rpm50 kPaCO
THCNOx
EGR
Speed
22Zheng
Peak Pressure Rise Timing and Rate Modulation
0
2
4
6
8
10
12
14
16
0 500 1000 1500Engine Cycle #
(dp/
d θ) m
ax [b
ar]
320
330
340
350
360
370
380
SO
I pilo
t, SO
I mai
n, C
A d
p max
[°C
A]1000 rpm
50 kPa
1500 rpm100 kPa
1000 rpm50 kPa
Adaptive Control Tests - Speed & Boost Transients1000 rpm/50kPa → 1500/100 →1000/50
dPmax & CA (dPmax) ModulationPinj: 90MPa
CA dPmax
SOCpilot
dPmax
SOCmain
SOC: Start of CombustionPilot and Main Injections:Timing and Quantity Control
23Zheng
Emission Results under Peak Pressure Rise Timing and Rate Modulation
Pilot&Main: timing & quantity control
0
100
200
300
400
500
4800 4900 5000 5100Time [sec]
NO
x &
THC
[ppm
], EG
R [%
]
0
1000
2000
3000
4000
5000
6000
CO
[ppm
], S
pped
[RP
M],
Boo
st [k
Pa]
Adaptive Control Tests - Speed & Boost Transients1000 rpm/50kPa → 1500/100 →1000/50
dPmax & CA (dPmax) ModulationPinj: 90MPa
1000
rpm
50 k
Pa 1500 rpm
100 kPa1000 rpm50 kPa
CO THC
NOxEGR
SpeedBoost
24Zheng
Peak Pressure Rise Timing and Rate Modulation under High EGR (NOx ~30ppm) Transients
330
340
350
360
370
380
0 1000 2000 3000Engine Cycle # [-]
SOI,
CA
(dp/
d θ) m
ax [°
CA
]
0
3
6
9
12
15
18
21
24
(dp/
d θ) m
ax, I
MEP
[bar
]
Adaptive Control Tests - Speed & Boost Transients1000 rpm/50 kPa → 1500/100 →1000/50
Pinj: 120 MPa
IMEP dPmax
1000 rpm
1500 rpm
SOCmain
dPmax & CA (dPmax) Modulation
SOCpilot
CA (dPmax)
high speed&boost high low d&b t
low speed&boost
SOC: Start of Combustion
25Zheng
Transient Low NOx Confirmation with NOx Sensor
0
20
40
60
80
100
120
3200 3400 3600 3800 4000Time [sec]
NO
x [p
pm],
Boo
st [k
Pa]
, EG
R [%
]
0
500
1000
1500
2000
Spe
ed [R
PM
]
Adaptive Control Tests - Speed & Boost Transients1000 rpm/50kPa ® 1500/100 ®1000/50
Pinj: 120MPa
Smart Nox Sensor NOx Analyzer
EGR
SpeedBoost
dPmax & CA (dPmax) Modulation
26Zheng
LTC ADAPTIVE CONTROL STRATEGIES
•
Structure of the CDEL Adaptive Control System
27Zheng
SYSTEMATIC AND ADAPTIVE CONTROL RESULTS
NOx as function of intake oxygen
0
400
800
1200
1600
2000
8 10 12 14 16 18 20 22Intake Oxygen [%]
NO
x [p
pm] 60MPa & 45kPa
90MPa & 45kPa90MPa & 75kPa120MPa & 45kPa150MPa & 45kPa150MPa & 75kPa100MPa & 50kPa130MPa & 50kPa
Single Shot LTC ExperimentsCA50% HR: ~365°CASpeed: 1500 RPM EGR Rate: 0 ~ 66%
IMEP ~8 bar
~6.5 bar~8.5 bar
NOx decreasesmonotonically
with EGR
-0.02
0.03
0.08
0.13
0.18
0.23
300 310 320 330 340 350 360 370 380Crank Angle [°CA]
Hea
t-Rel
ease
Rat
e [1
/ °C
A]
Diesel LTC Tests-3 Injections/CycleEngine Speed: 1800 RPMIMEP: 5.9~6.6 barTintake: 50~60°C
EGR: 41%IMEP: 5.9 barSmoke: 1.1FSN
EGR: 47%IMEP: 6 barSmoke: 0.96FSN
EGR: 56%IMEP: 6.6 barSmoke: 0.42FSN
IncreasingEGR
Last Injection
Heat-release rate for soot
reduction
28Zheng
Adaptive Control ON/OFF Comparison (High EGR, NOx ~20pm)
325
335
345
355
365
375
0 2500 5000 7500Engine Cycle # [-]
SO
I, C
A (d
p/d θ
) max
[°C
A]
0
4
8
12
16
20
IME
P &
(dp/
d θ) m
ax [b
ar]
Adaptive Control Tests - Speed & Boost Transients1000 rpm/50 kPa → 1500/100 →1000/50
Pinj: 90 MPa
SOCmain
dPmax
1000 rpm1500 rpm
dPmax & CA (dPmax) Modulation
SP:13 bar/°CA
SOCpilot
IMEP
Adaptive Control OFF Pilot OFF
11 bar/°CA 9 bar/°CA
CA dPmax
SOC: Start of Combustion
29Zheng
Pressure Rise Curves under Peak Rise Timing and Rate Control
-4
-2
0
2
4
6
8
10
12
14
355 360 365 370 375
Crank Angle [°CA]
(dP
/dθ)
max
[bar
/°C
A]
SP: 13 bar
SP: 11 bar
SP: 9 bar
OFF with pilot
OFF
Adaptive Control Tests - Speed & Boost TransientsSpeed: 1000 rpm Boost: 50 kPaIMEP: 6.7~7.2 bar Pinj: 90 MPa
IMEP ~6 bar withAdaptive OFF
All Cases: High EGR NOx ~20ppm
30Zheng
IMEP Compensation (high EGR, NOx ~30ppm)
100
150
200
250
300
350
400
450
0 1000 2000 3000 4000Engine Cycle # [-]
Ada
pted
Pos
t Inj
Dur
atio
n [ μ
s]
5
6
7
8
9
10
11
12
13
IME
P [b
ar]
Adaptive Control Tests - Speed & Boost Transients1000 rpm/50 kPa → 1500/100 →1000/50 Pinj: 150 MPa Baseline IMEP: 8.5 bar
IMEP Postduration
1000 rpm1500 rpm
Post-TDC IMEPModulation within each
Combustion Cycle
ΔIMEP
Control OFF
Main: 420μs@359°CAPost: 180~350μs@372°CA
Main: 380μs@359°CAPost: 250μs@372°CA
31Zheng
Sample cylinder pressure and heat release characteristics with
adaptive control
0
10
20
30
40
50
60
70
80
90
100
300 330 360 390 420Crank Angle [°CA]
Cyl
inde
r Pre
ssur
e [b
ar]
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
0.2
Nor
mal
ized
Hea
t Rel
ease
Rat
e [1
/°C
A]
1000 RPM, Pint=1.5 bar abs(dp/dθ)max
=8.6 bar/°CA
1000 RPMPinj=1200 barCommanded fuel injection:230µs@330°CA450µs@353°CAAdaptive control:(dp/dθ)max=10 bar/°CACA of (dp/dθ)max=363°CAAcutal fuel injection:130µs@335°CA510µs@355°CA 1500 RPM
Pint=2 bar abs(dp/dθ)max
=6.3 bar/°CA
TDC
2-shots
mpilot ↓mmain
↑
-4
-2
0
2
4
6
8
10
300 330 360 390 420Crank Angle [°CA]
Cyl
inde
r Pre
ssur
e [b
ar]
TDC
dPmax Ceiling <10bar/°CA
Pilot turned ONto lower dPmax
Pilot turned OFFbecause of no needfor lowering dPmax
32Zheng
Progresses in LTC Control -
Reduce reliance on de-NOx after-treatment
1.
The simulations and empirical results indicate that the combustion phasing dominates the maximum attainable fuel efficiency of the engine. However, the phasing domination cedes to high HC when the fuel efficiency is severely deteriorated such as by excessive EGR.
2.
The energy deficiency of typical LTC heat release patterns has been further quantified by comparing with HC and CO emissions with combustion phasing deficiency across the engine load spectra.
3.
Adaptive control strategies based on cylinder pressure and heat release characteristics are implemented to stabilize and enable the low-temperature combustion from mid to high loads especially when high boost and EGR are applied.
4.
Further, oxygen and NOx sensors at the intake and exhaust of the
engine are devised to comprehend the transient impacts of EGR, boost, and load variations.
5.
The multi-pulse scheduling is effective to prevent premature ignition and elevated NOx and soot.
33Zheng
Prospective LTC Load Control Improvements
1.
The mode of EGR enabled LTC
is suitable for low load operations, in which a single shot of fuel is delivered close to the top dead center (TDC). The heat release phasing is fully controllable via injection timing control and thus high energy efficiency in attainable.
2.
The mode of early injection HCCI
is suitable for mid load operations, in which the fuel is delivered in multiple events and by milliseconds prior to TDC and thus the heat release phasing is not directly controllable. EGR is commonly applied suppress premature ignition and combustion noise.
3.
The mode of split burning LTC
is suitable for high load operations, in which a partial amount of fuel is delivered to produce HCCI combustion and the remaining for post TDC late combustion. The latter may be benefited from the virtual EGR produced by the prior HCCI burning and timed to best eliminate combustibles and raise power output.
34Zheng
ACKNOWLEDGEMENTS
The research is sponsored by the Canada Research Chair
program. NSERC, CFI, OIT,
AUTO21, Ford Motor Company, University of Windsor and other non-disclosed OEMs have supported the research programs at Clean Diesel Engine Lab.