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Transcript of Internal Combustion Engine Group The effect of compression ratio on exhaust emissions from a PCCI...
Internal Combustion Engine GroupInternal Combustion Engine Group
The effect of compression ratio on exhaust emissions from a PCCI Diesel engine
ECOS 2006
12-14 July 2006
Laguitton, Crua, Cowell, Heikal, Gold
• Introduction• Experimental set-up• Validation of single cylinder design• Strategy for low NOx, soot and FC• Conclusions
Content
Highly pre-mixed and cool combustion
IMPROVED AIR SYSTEM EFFICIENCY
INCREASED IGNITIONDELAY
INCREASED EGR RATES AND
TEMPERATURE MANAGEMENT
ROBUSTNESS CONTROL
IMPROVED AIR/FUEL MIXING
REDUCED COMPRESSION
RATIO COMBUSTION SYSTEM DESIGN
ADVANCED AIR/EGR SYSTEMS
ADVANCED COMBUSTION & AIR
PATH CONTROL
ADVANCED FIE TECHNOLOGY
COLD STARTTECHNOLOGY
REDUCE OXYGENCONCENTRATION
INCREASE EFFICIENCY+
Oxygen concentration
Source: MTZ 11/2002: Toyota
Temperature /(K)
Lo
cal
Eq
uiv
alen
ce R
atio
1000 1400 1800 2200 2600 3000
1
4
3
2
5
6
7
8
9
10
Soot formation area
NOx formation area
Combustion trend to more pre-mixed and lower temperature
Euro 4 – O2 Concentration Map
100 %
85 %
70 %
Level 3 – O2 Concentration Map
100 %85 %
70 %
Approach is to reduce the oxygen concentration characteristics over the engine speed and load operating area:– Oxygen concentration in the flame is reduced– Less NOx are formed
Time
Drive current
Rate of injection
Injection pulse
Start of combustion
SOC – Real SOI
Injectionperiod
0.00
2.00
4.00
6.00
8.00
10.00
0.00 5.00 10.00 15.00 20.00 25.00 30.00
Injection period (°CA)
SO
C -
re
al
SO
I (°
CA
)
100 % 66 % 50 %
Low NOx strategy
Improved air/fuel mixing to achieve low soot and good combustion efficiency Euro 4
Level 2
Level 3
Level of premixed fuel
Increasing Load
Trend is clear:- Injection durations reduced by increased
injection pressure and nozzle flow- Ignition delay increased by changes to
air/fuel, CR, intake temperature and EGR
Single cylinder engine facility
Single cylinder – Ricardo HYDRA:– 500cc swept volume (86mmx86mm)– 2.0L high-flow head– Variable swirl (1.0-3.5 Rs) – Compression Ratio 18.4:1 and 16.0:1– Off-engine HP pump + common rail– Delphi injector– Delphi nozzle library – EmTronix FIE controller – Reference ultra low sulphur diesel fuel
Test bed:– Horiba gas analyser MEXA 7100DEGR– AVL733 dynamic fuel meter– AVL415 variable sampling smoke meter– High speed data logger– Custom-built low speed data logger– TDM post processing
Piston-bowl cross-sections
Validation of single cylinder design
Full Load Results
0
10
20
30
40
50
1500 rpm2 bar
2000 rpm6 bar
2000 rpm16 bar
1000 rpmFull Load
2000 rpmFull Load
4000 rpmFull Load
EG
R R
ate
[%] Single
Multi
0
5
10
15
20
25
30
35
1500 rpm2 bar
2000 rpm6 bar
2000 rpm16 bar
1000 rpmFull Load
2000 rpmFull Load
4000 rpmFull Load
AF
R
Single
Multi
0
5
10
15
20
25
1500 rpm2 bar
2000 rpm6 bar
2000 rpm16 bar
1000 rpmFull Load
2000 rpmFull Load
4000 rpmFull Load
Net
IM
EP
[b
ar] Single
Multi
Part Load Results
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0 5 10 15 20 25 30
NOx [g/h]
Sm
ok
e [
FS
N]
Single
Multi
1500 rpm, 2 bar
2000 rpm,6 bar 2000 rpm,
16 bar
2000 rpm,10 bar
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
1000 1500 2000 2500 3000 3500 4000
Engine Speed [rev/min]
Sm
ok
e [
FS
N]
Multi
Single
Effect of compression ratio on NOx emissions
0.00
2.00
4.00
6.00
8.00
10.00
12.00
-10.0 -5.0 0.0 5.0 10.0
Main injection timing (deg CA ATDC)
NO
x m
ass
flo
w (
g/h
)
-0.0002
0.0000
0.0002
0.0004
0.0006
0.0008
-60.0 -20.0 20.0 60.0 100.0
Crankangle (deg CA)
Insta
nta
neo
us h
eat
rele
ase
0.0
20.0
40.0
60.0
80.0
-60.0 -20.0 20.0 60.0 100.0
Pre
ssu
re (
bar
)
2000 rev/min 7.7 bar GIMEPLEVEL 2: CR 18.4 and CR 16.0:1
2000 rev/min 10.8 bar GIMEP
2000 rev/min 7.7 bar GIMEP
1500 rev/min 3.0 bar GIMEP
Reduced CR decreases NOx emissions especially at high loads. At low loads (1500 rev/min 3.0 bar GIMEP), slight improvements but combustion is already fully premixed, hence reduced benefits
Fixed calibration
Effect of compression ratio on auto-ignition delay
0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
16.0
-10.0 -5.0 0.0 5.0 10.0
Main injection timing (deg CA ATDC)
An
gle
of
SO
C (
deg
CA
AT
DC
)
0.0
20.0
40.0
60.0
80.0
100.0
120.0
-10.0 -5.0 0.0 5.0 10.0
Ma
xim
um
dP
/dT
(b
ar/
ms)
30.0
40.0
50.0
60.0
70.0
80.0
90.0
-10.0 -5.0 0.0 5.0 10.0
Main injection timing (deg CA ATDC)
Pre
ssu
re a
t S
OC
(b
ar)
2000 rev/min 10.8 bar GIMEP
2000 rev/min 7.7 bar GIMEP
1500 rev/min 3.0 bar GIMEP
Reduced CR decreases in-cylinder pressures. Combustions occur later, increasing the level of premixed leading to higher maximum pressure variations but lower NOx
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
-25.0 -20.0 -15.0 -10.0 -5.0 0.0 5.0
Main injection timing (°CA ATDC)
NO
x (g
/kW
h)
F
C (
kg/h
)
-2.00
-1.60
-1.20
-0.80
-0.40
0.00
0.40
0.80
1.20
1.60
2.00
So
ot
(g/k
Wh
)
Potential operating zone
3.06 FSN
Responses at 43% EGR
Late injection strategy for low NOx and soot
Summary of single injection timing responses at 1500 rev/min 6.6 bar GIMEP
(43% EGR rate, 1000 bar rail pressure)
19.0:1 AFR17.0:1 AFR
High FC penalty with veryretarded single injections
DOE Model: Soot (g/h)
Test data for FC (kg/h)
DOE model: NOx (g/h)
NOx reduced by high EGR and low AFR Low soot and good fuel consumption is achieved
through improved air/fuel mixing- Low CR, swirl and rail pressure enhancement is
critical Good fuel consumption is achieved by optimising
50% burn after TDC. Late combustion is avoided by shortening combustion duration
DOE modelling
0.0
20.0
40.0
60.0
80.0
100.0
-60.0 -30.0 0.0 30.0 60.0
Crankangle (°CA ATDC)
Pre
ssu
re (
bar)
Insta
nta
neo
us h
eat
rele
ase
Combustion phasing for optimum fuel consumption
Good combustion efficiency:- Rapid combustion- Centred between 0 and 10 °CA ATDC
Test data for FC (kg/h)
This is a conflicting requirement with low NOx combustion strategies, which require slow and late combustion
A compromise to minimise impact on combustion efficiency is to operate:
- Slow combustion- Well phased combustion
Conclusions
A good comparison with multi cylinder baseline results was achieved
Ultra low NOx has been achieved through highly pre-mixed and cool combustion
At 1500 rev/min, 3.0 bar GIMEP - a twin early injection strategy achieved improved HC and CO results compared to a pilot + “late” main strategy
At 1500 rev/min, 6.6 bar GIMEP - testing showed that a late injection strategy was essential for low NOx. A single late injection with high EGR achieved the best overall results
With 16:1 CR, an early injection strategy was only beneficial below 3.0 bar GIMEP. Late, high pressure injection combined with EGR is recommended
With the combustion bowl geometry tested, 10 and 12 hole nozzles did not offer an advantage at rated power. Reduced spray penetration, bowl interaction and air utilisation was detrimental at the higher loads and speed