A Comparison of Combustion and Emissions of Diesel Fuels ... · A Comparison of Combustion and...
Transcript of A Comparison of Combustion and Emissions of Diesel Fuels ... · A Comparison of Combustion and...
A Comparison of Combustion and Emissions of Diesel Fuels and Oxygenated Fuels in a
Modern DI Diesel Engine
Eric Kurtz, Douglas Kuhel, James E. Anderson, Sherry A. Mueller
This work was supported by the U.S. Department of Energy, under special project number DE-FC26-07NT43278.
Acknowledgement: Dennis Miller, Lars Peereboom, and Carl Lira at Michigan State University for supplying the fuels used in this study.
Outline
• Background • Experimental Method • Experimental Results • Summary & Conclusions
This work has been published in SAE 2012-01-1695
MSU Fuels Investigations • Canola-based FAMEs (CME) has relatively good cold
flow properties & oxidative stability.
• DBS further improves the cold flow properties of CME.
• To stay within the 40 CN U.S requirement, DBS content in CME must be limited to 40%.
Tem
pera
ture
(oC
)
Dibutyl succinate (DBS)
Single-Cylinder Study Objectives
Study the influence of selected oxygenated fuels on combustion and emissions in a modern diesel engine
– Conventional Combustion – Low Temperature Combustion (LTC)
Fuels Tested Mineral Diesel Fuels
(Control group) Oxygenated Fuels
720 727 668* CME 60-40
Cetane No. 45.6 41.8 56.5 50.8 40.8
NHV (MJ/kg) 42.9 42.4 43.2 37.4 33.2
H:C ratio 1.81 1.775 1.952 1.88 1.86
O:C ratio 0 0 0 0.11 0.19
Aromatics 28.6% 32.4% <5% 0% 0%
*A low aromatic diesel fuel included in the study (97.7% saturates)
Test Conditions
CC1 CC2
CC3 CC4
CC5
CF1
CF2 CF3
A100 C100
25-4
• A single-cylinder version of the production 6.7L V8 PowerStroke®. • Evaluated over the entire engine map.
Test Procedure Testing attempted to mimic diesel engine controls
• Calibration settings are based on engine speed and fuel quantity – Fuel pressure – Pilot fuel quantity
Test Procedure • Established base calibration settings using 720 fuel (46 CN) • Identical settings for all fuels:
• Select conditions also tested with constant injected fuel energy by adjusting the quantity of each fuel pulse (adjusted for fuel NHV).
– Main SOI – Pilot SOI
– EGR rate – Boost pressure
Rail pressure
Main quantity
Pilot quantity
Pilot SOI
Main timing
EGR rate
Conventional 720 calibration setting 720 SOI Sweep LTC 720 cal. settings No pilot 720 SOC Sweep
Outline
• Background • Experimental Method • Experimental Results
– Emissions – Combustion noise (not presented) – BSFC & Efficiency (not presented)
• Summary & Conclusions
NOx and Oxygenated Fuels
• NOx emissions appear to be primarily a function of intake oxygen concentration for both fuels (independent of fuel oxygen content)
• At the same intake O2, no statistical difference in NOx was observed with oxygenated fuels
• EGR is typically controlled based on a EGR rate or air mass flow
• Fuel O increases the total intake O2 for a given EGR rate – NOx increases
14.0 14.5 15.0 15.5 16.0 16.5 17.0 17.5 18.0 18.5 19.0Intake Oxygen Concentration
24 26 28 30 32 34 36 38 40 42 44 46 48 50EGR Rate
V8_p
rj.TP
.BSN
OX
[g/k
Wh]
-0.4
0.0
0.4
0.8
1.2
1.6
2.0
2.4
Increasing EGR Increasing EGR
Proj
ecte
d BS
NO
X [g
/kW
h]
Proj
ecte
d BS
NO
X [g
/kW
h]
720 diesel fuel100% CME
1200 1500 1800 2100 2400 2700 3000 3300 3600 3900 4200 4500Engine_Speed [rpm]
BMEP
[bar
]
0
2
4
6
8
10
12
14
16
18
20
5
10
15
2025
30
3545
Decreasing EGR
1200 1500 1800 2100 2400 2700 3000 3300 3600 3900 4200 4500Engine_Speed [rpm]
BMEP
[bar
]
0
2
4
6
8
10
12
14
16
18
20
5
10
15
2025
30
3545
Decreasing EGR
BM
EP [b
ar]
Engine Speed [rpm]
24 26 28 30 32 34 36 38 40 42 44 46 48 50EGR Rate
-0.4
0.0
0.4
0.8
1.2
1.6
2.0
2.4
Increasing EGR
Proj
ecte
d BS
NO
X [g
/kW
h]
Example Control Scenario • Commanded fuel quantity will increase
to adjust for lower fuel energy.
• As commanded fuel quantity increases, typically EGR rate decreases, boost and injection pressure increase.
• Leads to a further increase in NOx emissions.
1
2
1 – higher intake O2
2 – lower EGR rate, higher boost pressure, higher injection pressure
720 diesel fuel100% CME
Fuel
Qua
ntity
Particulate Emissions
80.0
82.5
85.0
87.5
90.0
92.5
95.0
97.5
100.0
CME 60-40Perc
ent P
M R
educ
tion
vs. 7
20 F
uel
CC2CC3CC4CC5A100C100LTC_CC2LTC_CC3LTC25-4
• Large PM reductions with both oxygenated fuels • Mechanism #1: PM reduction is due to displacement of aromatic
− A relatively small PM reduction with low aromatic fuel (668) − PM reduction with 668 was not statistically significant
• Mechanism #2: PM reduction is the result of fuel oxygen − PM reduction is consistent with fuel oxygenation − Consistent with estimated oxygen equivalence ratio at the lift-off length
CME 60-40
~97%
~91%
%PM
redu
ctio
n vs
. 720
[g
/kW
h]
CC2CC3CC4CC5A100C100LTC_CC2LTC_CC3LTC25-4
Hydrocarbon Emissions
-18 -12 -6 0 6 12 18 24 30 36CA [deg]
Cyl1.
RoHR
[J/de
g]
-40
-20
0
20
40
60
80
100
120
Inj.AS
E-OL
[volt
s]
-10
0
Pilot injection command
Main injection command
Rat
e of
Hea
t Rel
ease
(J/d
eg)
Inje
ctio
nRed – 720 (46 cetane)Green – 60-40 (41 cetane)Black – CME (51 cetane)
-18 -12 -6 0 6 12 18 24 30 36CA [deg]
Cyl1.
RoHR
[J/de
g]
-40
-20
0
20
40
60
80
100
120
Inj.AS
E-OL
[volt
s]
-10
0
Pilot injection command
Main injection command
Rat
e of
Hea
t Rel
ease
(J/d
eg)
Inje
ctio
nRed – 720 (46 cetane)Green – 60-40 (41 cetane)Black – CME (51 cetane)
Conventional Combustion • Higher HC emissions observed
with the 60-40 blend. • Pilot heat release was weak with
the 60-40 blend due to low energy content and low cetane number.
LTC • Results track with cetane
number rather than oxygenation − 668 & CME: low HC − 727 & 60-40: high HC
• True also of combustion noise (not shown)
∆H
C v
s. 7
20 F
uel [
g/kW
h]
High cetane
Low cetane
HC Emissions with Compensation
-1
0
1
2
3
CC3 CC4 A100 LTC_CC2 LTC_CC3
BSHC
Diff
eren
ce R
elat
ive
to 7
20 F
uel [
g/kW
-h]
CMECME w/comp60-4060-40 w/comp
• Equivalent HC emissions with the 60-40 blend vs. the base fuel once injected quantity was adjusted for fuel energy content
• Adjusting quantity reduced HC in LTC for both oxygenated fuels − Increased load − Shorter ignition dwell
CME
CME w/comp60-4060-40 w/comp
∆H
C v
s. 7
20 F
uel [
g/kW
h]
Effect of Oxygenation - Summary
Conventional Combustion
Low temperature Combustion
NOx Same as diesel fuel1
PM Decreased significantly w/ fuel oxygen HC Same as diesel2 Function of cetane3
Noise Same as diesel2 Function of cetane
Thermal Efficiency Same as diesel2
Fuel Consumption Degraded due to lower NHV4
1 Maintaining calibration settings, including intake O2. 2 Adjusting injected fuel quantity for fuel energy content. 3 Lower HC when injected fuel quantity adjusted for fuel energy content. 4 A function of fuel energy density.
Conventional Combustion
Low Temperature Combustion
NOx Oxygenation had no effect1
PM Decreased significantly w/ fuel oxygen HC Same as diesel2 Function of cetane3
Noise Same as diesel2 Function of cetane
Thermal Efficiency Oxygenation had no effect2
Engine Description
Type Single-cylinder Cycle 4-stroke Valves per cylinder 4 Bore 99 mm Stroke 108 mm Displacement 0.83 L Compression Ratio 16.2:1 Maximum Rail Pressure 2000 bar Combustion system design Chamfered * Engine & combustion system specifications matched the production 6.7L PowerStroke®
Combustion Noise
• Differences in combustion noise correlate with cetane number of the test fuel in both conventional combustion and LTC.
• Compensation for NHV reduces slightly difference from 720 fuel.
High Cetane Low Cetane 668 CME 727 60-40
CDC Lower Similar LTC Similar Lower
∆N
oise
vs.
720
[g/k
Wh]
BSFC & Thermal Efficiency • Higher BSFC with
oxygenated fuels − Lower NHV − Lower BMEP
• Thermal efficiency of CME was comparable to the diesel fuels
-8.0
-6.0
-4.0
-2.0
0.0
2.0
4.0
Ther
mal
Effi
cien
cy d
iffer
ence
from
720
Fue
l
727668CME60-40
CC1 CC2 CC3 25-4CC1 CC2 CC3 CC4 CC5 A100 C100 LTC LTC LTC LTC
Chassis Cert Part Load Dyno Cert LTC
-8.0
-6.0
-4.0
-2.0
0.0
2.0
4.0
Ther
mal
Effi
cien
cy d
iffer
ence
from
720
Fue
l
727668CME60-40
CC1 CC2 CC3 25-4CC1 CC2 CC3 CC4 CC5 A100 C100 LTC LTC LTC LTC
Chassis Cert Part Load Dyno Cert LTC
-1.5
-1
-0.5
0
0.5
1
1.5
2
2.5
CC3 CC4 A100 LTC_CC2 LTC_CC3
Proj
ecte
d Br
ake
Ther
mal
Effi
cien
cy D
iffer
ence
Rel
ativ
e to
72
0 [a
bs %
]
CMECME w/comp60-4060-40 w/comp
• Lower thermal efficiency with the 60-40 blend without fuel quantity adjustment – later combustion phasing
• Similar thermal efficiency for all fuels when injection quantity was adjusted for energy content
CME
CME w/comp60-4060-40 w/comp
∆B
TE v
s. 7
20 [%
] ∆
BTE
vs.
720
[%]
Additional Conclusions It is speculated that NOx increase found in the literature may be due to
– An increase in intake O2 with fuel oxygen content when EGR rate or air mass flow are controlled
– Reduced EGR, increased boost and increased injection pressure when the commanded fueling injection is increased to meet torque demand with oxygenated fuels (lower energy content)
– When the intake O2 and engine calibration are the controlled to the same value, oxygenated fuels do not appear to have a negative impact on NOx emissions in a modern diesel engine