Combustion and Emissions
Characteristics of Biodiesel Fuel
Alan C. Hansen
Department of Agricultural and Biological Engineering
University of Illinois
CABER Seminar May 5, 2008
Outline of Presentation
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Introduction
What is biodiesel?
What are its advantages and disadvantages?
How is biodiesel produced?
How much is being used at present?
How does it compare to other fuels?
Some fundamentals of combustion and emissions
Combustion and emissions comparisons between
biodiesel and diesel fuel using engine measurements
and models
Final comments
What is Biodiesel?
Technical Definition for Biodiesel
(ASTM D 6751):
Biodiesel, n—a fuel comprising mono-alkyl esters of long chain
fatty acids derived from vegetable oils or animal fats, designated
B100, and meeting the requirements of ASTM D 6751.
Conversion to ester reduces viscosity
to same level as diesel fuel and potentially
increases cetane number to be the same or
even higher than diesel fuel
What are the advantages of biodiesel fuel?
•
Renewable
– carbon neutral
•
Biodegradable
– benefits environment
•
Domestically grown
– reducing imported oils
•
Low emissions
– except maybe NOx
•
No engine modifications required
– except replacing some fuel lines for older engines
•
Safer
– less flammable
•
Non-toxic
Advantages of Biodiesel (cont.)
•
•
•
•
•
Very favorable energy balance, 3.2 to 1
Can be blended in any proportion with petroleum
diesel fuel
High cetane number and excellent lubricity
Very high flashpoint (>300°F)
Can be made from waste restaurant oils and
animal fats
What are the disadvantages of biodiesel fuel?
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Lower energy content
– 6-9% less energy per unit volume for B100
– Effect of B2 – B10 on power less than 1%
Soybean oil-based biodiesel will start to crystallize at
around 0°C. This can be mitigated by blending with
diesel fuel or with additives.
• Biodiesel is less oxidatively stable than petroleum diesel
fuel. Old fuel can become acidic and form sediments
and varnish. Additives can prevent this.
• There is limited supply. Soybean oil is widely available
but expensive. Inedible animal fats are less expensive
but have limited supply.
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Disadvantages of biodiesel
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Cost is high and is feedstock sensitive
– Government subsidies allow biodiesel to compete
with petroleum-based diesel fuel
3%
2%
7%
1%
12%
75%
Oil Feedstock
Energy
General Overhead
Chemical Feedstocks
Direct Labor
Depreciation
(Source: Van Gerpen, J., 2004)
How is biodiesel produced?
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A simplified representation of biodiesel production:
Transesterification
Chemical reaction between methanol or ethanol and a vegetable
oil or animal fat
Requires a catalyst, such as caustic soda (NaOH) or KOH
Removal of glycerin reduces viscosity
Biodiesel Production: Soybeans
One Bushel
Soybeans
~1.5 gallons
Soybean oil
~1.5 gallons
Biodiesel
~10 litres
Soybean oil
~10 litres
Biodiesel
OR
100 kg
Soybeans
Why not use straight vegetable oil?
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Viscosity too high (x 10 that of biodiesel)
Cetane number too low (below ASTM limit of 40)
Poor atomization causes coking and deposits in
combustion chamber
Reacts with lubricating oil to create sludge and
compromise lubrication
U.S. Biodiesel Production
450
400
350
300
Million
250
Gallons
200
Biodiesel
150
100
50
0
1999 2000 2001 2002 2003 2004 2005 2006 2007*
est.
(Source: National Biodiesel Board - www.biodiesel.org)
NBB goal: Replace equivalent of 5 % of nation’s on-road diesel
fuel with biodiesel by 2015
EU Biodiesel Cons.
(millions gallons)
Biodiesel Production in EU
1600
1400
1200
1000
800
600
400
200
0
EU Production
Capacity:
3 billion
gallons
1998 2000 2002 2003 2004 2005 2006 2007
Source: European Biodiesel Board (www.ebb-eu.org)
US and EU Biodiesel Production Comparison
3
2.5
2
Billion
1.5
Gallons/Year
1
0.5
0
US
US
EU
EU
Production Production Production Production
2007
Capacity
2006
Capacity
2007
2006
Diesel versus biodiesel consumption
US Gasoline Consumption: 146 Billion Gallons/year
60
50
40
Billion
30
Gallons/Year
20
10
0
US
US Diesel
Consumption Production
2007
2007
US
Production
Capacity
2007
EU
Production
2006
EU
Production
Capacity
2006
Biodiesel Usage at Present (U.S.)
•
as a low-level blend (B2 – B5, B11)
– for lubricity purposes – non-sulfur formula
– US EPA requirement for sulfur
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15 ppm Oct 2006 for on-road vehicles
as a medium-level blend (B20-B50)
– Energy Policy Act credit; federal incentive
•
as a neat fuel (B100)
6000
5000
4000
SL-BOCLE ASTM D 6078
Lubricity test
3400
3000
2000
5450
Increasing lubricity
with increasing
biodiesel %
3500
2600
2100
1000
(Source: Schumacher, L.G., 2004)
0
#2 Diesel
1/2% BD
1% BD
2% BD
100% BD
Source: McCormick (2006)
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36
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et
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Pr
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se
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in
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Bu
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G
as
Bi
od
i
D
ie
Energy Content (kJ/Litre)
Energy Density of Fuels
45000
40000
35000
30000
25000
20000
15000
10000
5000
0
Fossil Energy Ratio
Source: McCormick (2006)
Do we have enough land for oil crops from which to
produce biodiesel?
6,000-36,000 lbs
oil/acre
4500
4000
3500
3000
2000
1500
1000
500
Crop
ae
A
lg
Pa
lm
0
So
yb
e
Su an
nf
lo
w
er
Pe
an
ut
C
an
ol
a
O
liv
e
C
as
to
r
Ja
tr
op
ha
C
oc
on
ut
lbs oil/acre
2500
Source: Wikipedia
Soybean Fatty Acid Composition
90
Percentage Content
80
70
60
50
40
30
20
10
0
Palmitic Acid Stearic Acid
(C16:0)
(C18:0)
Min-Graboski
Max-NSRL2000
Oleic Acid
(C18:1)
Linoleic Acid Linolenic Acid
(C18:2)
(C18:3)
Max-Graboski
High Oleic Acid
Min-NSRL2000
Graboski, M.S. and R.L. McCormick, 1998. Combustion of fat and vegetable oil derived fuels in diesel engines.
Prog. Energy Combust. Sci. 24:125-164
NSRL, 2000. Illinois variety trials (2000), Varietal Information Program for Soybeans, NSRL
Range of Fatty Acid Composition
100
Percentage in Oil or Fat
90
80
70
60
50
Soybean
Rapeseed
Beef Tallow
Peanut
Canola
Olive
Coconut
Corn
Palm
Safflower
Sunflower
Sunola
Butterfat
Lard
Cottonseed
Crambe
Linseed
H.O. Safflower
Sesame
40
30
20
Upper
Lower
Average
10
0
C8:0 C10:0 C12:0 C14:0 C16:0 C18:0 C20:0 C22:0 C24:0 C18:1 C22:1 C18:2 C18.3
Fatty Acids
Cetane Number and Fatty Acids
(Source: Graboski and McCormick, 1998)
90
80
Cetane Number
70
60
50
40
30
20
10
0
Palmitic
(C16:0)
Stearic
(C18:0)
Oleic
(C18:1)
Linoleic
(C18:2)
Linolenic
(C18:3)
Methyl Esters
CN increase with increasing saturation and with increasing chain length
How a Four-Stroke Engine Works
Comparison of Conventional Engines and HCCI/LTC
“Making gasoline engines run more like diesels and diesel engines more like gasoline”
Some Combustion Chemistry:
Lean vs Rich Mixtures
Diesel fuel molecule represented as C16H34
• Chemically correct air-fuel ratio assumes all fuel burnt
to CO2 and H2O
• C16H34 + 24.5O2 + 92N2 Î 92N2 + 16CO2 + 17H2O
•
1 kg
14.9 kg
3.1 kg
Chemically correct air to fuel ratio: 14.9: 1
Soybean biodiesel fuel molecule: C19H36O2
• 1 kg fuel and 12.5 kg air Î 2.8 kg CO2
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Chemically correct air to fuel ratio: 12.5: 1
Requires less air
than diesel
Note the
Oxygen in
the fuel
molecule
Air-Fuel Mixing in Diesel Engines
•
Impossible to obtain uniform mixing of air & fuel in diesel
engine
Single spray plume
from injector
Rich Spray
Core
Correct
A/F Ratio
Lean A/F
Mixture
Very Lean
In betweencombustible
A/F ratio
Very
Rich
How is energy released in diesel combustion?
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Premixed combustion
– Fuel that evaporates and mixes with
air during ignition delay burns
simultaneously, producing sharp
peak in energy release
•
Diffusion (mixing-controlled)
combustion
– Air and fuel vapor diffuse toward
each other to continue combustion
– Slower process than premixed phase
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Ignition delay controls proportions
of energy released in premixed &
diffusion combustion phases
IGNITION
DELAY
START
INJECTION
START
COMBUSTION
HDC
NOx/Soot Trade-Off and LTC Combustion
Fuel-Air Mixture
Leaner Richer
Increased
Soot Formation
LTC
Target
al
n
tio t
n
e oo
v
n /S ff
C o O x e- o
N ad
Tr
Increased
NOx Formation
Low
Combustion Temperature
LTC – Low Temperature Combustion
High
Nonroad EPA Emission Standards
0.6
Tier I (1996)
PM (g/kWh)
0.5
EPA Emission Standards: Nonroad Diesel Engines
130kW ≤ Power ≤ 560 kW
0.4
0.3
Tier 3 (2006)
0.2
Tier 2 (2001-2003)*
Tier 4 (2011-2014)**
0.1
0
0
2
*Dependent on power range
**PM full compliance by 2011
NOx 50% compliance 2011-2013
4
6
8
10
NOx (g/kWh)
Source: www.dieselnet.com
Nonroad EU Emission Standards
0.6
Stage I (1999)
PM (g/kWh)
0.5
Europe Emission Standards: Nonroad Diesel Engines
130kW ≤ Power ≤ 560 kW
0.4
0.3
Stage IIIA (2006)
0.2
Stage II (2002)
Stage IV (2014)
0.1
Stage IIIB (2011)
0
0
2
4
6
NOx (g/kWh)
8
10
Source: www.dieselnet.com
Impact of Biodiesel on Emissions
0.25
0.12
1.60
1.40
0.20
-17%
1.00
0.80
0.10
0.05
-11%
5.00
-41%
4.80
-38%
0.06
4.60
0.04
4.50
0.02
0.20
B20
D2
4.40
0.00
0.00
B100
3%
4.70
0.40
0.00
10%
4.90
0.08
0.60
-84%
NOx emission (g/hp-hr)
5.10
0.10
-15%
1.20
0.15
PM emission (g/hp-hr)
CO emission (g/hp-hr)
HC emission (g/hp-hr)
B100
B20
D2
4.30
B100
B20
D2
B100
B20
D2
Key regulated emissions for compression-ignition (diesel)
engines are particulate matter (PM) and Oxides of Nitrogen
(NOx)
• PM created from incomplete combustion
• NOx caused by high temperatures in combustion chamber
oxidizing nitrogen
•
(Sharp et al., 2000)
U.S. EPA Emissions Regulations
0.7
Tier 1
0.6
C16:0
C18:0
PM (g/kWh)
0.5
C18:1
C18:2
0.4
C18:3
0.3
Diesel
Tier 2
Soydiesel
Tier 1
0.2
Tier 3
Tier 4
0.1
Tier 2
Tier 3
Tier 4
0
0
2
4
6
8
NOx (g/kWh)
Saturated fatty acid esters produce lower emissions
(Data Source: Graboski and McCormick, 1998)
10
MechSE Optical Engine Facility
Quartz Piston
Side Window
3-D Imaging
Piston Extension
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Hydraulic System
•
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Implement high speed camera and laser
techniques
Analyze combustion products and
exhaust gases
Investigate effect of multiple injection
strategies for Low Temperature
Combustion (LTC)
Soot Diagnostics: Back Illumination Light Extinction
Fiber from
Copper vapor laser
Light
Diffuser
Band pass
Filter
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Narrow band pass filters (~ 5nm) to reduce combustion noise,
Frame rate: 12000 fps
Measurement area denoted by the black rectangle
Due to the curvature of two side-windows only part of soot is
measured
Single versus Split Injection
Single
Split
Effect of Split Injection
Up to 5 independent fuel injections per cycle are now achievable
at the prototype level from the major Fuel Injection Equipment
suppliers
SAE 940897
Effect of Split Injection (cont.)
SAE 940897
Flame Development Comparison: B0 and B100
B0: -20, 0
B100: -20, 0
-7.00
3.50
5.75
8.00
14.00
20.00
26.00
38.00
18.50
20.00
26.00
38.00
B100: - 30, 10
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Biodiesel fuel results in faster late
cycle burning of soot than European
low sulfur diesel fuel
Increasing gap between first injection and main injection helps reduce soot
emissions
(Lee et al. 2006)
Soot Images Comparison: B0 and B100
B0: -20, 0
Crank angles: 41, 47, 53, 65, 77, 89,
128 CAD ATDC
B100: -20, 0
Crank angles: 41, 47, 53, 65, 77, 89,
128 CAD ATDC
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Bio-diesel leads to weaker soot signal
than European low sulfur diesel fuel
(Lee et al. 2006)
Biofuel Combustion and Emissions Modeling
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KIVA combustion model modified for
biodiesel and LTC
– KIVA-3V: 3-D chemically reacting CFD model
developed by Los Alamos National Laboratory to
simulate work of internal combustion engines
– Sub-models for wall heat transfer, evaporation,
turbulence, spray breakup, ignition, combustion
and emissions formation
– Both biodiesel and biodiesel-diesel blend
combustion modeled
Biodiesel Property Measurement and
Computation for Combustion Modeling
Fatty Acid Profiles for Five Biodiesel Types
70
60
50
Percentage
Soybean
Rapeseed
40
Coconut
30
Palm
Beef Lard
20
10
•Measured properties of biodiesel
produced from source materials with a
broad range of fatty acid compositions
•Updated computational models for
estimating viscosity, surface tension,
density, thermal conductivity for engine
combustion modeling
0
C12:0
C14:0
C16:0
C18:0
C18:1
C18:2
C18:3
Fatty Acid
Kinematic
Viscosity of
Biodiesel
from five
different
source
materials
9
Kinematic Viscosity,mm^2/s
8
Soybean
Rapeseed
Coconut
Palm
Beef Lard
#2 Diesel
7
6
5
Max. limit ASTM D975 @ 40°C
4
3
2
1
0
20
30
40
50
60
70
Temperature, °C
80
90
100
BDProp
Program for
computing
biodiesel fuel
properties
KIVA Combustion Model results
Biodiesel
Diesel
Fuel injections at 330° and 370°
(Lee et al. 2008)
NOx Emissions from Biodiesel (Lee et al. 2008)
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Retarding main injection effectively reduces the emission
Biodiesel may or may not increase NOx emission
NOx Emissions from Biodiesel
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National Renewable Energy Lab reports no consistent effect
Lab tests tend to show increase
Chassis tests not conclusive
Emissions affected by test cycle and engine technology
Metal Engine Experiments
6.0
•
John Deere 4045HF475 4-cylinder
4.5L engine (Tier II)
Effect of Exhaust Gas Recirculation on
NOx emissions from biodiesel and
blends
1400 rpm, 500 Nm
5.0
BSNOX (g/kw-h)
•
4.0
3.0
2.0
D2
1.0
Particulate filter
0
5
10
B2
15
EGR (%)
Heat exchanger
EGR Valve
Low Pressure
EGR System
B20
20
B100
25
Graduate Automotive Technology Education
Center of Excellence
for
Advanced Automotive Bio-Fuel Combustion Engines
Mechanical Science
and Engineering
Agricultural and
Biological Engineering
Comprehensive GATE
syllabus (M.S./Ph.D)
DOE support
(GATE fellowships)
Industrial advisory
board
Highly skilled UIUC graduates who can lead
industrial application of bio-fuel engine technology
Final Comments
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Biodiesel fuel as an alternative to petroleumbased diesel fuel has many advantages
Fuel cost still plays a major role
Source material can affect biodiesel fuel
properties substantially
While CO, HC and PM emissions are
reduced, NOx emissions may increase in
some engines
Optical engine tests and combustion
modeling provide insight into combustion
and emissions processes
Biodiesel shows some advantages over diesel
fuel when Low Temperature Combustion
strategies are applied
……Thank you!
achansen@uiuc.edu