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2.61 Internal Combustion Engines
Spring 2008
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Bio-fuels and hybrids
Prof. Wai Cheng
Sloan Automotive Lab, MIT
1
The backdrop
2
Transportation and Mobility
• Transportation/mobility is a vital to
modern economy
– Transport of People
– Transport of goods and produce
• People get accustomed to the ability to
travel
3
Transportation needs special kind of energy source
• Vehicles need to carry source of energy on
board
• Hydrocarbons are unparalleled in terms of
energy density
– For example, look at refueling of gasoline
• ~40 Liters in 2 minutes (~0.25 Kg/sec)
– Corresponding energy flow
= 0.25 Kg/sec x 44 MJ/Kg
= 11 Mega Watts
Liquid hydrocarbons !
4
What is in a barrel of oil ?
(42 gallon oil → ~46 gallon products)
Typical US output
Lubricants
0.90%
Other Refined Products
1.50%
Asphalt and Road Oil
1.90%
Liquefied Refinery Gas
2.80%
Residual Fuel Oil
3.30%
Marketable Coke
5.00%
Still Gas
5.40%
Jet Fuel
12.60%
Distillate Fuel Oil
15.30%
Finished Motor Gasoline
51.40%
Source: California Energy Commission, Fuels Office
5
US Use of Petroleum by sector
Millions of Barrels/day
25
Electric utilities
Commercial
Residential
20
15
Industrial
10
Transportation
5
0
1970
1980
1990
2000
2010
Year
Source: US Dept. of Energy
6
Oil Supply (annual average up to 2007)
100
Million Barrels/day
90
80
70
60
Others
50
40
30
20
OPEC
10
US
0
1960
1970
1980
1990
2000
2010
Year
Hubbert peak
Source: EIA
7
The world Hubbert peak
(excluding OPEC & Russian production)
2003
Image removed due to copyright restrictions. Please see Fig. 9 in Zittel, Werner, and Jörg Schindler.
"Future World Oil Supply." Salzburg, Germany: International Summer School on the Politics and Economics of
Renewable Energy, July 2002.
Source: http://www.fossil.energy.gov/programs/reserves/npr/publications/npr_strategic_significancev1.pdf
8
Petroleum price
Decrease in demand, increase in
non-OPEC supply
120.00
100.00
Saudi increase
production
Constant 2004$
$/Barrel
$ of the day
80.00
6/6/08
@$118/Barrel
Iran/Iraq War
Iranian Revolution
Yom Kippur War
Arab Oil Embargo
60.00
40.00
2008 av. value
up to June;
Gulf
War
20.00
Iraq war
Demand of
emerging
market;
limited
refinery
capacity
0.00
1860
1880
1900
1920
1940
1960
1980
2000
9/11
Oil from North Sea, Alaska
Sources:
Data from EIA; event labels from WTRG Economics
9
CO2 emissions from fossil fuel
Million metric tons of Carbon/year
104
8000
7000
103
6000
Total
5000
Total
4000
3000
102
Liquid fuel
2000
Liquid fuel
10
1000
0
1750
1800
1850
1900
Year
1950
2000
1
1750
1800
1850
1900
1950
2000
Year
Source: EIA
10
The drive to bio-fuel
• Increasing demand of liquid fuel for transportation
– Population
– Society affluence
• Drive for lower CO2 production
• Perceived decline of petroleum reserve
• Fuel price
• Government Policy
– Tax credit
– Required bio-fuel content
11
What is bio-fuel?
12
Dominant biofuels
Sugar based
(corn, sugarcane, …)
Cellulosic based
(switchgrass, wood, …)
Crop based
(rapeseed, soybean, …)
Wasted oil/ animal fat
Usage
Ethanol
E10, E20, E85, …
Compatible with current engine
technology and fuel infra structure
Bio-diesel
B10, B20, ….
Algae
(BTL fuel not included in this discussion)13
Example: Ethanol production from corn
Ethanol fuel
Resources:
Energy
Materials
Ethanol + CO2
Labor
Sugar
Purification
(removal of water, …)
Fermentation
Starch
Corn
By-products
14
Example: bio-diesel production
Bio-diesel (esters)
Resources:
Energy
Materials
Labor
Purification
(removal of glycerol,
alkaline, fatty acid, …)
Esters and glycerol
Transesterification using alcohol
(methanol) with alkaline catalyst
Oil (tri-glyceride)
Mechanical or solvent (hexane)
extraction + water removal
Soy,
rapeseed, …
Tri-glyceride
Alkaline
Catalyst
(KOH)
Esters
Glycerol
CH2-OOC-R1
R-OOC-R1
|
CH-OOC-R2 +3ROH ↔ R-OOC-R2 +(CH2OH)2-CHOH
|
CH2-OOC-R3
R-OOC-R3
(typically 8-22 C to 2 O)
15
Combustion characteristics of bio-fuel
Diesel
Soybean oil methylester
Rapeseed oil methylester
Sunflower oil methylester
Frying oil ethylester
Cetane
number
s.g.
LHV
(MJ/kg)
LHV
(MJ/L)
B10 LHV
(MJ/L)
45-55
50.9
52.9
49
61
0.820
0.885
0.882
0.880
0.872
43.22
37.01
37.30
38.53
37.19
35.44
32.76
32.90
33.91
32.41
35.17
35.19
35.29
35.14
s.g.
LHV
(MJ/kg)
LHV
(MJ/L)
E10 LHV
(MJ/L)
34.32
21.12
33.00
Octane
number
Gasoline
Ethanol
95
107
0.780
0.785
44.00
26.90
B20 LHV LHV B10/ LHV B20/
(MJ/L)
Diesel Diesel (by
(by vol.)
vol.)
34.91
34.93
35.14
34.84
0.992
0.993
0.996
0.991
0.985
0.986
0.991
0.983
E85 LHV LHV E10/ LHV E85/
(MJ/L) Gasoline Gasoline
(by vol.) (by vol.)
23.10
0.962
0.673
Bio-ester data from Graboski and McCormick, Prog. Energy Comb. Sc., Vol. 24, 1998
16
Stoichiometric requirement for different fuels
18
(A/F)
stoiciometric
16
Gasoline
and diesel
Gasoline with 11% MTBE
O/C = 0
14
O/C ratios of bio-diesel
esters ~ 0.12
B100
12
Gasoline with 10% Ethanol
10
Ethanol
E85
O/C = 0.5
8
O/C = 1
6
Methanol
4
2
1
1.5
2
2.5
3
Fuel H to C ratio
3.5
4
17
Relative CO2 production from burning different fuel molecules
Image removed due to copyright restrictions. Please see Amann, Charles A. “The Passenger Car and The Greenhouse Effect.”
SAE Journal of Passenger Cars 99 (October 1990): 902099.
C. Amann, SAE Paper 9092099 18
Effects of Oxygenates on PM emission
100% Methanol
{
80
60
100% Dimethyl ether (DME),
100% Ethanol
Water/Diesel emulsion (15 to 20% water)
{
40
100% Rapeseed methyl ester (RME)
20
{
Soot reduction - %
100
0
0
Diglyme, methylal added to diesel fuel
(6 to 14% wt.)
10
20
30
40
50
Fuel oxygen content - %
Figure by MIT OpenCourseWare.
AVL Publication (by Wofgang Cartellieri in JSME 1998 Conference in Toykyo)
19
Bio-fuel combustion properties
• Bio-diesels and ethanol are fundamentally clean and
attractive fuels to be used in engines
• The use of these fuels as supplements to petroleum
base fuel are compatible with current engine
configuration and fuel infra-structure
• Practical issues can be adequately handled by
engineering
– Fuel quality
– Engine calibration
– Materials compatibility, viscosity, …
Burning the fuel is the least of the problem !!!
20
Status of bio-fuel production
21
World liquid fuel production (2005)
HYDROCARBONS
RENEWABLES
Image removed due to copyright restrictions. Please see p. 2 in Budny, Daniel. "The Global Dynamics of Biofuels."
Brazil Institute Special Report. Washington, DC: Woodrow Wilson International Center for Scholars, April 2007.
22
Millions of barrels per day oil equivalent
Liquid fuel supply projection
120
100
80
60
40
20
Source: ExxonMobil – JSAE meeting, Kyoto, July 23-26, 2007
0
1980
1990
2000
2010
2020
2030
23
US bio-fuel capacity
US biofuels
US harvested crop land (US agriculture census 2002), hectare 1.23E+08
US all distillate use (diesel+jet+power gen etc.) EIA2007; L/yr 3.34E+11
US gasoline use, EIA 2007; L/yr
5.40E+11
Limit of
Limit of Energy
production production ratio of
(gal)
(L)
limit to
gal/acre L/hectare
demand
bio-diesel
palm oil
coconut
rapeseed
soy
peanut
sunflower
jatropia (SE Asia)
algae (?)
5.08E+02 4,756
2.30E+02 2,153
1.02E+02
955
6.00E+01
562
9.00E+01
843
8.20E+01
768
2.00E+02 1,872
1.80E+03 16,850
1.54E+11
6.99E+10
3.10E+10
1.82E+10
2.73E+10
2.49E+10
6.08E+10
5.47E+11
5.85E+11
2.65E+11
1.17E+11
6.91E+10
1.04E+11
9.44E+10
2.30E+11
2.07E+12
1.63
0.74
0.33
0.19
0.29
0.27
0.64
5.78
ethanol
corn
sugar cane (Brazil)
3.44E+02
8.00E+02
1.04E+11 3.96E+11
2.43E+11 9.21E+11
0.71
1.71
3,217
7,489
Crop based bio-fuels do not have enough
capacity to meet the liquid fuel demand !!!
Yield dependent on location and weather
24
Algae: micro-seaweeds
Issues
• Production
– Need high lipid
content
species
– Need fast
growth species
– Growth in
dense
environment
• Harvest techniques
• Oil extraction
Courtesy of Robert Dibble. Used with permission.
25
Current largest algae plant
(production of algae for salmon feeding)
Hawaii
Courtesy of Robert Dibble. Used with permission.
26
Sustainability
27
Energy balance
Example: Corn ethanol in US
Ethanol from corn
• Several studies of the overall energy budget
– P = energy used in production
• feedstock production/ transport + processing
– E = Energy of the ethanol output
– Return (%) = (E – P) / E
• Studies
Verdict:
Substantial
environmental
and economic
cost; return not
clear
– Pimentel and Patzek (2003, 2005): negative return
• Return = - 29%
– USDA (Shapouri et al 2002, 2004): positive return
• Return* = +5.6%
• Return* = +40% if by products (Corn gluten meal, etc.)
are accounted for
* For comparison purpose, these figures were converted from the
values of (E-P)/P of +5.9% and +67% in the original publication
28
Other bio-fuels
•
•
•
Pimentel and Patzek also estimated energy budget for other biofuels. Returns:
– Ethanol from switchgrass = -50%
– Ethanol from wood biomass = -57%
– Bio-diesel from soybean = -27%
– Bio-diesel from sunflower = -118%
Other more positive estimates:
– Bio-diesel from rapeseed = +32% (EU)
– Bio-diesel production = +324% (US National Bio-diesel Board)
Outlook: NOT CLEAR
– New technology needed to change the picture
29
Technical difficulties of producing liquid fuel from plants
• Glucose fermentation produces significant CO2 out and energy loss
ΔHf per mol C6H12O6 → 2C2H5OH + 2CO2 + 219.2 KJ
of carbon
atom
-67.8 KJ
-117.3 KJ
- 393.5 KJ
• Cellulose much more difficult to break down than sugar
Glucose
Source: Wikipedia
Cellulose
30
Effect of government policy on bio-fuel
• Current US demand for ethanol is driven by
government regulations and incentives
– Ethanol flex-fuel vehicles produced because of the 74%
credit towards CAFE requirement
• (E85 vehicle equivalent mph = mpg x 1.74)
– Gasoline oxygenate mandate, and phase out of MTBE
– Energy bill (Aug. 05) mandated a threshold of 7.5 billion
gallons (180 million barrels) production by 2012
– Tax subsidy
• blender’s tax credit $0.51/gallon alcohol
• $0.051/gallon fuel tax exemption for gasohol
– minimum 10 vol % alcohol
31
Economic impact of crop-based bio-fuel
Example: Corn ethanol in US (~20% of total corn production in 2007)
Fresh whole milk retail price (up to May, 08)
4
3.8
Annual average or averaged
up to current month
$ per gallon
3.6
3.4
3.2
3
2.8
2008
2007
2006
2005
2004
2003
2002
2001
2000
1999
1998
1997
1996
2.2
2
1995
2.6
2.4
400
Spot price 5/12/08:
$ 2.50/gal
350
300
Cents per gal
U.S. All Grades Conventional Retail
Gasoline Prices (Cents per Gallon)
)
250
200
150
100
May 08 spot price: $2.50/gal
Retail price: $3.80/gal
50
Source: California Energy Commission, 2006
Jan 08
Jan 07
Jan 06
Jan 05
Jan 04
Jan 03
Jan 02
Jan 01
Jan 00
Jan 99
Jan 98
Jan 97
Jan 96
0
Jan 95
Millions of barrels
Annual fuel ethanol production
180
160
140
120
100
80
60
40
20
0
1992 1994 1996 1998 2000 2002 2004 2006 2008
32
Carbon intensity
(net mass of CO2 produced per unit fuel energy)
Source: http://en.wikipedia.org/wiki/Biodiesel
33
Carbon intensity
Source: http://en.wikipedia.org/wiki/Biodiesel
34
Other environmental impact
•
•
•
•
•
Water resources
Fertilizer
Soil
Bio-diversity
Plant waste treatment
35
Closure
• Bio-diesel and alcohols are excellent fuels for
transportation use
– Good combustion characteristics
– Compatible with current engine technology
• Sustainability
– Bio-fuels from crops are not likely to make any
significant impact on the global liquid fuel supply
picture
• Land capacity
• Effect on food price
– Further development on other feed stocks needed
• Algae for bio-diesel production
• Cellulosic alcohol
36
Closure (continue)
• Sustainability issues
– Energy budget
– Water use
– CO2 intensity especially with land use
replacement
– Bio-diversity
– Other issues
¾Bio-fuel plant waste treatment
¾Resources requirement
37
Hybrid vehicles
Configuration:
IC Engine + Generator + Battery + Electric Motor
Concept
• Eliminates external charging
• As “load leveler”
• Improved overall efficiency
• Regeneration ability
• Plug-in hybrids: use external electricity supply
38
Hybrid Vehicles
External charging for plug-in’s
Regeneration
Battery/ ultracapacitor
Parallel Hybrid
MOTOR
DRIVETRAIN
ENGINE
External charging for plug-in’s
Series Hybrid
ENGINE
GENERATOR
Battery/ ultracapacitor
MOTOR
DRIVETRAIN
External charging for plug-in’s
Power split
Hybrid
ENGINE
Regeneration
GENERATOR
Regeneration
Battery/ ultracapacitor
MOTOR
DRIVETRAIN
Examples: Parallel hybrid: Honda Insight
Series hybrid: GM E-Flex System
Power split hybrid: Toyota Prius
39
Hybrids and Plug-in hybrids
Hybrids (HEV)
• “Stored fuel centered”
– Full hybrid
– Mild hybrid /power assist
Plug-in hybrids (PHEV)
• “Stored electricity centered”
– Blended PHEV
– Urban capable PHEV
– AER/ E-REV
Images removed due to copyright restrictions. Please see Fig. 5 and 7 in Tate, E. D., Michael O. Harpster, and Peter J. Savagian.
"The Electrification of the Automobile: From Conventional Hybrid, to Plug-In Hybrids, to Extended-Range Electric Vehicles."
SAE International Journal of Passenger Cars - Electronic and Electrical Systems 1 (April 2008): 2008-01-0458.
40
Engine/ motor sizing
Images removed due to copyright restrictions. Please see Fig. 14 in
Komatsu, Masayuki, et al. "Study on the Potential Benefits of PlugIn Hybrid Systems." SAE International Journal of Passenger Cars Electronic and Electrical Systems 1 (April 2008): 2008-01-0456.
and
Fig. 8 in Tate, E. D., Michael O. Harpster, and Peter J. Savagian.
"The Electrification of the Automobile: From Conventional Hybrid,
to Plug-In Hybrids, to Extended-Range Electric Vehicles."
SAE International Journal of Passenger Cars - Electronic
and Electrical Systems 1 (April 2008): 2008-01-0458.
The optimal component
sizing and power
distribution strategy
depend on the required
performance, range,
and drive cycle
41
The reduced load/ speed dynamic range required from the engine offers
design opportunities
Image removed due to copyright restrictions. Please see Fig. 3 in Aoki, Kaoru, et al.
"Development of an Integrated Motor Assist Hybrid System: Development of the 'Insight', a Personal Hybrid Coupe."
SAE Journal of Engines 109 (June 2000): 2000-01-2216.
42
HEV TECHNOLOGY
Toyota Prius
• Engine: 1.5 L, Variable Valve Timing, Atkinson/Miller
Cycle (13.5 expansion ratio), Continuously Variable
Transmission
– 57 KW at 5000 rpm
• Motor - 50 KW
• Max system output – 82 KW
• Battery - Nickel-Metal Hydride, 288V; 21 KW
• Fuel efficiency:
– 66 mpg (Japanese cycle)
– 43 mpg (EPA city driving cycle)
– 41 mpg (EPA highway driving cycle)
• Efficiency improvement (in Japanese cycle) attributed to:
– 50% load distribution; 25% regeneration; 25% stop and go
• Cost: ~$20K
43
Efficiency improvement:
Toyota Hybrid System (THS)
Image removed due to copyright restrictions. Please see Fig. 2 in Inoue, Toshio, et al.
"Improvement of a Highly Efficient Hybrid Vehicle and Integrating Super Low Emissions."
SAE Journal of Fuels and Lubricants 109 (October 2000): 2000-01-2930.
44
Operating map in LA4 driving cycle
Toyota THS II
Data from SAE 2004-01-0164
Typical passenger car engine
8
BMEP (bar)
8
BMEP (bar)
6
4
6
4
2
2
0
0
0
500
1000
1500
2000
2500
3000
3500
Speed (rpm)
0
500
1000 1500 2000 2500 3000 3500
45
Cost factor
If
Δ$ is price premium for hybrid vehicle
P is price of gasoline (per gallon)
δ is fractional improvement in mpg
Then mileage (M) to be driven to break even is
Δ$ x mpg
M=
Pxδ
(assume that interest rate is zero)
46
Cost Factor
Example:
Honda Civic and Civic-Hybrid
Price premium (Δ$, MY08 listed)
mpg (city and highway av.)
hybrid improvement in mpg(%)
= $7155 ($22600-15445)
= 29 mpg (42 for hybrid)
= 45%
At gasoline price of $4.00 per gallon, mileage (M) driven
to break even is
$7155 x 29
= 115,000 miles
M=
$4 x 45%
(excluding interest cost)
47
Barrier to Hybrid Vehicles
• Cost factor
– difficult to justify especially for the small,
already fuel efficient vehicles
• Battery replacement (not included in the previous
breakeven analysis)
– California ZEV mandate, battery packs
must be warranted for 15 years or 150,000
miles : a technical challenge
48
Hybrid Vehicle Outlook
• Hybrid configuration will capture a fraction of the
passenger market, especially when there is significant
fuel price increase
• Competition
– Customers downsize their cars
– Small diesel vehicles
• Plug-in hybrids?
– Weight penalty (battery + motor + engine)
– No substantial advantage for overall CO2 emissions
– Limited battery life
49
400
4
300
3
200
2
100
1
0
0
% of new light duty vehicle sale
Sales (thousands)
Sales figure for hybrid vehicles
2009
2008
2007
2006
2005
2004
2003
2002
2001
2000
1999
50