Alternative Fuels for Transit Buses Institute of Transportation Studies University of California,...
-
Upload
francis-whitebread -
Category
Documents
-
view
213 -
download
0
Transcript of Alternative Fuels for Transit Buses Institute of Transportation Studies University of California,...
Alternative Fuels for Transit Buses
Institute of Transportation StudiesUniversity of California, Davis
Marshall MillerUC Davis
June 3, 2008
2
CARB Transit Bus Emissions Standards• Original CARB regulations required very
strict NOX reduction
2003 4.0 g/bhph
2004-2006 2.4 g/bhph (NOX + HC)
2007 0.2 g/bhph
• Later CARB modified regulations to be equivalent to US EPA
2007 –20091.2 g/bhph
2010 0.2 g/bhph
3
Fuel Technologies
•Battery electric
•Stoichiometric Natural Gas
•Diesel
•Gasoline Hybrid
•Hydrogen Enriched Natural Gas
•Fuel Cells (hydrogen)
4
Battery Electric• Niche Markets
Small buses + daily mileage < ~ 100 miles
• Lower energy storage
No emissions (Zero Emission Bus), Meet CARB 2010 standard
• Problems Low range
Long charge times
• New Battery Technologies (Lithium Ion) Significant range ( > 200 miles)
• > 7000 lbs
• > $100,000 - $200,000 (might be optimistic)
• Charge times still very high or MW chargers
5
Stoichiometric CNG• Cummins Westport ISL G engine
Only engine certified to CARB 2010 standard for NOX
Stoichiometric operation with 3 way catalyst
Concerns about high heat production causing maintenance issues
6
Diesel•No current engine certified to CARB
2010 NOX standard
•Selective Catalytic Reduction (SCR) using urea
•Concerns Contaminants (O2 or sulfur) in exhaust
stream may reduce effectiveness Temperature control of exhaust is critical On board urea storage (space) Urea not required for proper vehicle
operation, but necessary for NOX reduction.
7
Gasoline Hybrid• ISE Corporation
Certified at 0.4 g/bhph NOX Hybrid driveline increases fuel economy ~ 20-
25% (roughly equivalent with diesel on energy basis)
Ford V10 engine New engine (3 value V10) and better controls
expected to meet 2010 standard (0.2 g/bhph)
• Diesel Hybrid Results vary considerably 25-50% increase in fuel economy
~ 40% NOX reduction
8
Hydrogen / Natural Gas Blends
• Blends with < 20% hydrogen called hythane®
• Blends with > 20% hydrogen are called HCNG
• Hythane® NOX reductions are limited but physical changes to bus engine are not required
• HCNG must be used to reduce engine out emissions to meet the CARB 2010 standard but requires engine modifications
9
Hydrogen / Natural Gas Buses• Issues
Range reduction (hydrogen less energy per volume than natural gas)
Tradeoffs between emissions, power, efficiency
• Hythane® (20% hydrogen by volume) NOX emissions reductions up to 50% Range reduction ~ 10-15%
• HCNG (30% hydrogen by volume) NOX emissions reductions up to 95% (meets
CARB 2010 standards Range reduction ~ 15-20%
10
Why 30% Hydrogen?
0 .0
0 .4
0 .8
1 .2
1 .6
2 .0
Bra
ke S
peci
fic
NO
x (
g/kW
h)N a tu ra l G as 20 % H yd rog en30 % H yd rog en
L ea n L im it
N a tu ra l G a s2 0 % H y d ro g en3 0 % H y d ro g en
0 .7 5 0 .7 0 0 .6 5 0 .6 0 0 .5 5 0 .5 0 0 .4 5 0 .4 0E q u iv a len ce R a t io
11
NOX Emissions
3 0 0 4 0 0 5 0 0 6 0 0 7 0 0 8 0 0 9 0 0T o rq u e (f t/lb s)
0
0 .0 5
0 .1
0 .1 5
0 .2
Oxi
des
of N
itrog
en (
NO
x) g
/hp-
hr
U n trea ted R a w E m iss io n s3 0 % H 2 E n rich e d N a tu ra l G a s
W O T
8 0 0 R P M9 0 0 R P M1 0 0 0 R P M1 2 0 0 R P M1 3 5 0 R P M1 4 0 0 R P M1 6 0 0 R P M1 8 0 0 R P M2 0 0 0 R P M2 2 0 0 R P M
1 1 lite r C ity E n g in eO x id e s o f N itro g e n v s T o rq u e (f t/lb s )
12
Hydrogen / Natural Gas Blend Buses (Transition Strategy)
• Present transit: Diesel fleets with CNG fleets growing
• Present Problems: emissions, global warming gases, imported fuel dependence
• Future Solution: Hydrogen fuel cell buses
• Problems
2 new technologies: Fuel cells and Hydrogen Infrastructure
high cost, fuel cell lifetime questions
13
Hydrogen / Natural Gas Blend Buses (Transition Strategy)
• How do we get from the present to Hydrogen fuel cell buses?
• Hydrogen / Natural Gas Blend fleets
significantly reduce emissions
• Hydrogen infrastructure
Transit agencies can prepare for introduction of fuel cell buses when they are both affordable and available
14
Fuel Cell (hydrogen)• Future of Transit Buses?
• Benefits Zero emission Bus (Zero greenhouse gas emissions if
hydrogen produced renewably) Hydrogen can be produced from many feedstocks (natural
gas, coal, electrolysis, biomass) and produced locally Future hydrogen cost ~ $2.50 - $4.00/ gallon gasoline
equivalent Very efficient, quiet Central fueling (less infrastructure than light duty
vehicles)
• Problems Cost Fuel cell lifetime Less interest than light duty vehicles
15
Summary•Strict CARB regulations difficult to
meet
•Many potential fuel technologies could play role
•Fuel cells (as with light duty vehicles) considered future of bus technology
•What fuel path(s) will ultimately be taken?
•What is timescale for various technologies?
16
Thank You