Alternative Fuels for Transit Buses

Institute of Transportation StudiesUniversity of California, Davis

Marshall MillerUC Davis

June 3, 2008

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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

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Fuel Technologies

•Battery electric

•Stoichiometric Natural Gas

•Diesel

•Gasoline Hybrid

•Hydrogen Enriched Natural Gas

•Fuel Cells (hydrogen)

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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

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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

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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.

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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

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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

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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%

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Why 30% Hydrogen?

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NOX Emissions

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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 )

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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

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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

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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

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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?

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Thank You