Environmental Benefits of Alternative Fuels and Advanced Technology in Public Transit

1

Environmental Benefits of Alternative Fuels and Advanced

Technology in Public Transit

Environmental Benefits of Alternative Fuels and Advanced

Technology in Public Transit

Jairo A. Sandoval and W. Scott Wayne, PhDCenter for Alternative Fuels, Engines & EmissionsDept. of Mechanical & Aerospace EngineeringWest Virginia University, Morgantown, WV

American Public Transportation Association2007 Bus Technical, Maintenanceand Procurement WorkshopNew Orleans, LAOctober 29, 2007

FTA REPORT No. 26-7003-07.2

2

This report evaluates potential environmental effects that could be affected through increased use of alternative fuels and advanced powertrain technologies in the U.S. transit bus industry.

Background

3

ObjectivesMethodologyEmissions From the Baseline U.S. Fleet Emissions Impacts of the “natural course” of Transit Bus ProcurementsImplications of Greater Use of Alternative Fuels and TechnologiesGreenhouse Gas EmissionsObservations and ConclusionsRecommendations for further study

Presentation Overview

4

Predict the emissions of the existing (2003) U.S. transit bus fleet as a baseline

Predict the emissions reductions from current bus procurements through 2009

Evaluate emissions reductions from implementation of alternative fuels and/or advanced technologies

Objectives

5

Technologies Considered

2007 and newer “clean-diesel” technology with ultra-low sulfur diesel fuel

Stoichiometric compressed natural gas (CNG)

Diesel-electric hybrid drive buses

Gasoline-electric hybrid drive buses

B20 biodiesel fuel (80% diesel, 20% biodiesel)

Objectives (cont.)

6

Carbon monoxide (CO),

Nitrogen oxides (NOx),

Non-methane hydrocarbons (NMHC),

Methane (CH4),

Total particulate matter (PM)

Carbon dioxide (CO2)

Fuel consumption

Emissions Evaluated

7

MethodologyAnalysis uses an atmospheric emissions inventory approach using existing chassis dynamometer test data.

Existing data uses a range of different test cycles which presents a difficulty in comparing test results

An approach was adopted to normalize data to the Orange County Bus Cycle.

Total MassEmissions

= ∑ *MilesTraveled

Test emissions[g/mile]

8

Methodology (cont.)

Not Considered in this AnalysisAnalysis does not include cutaways, and light-duty vans

Electrified Trolleybuses

Idle operation at bus garage and at waypoints

Deadheading between bus garage and start of route

Heating Ventilation and Air Conditioning Loads

Bus Lighting and Other Auxiliary (hotel) Loads

Life Cycle of Biodiesel fuel

9

Baseline (2003) Transit Bus Fleet

265

49,938

6,606

1,003 672 4890

10,000

20,000

30,000

40,000

50,000

60,000

Diesel Fuel/Jet A

Compressed Natural Gas

Liquefied Natural Gas

Trolleys (electric

catenary)

Diesel-Electric

Hybrid

Propane (liquefied petro

leum gas)

Fuel/Power System Technology

Nu

mb

er

of

Ac

tiv

e B

us

es

80

57

3928

5 3 3

0

20

40

60

80

100

Biodies

el

CNG-Dies

el Pilo

t Inje

...

CNG-Elec

tric H

ybrid

Gasoli

ne

CNG & G

asoli

ne

Propa

ne-E

lectri

c Hyb

rid

Hydro

gen

Diesel + CNG + LNG + Diesel-Electric Hybrid = 99.2%

Trolleybuses were excluded from the analysis

Distribution by fuel/powertrain type in 2003

10

4,31

7

5,34

5

10,6

85

20,0

66

6,00

1

4 8 217 1,48

3 4,91

4

983

0 0 0 0 32 457

3,52

4

0

5,000

10,000

15,000

20,000

25,000

Pre-1

988

1988

-199

0

1991

-199

3

1994

-199

7

1998

-200

2

2003

-200

5

Vehicle Model Year

Act

ive

Bu

ses

Diesel

CNG + LNG

Diesel-Electric Hybrid

Distribution by Model Year

Model year bins according to applicable EPA emissions regulation

11

Total annual VMT: 2,420.8 million miles

Number of Buses

COtons

NMHCtons

CH4

tons

NOx

tonsPMtons

CO2

tonsFuel Consumed (a)

thousands of gallons

Total Emissions

Diesel 49,938 15,886 2,611 65,669 1,494 6,497,649 589,135

CNG/LNG 7,609 1,194 308 5,879 6,318 7 796,630 100,393

Diesel Hybrid 489 5 0.6 220 0.5 35,865 3,361

Total 58,036 17,085 2,920 5,879 72,207 1,502 7,330,143 692,889

Average Emissions Levels per Bus

COg/mile

NMHCg/mile

CH4

g/mile

NOx

g/milePM

g/mileCO2

g/mileFuel Economy

mile/gal

Diesel 6.98 1.15 28.84 0.66 2,853 3.51

CNG/LNG 3.44 0.89 16.94 18.21 0.02 2,296 3.14

Diesel Hybrid 0.22 0.03 9.87 0.02 1,608 6.02

(a) Fuel consumed is expressed in Diesel-equivalent gallons

Emissions from Baseline Fleet (2003)

12

In progress and planned procurements were determined from the 2005 APTA Transit Vehicle Database

The majority of new buses purchase will be used to replace aging buses

6.5% growth in the national bus fleet by year 2009

4% increase in vehicle miles traveled by 2009

2007-2009 emissions levels were estimated:

Diesel + Hybrids → 2004/2007 EPA certification limits ratio

CNG → European stoichiometric buses (VTT)

Impacts of “Natural” Procurements

13

0

4,5

39

10,6

85

20,0

66

10,7

31

3,9

82

4 8 217 1,4

83 4

,914

2,2

04

1,2

34

0 0 32 744

749

0

0

5,000

10,000

15,000

20,000

25,000

Vehicle Model Year

Acti

ve B

uses

Diesel

CNG + LNG

Diesel-Electric Hybrid4,

317

5,34

5

10,6

85

20,0

66

6,00

1

4 8 217 1,48

3 4,91

4

983

0 0 0 0 32 457

3,52

4

0

5,000

10,000

15,000

20,000

25,000

Pre-1

988

1988

-199

0

1991

-199

3

1994

-199

7

1998

-200

2

2003

-200

5

Vehicle Model Year

Act

ive

Bu

ses

Diesel

CNG + LNG

Diesel-Electric Hybrid

2009

2003

Distributions by vehicle model year:Replaced All Pre-1990 diesel buses

Power Source2004-2006

2007-2009

Total

Diesel 4,730 3,982 8,712

CNG 1,159 1,164 2,323

LNG 62 70 132

Diesel Hybrid 287 749 1,036

Gasoline-Electric Hybrid

85 46 131

Biodiesel 32 27 59

Hydrogen 25 4 29

Propane (LPG) 19 4 23

Gasoline 5 1 6

Total 6,404 6,047 12,451

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Number of Buses

COtons

NMHCtons

CH4

tons

NOx

tonsPMtons

CO2

tonsFuel Consumed


Total Annual Emissions

Diesel 50,003 9,577 1,667 53,981 843 6,289,918 573,989

CNG/LNG 10,064 1,331 364 6,902 7,229 9 1,003,149 125,818

Diesel Hybrid 1,525 12 2 489 1 107,814 9,805

Total 61,592 10,920 2,032 6,902 61,699 853 7,400,881 709,612

Relative Change 6% 36% 30% 17% 15% 43% 1% 2%


COg/mile

NMHCg/mile

CH4

g/mile

NOx

g/milePM

g/mileCO2

g/mileFuel Economy

mile/gal

Diesel 4.31 0.75 24.32 0.38 2,833 3.51

CNG/LNG 2.98 0.81 15.45 16.18 0.02 2,245 3.22

Diesel Hybrid 0.18 0.03 7.22 0.02 1,592 6.26

2003 - Average Emissions Levels per Bus

COg/mile

NMHCg/mile

CH4

g/mile

NOx

g/milePM

g/mileCO2

g/mileFuel Economy

mile/gal

Diesel 6.98 1.15 28.84 0.66 2,853 3.51

CNG/LNG 3.44 0.89 16.94 18.21 0.02 2,296 3.14

Diesel Hybrid 0.22 0.03 9.87 0.02 1,608 6.02

Estimated Emissions of 2009 Fleet

Reductions in CO and NMHC due largely to advent of diesel particulate filters. Lower CO emissions from stoichiometric CNG buses offset the increase in number of CNG buses

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Number of Buses

COtons

NMHCtons

CH4

tons

NOx

tonsPMtons

CO2

tonsFuel Consumed



Diesel 50,003 9,577 1,667 53,981 843 6,289,918 573,989

CNG/LNG 10,064 1,331 364 6,902 7,229 9 1,003,149 125,818

Diesel Hybrid 1,525 12 2 489 1 107,814 9,805

Total 61,592 10,920 2,032 6,902 61,699 853 7,400,881 709,612

Relative Change 6% 36% 30% 17% 15% 43% 1% 2%


COg/mile

NMHCg/mile

CH4

g/mile

NOx

g/milePM

g/mileCO2

g/mileFuel Economy

mile/gal

Diesel 4.31 0.75 24.32 0.38 2,833 3.51

CNG/LNG 2.98 0.81 15.45 16.18 0.02 2,245 3.22

Diesel Hybrid 0.18 0.03 7.22 0.02 1,592 6.26


COg/mile

NMHCg/mile

CH4

g/mile

NOx

g/milePM

g/mileCO2

g/mileFuel Economy

mile/gal

Diesel 6.98 1.15 28.84 0.66 2,853 3.51

CNG/LNG 3.44 0.89 16.94 18.21 0.02 2,296 3.14

Diesel Hybrid 0.22 0.03 9.87 0.02 1,608 6.02


Particulate Filters “mandated” on all 2007 and newer diesel buses + increase in inherently low PM emitting CNG buses

NOx reductions largely attributable to reduction in NOx limit from 2.5 g/bhpr to

1.2 g/bhphr in 2007

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Number of Buses

COtons

NMHCtons

CH4

tons

NOx

tonsPMtons

CO2

tonsFuel Consumed



Diesel 50,003 9,577 1,667 53,981 843 6,289,918 573,989

CNG/LNG 10,064 1,331 364 6,902 7,229 9 1,003,149 125,818

Diesel Hybrid 1,525 12 2 489 1 107,814 9,805

Total 61,592 10,920 2,032 6,902 61,699 853 7,400,881 709,612

Relative Change 6% 36% 30% 17% 15% 43% 1% 2%


COg/mile

NMHCg/mile

CH4

g/mile

NOx

g/milePM

g/mileCO2

g/mileFuel Economy

mile/gal

Diesel 4.31 0.75 24.32 0.38 2,833 3.51

CNG/LNG 2.98 0.81 15.45 16.18 0.02 2,245 3.22

Diesel Hybrid 0.18 0.03 7.22 0.02 1,592 6.26


COg/mile

NMHCg/mile

CH4

g/mile

NOx

g/milePM

g/mileCO2

g/mileFuel Economy

mile/gal

Diesel 6.98 1.15 28.84 0.66 2,853 3.51

CNG/LNG 3.44 0.89 16.94 18.21 0.02 2,296 3.14

Diesel Hybrid 0.22 0.03 9.87 0.02 1,608 6.02


Very modest increase in CO2 and fuel consumption despite increase in number of buses and miles traveled … largely offset by increase in hybrid buses

Methane emissions increase due to higher number of CNG buses

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Number of Buses

COtons

NMHCtons

CH4

tons

NOx

tonsPMtons

CO2

tonsFuel Consumed



Diesel 50,003 9,577 1,667 53,981 843 6,289,918 573,989

CNG/LNG 10,064 1,331 364 6,902 7,229 9 1,003,149 125,818

Diesel Hybrid 1,525 12 2 489 1 107,814 9,805

Total 61,592 10,920 2,032 6,902 61,699 853 7,400,881 709,612

Relative Change 6% 36% 30% 17% 15% 43% 1% 2%


COg/mile

NMHCg/mile

CH4

g/mile

NOx

g/milePM

g/mileCO2

g/mileFuel Economy

mile/gal

Diesel 4.31 0.75 24.32 0.38 2,833 3.51

CNG/LNG 2.98 0.81 15.45 16.18 0.02 2,245 3.22

Diesel Hybrid 0.18 0.03 7.22 0.02 1,592 6.26


COg/mile

NMHCg/mile

CH4

g/mile

NOx

g/milePM

g/mileCO2

g/mileFuel Economy

mile/gal

Diesel 6.98 1.15 28.84 0.66 2,853 3.51

CNG/LNG 3.44 0.89 16.94 18.21 0.02 2,296 3.14

Diesel Hybrid 0.22 0.03 9.87 0.02 1,608 6.02


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Greater Use of Alternative Fuels & Technology

Consider the national emissions impact of replacement of 15% of the existing fleet with each of the following new technologies:

Clean-diesel,

CNG,

Diesel-electric hybrid,

Gasoline-electric hybrid and

Biodiesel powered buses

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COtons

NMHCtons

CH4

tons

NOx

tonsPMtons

CO2



Clean Diesel 1,723 377 - 3,291 201 35,251 2,664

CNG 689 341 422 4,239 205 220,758 2,154

Diesel Hybrid 1,776 366 - 4,418 202 491,352 50,658

Gasoline Hybrid 6,178 211 - 5,963 199 74,114 2,833

Biodiesel (B20) (a) 384 166 - 369 38 25,087 3,876

Percent Incremental Change

Clean Diesel 16% 19% - 5% 24% 0% 0%

CNG 6% 17% 6% 7% 24% 3% 0%

Diesel Hybrid 16% 18% - 7% 24% 7% 7%

Gasoline Hybrid 57% 10% - 10% 23% 1% 0%

Biodiesel (B20) (b) 4% 8% - 1% 4% 0% 1%

(a) Fuel consumed is expressed in Diesel-equivalent gallons(b) Implemented in the older diesel buses of the fleet

Greater Use of Alternative Fuels & TechnologyReductions are in addition to those shown in the previous table

Conventional & hybrid diesel buses have similar reductions in CO, NMHC and PM emissions because they benefit from the same engine advancements. Diesel hybrid buses gain an advantage in NOx emissions over conventional diesels.

Conventional & hybrid diesel buses have similar reductions in CO, NMHC and PM emissions because they benefit from the same engine advancements. Diesel hybrid buses gain an advantage in NOx emissions over conventional diesels.

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COtons

NMHCtons

CH4

tons

NOx

tonsPMtons

CO2



Clean Diesel 1,723 377 - 3,291 201 35,251 2,664

CNG 689 341 422 4,239 205 220,758 2,154

Diesel Hybrid 1,776 366 - 4,418 202 491,352 50,658

Gasoline Hybrid 6,178 211 - 5,963 199 74,114 2,833

Biodiesel (B20) (a) 384 166 - 369 38 25,087 3,876


Clean Diesel 16% 19% - 5% 24% 0% 0%

CNG 6% 17% 6% 7% 24% 3% 0%

Diesel Hybrid 16% 18% - 7% 24% 7% 7%

Gasoline Hybrid 57% 10% - 10% 23% 1% 0%

Biodiesel (B20) (b) 4% 8% - 1% 4% 0% 1%



Conventional diesel, stoichiometric CNG, diesel hybrid and gasoline hybrid offer near identical reductions in particulate emissions.

Conventional diesel, stoichiometric CNG, diesel hybrid and gasoline hybrid offer near identical reductions in particulate emissions.

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COtons

NMHCtons

CH4

tons

NOx

tonsPMtons

CO2



Clean Diesel 1,723 377 - 3,291 201 35,251 2,664

CNG 689 341 422 4,239 205 220,758 2,154

Diesel Hybrid 1,776 366 - 4,418 202 491,352 50,658

Gasoline Hybrid 6,178 211 - 5,963 199 74,114 2,833

Biodiesel (B20) (a) 384 166 - 369 38 25,087 3,876


Clean Diesel 16% 19% - 5% 24% 0% 0%

CNG 6% 17% 6% 7% 24% 3% 0%

Diesel Hybrid 16% 18% - 7% 24% 7% 7%

Gasoline Hybrid 57% 10% - 10% 23% 1% 0%

Biodiesel (B20) (b) 4% 8% - 1% 4% 0% 1%



Gasoline hybrids offer the largest overall NOx reductionsGasoline hybrids offer the largest overall NOx reductions

22

COtons

NMHCtons

CH4

tons

NOx

tonsPMtons

CO2



Clean Diesel 1,723 377 - 3,291 201 35,251 2,664

CNG 689 341 422 4,239 205 220,758 2,154

Diesel Hybrid 1,776 366 - 4,418 202 491,352 50,658

Gasoline Hybrid 6,178 211 - 5,963 199 74,114 2,833

Biodiesel (B20) (a) 384 166 - 369 38 25,087 3,876


Clean Diesel 16% 19% - 5% 24% 0% 0%

CNG 6% 17% 6% 7% 24% 3% 0%

Diesel Hybrid 16% 18% - 7% 24% 7% 7%

Gasoline Hybrid 57% 10% - 10% 23% 1% 0%

Biodiesel (B20) (b) 4% 8% - 1% 4% 0% 1%



B20 used in older model buses without DPFs results in slight increase in NOx emissions and modest decrease in PM emissions. B20 also results in a modest increase in gallons of fuel consumed due to lower energy content; however biodiesel displaces use of imported petroleum.

B20 used in older model buses without DPFs results in slight increase in NOx emissions and modest decrease in PM emissions. B20 also results in a modest increase in gallons of fuel consumed due to lower energy content; however biodiesel displaces use of imported petroleum.

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COtons

NMHCtons

CH4

tons

NOx

tonsPMtons

CO2



Clean Diesel 1,723 377 - 3,291 201 35,251 2,664

CNG 689 341 422 4,239 205 220,758 2,154

Diesel Hybrid 1,776 366 - 4,418 202 491,352 50,658

Gasoline Hybrid 6,178 211 - 5,963 199 74,114 2,833

Biodiesel (B20) (a) 384 166 - 369 38 25,087 3,876


Clean Diesel 16% 19% - 5% 24% 0% 0%

CNG 6% 17% 6% 7% 24% 3% 0%

Diesel Hybrid 16% 18% - 7% 24% 7% 7%

Gasoline Hybrid 57% 10% - 10% 23% 1% 0%

Biodiesel (B20) (b) 4% 8% - 1% 4% 0% 1%



Diesel-hybrid buses appear to offer the greatest overall environmental advantage.Diesel-hybrid buses appear to offer the greatest overall environmental advantage.

24

6.876.78

6.40

6.656.886.856.76

0

1

2

3

4

5

6

7

8

2003 Bus Fleet

2009 Bus Fleet

Clean DieselCNG

Diesel Hybrid

Gasoline Hybrid

Biodiesel

Te

rag

ram

s (

Tg

) C

O2 E

qu

iva

len

t G

WP

CH4

CO2

(a) B20 Implemented in the older diesel buses of the fleet Tailpipe only

Global Warming Potential

If B100 in all the fleet:Life cycle Life cycle emissionsemissions↓ ~ 40%

25

Observations & ConclusionsReplacement of older model diesel buses with lower emitting buses equipped with advanced NOx control technologies and catalyzed diesel particulate filters brings about substantial emissions reductions

NOx reductions from CNG are slightly better than predicted for clean-diesel buses

Compared to clean-diesel buses, CNG buses offer superior reductions in CO2 emissions, less advantage in terms of CO emissions and produce methane emissions

Diesel hybrid buses yield the largest reductions in CO2 emissions and are the only technology to show a reduction in fuel consumption

Gasoline-electric hybrid buses offer the highest NOx emissions reductions due to the vanishingly low NOx levels of gasoline engines with 3-way catalysts

26

Comments of Biodiesel ImplementationThe results indicate that the maximum benefit of B20 biodiesel usage would be achieved by converting the oldest buses in the fleet to biodiesel rather than newer buses

There is a broad consensus that biodiesel and biodiesel blends produce significant reductions in PM emissions and increase in NOx emissions for engines up to about 1997 model year

For newer engines there are very little data available but ongoing research exists

Data indicate that biodiesel increases the reactivity of PM in a diesel particulate filter thereby improving regeneration of DOCs and diesel particulate filters (DPFs)

Production and use of soybean based biodiesel (B100) releases 59% of the net greenhouse gas emissions of an energetically equivalent amount of petroleum diesel

27

Update the analysis with latest APTA data

Repeat and extend the analysis to include actual 2007 compliant bus emissions data + Estimated 2010 compliant buses

Further emissions testing needs to be conducted to better quantify and understand the impact of biodiesel fuels on emissions of both legacy and new technology diesel engines and vehicles

The emissions and fuel economy of hybrid transit buses is highly affected by driving conditions (i.e. route duty cycles) and power train configuration. Further study is needed to better understand and quantify these effects in order to enable that hybrid buses are utilized in applications which maximize their benefits

Recommendations

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Include transit operation information (e.g. duty-cycles)

Account for idle and auxiliary loads

Consider Variability and Uncertainty (Monte Carlo Simulations)

Future work – Bus inventory modeling

29

U.S. Department of Transportation, Federal Transit Administration, “Environmental Benefits of Alternative Fuels and Advanced Technology in Transit.” FTA-WV-26-7003-07.2, Washington, DC, 2007.

Wayne, W.S., Sandoval, J.A., and N.N. Clark, “Emissions benefits from alternative fuels and advanced technology in U.S. transit bus fleet.” Energy & Environment, 2009, 20(4), 497-515.

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