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Environmental Benefits of Alternative Fuels and Advanced Technology in Public Transit
 

Environmental Benefits of Alternative Fuels and Advanced Technology in Public Transit

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Presentation given at APTA’s 2007 Bus Technical, Maintenance and Procurement Workshop

Presentation given at APTA’s 2007 Bus Technical, Maintenance and Procurement Workshop

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    Environmental Benefits of Alternative Fuels and Advanced Technology in Public Transit Environmental Benefits of Alternative Fuels and Advanced Technology in Public Transit Presentation Transcript

    • Environmental Benefits of Alternative Fuels and Advanced Technology in Public Transit Jairo A. Sandoval and W. Scott Wayne, PhD Center for Alternative Fuels, Engines & Emissions Dept. of Mechanical & Aerospace Engineering West Virginia University, Morgantown, WV American Public Transportation Association 2007 Bus Technical, Maintenance and Procurement Workshop New Orleans, LA October 29, 2007 FTA REPORT No. 26-7003-07.2
      • 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
      • Objectives
      • Methodology
      • Emissions From the Baseline U.S. Fleet
      • Emissions Impacts of the “ natural course ” of Transit Bus Procurements
      • Implications of Greater Use of Alternative Fuels and Technologies
      • Greenhouse Gas Emissions
      • Observations and Conclusions
      • Recommendations for further study
      Presentation Overview
      • 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
      • 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.)
      • Carbon monoxide (CO),
      • Nitrogen oxides (NO x ),
      • Non-methane hydrocarbons (NMHC),
      • Methane (CH 4 ),
      • Total particulate matter (PM)
      • Carbon dioxide (CO 2 )
      • Fuel consumption
      Emissions Evaluated
    • Methodology
      • Analysis 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 Mass Emissions = ∑ * Miles Traveled Test emissions [g/mile]
    • Methodology (cont.)
      • Not Considered in this Analysis
        • Analysis 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
    • Baseline (2003) Transit Bus Fleet
      • Diesel + CNG + LNG + Diesel-Electric Hybrid = 99.2%
      • Trolleybuses were excluded from the analysis
      Distribution by fuel/powertrain type in 2003
    • Distribution by Model Year Model year bins according to applicable EPA emissions regulation
    • Emissions from Baseline Fleet (2003) Total annual VMT: 2,420.8 million miles (a) Fuel consumed is expressed in Diesel-equivalent gallons Number of Buses CO tons NMHC tons CH 4 tons NO x tons PM tons CO 2 tons Fuel 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 CO g/mile NMHC g/mile CH 4 g/mile NO x g/mile PM g/mile CO 2 g/mile Fuel 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
      • 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
    • Distributions by vehicle model year: 2009 2003 Replaced All Pre-1990 diesel buses Power Source 2004-2006 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
    • Estimated Emissions of 2009 Fleet Number of Buses CO tons NMHC tons CH 4 tons NO x tons PM tons CO 2 tons Fuel Consumed thousands of gallons 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% Average Emissions Levels per Bus CO g/mile NMHC g/mile CH 4 g/mile NO x g/mile PM g/mile CO 2 g/mile Fuel 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 CO g/mile NMHC g/mile CH 4 g/mile NO x g/mile PM g/mile CO 2 g/mile Fuel 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 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
    • Estimated Emissions of 2009 Fleet Number of Buses CO tons NMHC tons CH 4 tons NO x tons PM tons CO 2 tons Fuel Consumed thousands of gallons 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% Average Emissions Levels per Bus CO g/mile NMHC g/mile CH 4 g/mile NO x g/mile PM g/mile CO 2 g/mile Fuel 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 CO g/mile NMHC g/mile CH 4 g/mile NO x g/mile PM g/mile CO 2 g/mile Fuel 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 NO x reductions largely attributable to reduction in NO x limit from 2.5 g/bhpr to 1.2 g/bhphr in 2007
    • Estimated Emissions of 2009 Fleet Number of Buses CO tons NMHC tons CH 4 tons NO x tons PM tons CO 2 tons Fuel Consumed thousands of gallons 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% Average Emissions Levels per Bus CO g/mile NMHC g/mile CH 4 g/mile NO x g/mile PM g/mile CO 2 g/mile Fuel 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 CO g/mile NMHC g/mile CH 4 g/mile NO x g/mile PM g/mile CO 2 g/mile Fuel 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 CO 2 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
    • Estimated Emissions of 2009 Fleet Number of Buses CO tons NMHC tons CH 4 tons NO x tons PM tons CO 2 tons Fuel Consumed thousands of gallons 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% Average Emissions Levels per Bus CO g/mile NMHC g/mile CH 4 g/mile NO x g/mile PM g/mile CO 2 g/mile Fuel 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 CO g/mile NMHC g/mile CH 4 g/mile NO x g/mile PM g/mile CO 2 g/mile Fuel 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
    • 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
    • (a) Fuel consumed is expressed in Diesel-equivalent gallons (b) Implemented in the older diesel buses of the fleet Greater Use of Alternative Fuels & Technology Reductions are in addition to those shown in the previous table CO tons NMHC tons CH 4 tons NO x tons PM tons CO 2 tons Fuel Consumed (a) thousands of gallons 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% 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 NO x emissions over conventional diesels.
    • (a) Fuel consumed is expressed in Diesel-equivalent gallons (b) Implemented in the older diesel buses of the fleet Greater Use of Alternative Fuels & Technology Reductions are in addition to those shown in the previous table CO tons NMHC tons CH 4 tons NO x tons PM tons CO 2 tons Fuel Consumed (a) thousands of gallons 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% Conventional diesel, stoichiometric CNG, diesel hybrid and gasoline hybrid offer near identical reductions in particulate emissions.
    • (a) Fuel consumed is expressed in Diesel-equivalent gallons (b) Implemented in the older diesel buses of the fleet Greater Use of Alternative Fuels & Technology Reductions are in addition to those shown in the previous table CO tons NMHC tons CH 4 tons NO x tons PM tons CO 2 tons Fuel Consumed (a) thousands of gallons 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% Gasoline hybrids offer the largest overall NOx reductions
    • (a) Fuel consumed is expressed in Diesel-equivalent gallons (b) Implemented in the older diesel buses of the fleet Greater Use of Alternative Fuels & Technology Reductions are in addition to those shown in the previous table CO tons NMHC tons CH 4 tons NO x tons PM tons CO 2 tons Fuel Consumed (a) thousands of gallons 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% B20 used in older model buses without DPFs results in slight increase in NO x 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.
    • (a) Fuel consumed is expressed in Diesel-equivalent gallons (b) Implemented in the older diesel buses of the fleet Greater Use of Alternative Fuels & Technology Reductions are in addition to those shown in the previous table CO tons NMHC tons CH 4 tons NO x tons PM tons CO 2 tons Fuel Consumed (a) thousands of gallons 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% Diesel-hybrid buses appear to offer the greatest overall environmental advantage.
    • Global Warming Potential (a) B20 Implemented in the older diesel buses of the fleet Tailpipe only If B100 in all the fleet: Life cycle emissions ↓ ~ 40%
    • Observations & Conclusions
      • Replacement of older model diesel buses with lower emitting buses equipped with advanced NO x control technologies and catalyzed diesel particulate filters brings about substantial emissions reductions
      • NO x reductions from CNG are slightly better than predicted for clean-diesel buses
      • Compared to clean-diesel buses, CNG buses offer superior reductions in CO 2 emissions, less advantage in terms of CO emissions and produce methane emissions
      • Diesel hybrid buses yield the largest reductions in CO 2 emissions and are the only technology to show a reduction in fuel consumption
      • Gasoline-electric hybrid buses offer the highest NO x emissions reductions due to the vanishingly low NO x levels of gasoline engines with 3-way catalysts
    • Comments of Biodiesel Implementation
      • The 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 NO x 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
      • 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
      • 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
      • 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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