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New York City Transit Hybrid and CNG Transit Buses: Interim Evaluation Results - page 16 / 64

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1990

15.5

1.3

6.0

0.60

1991-1992

15.5

1.3

5.0

0.25

1993

15.5

1.3

5.0

0.10

1994-1995

15.5

1.3

5.0

0.07

1996-1997

15.5

1.3

5.0

0.05

1998-2003

15.5

1.3

4.0

0.05

all on-road diesel vehicles to 0.01 g/bhp-hr starting in 2007, and DPF technology has been proven to reliably address this PM level3.

Model Y ears

NOx levels were reduced from 4.0 g/bhp-hr in 1998 to 2.4 g/bhp-hr combined NOx and HC in 2004 (CNG levels are 2.5 g/bhp-hr NMHC + NOx with a limit of 0.5 g/bhp-hr NMHC). The 2004 level was actually moved up to 2002 based on an agreement between EPA and diesel engine manufacturers. The emissions reduction down to 2.4 g/bhp-hr HC + NOx caused several diesel engine manufacturers to use EGR to help reduce NOx levels. The use of EGR has been reported in some locations to result in significant soot in the engine oil, caused major maintenance problems when combined with the use of DPF technology, and has been reported to have had some negative impact on fuel economy.

2004-2006*

15.5

of 0.5 for non-methane hydrocarbons

0.05

2007-2010

15.5

0.14**

0.2

0.01

Table 2. EPA Emissions Requirements for Transit Buses

2.4 combined or 2.5 with a limit

  • *

    The 2004 standard was moved up to 2002 as part of an agreement between the U.S. Environmental Protection

Agency (EPA) and engine manufacturers. ** Non-methane hydrocarbons (NMHC)

NOx

PM

g/bhp-hr

g/bhp-hr

Carbon Monoxide (CO)

g/bhp-

hr

Hydrocarbons (HC)

g/bhp-hr

NOx certification levels are to be lowered to 0.2 g/bhp-hr by 2010 with a phase-in period from 2007 through 2009. During the phase in period, only half of the new engines (of a particular engine family) need to meet the 0.2 g/bhp-hr NOx level or all of the engines (of that particular family) must have NOx emissions levels less than 1.2 g/bhp-hr (or half the current standard). Most heavy diesel engine manufacturers are choosing the latter option (all engines in a family meeting the 1.2 g/bhp-hr NOx) during the phase-in period. The PM level is to be 0.01 g/bhp-hr regardless of the NOx reduction strategy. At the same time, the HC level is also being restricted down to 0.14 g/bhp-hr (or NMHC for natural gas) with a phase-in similar to NOx. For more details on this topic, see EPA’s latest public report, Highway Diesel Progress Review Report 2, March 2004, EPA420-R-04-004.

For the 2010 model year and beyond, the heavy diesel engine manufacturers are exploring selective catalytic reduction (SCR) and NOx adsorber technologies to keep NOx emissions at these extremely low levels. These emissions control technologies require low sulfur levels in the diesel fuel for the catalysts to work effectively. These emissions reductions are expected to come

3 Emissions Reductions and Operational Experiences with Heavy-Duty Diesel Fleet Vehicles Retrofitted with Continuously Regenerated Diesel Particulate Filters in Southern California, 2001, SAE International, 2001-01-0512.

11

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