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ON HIGHWAY - USA

Emission Standards - USA: Heavy-Duty Truck and Bus Engines
Applicability and Test Cycles
The following emission standards apply to new diesel engines used in heavy-duty highway vehicles. The current federal definition of a compression-ignition (diesel) engine is based on the engine cycle, rather than the ignition mechanism, with the presence of a throttle as an indicator to distinguish between diesel-cycle and otto-cycle operation. Regulating power by controlling the fuel supply in lieu of a throttle corresponds with lean combustion and the diesel-cycle operation (this allows the possibility that a natural gas-fueled engine equipped with a sparkplug is considered a compression-ignition engine).
Heavy-duty vehicles are defined as vehicles of GVWR (gross vehicle weight rating) of above 8,500 lbs in the federal jurisdiction and above 14,000 lbs in California (model year 1995 and later). Diesel engines used in heavy-duty vehicles are further divided into service classes by GVWR, as follows.

• Light heavy-duty diesel engines: 8,500 < LHDDE < 19,500 (14,000 < LHDDE < 19,500 in California, 1995+)
• Medium heavy-duty diesel engines: 19,500 ≤ MHDDE ≤ 33,000
• Heavy heavy-duty diesel engines (including urban bus): HHDDE > 33,000

Under the federal light-duty Tier 2 regulation (phased-in beginning 2004) vehicles of GVWR up to 10,000 lbs used for personal transportation have been re-classified as “medium-duty passenger vehicles” (MDPV - primarily larger SUVs and passenger vans) and are subject to the light-duty vehicle legislation. Therefore, the same diesel engine model used for the 8,500 - 10,000 lbs vehicle category may be classified as either light- or heavy-duty and certified to different standards, depending on the application.
Current federal regulations do not require that complete heavy-duty diesel vehicles be chassis certified, instead requiring certification of their engines (as an option, complete heavy-duty diesel vehicles under 14,000 lbs can be chassis certified). Consequently, the basic standards are expressed in g/bhp·hr and require emission testing over the Transient FTP engine dynamometer cycle (however, chassis certification may be required for complete heavy-duty gasoline vehicles with pertinent emission standards expressed in g/mile).
Additional emission testing requirements, first introduced in 1998, include the following:

• Supplemental Emission Test (SET)
• Not-to-Exceed (NTE) limits

These tests were introduced for most signees of the 1998 Consent Decrees between the EPA and engine manufacturers for the period 1998 - 2004. Federal regulations require the supplemental testing from all engine manufacturers effective 2007. In California, the tests are required for all engines effective model year 2005.
The SET is a 13-mode steady-state test that was introduced to help ensure that heavy-duty engine emissions are controlled during steady-state type driving, such as a line-haul truck operating on a freeway. The test is based on the EU 13-mode ESC schedule (in the US commonly referred to as the “Euro III” cycle).
The NTE limits have been introduced as an additional instrument to make sure that heavy-duty engine emissions are controlled over the full range of speed and load combinations commonly experienced in use. The NTE approach establishes an area (the “NTE zone”) under the torque curve of an engine where emissions must not exceed a specified value for any of the regulated pollutants.
The NTE test procedure does not involve a specific driving cycle of any specific length (mileage or time). Rather it involves driving of any type that could occur within the bounds of the NTE control area, including operation under steady-state or transient conditions and under varying ambient conditions. Emissions are averaged over a minimum time of thirty seconds and then compared to the applicable NTE emission limits.
Model Year 1987-2003
Model year 1988-2003 US federal (EPA) and 1987-2003 California (ARB) emission standards for heavy-duty diesel truck and bus engines are summarized in the following tables. Applicable to the 1994 and following year standards, sulfur content in the certification fuel has been reduced to 500 ppm wt.

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Useful Life and Warranty Periods
Compliance with emission standards has to be demonstrated over the useful life of the engine, which was adopted as follows (federal & California):

• LHDDE - 8 years/110,000 miles (whichever occurs first)
• MHDDE - 8 years/185,000 miles
• HHDDE - 8 years/290,000 miles

Federal useful life requirements were later increased to 10 years, with no change to the above mileage numbers, for the urban bus PM standard (1994+) and for the NOx standard (1998+).
The emission warranty period is 5 years/100,000 miles (5 years/100,000 miles/3,000 hours in California), but no less than the basic mechanical warranty for the engine family.
Clean Fuel Fleet Program
Table 3 shows a voluntary Clean Fuel Fleet (CFF) emission standard. It is a federal standard that applies to 1998-2003 model year engines, both CI and SI, over 8,500 lbs GVWR. In addition to the CFF standard, vehicles must meet applicable conventional standards for other pollutants.

Model Year 2004 and Later
In October 1997, EPA adopted new emission standards for model year 2004 and later heavy-duty diesel truck and bus engines. These standards reflects the provisions of the Statement of Principles (SOP) signed in 1995 by the EPA, California ARB, and the manufacturers of heavy-duty diesel engines. The goal was to reduce NOx emissions from highway heavy-duty engines to levels approximately 2.0 g/bhp·hr beginning in 2004. Manufacturers have the flexibility to certify their engines to one of the two options shown in Table 4.

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All emission standards other than NMHC and NOx applying to 1998 and later model year heavy duty engines (Table 1) will continue at their 1998 levels.
EPA established a revised useful engine lives, with significantly extended requirements for the heavy heavy-duty diesel engine service class, as follows:

• LHDDE - 110,000 miles/10 years
• MHDDE - 185,000 miles/10 years
• HHDDE - 435,000 miles/10 years/22,000 hours

The emission warranty remains at 5 years/100,000 miles.
The federal 2004 standards for highway trucks are harmonized with California standards, with the intent that manufacturers can use a single engine or machine design for both markets. However, California certifications for model years 2005-2007 additionally require the Supplemental Emission Test and NTE limits of 1.25 times the FTP standards. California also adopted a different standard for urban bus engines.
Consent Decrees
In October 1998, a court settlement was reached between the EPA, Department of Justice, California ARB and engine manufacturers (Caterpillar, Cummins, Detroit Diesel, Volvo, Mack Trucks/Renault and Navistar) over the issue of high NOx emissions from heavy-duty diesel engines during certain driving modes. Since early 1990’s, the manufacturers used engine control software that caused engines to switch to a more fuel efficient (but higher NOx) driving mode during steady highway cruising. The EPA considered this engine control strategy an illegal “emission defeat device”.
Provisions of the Consent Decree included the following:

• Civil penalties for engine manufacturers and requirements to allocate funds for pollution research
• Upgrading existing engines to lower NOx emissions
• Supplemental Emission Test (steady-state) with a limit equal to the FTP standard and NTE limits of 1.25 × FTP (with the exception of Navistar)
• Meeting the 2004 emission standards by October 2002, 15 months ahead of time

California Urban Bus Standard (2002)
In February, 2000, the California ARB adopted a new regulation to reduce emissions of NOx and PM from urban transit buses. The rule includes a number of components that affect both engine manufacturers and bus fleet operators. Fleet operators have to choose between a “diesel path” and an “alternative fuel path” for their future bus procurements. The alternative fuel path requires that 85% of buses purchased or leased each year through model year 2015 are fueled by alternative fuels. Transit operators who stay on the diesel path can purchase diesel fueled buses, but are required to follow a more aggressive emission reduction schedule. When the regulation is fully implemented, buses on both paths will produce the same near-zero emission levels.
The regulation provides numerous detailed provisions and schedules, which can be summarized as follows:

• A NOx fleet average of 4.8 g/bhp-hr begins in 2002 for both diesel and alternative fuel paths, which will require some transit agencies to retire their oldest, highest polluting buses.
• Ultra low sulfur diesel fuel (15 ppm wt.) is required beginning July 1, 2002.
• All pre-2004 diesel buses have to be retrofitted with ARB-certified, 85% efficient diesel particulate filters. The retrofit begins in 2003 and will be completed through 2007.
• New bus engines have to be certified to increasingly more stringent emission standards (Table 5).
• Ultimately, 15% of new purchases have to be zero emission buses, ZEB (Table 5).

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The urban transit bus fleet rule requirements and emission standards are summarized in the following table.

Model Year 2007 and Later
On December 21, 2000 the EPA signed emission standards for model year 2007 and later heavy-duty highway engines (the California ARB adopted virtually identical 2007 heavy-duty engine standards in October 2001). The rule includes two components: (1) emission standards, and (2) diesel fuel regulation.
The first component of the regulation introduces new, very stringent emission standards, as follows:

• PM - 0.01 g/bhp-hr
• NOx - 0.20 g/bhp-hr
• NMHC - 0.14 g/bhp-hr

The PM emission standard will take full effect in the 2007 heavy-duty engine model year. The NOx and NMHC standards will be phased in for diesel engines between 2007 and 2010. The phase-in would be on a percent-of-sales basis: 50% from 2007 to 2009 and 100% in 2010 (gasoline engines are subject to these standards based on a phase-in requiring 50% compliance in 2008 and 100% compliance in 2009).
Emission certification requirements also include the SET test, with limits equal to the FTP standards, and NTE limits of 1.5 × FTP standards.
Effective 2007 model year, the regulation also eliminates the earlier crankcase emission control exception for turbocharged heavy-duty diesel engines. Crankcase emissions from these engines are treated the same as (i.e., added to) other exhaust emissions. Manufacturers are expected to control crankcase emissions by routing them back to the engine intake or to the exhaust stream upstream of the exhaust emission control devices.
The diesel fuel regulation limits the sulfur content in on-highway diesel fuel to 15 ppm (wt.), down from the previous 500 ppm. Refiners will be required to start producing the 15 ppm S fuel beginning June 1, 2006. At the terminal level, highway diesel fuel sold as low sulfur fuel must meet the 15 ppm> sulfur standard as of July 15, 2006. For retail stations and wholesale purchasers, highway diesel fuel sold as low sulfur fuel must meet the 15 ppm sulfur standard by September 1, 2006.
Refiners can also take advantage of a temporary compliance option that will allow them to continue producing 500 ppm> fuel in 20% of the volume of diesel fuel they produce until December 31, 2009. In addition, refiners can participate in an averaging, banking and trading program with other refiners in their geographic area.>
Ultra low sulfur diesel fuel has been introduced as a “technology enabler” to pave the way for advanced, sulfur-intolerant exhaust emission control technologies, such as catalytic diesel particulate filters and >NOx catalysts, which will be necessary to meet the 2007 emission standards.
The EPA estimates the cost of reducing the sulfur content of diesel fuel will result in a fuel price increase of approximately 4.5 to 5 cents per gallon. The EPA also estimates that the new emission standards will cause an increase in vehicle costs between $1,200 to $1,900 (for comparison, new heavy-duty trucks typically cost up to $150,000 and buses up to $250,000).
Source: DieselNet Web Site. Retrieved October 4, 2004 from www.dieselnet.com/standards/us/hd.html

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