美国非道路用柴油机排放标准
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美国非道路用柴油机排放标准

Background

Tier 1-3 Standards. The first federal standards (Tier 1) for new nonroad (or off-road) diesel engines were adopted in 1994 for engines over 37 kW (50 hp), to be phased-in from 1996 to 2000. In 1996, a Statement of Principles (SOP) pertaining to nonroad diesel engines was signed between EPA, California ARB and engine makers (including Caterpillar, Cummins, Deere, Detroit Diesel, Deutz, Isuzu, Komatsu, Kubota, Mitsubishi, Navistar, New Holland, Wis-Con, and Yanmar). On August 27, 1998, the EPA signed the final rule reflecting the provisions of the SOP. The 1998 regulation introduced Tier 1 standards for equipment under 37 kW (50 hp) and increasingly more stringent Tier 2 and Tier 3 standards for all equipment with phase-in schedules from 2000 to 2008. The Tier 1-3 standards are met through advanced engine design, with no or only limited use of exhaust gas aftertreatment (oxidation catalysts). Tier 3 standards for NOx+HC are similar in stringency to the 2004 standards for highway engines, however Tier 3 standards for PM were never adopted.

Tier 4 Standards. On May 11, 2004, the EPA signed the final rule introducing Tier 4 emission standards, which are to be phased-in over the period of 2008-2015 [69 FR 38957-39273, 29 Jun 2004]. The Tier 4 standards require that emissions of PM and NOx be further reduced by about 90%. Such emission reductions can be achieved through the use of control technologies—including advanced exhaust gas aftertreatment—similar to those required by the 2007-2010 standards for highway engines.

Nonroad Diesel Fuel. At the Tier 1-3 stage, the sulfur content in nonroad diesel fuels was not limited by environmental regulations. The oil industry specification was 0.5% (wt., max), with the average in-use sulfur level of about 0.3% = 3,000 ppm. To enable sulfur-sensitive control technologies in Tier 4 engines—such as catalytic particulate filters and NOx adsorbers—the EPA mandated reductions in sulfur content in nonroad diesel fuels, as follows:

  • 500 ppm effective June 2007 for nonroad, locomotive and marine (NRLM) diesel fuels
  • 15 ppm (ultra-low sulfur diesel) effective June 2010 for nonroad fuel, and June 2012 for locomotive and marine fuels

California. In most cases, federal nonroad regulations also apply in California, whose authority to set emission standards for new nonroad engines is limited. The federal Clean Air Act Amendments of 1990 (CAA) preempt California’s authority to control emissions from new farm and construction equipment under 175 hp [CAA Section 209(e)(1)(A)] and require California to receive authorization from the federal EPA for controls over other off-road sources [CAA Section 209 (e)(2)(A)].

The US nonroad emission standards are harmonized to a certain degree with European nonroas emission standards.

EPA emission standards for nonroad diesel engines are published in the US Code of Federal Regulations, Title 40, Part 89 [40 CFR Part 89].

 

Applicability

The nonroad standards cover mobile nonroad diesel engines of all sizes used in a wide range of construction, agricultural and industrial equipment. The EPA definition of the nonroad engine is based on the principle of mobility/portability, and includes engines installed on (1) self-propelled equipment, (2) on equipment that is propelled while performing its function, or (3) on equipment that is portable or transportable, as indicated by the presence of wheels, skids, carrying handles, dolly, trailer, or platform [40 CFR 1068.30]. In other words, nonroad engines are all internal combustion engines except motor vehicle (highway) engines, stationary engines (or engines that remain at one location for more than 12 months), engines used solely for competition, or engines used in aircraft.

Effective May 14, 2003, the definition of nonroad engines was changed to also include all diesel powered engines—including stationary ones—used in agricultural operations in California. This change applies only to engines sold in the state of California; stationary engines sold in other states are not classified as nonroad engines.

The nonroad diesel emission regulations are not applicable to all nonroad diesel engines. Exempted are the following nonroad engine categories:

  • Engines used in railway locomotives; those are subject to separate EPA regulations.
  • Engines used in marine vessels, also covered by separate EPA regulations. Marine engines below 37 kW (50 hp) are subject to Tier 1-2—but not Tier 4—nonroad standards. Certain marine engines that are exempted from marine standards may be subject to nonroad regulations.
  • Engines used in underground mining equipment. Diesel emissions and air quality in mines are regulated by the Mine Safety and Health Administration (MSHA).
  • Hobby engines (below 50 cm3 per cylinder)

Examples of regulated applications include farm tractors, excavators, bulldozers, wheel loaders, backhoe loaders, road graders, diesel lawn tractors, logging equipment, portable generators, skid steer loaders, or forklifts.

A new definition of a compression-ignition (diesel) engine is used in the regulatory language since the 1998 rule, that is consistent with definitions established for highway engines. The definition focuses 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 diesel-cycle operation. This language allows the possibility that a natural gas-fueled engine equipped with a sparkplug is considered a compression-ignition engine.

 

Tier 1-3 Emission Standards

The 1998 nonroad engine regulations are structured as a 3-tiered progression. Each tier involves a phase in (by horsepower rating) over several years. Tier 1 standards were phased-in from 1996 to 2000. The more stringent Tier 2 standards take effect from 2001 to 2006, and yet more stringent Tier 3 standards phase-in from 2006 to 2008 (Tier 3 standards apply only for engines from 37-560 kW).

Tier 1-3 emissions standards are listed in Table 1. Nonroad regulations are in the metric system of units, with all standards expressed in grams of pollutant per kWh.

Table 1
EPA Tier 1-3 Nonroad Diesel Engine Emission Standards, g/kWh (g/bhp·hr)

Engine Power

Tier

Year

CO

HC

NMHC+NOx

NOx

PM

kW < 8
(hp < 11)

Tier 1

2000

8.0 (6.0)

-

10.5 (7.8)

-

1.0 (0.75)

Tier 2

2005

8.0 (6.0)

-

7.5 (5.6)

-

0.8 (0.6)

8 ≤ kW < 19
(11 ≤ hp < 25)

Tier 1

2000

6.6 (4.9)

-

9.5 (7.1)

-

0.8 (0.6)

Tier 2

2005

6.6 (4.9)

-

7.5 (5.6)

-

0.8 (0.6)

19≤ kW < 37
(25 ≤ hp < 50)

Tier 1

1999

5.5 (4.1)

-

9.5 (7.1)

-

0.8 (0.6)

Tier 2

2004

5.5 (4.1)

-

7.5 (5.6)

-

0.6 (0.45)

37 ≤ kW < 75
(50 ≤ hp < 100)

Tier 1

1998

-

-

-

9.2 (6.9)

-

Tier 2

2004

5.0 (3.7)

-

7.5 (5.6)

-

0.4 (0.3)

Tier 3

2008

5.0 (3.7)

-

4.7 (3.5)

-

-†

75 ≤ kW < 130
(100 ≤ hp < 175)

Tier 1

1997

-

-

-

9.2 (6.9)

-

Tier 2

2003

5.0 (3.7)

-

6.6 (4.9)

-

0.3 (0.22)

Tier 3

2007

5.0 (3.7)

-

4.0 (3.0)

-

-†

130 ≤ kW < 225
(175 ≤ hp < 300)

Tier 1

1996

11.4 (8.5)

1.3 (1.0)

-

9.2 (6.9)

0.54 (0.4)

Tier 2

2003

3.5 (2.6)

-

6.6 (4.9)

-

0.2 (0.15)

Tier 3

2006

3.5 (2.6)

-

4.0 (3.0)

-

-†

225 ≤ kW < 450
(300 ≤ hp < 600)

Tier 1

1996

11.4 (8.5)

1.3 (1.0)

-

9.2 (6.9)

0.54 (0.4)

Tier 2

2001

3.5 (2.6)

-

6.4 (4.8)

-

0.2 (0.15)

Tier 3

2006

3.5 (2.6)

-

4.0 (3.0)

-

-†

450 ≤ kW < 560
(600 ≤ hp < 750)

Tier 1

1996

11.4 (8.5)

1.3 (1.0)

-

9.2 (6.9)

0.54 (0.4)

Tier 2

2002

3.5 (2.6)

-

6.4 (4.8)

-

0.2 (0.15)

Tier 3

2006

3.5 (2.6)

-

4.0 (3.0)

-

-†

kW ≥ 560
(hp ≥ 750)

Tier 1

2000

11.4 (8.5)

1.3 (1.0)

-

9.2 (6.9)

0.54 (0.4)

Tier 2

2006

3.5 (2.6)

-

6.4 (4.8)

-

0.2 (0.15)

† Not adopted, engines must meet Tier 2 PM standard.

 

Voluntary, more stringent emission standards that manufacturers could use to earn a designation of “Blue Sky Series” engines (applicable to Tier 1-3 certifications) are listed in Table 2.

Table 2
EPA Voluntary Emission Standards for Nonroad Diesel Engines, g/kWh (g/bhp·hr)

Rated Power (kW)

NMHC+NOx

PM

kW < 8

4.6 (3.4)

0.48 (0.36)

8 ≤ kW <19

4.5 (3.4)

0.48 (0.36)

19 ≤ kW <37

4.5 (3.4)

0.36 (0.27)

37 ≤ kW < 75

4.7 (3.5)

0.24 (0.18)

75 ≤ kW <130

4.0 (3.0)

0.18 (0.13)

130 ≤ kW < 560

4.0 (3.0)

0.12 (0.09)

kW ≥ 560

3.8 (2.8)

0.12 (0.09)

Engines of all sizes must also meet smoke standards of 20/15/50% opacity at acceleration/lug/peak modes, respectively.

The regulations include several other provisions, such as averaging, banking and trading of emission credits and maximum “family emission limits” (FEL) for emission averaging.

 

Tier 4 Emission Standards

The Tier 4 emission standards—to be phased-in from 2008-2015— introduce substantial reductions of NOx (for engines above 56 kW) and PM (above 19 kW), as well as more stringent HC limits. CO emission limits remain unchanged from the Tier 2-3 stage.

Engines up to 560 kW. Tier 4 emission standards for engines up to 560 kW are listed in Table 3.

Table 3
Tier 4 Emission Standards—Engines up to 560 kW, g/kWh (g/bhp-hr)

Engine Power

Year

CO

NMHC

NMHC+NOx

NOx

PM

kW < 8
(hp < 11)

2008

8.0 (6.0)

-

7.5 (5.6)

-

0.4a (0.3)

8 ≤ kW < 19
(11 ≤ hp < 25)

2008

6.6 (4.9)

-

7.5 (5.6)

-

0.4 (0.3)

19 ≤ kW < 37
(25 ≤ hp < 50)

2008

5.5 (4.1)

-

7.5 (5.6)

-

0.3 (0.22)

2013

5.5 (4.1)

-

4.7 (3.5)

-

0.03 (0.022)

37 ≤ kW < 56
(50 ≤ hp < 75)

2008

5.0 (3.7)

-

4.7 (3.5)

-

0.3b (0.22)

2013

5.0 (3.7)

-

4.7 (3.5)

-

0.03 (0.022)

56 ≤ kW < 130
(75 ≤ hp < 175)

2012-2014c

5.0 (3.7)

0.19 (0.14)

-

0.40 (0.30)

0.02 (0.015)

130 ≤ kW ≤ 560
(175 ≤ hp ≤ 750)

2011-2014d

3.5 (2.6)

0.19 (0.14)

-

0.40 (0.30)

0.02 (0.015)

a - hand-startable, air-cooled, DI engines may be certified to Tier 2 standards through 2009 and to an optional PM standard of 0.6 g/kWh starting in 2010
b - 0.4 g/kWh (Tier 2) if manufacturer complies with the 0.03 g/kWh standard from 2012
c - PM/CO: full compliance from 2012; NOx/HC: Option 1 (if banked Tier 2 credits used)—50% engines must comply in 2012-2013; Option 2 (if no Tier 2 credits claimed)—25% engines must comply in 2012-2014, with full compliance from 2014.12.31
d - PM/CO: full compliance from 2011; NOx/HC: 50% engines must comply in 2011-2013

In engines of 56-560 kW rated power, the NOx and HC standards are phased-in over a few year period, as indicated in the notes to Table 3. The initial standards (PM compliance) are sometimes referred to as the ‘interim Tier 4’ (or ‘Tier 4i’), ‘transitional Tier 4’ or ‘Tier 4 A’, while the final standards (NOx/HC compliance) are sometimes referred to as ‘Tier 4 B’.

As an alternative to introducing the required percentage of Tier 4 compliant engines, manufacturers may certify all their engines to an alternative NOx limit in each model year during the phase-in period. These alternative NOx standards are:

  • Engines 56-130 kW:
    • Option 1: NOx = 2.3 g/kWh = 1.7 g/bhp-hr (Tier 2 credits used to comply, MY 2012-2013)
    • Option 2: NOx = 3.4 g/kWh = 2.5 g/bhp-hr (no Tier 2 credits claimed, MY 2012-2014)
  • Engines 130-560 kW: NOx = 2.0 g/kWh = 1.5 g/bhp-hr (MY 2011-2013)

Engines Above 560 kW. Tier 4 emission standards for engines above 560 kW are listed in Table 4. The 2011 standards are sometimes referred to as ‘transitional Tier 4’, while the 2015 limits represent final Tier 4 standards.

Table 4
Tier 4 Emission Standards—Engines Above 560 kW, g/kWh (g/bhp-hr)

Year

Category

CO

NMHC

NOx

PM

2011

Generator sets > 900 kW

3.5 (2.6)

0.40 (0.30)

0.67 (0.50)

0.10 (0.075)

All engines except gensets > 900 kW

3.5 (2.6)

0.40 (0.30)

3.5 (2.6)

0.10 (0.075)

2015

Generator sets

3.5 (2.6)

0.19 (0.14)

0.67 (0.50)

0.03 (0.022)

All engines except gensets

3.5 (2.6)

0.19 (0.14)

3.5 (2.6)

0.04 (0.03)

Other Provisions. Existing Tier 2-3 smoke opacity standards and procedures continue to apply in some engines. Exempted from smoke emission standards are engines certified to PM emission standards at or below 0.07 g/kWh (because an engine of such low PM level has inherently low smoke emission).

The Tier 4 regulation does not require closed crankcase ventilation in nonroad engines. However, in engines with open crankcases, crankcase emissions must be measured and added to exhaust emissions in assessing compliance.

Similarly to earlier standards, the Tier 4 regulation includes such provisions as averaging, banking and trading of emission credits and FEL limits for emission averaging.

 

Engine Useful Life

Emission standards listed in the above tables must be met over the entire useful life of the engine. EPA requires the application of deterioration factors (DFs) to all engines covered by the rule. The DF is a factor applied to the certification emission test data to represent emissions at the end of the useful life of the engine.

The engine useful life and the in-use testing liability period, as defined by the EPA for emission testing purposes, are listed in Table 5 for different engine categories. The Tier 4 rule maintains the same engine useful life periods.

Table 5
Useful Life and Recall Testing Periods


Power Rating

Rated Engine Speed

Useful Life

Recall Testing Period

 

hours

years

hours

years

 

< 19 kW

all

3000

5

2250

4

 

19-37 kW

constant speed engines
≥3000 rpm

3000

5

2250

4

 

all others

5000

7

3750

5

 

>37 kW

all

8000

10

6000

7

 

 

 

Environmental Benefit and Cost

1998 Regulation

At the time of signing the 1998 rule, the EPA estimated that by 2010 NOx emissions would be reduced by about a million tons per year, the equivalent of taking 35 million passenger cars off the road.

The costs of meeting the emission standards were expected to add under 1% to the purchase price of typical new nonroad diesel equipment, although for some equipment the standards may cause price increases on the order of 2-3%. The program was expected to cost about $600 per ton of NOx reduced.

Tier 4 Regulation

When the full inventory of older nonroad engines are replaced by Tier 4 engines, annual emission reductions are estimated at 738,000 tons of NOx and 129,000 tons of PM. By 2030, 12,000 premature deaths would be prevented annually due to the implementation of the proposed standards.

The estimated costs for added emission controls for the vast majority of equipment was estimated at 1-3% as a fraction of total equipment price. For example, for a 175 hp bulldozer that costs approximately $230,000 it would cost up to $6,900 to add the advanced emission controls and to design the bulldozer to accommodate the modified engine.

EPA estimated that the average cost increase for 15 ppm S fuel will be 7 cents per gallon. This figure would be reduced to 4 cents by anticipated savings in maintenance costs due to low sulfur diesel.

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