Tier 4 Emission Standards
The Tier 4 emission standards—phased-in from 2008 through 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. The Tier 4 regulation and later amendments include a number of additional provisions:
- Smoke Opacity—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).
- Crankcase Ventilation—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.
- DEF Refill Interval—For SCR-equipped nonroad diesel engines, a minimum DEF (urea solution) refill interval is defined as at least as long (in engine-hours) as the vehicle’s fuel capacity [3408].
- Ammonia Emissions—While ammonia emissions are unregulated, the EPA recommends that ammonia slip should be below 10 ppm average over the applicable test cycles [3693].
- Emergency Operation—To facilitate the use of certain nonroad engines in temporary emergency situations, the engines can be equipped with an AECD to override performance inducements related to the emission control system—for example, to allow engine operation without urea in the SCR system during an emergency [3408]. This flexibility is intended primarily for engines used in construction equipment and portable equipment used for temporary power generation and flood control.
- ABT Program—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.
Test Cycles and Fuels
Nonroad engine emissions are measured on a steady-state test cycle that is equivalent to the ISO 8178 C1, 8-mode steady-state test cycle. Other ISO 8178 test cycles are allowed for selected applications, such as constant-speed engines (D2 5-mode cycle), variable-speed engines rated under 19 kW (G2 cycle), and marine engines (E3 cycle).
Transient Testing. Tier 4 standards have to be met over both the steady-state test and the nonroad transient cycle, NRTC. The transient testing requirements started with MY 2013 for engines below 56 kW, MY 2012 for 56-130 kW, and MY 2011 for 130-560 kW engines. Engines above 560 kW are not tested on the transient test. Also constant-speed, variable-load engines of any power category are not subject to transient testing. The NRTC protocol includes a cold start test. The cold start emissions are weighted at 5% and hot start emissions are weighted at 95% in calculating the final result.
Tier 4 nonroad engines must also meet not-to-exceed standards (NTE), which are measured without reference to any specific test schedule. The NTE standards became effective in 2011 for engines above 130 kW; in 2012 for 56-130 kW; and in 2013 for engines below 56 kW. In most engines, the NTE limits are set at 1.25 times the regular standard for each pollutant. In engines certified to NOx standards below 2.5 g/kWh or PM standards below 0.07 g/kWh, the NTE multiplier is 1.5. The NTE standards apply to engines at the time of certification, as well as in use throughout the useful life of the engine. The purpose of the added testing requirements is to prevent the possibility of “defeating” the test cycle by electronic engine controls.
Certification Fuels. Fuels with sulfur levels no greater than 0.2 wt% (2,000 ppm) were used for certification testing of Tier 1-3 engines. From 2011, all Tier 4 engines are tested using fuels of 7-15 ppm sulfur content. The transition from the 2000 ppm S specification to the 7-15 ppm specification took place in the 2006-2010 period (see Certification Diesel Fuel).
A change from measuring total hydrocarbons to nonmethane hydrocarbons (NMHC) has been introduced in the 1998 rule. Since there is no standardized EPA method for measuring methane in diesel engine exhaust, manufacturers can either use their own procedures to analyze nonmethane hydrocarbons or measure total hydrocarbons and subtract 2% from the measured hydrocarbon mass to correct for methane.
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 would 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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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) |
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) |
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
Other Provisions. The Tier 4 regulation and later amendments include a number of additional provisions:
- Smoke Opacity—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).
- Crankcase Ventilation—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.
- DEF Refill Interval—For SCR-equipped nonroad diesel engines, a minimum DEF (urea solution) refill interval is defined as at least as long (in engine-hours) as the vehicle’s fuel capacity [3408].
- Ammonia Emissions—While ammonia emissions are unregulated, the EPA recommends that ammonia slip should be below 10 ppm average over the applicable test cycles [3693].
- Emergency Operation—To facilitate the use of certain nonroad engines in temporary emergency situations, the engines can be equipped with an AECD to override performance inducements related to the emission control system—for example, to allow engine operation without urea in the SCR system during an emergency [3408]. This flexibility is intended primarily for engines used in construction equipment and portable equipment used for temporary power generation and flood control.
- ABT Program—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.
Test Cycles and Fuels
Nonroad engine emissions are measured on a steady-state test cycle that is equivalent to the ISO 8178 C1, 8-mode steady-state test cycle. Other ISO 8178 test cycles are allowed for selected applications, such as constant-speed engines (D2 5-mode cycle), variable-speed engines rated under 19 kW (G2 cycle), and marine engines (E3 cycle).
Transient Testing. Tier 4 standards have to be met over both the steady-state test and the nonroad transient cycle, NRTC. The transient testing requirements started with MY 2013 for engines below 56 kW, MY 2012 for 56-130 kW, and MY 2011 for 130-560 kW engines. Engines above 560 kW are not tested on the transient test. Also constant-speed, variable-load engines of any power category are not subject to transient testing. The NRTC protocol includes a cold start test. The cold start emissions are weighted at 5% and hot start emissions are weighted at 95% in calculating the final result.
Tier 4 nonroad engines must also meet not-to-exceed standards (NTE), which are measured without reference to any specific test schedule. The NTE standards became effective in 2011 for engines above 130 kW; in 2012 for 56-130 kW; and in 2013 for engines below 56 kW. In most engines, the NTE limits are set at 1.25 times the regular standard for each pollutant. In engines certified to NOx standards below 2.5 g/kWh or PM standards below 0.07 g/kWh, the NTE multiplier is 1.5. The NTE standards apply to engines at the time of certification, as well as in use throughout the useful life of the engine. The purpose of the added testing requirements is to prevent the possibility of “defeating” the test cycle by electronic engine controls.
Certification Fuels. Fuels with sulfur levels no greater than 0.2 wt% (2,000 ppm) were used for certification testing of Tier 1-3 engines. From 2011, all Tier 4 engines are tested using fuels of 7-15 ppm sulfur content. The transition from the 2000 ppm S specification to the 7-15 ppm specification took place in the 2006-2010 period (see Certification Diesel Fuel).
A change from measuring total hydrocarbons to nonmethane hydrocarbons (NMHC) has been introduced in the 1998 rule. Since there is no standardized EPA method for measuring methane in diesel engine exhaust, manufacturers can either use their own procedures to analyze nonmethane hydrocarbons or measure total hydrocarbons and subtract 2% from the measured hydrocarbon mass to correct for methane.
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 would be 7 cents per gallon. This figure would be reduced to 4 cents by anticipated savings in maintenance costs due to low sulfur diesel.
The origin of this article: https://www.dieselnet.com/standards/us/nonroad.php#tier3
