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Emission Standards

USA: Stationary Engines: CI Engines (NSPS)


The new source performance standards (NSPS) for reciprocating internal combustion engines (RICE) establish US federal emission requirements for compression ignition (CI) stationary engines. The Compression Ignition NSPS rule was adopted in 2006 [3354] and amended on several occasions [3113][3407]. NSPS emission regulations for stationary CI engines are published in the Code of Federal Regulations (CFR), Title 40, Part 60, Subpart IIII.

The emission standards apply to engines whose construction, modification or reconstruction commenced after July 11, 2005—the date the proposed rule was published in the Federal Register.

Fuel Program. The NSPS rule introduced low sulfur fuel requirements for CI stationary engines, as follows:

  • Engines below 30 liters per cylinder:
    • No more than 500 ppm sulfur by October 2007,
    • Ultra-low sulfur diesel (15 ppm sulfur) by October 2010.
  • Engines ≥ 30 liters per cylinder: 1,000 ppm sulfur fuel from 2014.

These fuel requirements are consistent with those for mobile nonroad engines and marine engines. Some of the fuel quality requirements are delayed in areas of Alaska.

Economic Impact. The EPA estimated that the 2006 rule would affect 81,500 new stationary diesel engines. Emission reductions would occur gradually from 2005 to 2015, with the total nationwide annual costs for the rule to be $57 million in 2015.

The following are EPA estimates of the price increase for the compliant equipment due to the added cost of emission controls (year 2015):

  • Irrigation systems: 2.3%
  • Pumps and compressors: 4.3%
  • Generator sets and welding equipment: 10.0%

Emission Standards

The standards apply to emissions of NOx, PM, CO, and NMHC. They are expressed in units of g/kWh and smoke standards as a percentage. No new emission limits were developed for stationary engines. Rather, the engines are required to meet emission standards for various types of mobile engines, depending on the engine size and application:

  1. Engines of displacement below 10 liters per cylinder must meet Tier 1 through Tier 4 emission standards for mobile nonroad diesel engines (almost all stationary engines in the USA belong to this size category). Engines used only for emergencies, for example stand-by generator sets, are exempted from the most stringent Tier 4 emission requirements.
  2. Engines of displacement above 10 liters per cylinder must meet emission standards for marine engines.

Two groups of standards have been adopted: (1) for engine manufacturers, and (2) for engine owners/operators. Beginning with model year (MY) 2007, engine manufactures are required to emission certify stationary engines, and so they are responsible for compliance. During the transitional period before the MY 2007, engines can be sold that are not emission certified. In that case, the engine owner/operator is responsible for emission compliance.

Standards for Engine Manufacturers. Emission certification requirements for stationary non-emergency diesel engines are summarized in Table 1. All stationary engines must be certified to the respective standards, as applicable for the model year and maximum engine power (and displacement per cylinder in marine standards).

Table 1
Emission requirements for non-emergency stationary engines
Displacement (D)PowerYearEmission Certification
D < 10 L per cylinder≤ 3000 hp2007+Nonroad Tier 2/3/4
> 3000 hp2007-2010Nonroad Tier 1
2011+Nonroad Tier 2/4
10 ≤ D < 30 L per cylinderAll2007+Marine Cat. 2 Tier 3/4/3/4
D ≥ 30 L per cylinderAll2010-2011Marine Cat. 3 Tier 1
2012+Marine Cat. 3 Tier 2/3

Engines in “remote areas” of Alaska are allowed to use Tier 3 engines in lieu of Tier 4 engines. The requirements to use Tier 4 engines with “add-on” emission controls were removed in two steps: in 2011 for NOx [3113] and in 2019 for PM [4562].

Stationary CI engines can be designed to allow operators to temporarily override performance inducements related to the emission control system—for instance, to allow engine operation without urea in the SCR system—in case of emergency that presents a risk to human life [3407]. This facilitates the use of stationary CI engines to perform life‐saving work during fires, floods, hurricanes, and other emergency situations. During the emergency situation, the engine must meet the Tier 1 emission standards.

Emission certification requirements also apply to emergency engines from 2007, but the certification levels are less stringent:

  • Emergency engines that are not fire pump engines must be certified to the standards shown in Table 1, with the exception of standards (including nonroad Tier 4 and marine Category 3 Tier 3) that require “add-on” controls such as diesel particulate filters or NOx reduction catalysts.
  • Emergency fire pump engines must be certified to standards that are generally based on nonroad Tier 1 and Tier 2, with Tier 2 becoming effective around 2008-2011, depending on the engine power category.

The time allowed for maintenance and testing of emergency engines is 100 hours per year.

Standards for Engine Owners/Operators. Depending on the engine category, owners and operators are responsible for emission compliance as follows:

  • Engines < 30 liters per cylinder
    • Pre-2007:
      • Engines < 10 liters per cylinder must meet nonroad Tier 1 emission standards.
      • Engines ≥ 10 liters per cylinder must meet MARPOL Annex VI NOx limits (Tier 1 marine standards)
    • 2007 and later: owners/operators must buy emission certified engines
  • Engines ≥ 30 liters per cylinder:
    • Under the 2006 rule, owners/operators are required to reduce NOx emissions by 90%, or alternatively they must limit NOx to 1.6 g/kWh (1.2 g/hp-hr). Owners/operators are also required to reduce PM emissions by 60%, or alternatively they must limit PM to 0.15 g/kWh (0.11 g/hp-hr).
    • Under the 2011 rule, engines must be certified to the standards shown in Table 1.

Owners/operators of pre-2007 engines < 30 liters per cylinder can demonstrate compliance by purchasing a certified engine. If a non-certified engine is purchased, compliance may be demonstrated using emission test results from a test conducted on a similar engine; data from the engine manufacturer; data from the control device vendor; or conducting a performance test. If in-use performance test is conducted, the owner would be required to meet not-to-exceed (NTE) emission standards instead of the respective certification emission standards. Pre-2007 engines must meet NTE standards of 1.25 × the applicable certification emission standard. The information which demonstrates engine compliance and the appropriate maintenance records must be kept on site.

Owners/operators of engines ≥ 30 liters per cylinder must conduct an initial performance test to demonstrate emissions compliance (NOx is measured using EPA Method 7E, PM using EPA Method 5 [40 CFR part 60 appendix A]). The NTE standards do not apply to engines ≥ 30 liters per cylinder.