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Emission Standards

United States: Stationary Engines


US federal emission requirements for stationary engines are adopted by the US EPA. The emission standards are covered by three rules:

  1. Spark Ignition NSPS rule—New Source Performance Standards (NSPS) - Standards of Performance for Stationary Spark Ignition Internal Combustion Engines, 40 CFR Part 60 Subpart JJJJ
  2. Compression Ignition NSPS rule—Standards of Performance for Stationary Compression Ignition Internal Combustion Engines, 40 CFR Part 60 Subpart IIII
  3. RICE NESHAP rule—National Emission Standard for Hazardous Air Pollutants (NESHAP) for Reciprocating Internal Combustion Engines (RICE), 40 CRF Part 63, Subpart ZZZZ

The EPA first proposed NSPS requirements for stationary engines in 1979, but the rule was never finalized. In the absence of federal regulations, emissions from stationary engines gradually became subject to a complex system of state and/or local regulations and permit policies.

The NESHAP and NSPS stationary engine emission requirements were eventually promulgated by the EPA between 2004 and 2008 (with a number of later amendments). However, the structure of federal emission requirements remained very complex—partly due to the fact that several of the stationary engine emission rules have been prompted by court actions against EPA by various environmental or industry groups.

NSPS Standards

The US Clean Air Act requires that new source performance standards (NSPS) be established to control emissions from new stationary sources [CAA, Section 111(b)]. An NSPS requires these sources to control emissions to the level achievable by best demonstrated technology (BDT), considering costs and any non-air quality health and environmental impacts and energy requirements.

New sources are defined as those whose construction, reconstruction, or modification begins after a standard for them is proposed. Therefore, while the standards are applicable to “new” engines, it does not mean “newly manufactured” engines—rather, the NSPS standards are applicable to both new and in-use engines that were manufactured or modified after a certain date.

NSPS standards are intended to control emissions of criteria pollutants. The standards typically introduce regulatory limits for the emissions of CO, HC, NOx and PM.

The NSPS standards for stationary engines were adopted through several regulations. The following are some of the important regulatory steps:

  • On July 11, 2006, the EPA promulgated emission regulations for stationary compression ignition (CI) engines [3354], which require that most new stationary diesel engines meet the Tier 1-4 emission standards for mobile nonroad engines.
  • On January 18, 2008, the EPA promulgated emission standards for stationary spark ignition (SI) internal combustion engines [3350].
  • On June 28, 2011, the EPA finalized amendments the NSPS standards for CI and SI engines [3113]. The regulation strengthened the standards for diesel engines of 10-30 liters per cylinder to levels required by marine engines of the same sizes, and introduced minor revisions to the SI engine requirements.

The NSPS standards apply to stationary spark ignition and compression ignition internal combustion engines as defined below:

  • A stationary internal combustion engine means any internal combustion engine (ICE), except combustion turbines, that converts heat energy into mechanical work and is not mobile. A stationary ICE differs from a mobile ICE in that a stationary internal combustion engine is not a nonroad engine as defined at 40 CFR 1068.30, and is not used to propel a motor vehicle or a vehicle used solely for competition. Stationary ICEs include reciprocating ICEs, rotary ICEs, and other ICEs, except combustion turbines.
  • A spark ignition engine means a gasoline, natural gas, or liquefied petroleum gas fueled engine or any other type of engine with a spark plug (or other sparking device) and with operating characteristics significantly similar to the theoretical Otto combustion cycle. Spark ignition engines usually use a throttle to regulate intake air flow to control power during normal operation.
  • A compression ignition engine means a type of stationary internal combustion engine that is not a spark ignition (SI) engine.
  • Dual fuel engines in which a liquid fuel (typically diesel fuel) is used for CI and gaseous fuel (typically natural gas) is used as the primary fuel at an annual average ratio of less than 2 parts diesel fuel to 100 parts total fuel on an energy equivalent basis are SI engines.

Typical examples of regulated stationary engines are engines used to generate electricity at power and manufacturing plants, or to operate compressors and pumps. The NSPS rules also cover stationary engines that are used in emergencies, including emergency generators of electricity and water pumps for fire and flood control.

NESHAP Standards

The National Emission Standards for Hazardous Air Pollutants (NESHAP) for Reciprocating Internal Combustion Engines (RICE) are intended to reduce emissions of toxic air pollutants, such as formaldehyde, acetaldehyde, acrolein, methanol and others. In lieu of setting emission limits for these compounds, the regulations can be expressed using emission limits for CO, which is considered a surrogate compound that is more convenient to measure. In some cases, limits are set for formaldehyde.

The regulations were adopted through a number of regulatory acts published between 2004 and 2013.

The NESHAP rules are applicable to “existing” and “new” diesel and SI engines, as determined by their date of construction. Generally, existing engines are those constructed before 2002-2006, and new engine are those constructed after 2002-2006 (the exact date depends on engine category and type of location). NESHAP regulations do not apply to emergency engines. Engines meeting NSPS standards are considered to also meet NESHAP requirements.

State and Local Regulations

Many states have regions that do not comply with ambient ozone level requirements. In these regions, it is possible that State Implementation Plans (SIP) require lower emission levels from stationary engines than those contained in the applicable federal regulations. For example, the NSPS 2010 limit for NOx from SI natural gas engines rated > 500 hp is 1.0 g/bhp-hr. Some regions of states with ozone compliance challenges set more stringent requirements that can range from 0.07 to 0.5 g/bhp-hr.

States that have special emission requirements and/or permit policies for stationary engines include California, Texas and the NESCAUM states.