Emission Regulations And Their Impact On Engine Choices And Costs

June 2010 Vol. 237 No. 6

Douglas Kiesling, Dresser Inc., Dresser Waukesha, Waukesha, WI

New emissions regulations from the U.S. Environmental Protection Agency (EPA) are scheduled to take effect in July and August. The regulations have a potentially large impact on domestic reciprocating engine usage and domestic energy production, but thus far, relatively little attention has been given to them.

On July 1, the next phase of the EPA’s new source performance standards (NSPS) for stationary spark-ignition (SI) internal combustion engines will take effect with new lower emissions standards for nitrogen oxides (NOx), carbon monoxide (CO) and volatile organic compounds (VOC).

In August, the EPA’s new regulations on hazardous air pollutants (HAPS) will be published.

Looking further to the future, greenhouse gases could be subject to regulation as early as 2011, which would further reduce allowable constituents of engine exhaust emissions. The EPA has also issued a proposal for lowering the ozone level with an effective date of 2012. Because ozone is not emitted directly into the air, but forms when emissions of precursors, including NOx, VOCs, CO and methane (CH4), “cook” in the sun, one can expect that these emission levels will be affected by this proposed legislation.

Besides these federal requirements, regional air boards in the U.S. and Canada have the authority to enact more stringent regulations as they see fit. So it is essential that owners and operators of gas compression equipment understand the effects these existing and pending regulations have on equipment purchases and fleet utilization decisions.

Before discussing the new EPA regulations and other new and pending clean air regulations, a brief review of the history of clean air legislation in the U.S. provides useful insights. While it may seem that the new EPA regulations have “come out of the blue,” they can be traced back almost 50 years to the Clean Air Act (CAA) of 1963. This landmark legislation is the foundation of air pollution control in the U.S. Since the original law was enacted, large and important amendments were added in 1970 and again in 1990, so that today the Clean Air Act enforces a comprehensive program for reducing air pollution.

As passed by Congress in 1963, the Clean Air Act offered federal research aid, urged the development of state control agencies, and involved the federal government in inter-state pollution issues1. In 1965, an amendment was added requiring the U.S. Department of Health, Education and Welfare (HEW) to create and enforce auto emission standards2. This amendment marked the beginning of the federal government’s active role in clean air policy. A 1967 amendment authorized the Secretary of HEW to designate air quality regions throughout the nation3. By doing this, the states were given primary responsibility for adopting and enforcing pollution control standards within those regions. However, by 1970, fewer than three dozen air quality regions had been designated, as compared to an anticipated number in excess of 100. In addition, not a single state had developed a full pollution control program4, so this approach was considered to be a failure.

As a result of the states’inaction, Congress moved to put the real power in the hands of the federal government with the passage of the Clean Air Act of 19705, which remains the basis for the nation’s air pollution control policy. It has four major components:

First, it established national ambient air quality standards. Targeted at major polluting chemicals, such standards, to be developed by the EPA, were intended to protect human health as well as the environment. Second, the EPA was to establish “new source performance standards” to determine how much pollution should be allowed by different industries. Third, the Act specified standards for controlling auto emissions with the aim of reducing various gases by almost 90%. Finally, the law encouraged states to develop plans to achieve such standards and then required those plans be approved by the EPA. If a state chose not to create a plan or did not complete it by a specified date, the EPA would take over the administration of the law for that state. The states were also required to enforce the Clean Air Act.

In 1977, more amendments were added to the Act. Among the provisions were measures to prevent air quality deterioration in areas where the air had previously been clean6. The Clean Air Act was last amended in 19907. These amendments mandated massive decreases in certain gas emissions in order to control acid rain; tighter regulation of toxic pollutants; set deadlines for the noncompliant areas; and phased out three major chemical contributors to ozone layer depletion.

Clean Air Act amendments in the early 1970s included stationary emissions sources. Individual states, and sometimes local air control districts, became responsible for controlling emissions from all stationary emission sources within their borders including reciprocating, internal combustion engines (RICE).

In 1979 the EPA, with CAA authority, proposed the first federal new source performance standards for stationary reciprocating, internal combustion engines. However, with a new administration in 1980, emphasis within EPA shifted and the proposed stationary reciprocating internal combustion engine new source performance standards rule was allowed to lapse – giving rise to the current patchwork of emissions regulations that exist across the nation. In the absence of an overriding federal rule, but with the CAA mandate to control stationary emission sources, the 50 states – and multiple local communities – published individual regulations and requirements to control stationary engine emissions.

However, with rare exceptions, all of those regulations technically apply to the owner or operator of the installation and not directly to the manufacturer. While engine manufacturers may become deeply involved due to competition and specific engine performance guarantees, it is the engine owners or operators who have the legal responsibility to maintain and, if necessary, prove compliance with whatever final emissions limits apply.

In 1996, the EPA again turned its attention to developing a national rule that would apply to stationary reciprocating, internal combustion engines. That rule was directed toward a list of 188 specific hazardous air pollutants, or HAPs, contained in the Clean Air Act itself. The resulting Maximum Achievable Control Technology (MACT) rule was published on June 15, 20048. However, as before, the rule was directed toward the owners and operators rather than the manufacturers.

That began to change with a lawsuit brought against the EPA by Environmental Defense Fund (EDF) in 20039. Its complaint was that the CAA specified that the EPA must promulgate new source performance standards controls for all major sources of air emissions and had not done so for stationary RICE. Because the EPA had previously determined that stationary reciprocating internal combustion engines constituted a major source of air pollution and had actually published a draft regulation in 1979, the court agreed with the EDF.

EPA entered into a consent decree in 2004 agreeing to promulgate rules by specific dates. Because compression ignition or diesel, engines were already regulated in their mobile configurations, EPA, with the court’s approval, agreed to promulgate a regulation for stationary diesels first to be followed a year later with a companion new source performance standards directed toward spark-ignited stationary reciprocating internal combustion engines.

The draft diesel new source performance standards was published in June 2005 and become final in June 2006. Its standards basically mimic those previously applied to mobile diesel engines but allow for a time lag to transfer the technology from mobile to stationary configurations.

The EPA first addressed the new – for them – area of stationary, spark-ignited engine emissions regulation. The final rule was signed on Dec. 20, 2007 and became effective on Jan. 18, 200810.

The complete new stationary, spark ignition reciprocating internal combustion engine new source performance standards can be found in the Federal Register at 73FR3567. The rule is complex, with requirements that vary by class of engine. However, the following is an overview of the highlights:

  • There are no size or power exemptions – all stationary, spark-ignited engines are covered.
  • There is no difference in emission limits between rich burn and lean burn engines. However, allowable emissions are higher for digester, landfill, and bio-gas fuels.
  • Compliance dates differ by engine size, fuel, and combustion type.
  • There are standards for nitrogen oxides (NOx), carbon monoxide (CO), and non-methane hydrocarbons (NMHC) but not particulate matter (PM).
  • The standards apply to new, modified, and reconstructed engines but not to existing engines.
  • Factory emissions certification is required for all gasoline-fueled engines and for rich burn liquefied petroleum gas (LPG) engines.
  • The standards are in two stages: Stage 1: 2008 to 2010/2011; Stage 2: 2010/2011 and beyond.
  • Emergency, reconstructed, and modified engines have only Stage 1 requirements.
  • There is a mandatory labeling requirement for all engines, whether factory-certified or non-certified.
  • Operators must follow factory maintenance specifications and schedule for factory-certified engines.
  • The relationship between engine manufacturer, after-treatment manufacturer and packager regarding warranty and emissions responsibilities was not specified in the rule itself. This may need to be worked out with the EPA by agreement later or by litigation.
  • EPA reference test methods or ASTM portable test methods must be used for all required emissions testing as applicable.
  • Recordkeeping and reporting is mandatory and may be onerous. This includes but is not limited to: (1) a startup, shutdown, and maintenance plan; (2) initial notifications as specified; (3) maintenance records; (4) reporting and deviation notification; (5) parameter monitoring; and (6) emergency engines must record hours of use and reason for use.

Table 1: A brief overview of the emission limits and timetable for the rule covering stationary, spark ignited engine emissions.

The emissions limits themselves are moderate and even the Stage 2 levels are achievable by many lean burn engines today without after treatment. This is because the EPA’s rule is intended to cover the entire nation rather than specific, non-attainment areas. However, as with most EPA stationary source rules, these emission standards are the minimum that must be met nationwide. Any state or local air district can have much more stringent requirements. California, Texas, the eastern seaboard and other areas have, and will retain, their significantly lower standards. Only areas of the nation that have no or few counties in non-compliance with the National Air Ambient Quality Standards (NAAQS) are expected to directly incorporate the spark ignition new source performance standards rule into their State Implementation Plan.

Emissions standards for hazardous air pollutants (HAPS) for reciprocating internal combustion engines will be addressed in the regulations to be published by the EPA in August. While final details have not been announced, the EPA’s initial proposal suggested the measurement of carbon monoxide as a surrogate for HAPS for four-stroke lean burn engines and formaldehyde as a surrogate for four-stroke rich burn engines. Dresser Waukesha and other engine manufacturers are proposing the use of total hydrocarbons as a surrogate for HAPS for rich burn engines. Until the final regulations are published, it is unclear what the timing or how engines will be affected, although it appears that both existing and new engines will be covered by the regulations.

Worldwide concern over global warming and the role of atmospheric “greenhouse gases” in climate change points to the next likely area of emissions regulation. One of the principal greenhouse gases is carbon dioxide (CO2). The volume of carbon dioxide emissions into the atmosphere is very high, particularly from burning of fossil fuels. It is likely that greenhouse gas legislation will monitor carbon dioxide emissions, although it is not clear at what levels carbon dioxide will be regulated. Methane, the principal component of natural gas, is itself a very potent greenhouse gas with the ability to trap heat almost 21 times more effectively than carbon dioxide12. As a result, methane is also likely to gain the attention of regulators as new emission regulations concerning greenhouse gases are proposed.

In addition to the existing and pending federal regulations, there are many state and local regions that have even stricter regulations than those of the federal government. Many of these regions are in EPA-designated non-attainment areas, and require emission levels considerably below the spark-ignited reciprocating internal combustion engine new source performance standards.

These non-attainment areas are also major sources of natural gas in the U.S. so understanding these local regulations is critical. One example is the regulations that govern emissions in the nine-county area surrounding Dallas/Fort Worth, known as the Barnett Shale area. Here, all new rich burn and lean burn, spark-ignited, reciprocating internal combustion engines are required to meet a 0.50 gram/bhp-hour NOx emissions level13. Other emissions constituents are governed at EPA levels.

Clearly, clean air regulation in the U.S. has gained strength and demonstrated staying power over its 50-year history. And although the regulation of emissions from spark-ignited, reciprocating internal combustion engines is relatively new, the trends point toward more stringent and increasingly complex regulation.

Consequently, manufacturers, owners and operators of spark-ignited reciprocating internal combustion engines must understand how pending and future emissions legislation will impact future decisions on purchasing these units. Here are some of the key considerations for everyone involved in the natural gas compression industry:

1) There is pending and proposed legislation that will likely be stricter and more burdensome to the operator than before;
2) There is a complex web of regional air board and federal regulations with varying restrictions and requirements that must be understood by engine fleet operators who typically move units from region to region, and
3) Some current engine offerings will not meet all of the current emissions requirements and therefore will not meet most of the proposed emissions requirements.

Essentially, a purchase decision today must look into the future and consider many more factors to accurately determine which engine will deliver the best long-term value. At Dresser Waukesha, we have coined the term “future-proofing” to describe this approach to making the investment in a gas compression engine. These factors include a review of the purchaser’s overall business strategy and a clear understanding of emissions compliance issues. It means looking at how current and proposed emissions regulations could affect an engine’s useful life and determining, based on the user’s needs, the best way to comply with future regulations at a reasonable cost. All the usual considerations such as efficiency, fuel costs, maintenance, and total life cycle cost still apply.

For an owner/operator considering the purchase of a spark-ignited, reciprocating internal combustion engine, there are two choices; rich burn and lean burn, because one technology does not fit all applications. Finding the optimal match between an engine and its intended application requires an understanding of the unique characteristics of each combustion technology, a clear definition of the how the engine will be used in both the short- and long-term and the degree to which the engine conforms to current and pending regulatory requirements.

Consider these realities of compression projects in the U.S. today. First, many compression sites are driven by fleet engines – units in the 1,000-2,000 horsepower range – that are moved from site to site as needed. Portability requires flexibility – to meet varying emissions requirements and to perform dependably despite widely variable operating conditions. Second, much of today’s natural gas production is occurring in shale plays which are primarily located in severe non-attainment areas where 0.50 gram/bhp-hr NOx requirements are typical, making low NOx emissions a must.

Engines with rich burn technology can address these critical issues. Typical engine-out NOx levels for a 1,700 horsepower engine are 15.0 gram/bhp-hr NOx. However, with the use of a three-way catalyst (TWC) properly formulated, sized and installed, these emissions levels can be cost-effectively reduced well below 0.5 gram/bhp-hr NOx, which gives the owner/operator a margin against future emissions regulation uncertainties.

A rich burn engine with a proper TWC also reduces carbon monoxide and hydrocarbon (HC) emissions to meet some of the most stringent levels required today. Typical emissions levels for carbon monoxide and hydrocarbons after catalyst are 0.60 gram/bhp-hr carbon monoxide and 0.70 gram/bhp-hr hydrocarbons14. This takes on added importance in light of the July 1 EPA requirements that will reduce allowable carbon monoxide emissions-out from 4.0 gram/bhp-hr to 2.0 gram/bhp-hr.

Compression engine operators face two other challenges to optimal engine performance – variable fuel composition and the impact of high altitudes – both of which can be mitigated with rich burn engines. Rich burn engines are capable of operating a wide range of fuel compositions without detonation or “knock,” a key consideration for a fleet engine which will be expected to perform in situations with widely varying fuel qualities. Rich burn engines also are capable of operating without derate at higher altitudes. Because these engines require significantly less air for the combustion process, they are able to operate in the lower density air that is characteristic of higher altitudes and temperature extremes.

Lean burn technology also has its place in natural gas compression applications, generally in larger installations where engines are typically in the 3,000-5,000 horsepower range. For these installations, lean burn engines offer good power density with proven technology and some fuel consumption advantages. However, the owner/operator must consider engine settings and the regulations governing the engine’s emissions. At a 2.0 gram/bhp-hr NOx output level, a lean burn engine is more fuel-efficient than a rich burn engine. However, as a lean burn engine is leaned out to achieve the 0.5 gram/bhp-hr NOx emissions level, fuel consumption can increase quickly.

When lean burn technology is coupled with an advanced engine control system, a lean burn engine is capable of meeting the stringent 0.5 gram/bhp-hr NOx limit required in many severe non-attainment areas. Lean burn technology should also meet current allowable HC emissions levels and the new carbon monoxide 2.0 gram/bhp-hr limit that takes effect in July without the use of any emissions after treatment equipment.

In the event the NOx and carbon monoxide requirements are reduced in the future, a selective catalytic reduction (SCR) system and oxidation catalyst can be put in place to further reduce emissions. Applying an SCR system brings with it a significant set of additional costs which we estimate to be equivalent to a 3-5% fuel consumption penalty.

Large, lean burn engines are a good choice for gas storage and transmission installations, which are typically at altitudes below 3,000 feet in the U.S.15 There are lean burn engines on the market today that operate at altitudes up to 3,000 feet without derate and can meet the new EPA spark-ignited reciprocating internal combustion engine new source performance standards regulations and area-specific 0.50 gram/bhp-hr NOx levels.

In conclusion, it is a given that emissions regulations will be a key consideration in engine purchase decisions going forward. Near-term emissions regulations have been clearly defined. What is less clear is the impact of future regulations on the gas-producing industry. But if history is a guide, we can be certain that future regulations will drive allowable emissions levels even lower. It is only a matter of time.

As a result, the traditional engine selection approach for gas compression applications, which relies almost entirely on technical specifications, will not work in today’s world of ever-tightening emissions regulations. Choosing between a rich burn and lean burn spark-ignited, reciprocating internal combustion engine requires a forward-looking approach that takes into account fuel flexibility, altitude requirements, fuel efficiency, after treatment initial cost and maintenance, and future regulations in the context of the engine’s intended use. Today, the equipment purchase decision process should include a cross-functional review and a business strategy that includes regulatory compliance, technological fit, and future mobility requirements needs.

Douglas A. Kiesling is Director of Design and Analytical Engineering for Dresser Waukesha. He leads a team of engineers and designers in the development of new products and product upgrades. He is also the product platform leader for the company’s recently introduced 275 Series product line, providing technical leadership on the project and working closely with marketing to set multi-generational product development plans and strategies. He has an undergraduate degree in Applied Mathematics from the University of Wisconsin and a Master of Science degree in Mechanical Engineering from Marquette University.


  1. Clean Air Act, Pub. L. no. 88-206
  2. Motor Vehicle Air Pollution Control Act, Pub. L. no. 89-272
  3. Air Quality Act, Pub. L. no. 90-148
  4. U.S. Environmental Protection Agency History – The Clean Air Act of 1970. September 10, 2009. Web February 8, 2010. http://www.epa.gov/history/topics/caa70/11.htm
  5. Clean Air Act Extension Pub. L. no. 91-604
  6. Clean Air Act Amendments Pub. L. no. 95-95
  7. Clean Air Act Amendments Pub. L. no. 101-549
  8. National Emission Standards for Hazardous Air Pollutants for Source Categories, 40 CFR, pt.63 (2004)
  9. Environmental Defense Fund. Web February 8, 2010 http://www.edf.org/pressrelease.cfm?contentID=4571
  10. Standards of Performance for Stationary Spark Ignited Internal Combustion Engines and National Emission Standards for Hazardous Air Pollutants for Reciprocating Internal Combustion Engines; Final Rule, 40 CFR, pt. 60,63,85 et al., January 18, 2008
  11. National Emission Standards for Hazardous Air Pollutants for Reciprocating Internal Combustion Engines; Proposed Rule, 40 CFR, pt. 63, March 5, 2009
  12. U.S. Environmental Protection Agency History – Methane. October 19th, 2006. Web February 8, 2010. http://www.epa.gov/outreach/scientific.html
  13. Control of Air Pollution from Nitrogen Compounds, Texas Administrative Code, Title 30, Part 1, Chapter 117
  14. Dresser Waukesha Internal Engineering Documentation
  15. Dresser Waukesha Internal Engineering Documentation
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