Background
Engine Categories. For the purpose of emission regulations, marine engines are divided into three categories based on displacement (swept volume) per cylinder, as shown in Table 1. Each of the categories represents a different engine technology. Categories 1 and 2 are further divided into subcategories, depending on displacement and net power output.
| Category | Displacement per Cylinder (D) | Basic Engine Technology |
|---|---|---|
| 1 | D < 5 dm3 (and power ≥ 37 kW) | Land-based nonroad diesel |
| 2 | 5 dm3 ≤ D < 30 dm3 | Locomotive engine |
| 3 | D ≥ 30 dm3 | Unique marine engine design |
Category 3 marine diesel engines typically range in size from 2,500 to 70,000 kW (3,000 to 100,000 hp). These are very large marine diesel engines used for propulsion power on ocean-going vessels such as container ships, oil tankers, bulk carriers, and cruise ships. Emission control technologies which can be used on these engines are limited. An important limitation is the fuel on which they are operated, called residual fuel. This fuel is the by-product of distilling crude oil to produce lighter petroleum products. It possesses high viscosity and density, which affects ignition quality, and it typically has high ash, sulfur and nitrogen content in comparison to marine distillate fuels. Furthermore, residual fuel parameters are highly variable because its content is not regulated. The EPA estimated that residual fuel can increase engine NOx emissions from 20-50% and PM from 750% to 1250% (sulfate particulates) when compared to distillate fuel.
Category 1 and Category 2 marine diesel engines typically range in size from about 500 to 8,000 kW (700 to 11,000 hp). These engines are used to provide propulsion power on many kinds of vessels including tugboats, pushboats, supply vessels, fishing vessels, and other commercial vessels in and around ports. They are also used as stand-alone generators for auxiliary electrical power on many types of vessels.
Regulatory Acts. Emissions from marine diesel engines (compression ignition engines) have been regulated through a number of rules—the first one issued in 1999—applicable to different engine categories. Certain overlap also exists with the regulations for mobile, land-based nonroad engines, which may be applicable to some types of engines used on marine vessels. The following are the major regulatory acts which establish emission standards for marine engines:
- 1999 Marine Engine Rule—On November 23, 1999, the EPA signed the final rule “Control of Emissions of Air Pollution from New CI Marine Engines at or above 37 kW” [40 CFR Parts 89, 92][64 FR 64 73300-73373, 29 Dec 1999]. The adopted Tier 2 standards for Category 1 and 2 engines are based on the land-based standard for nonroad engines, while the largest Category 3 engines are expected—but not required by the rule—to comply with IMO MARPOL Annex VI limits.
- 2002 Recreational Engine Rule—Diesel engines used in recreational vessels are covered in the “Emission Standards for New Nonroad Engines—Large Industrial Spark-ignition Engines, Recreational Marine Diesel Engines, and Recreational Vehicles” regulation, signed on September 13, 2002 [40 CFR Part 89 et al.][67 FR 68241-68447, 8 Nov 2002].
- 2003 Category 3 Engine Rule—The decision to leave the largest Category 3 engines unregulated triggered a law suit against the EPA by environmental organizations. A court settlement was reached that required the EPA to develop NOx emission limits for Category 3 engines. The final rule “Control of Emissions From New Marine Compression-Ignition Engines at or Above 30 Liters Per Cylinder” [40 CFR Part 9 and 94][68 FR 9745-9789, 28 Feb 2003]—signed by the EPA in January 2003—establishes Tier 1 emission standards for marine engines virtually equivalent to the IMO MARPOL Annex VI limits. The EPA also committed to impose more stringent Tier 2 standards for Category 3 engines in a rulemaking to be completed by April 2007.
Future. Plans for future emission standards for Category 1 and Category 2 marine engines were outlined in the Advance Notice of Proposed Rulemaking (ANPRM) signed by the EPA on 11 May 2004 [69 FR 39275-39289, 29 Jun 2004]. These emission standards would be modeled after the 2007/2010 highway engine program and the Tier 4 nonroad rule, with an emphasis on the use of emission aftertreatment technology. PM controls could be introduced starting in 2011, with NOx standards phased-in over 3 years.
To enable catalytic aftertreatment methods, the EPA established a sulfur cap in marine fuels (as part of the nonroad Tier 4 rule). Sulfur limit of 500 ppm becomes effective in June 2007, sulfur limit of 15 ppm in June 2012. However, the Tier 4 fuel regulations do not apply to high sulfur residual fuels, such as those often used in Category 2 engines. This may present a difficulty in applying such technologies as catalytic particulate filters on marine engines.
Applicability
1999 Marine Engine Rule. The scope of application of the marine engine rule covers all new marine diesel engines at or above 37 kW (50 hp) (engines below 37 kW will be covered by future marine emission standards; those engines must comply with the nonroad Tier 1 and 2 standards, but are not covered by the Tier 4 regulation). Regulated engines include both propulsion and auxiliary marine diesel engines. A propulsion engine is one that moves a vessel through the water or assists in guiding the direction of the vessel (for example, bow thrusters). Auxiliary engines are all other marine engines.
Classification of drilling rigs depends on their propulsion capability. Drilling ships are considered marine vessels, so their engines are subject to the marine rule. Semi-submersible drilling rigs which are moored to the ocean bottom, but have some propulsion capability, are also considered marine vessels. In contrast, permanently anchored drilling platforms are not considered marine vessels, so none of the engines associated with one of these facilities are marine engine.
Consistently with the land-based nonroad regulation, a portable auxiliary engine that is used onboard a marine vessel is not considered to be a marine engine. Instead, a portable auxiliary engine is considered to be a land-based auxiliary engine and is subject to the land-based nonroad requirements. To distinguish a marine auxiliary engine installed on a marine vessel from a land-based portable auxiliary engine used on a marine vessel, EPA specified in that rulemaking that an auxiliary engine is installed on a marine vessel if its fuel, cooling, or exhaust system are an integral part of the vessel or require special mounting hardware. All other auxiliary engines are considered to be portable and therefore land-based.
The following engine categories are exempted from the 1999 marine regulation:
- Engines used in recreational vessels (standards for recreational diesel engines were established by the 2002 rule)
- Emission certified new land-based engines modified for marine applications (provided certain conditions are met)
- Competition (racing) engines
- Engines used in military vessels (National Security Exemption)
- Other exemptions (testing, display, export, ...) may also apply to marine engines.
Not all of the above exemptions are automatic. Engine or vessel manufacturers, or vessel owners, may need to apply for a specific exemption to the EPA.
The 1999 rule also included so called Foreign-Trade Exemption which was available (for engines Category 1 and 2 used on ocean vessels with Category 3 propulsion) for US vessels that spend less than 25% of total operating time within 320 kilometers of US territory. The Foreign-Trade Exemption was eliminated for all engine categories by the 2003 (Category 3) regulation.
Under the 1999 rule, the same emission standards apply to engines fueled by diesel fuel and by other fuels.
2002 Recreational Vessel Rule. This rule applies to new recreational marine diesel engines over 37 kW (50 hp) that are used in yachts, cruisers, and other types of pleasure craft. The 2002 rule does not apply to outboard and personal watercraft spark ignited engines, which are regulated separately.
The same emission standards apply to recreational engines fueled by diesel fuel and by alternative fuels.
2003 Category 3 Rule. These standards apply to new marine engines and to new vessels that include marine engines. The rule applies only to vessels flagged or registered in the USA.
Emission Standards
Engines Category 3
In the 2003 rule, EPA has adopted Tier 1 NOx emission standards for Category 3 engines, which are equivalent to the internationally negotiated IMO MARPOL Annex VI limits. These limits range from 9.8 to 17 g/kWh depending on the engine speed, with higher limits for slower engines. The exact formulas were given in the article covering IMO emission regulations.
The EPA Tier 1 limits are in effect for new engines built in 2004 and later. These limits are to be achieved by engine-based controls, without the need for exhaust gas aftertreatment. Emissions other than NOx are not regulated.
Engines Category 1 And 2
Emission standards for engines category 1 and 2 are based on the land-based standard for nonroad and locomotive engines. The emission standards, referred to as Tier 2 Standards by the EPA, and their implementation dates are listed in the following table. The Tier 1 NOx standard, equivalent to MARPOL Annex VI, was voluntary under the 1999 rule, but was made mandatory by the 2003 (Category 3) rule for Category 2 and Category 1 engines of above 2.5 liter displacement per cylinder, effective 2004.
The regulated emissions include NOx+THC, PM, and CO. There are no smoke requirements for marine diesel engines. The regulators believed that the new PM standards will have a sufficient effect on limiting smoke emissions.
| Category | Displacement (D) | CO | NOx+THC | PM | Date |
|---|---|---|---|---|---|
| dm3 per cylinder | g/kWh | g/kWh | g/kWh | ||
| 1 | Power ≥ 37 kW D < 0.9 | 5.0 | 7.5 | 0.40 | 2005 |
| 0.9 ≤ D < 1.2 | 5.0 | 7.2 | 0.30 | 2004 | |
| 1.2 ≤ D < 2.5 | 5.0 | 7.2 | 0.20 | 2004 | |
| 2.5 ≤ D < 5.0 | 5.0 | 7.2 | 0.20 | 2007a | |
| 2 | 5.0 ≤ D < 15 | 5.0 | 7.8 | 0.27 | 2007a |
| 15 ≤ D < 20 Power < 3300 kW | 5.0 | 8.7 | 0.50 | 2007a | |
| 15 ≤ D < 20 Power ≥ 3300 kW | 5.0 | 9.8 | 0.50 | 2007a | |
| 20 ≤ D < 25 | 5.0 | 9.8 | 0.50 | 2007a | |
| 25 ≤ D < 30 | 5.0 | 11.0 | 0.50 | 2007a | |
| * - Tier 1 standards are equivalent to the MARPOL Annex VI NOx limits a - Tier 1 certification requirement starts in 2004 | |||||
In the earlier proposal, the EPA also listed a more stringent Tier 3 standard to be introduced between 2008 and 2010. The Tier 3 standard was not adopted in the final 1999 rule.
Blue Sky Series Program. The 1999 regulation sets a voluntary “Blue Sky Series” program which permits manufacturers to certify their engines to more stringent emission standards. The qualifying emission limits are listed in Table 3. The Blue Sky program begins upon the publication of the rule and extends through the year 2010.
| Displacement (D) | NOx+THC | PM |
|---|---|---|
| dm3 per cylinder | g/kWh | g/kWh |
| Power ≥ 37 kW & D < 0.9 | 4.0 | 0.24 |
| 0.9 ≤ D < 1.2 | 4.0 | 0.18 |
| 1.2 ≤ D < 2.5 | 4.0 | 0.12 |
| 2.5 ≤ D < 5.0 | 5.0 | 0.12 |
| 5.0 ≤ D < 15 | 5.0 | 0.16 |
| 15 ≤ D < 20 & Power < 3300 kW | 5.2 | 0.30 |
| 15 ≤ D < 20 & Power ≥ 3300 kW | 5.9 | 0.30 |
| 20 ≤ D < 25 | 5.9 | 0.30 |
| 25 ≤ D < 30 | 6.6 | 0.30 |
Recreational Vessels (2002 Rule)
Recreational vessels standards are phased-in beginning in 2006, depending on the size of the engine as listed in Table 4. These standards are similar to the Tier 2 standards for Category 1 commercial vessels.
| Displacement (D) | CO | NOx+HC | PM | Date |
|---|---|---|---|---|
| dm3 per cylinder | g/kWh | g/kWh | g/kWh | |
| 0.5 ≤ D < 0.9 | 5.0 | 7.5 | 0.40 | 2007 |
| 0.9 ≤ D < 1.2 | 5.0 | 7.2 | 0.30 | 2006 |
| 1.2 ≤ D < 2.5 | 5.0 | 7.2 | 0.20 | 2006 |
| D ≥ 2.5 | 5.0 | 7.2 | 0.20 | 2009 |
Recreational engines are also subject to NTE limits. There are no smoke requirements for recreational marine diesel engines. Similarly to commercial vessels, a voluntary “Blue Sky Series” limits exist for recreational vessels, which are based on a 45% emission reduction beyond the mandatory standards.
Test Cycles
Category 1/2 Engines. Emissions from Category 1 engines are tested on various ISO 8178 cycles (E2, E3, E5 cycles for various types of propulsion engines, D2 cycle for auxiliary engines). Engines belonging to Category 2 are tested on locomotive test cycles.
In addition to the ISO test cycle measurement, which are averages from several test modes, the regulation sets “not-to-exceed” (NTE) emission limits, which provide assurance that emissions at any engine operating conditions within an NTE zone are reasonably close to the average level of control. NTE zones are defined as areas on the engine speed-power map. The emission caps within the NTE zones represent a multiplier (between 1.2 and 1.5) times the weighted test result used for certification for all of the regulated pollutants (NOx+THC, CO, and PM).
The test fuel for marine diesel engine testing has a sulfur specification range of 0.03 to 0.80 %wt, which covers the range of sulfur levels observed for most in-use fuels.
Category 3 Engines. Category 3 engines are tested using methods similar to those stipulated by IMO MARPOL Annex VI (E2 and E3 cycles of the ISO 8178 test). The major differences between the EPA and MARPOL compliance requirements are: (1) EPA liability for in-use compliance rests with the engine manufacturer (it is the vessel operator in MARPOL), (2) EPA requires a durability demonstration (under MARPOL, compliance must be demonstrated only when the engine is installed in the vessel), (3) there are differences in certain test conditions and parameters in EPA and MARPOL testing (air and water temperatures, engine setting, etc.).
Category 3 engines have no NTE emission limits or test requirements.
Category 3 engines can be tested using distillate fuels, even though vessels with Category 3 marine engines use primarily residual fuels (this allowance is consistent with MARPOL Annex VI).
Other Provisions
Useful life and warranty periods for marine engines are listed in Table 5. The periods are specified in operating hours and in years, whichever occurs first. The relatively short useful life period for Category 3 engines is based on the time that engines operate before being rebuilt for the first time.
| Category | Useful Life | Warranty Period | ||
|---|---|---|---|---|
| hours | years | hours | years | |
| Category 3 | 10,000 | 3 | 10,000 | 3 |
| Category 2 | 20,000 | 10 | 10,000 | 5 |
| Category 1 | 10,000 | 10 | 5,000 | 5 |
| Recreational | 1,000 | 10 | 500 | 3 |
The periods in the table are the minimum periods specified by the regulations. In certain cases, longer useful life/warranty periods may be required (e.g., in most cases the emission warranty must not be shorter than the warranty for the engine or its components).
The regulations contain several other provisions, such as emission Averaging, Banking, and Trading (ABT) program, deterioration factor requirements, production line testing, in-use testing, and requirements for rebuilding of emission certified engines.