These are very large high-power engines that are used almost exclusively for propulsion on vessels engaged in international trade.
We further divide Category 1 engines into several subgroups. These subgroups are similar to the land-based nonroad diesel engine subgroups, except that the subgroups are based on per-cylinder displacement rather than on engine power.
The final rule also divides Category 2 into subgroups, with gradually increasing emission standards for larger engines. Engines between 5 and 15 L/cyl are generally derived from locomotive engines and have corresponding emission standards. The current range of marine engine models over 15 L/cyl have design constraints that limit their ability to control emissions. Since engines under 15 L/cyl may not currently be capable of providing adequate propulsion power for all vessels in this size range, we believe the best approach is to accommodate the technology constraints of these engines by setting emission standards less stringent than for locomotive-derived engines. These standards reflect the reduced capability of controlling emissions from engines designed to operate on heavy fuel (and the need to reduce emissions from a higher baseline level).
Engines models between 15 and 20 L/cyl in particular are in a somewhat transitional category. These engines are sometimes used in harbor and inland river applications alongside locomotive-derived engines. Higher-power models are used in coastal and open-sea operations alongside engines with much larger per-cylinder displacement. The final rule separates engines between 15 and 20 L/cyl into two subgroups, those with a rated power less than 3300 kW and those with a rated power 3300 kW or greater. Locomotive engine manufacturers are developing new locomotive engines between 15 and 20 L/cyl (up to about 4500 kW), but it is not clear if these engines will be made available for marine application. In the Tier 2 time frame, we therefore believe it is appropriate to set emission standards based on what is achievable for the engines currently available. If it appears that these larger locomotive engines will become available as marine engines in the future, we would need to reconsider this approach to take into account the emission-control capabilities of these engines.
There are several marine engine models available worldwide with per-cylinder displacement between 20 and 30 liters. Very few of these engines are currently installed in vessels that are flagged and used in the United States, In the final rule we expand Category 2 to include engines up to 30 L/cyl. We subdivide the category with graduated emission standards for 20 to 25 L/cyl and 25 to 30 L/cyl engines reflecting the emission control capability of those engines. This should prevent high-emission engines from displacing smaller engines in common applications.
IV. Emission Standards and Related Provisions
This section describes the emission standards for commercial marine diesel engines at or above 37 kW. It also describes provisions that will ensure that engines comply with the emission limits across all engine speed and load combinations, throughout their useful life. We discuss in this section requirements related to test procedures, fuel specifications, certification, and compliance.
A. Standards and Dates
1. MARPOL Annex VI
MARPOL Annex VI specifies that any diesel engine over 130 kW installed on a vessel constructed on or after January 1,2000 and to any engine that undergoes a major conversion after that date must comply with the Annex VI NOx limits.3 These NOx requirements, listed in Table 2, are intended to apply to all vessels in a country's fleet. However, according to Regulation 13(1)(b)(ii) of the Annex, a country has the option of setting alternative NOx control measures for engines on vessels that are not operated internationally. This final rule is intended to be an alternative NOx Control measure under the Annex for engines on US-flagged vessels that are not operated internationally.
In this final rule, we are not adopting the MARPOL Annex VI NOx emission limits under U.S. law. However, we are encouraging engine manufacturers to make Annex VI compliant engines available and ship owners to purchase and install them on all vessels constructed on or after January 1, 2000. Because this voluntary emission control program is the first set of standards for marine diesel engines at or above 37 kW in the U.S., we sometimes refer to them as Tier 1 standards. We are also not finalizing emission limits for Category 3 engines in this rule, and the voluntary MARPOL Annex VI NOx limits will be the sole emission control applicable to those engines.
3 The Annex VI emission limits are not enforceable until the annex goes into effect: 12 months after it is ratified by 15 countries representing at least 50 percent of the gross tonnage of the world's merchant shipping.
To encourage vessel owners to purchase MARPOL Annex VI compliant engines prior to the date the Annex goes into force for the United States, we have developed a voluntary certification program that will allow engine manufacturers to obtain a Statement of Voluntary Compliance to the MARPOL Annex VI NOx limits. Owners of vessels that are not operated internationally but that will be subject to the MARPOL survey requirements after Annex VI goes into effect for the United States should be aware that they may be required to demonstrate compliance with the Annex VI NOx limits when they apply for their International Air Pollution Prevention (IAPP) certificate. Owners of vessels that are operated internationally may also be required to demonstrate compliance with the MARPOL limits after the Annex goes into effect, both because they will be required to have an IAPP and because they may be subject to port state controls. For all of these reasons, we expect ship owners to begin purchasing compliant engines for installation on ships constructed on or after January 1, 2000, and to bring engines into compliance when they undergo a major conversion after that date. Ship owners who fail to comply with the MARPOL VI NOx requirements may face compliance and liability problems after U.S. ratification or the Annex goes into force internationally. Bringing engines into compliance at that time may involve retrofitting or replacing noncomplying engines. Ship owners may also be required to remove their vessels from service while these issues are resolved.
