Analysis: Emissions rules are fair for marine diesels


New federal standards take into account the way diesels are used in recreational boats


The EPA has issued the final rule for emissions standards for Nonroad Engines, Equipment and Vehicles, including marine compression-ignition (diesel) engines.

The new rules, some of which are already in effect, between now and 2016 will progressively clear the air by significantly reducing the exhaust emissions of virtually every new diesel sold in the United States and by requiring that many of the most heavily used and long-service-life engines be brought into compliance when they are overhauled. How will this affect you and your client boat owners and buyers?

The good news is that the exhaust emissions rules that apply to engines used in recreational vessels are the result of consultation and cooperation between the EPA, engine manufacturers and boating industry representatives, particularly the National Marine Manufacturers Association, represented by John McKnight, director of environmental and safety compliance. The new standards take into account the significant differences between the way diesel engines are used in recreational boats and their use profile in commercial vessels, locomotives and other applications. The new rule does the job of cleaning up recreational marine diesel exhaust without imposing impractical requirements on the engines now being used in our boats and yachts or on new engines that will have to comply with the Tier 3 standards that will be imposed in the next few years.

The publication of the new emissions standards in the Federal Register ran for more than 300 pages, therefore it is not surprising that many questions are being asked by those in the boating industry. For example, a person considering the purchase of a used boat asked if the boat's propulsion engines and genset engine would have to be replaced with new emissions-conforming engines or modified to bring them into compliance with the new standards. Others asked if the diesels that comply with the 2009 rules have to be modified to comply with the progressively more stringent rules that will come into effect through 2016.


Some, aware of the impact of the new rules on "road engines," have asked if the non-road emission control standards would require the use of the techniques being used in other diesel engine applications: selective catalytic reduction (SCR) that uses urea (fertilizer) injection into the exhaust stream and a catalytic converter or exhaust gas recirculation (EGR), both of which would be difficult to engineer into a boat or yacht. Fortunately, the cooperative work done by the EPA and the boating industry, engine manufactures and boatbuilders provides workable and agreeable answers.

Existing engines in recreational vessels (with one exception) may continue to be used, repaired and rebuilt without having to be modified to comply with new emissions regulations. The one exception will be an engine rated at more than 600 kW (800 hp) used to power a genset, which will have to be brought up to the latest standard whenever it is rebuilt. Per the EPA, a rebuild occurs whenever all of the engine's cylinder liners are replaced within a five-year period. If, at that time, an approved rebuild kit is available, the engine will have to comply with the new standards (unless the work is done by a company whose gross annual sales are less than $5 million, a provision written into the law to prevent an undue burden on small companies).

I have cited the rebuild rule for 600 kW gensets in the interest of full disclosure. I believe the only reason a yacht would carry a genset powered by an 800-hp diesel is that it uses diesel-electric propulsion, in which case an argument could be made that the engine is a propulsion engine and, therefore, is exempt from the rebuild rule - or if the yacht owner's hobby was arc welding of truly massive works of art. The update-on-rebuild requirement imposed on engines capable of delivering more than 600 kW reflects the fact that large diesels used in locomotives and commercial vessels may remain in service, with periodic overhaul, for 20 to 30 years. Allowing these engines to continue to be used without change in their exhaust emissions would exempt a significant number of engines from the improvement program.

The new Tier 3 rules will progressively tighten the emissions standards for engines used in recreational boats beginning with this year's reduced limits for particulate matter (PM), which reduces the allowable emissions from engines whose per-cylinder volume is less than 0.9 liter and less than 19 kW from 0.8 to 0.4 grams per kilowatt-hour. The PM limits for similar displacement engines with power ratings up to 75 kW are reduced from 0.6 to 0.3 g/kW-hr. Limits on oxides of nitrogen and hydrocarbons (NOx+HC) remain unchanged for these engines. A further reduction in allowable NOx+HC will take effect for engines built after 2013.

Changes in emissions standards for larger engines - those whose per-cylinder displacement is not more than 7 liters - will begin to be applied in 2012 through 2014 and will limit PM to between 0.15 and 0.12 g/kW-hr depending on per-cylinder displacement, with NOx+HC limits reduced to between 5.8 and 5.4     g/kW-hr. The much more aggressive limits of the Tier 4 regulations will not be applied to recreational engines.

Although they did not want to make binding commitments, each of the engine manufacturers I contacted say they plan to meet the new standards by more closely controlling the combustion process in each cylinder, using advanced computer control, injection pressures that may exceed 30,000 psi, and progressively faster-operating fuel injectors. There has been some speculation that combustion temperatures may have to be reduced somewhat to ensure that the production of NOx remains within limits, possibly causing a minor increase in fuel consumption.

There were a number of justifications for not imposing the Tier 4 emissions standards on diesels used in recreational boats, including the fact that engines designed to comply with Tier 4 must use ultra-low sulfur diesel fuel, or ULSD, with a sulfur content that may not exceed 15 parts per million. (Even lower sulfur contents are required in Europe - 10 ppm - with even "cleaner" fuel containing 2 to 5 ppm in use in Sweden.) The EPA's decision to exempt the engines used in large yachts from the Phase 4 emissions rules took into account the fact that these vessels frequently operate and must refuel in places where ULSD may not be available.

Overall, the new emissions standards that are being applied to each class and type of diesel engine, especially those used in locomotives and commercial vessels that account for the majority of engine operating hours, will by 2030 reduce annual emissions of NOx and PM by 765,000 and 28,000 tons, respectively. The combination of these reductions in pollutants from non-road engines, coupled with the equally aggressive efforts being applied to diesels used in road transport and the like, can be expected to deliver a major improvement in air quality wherever diesel engine power is used.


This article originally appeared in the August 2009 issue.


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