D. Smoke Requirements
We are not setting smoke requirements for marine diesel engines. Manufacturers have stated that many of these engines, though currently unregulated, are manufactured with smoke limiting controls at the request of the engine purchasers. Users seek low smoke emissions, both because they dislike the associated residue on decks and because they can be subject to penalties in ports that have smoke emission requirements. In many cases, marine engine exhaust gases are mixed with water prior to being released. This practice reduces the significance of smoke emissions, since smoke becomes significantly less visible when mixed with water. Moreover, we believe that the new PM standards will have the effect of further limiting smoke emissions.
E. Alternative Fuels
The new emission standards apply to marine diesel engines, without regard to the type of fuel they use. This is consistent with nonroad diesel engine regulations of 40 CFR Part 89. It is also generally consistent with the locomotive regulations; however, the locomotive regulations apply even more broadly because they also include spark-ignited engines. We are aware that there are currently very few alternative-fueled marine engines, but we believe that it is important to make clear to manufacturers what standards will apply if they produce these engines.
Heavy fuel (or residual fuel) is fundamentally different than the distillate fuel used for testing and most in-use operation. We therefore treat it as an alternative fuel. If manufacturers produce their engines with sufficient hardware to be capable of operating on heavy fuel, they should submit test data with their application for certification showing that they meet the emission standards using both distillate and heavy fuel. The Clean Air Act prohibits removing or rendering inoperative elements of design in regulated engines. If operators add fuel heating and filtering equipment and other hardware to make a certified engine capable of operating on heavy fuel, we would likely consider that to be making the emission control system inoperative. We are requiring a statement on the engine label for engines that can be modified to operate on heavy fuel to discourage operators from making this modification.
To properly address the range of possible alternative-fuel engines, it was necessary to modify the form of the HC standard. In the regulation of highway vehicles and engines, we determined that it is not appropriate to apply total hydrocarbon standards to engines fueled with natural gas, which is primarily methane (59 FR 48472, September 21, 1994). Rather, nonmethane hydrocarbon (NMHC) standards should apply to natural gas engines. We are therefore setting NMHC+NOx standards for diesel-cycle marine engines that operate on natural gas. The same numerical standards apply to both types of engines. For example, an emission standard of 7.2 g/kW-hr THC+THC that applies to diesel-fueled engines becomes 7.2 g/kW-hr NMHC+NOx for natural gas engines. Similarly, reported emissions from alcohol-fueled engines are on a basis of total HC-equivalent (THCE). THC-equivalent emissions are calculated from the oxygenated organic components and non-oxygenated organic components of the exhaust, summed together based on the amount of organic carbon present in the exhaust. Refer to the April 11, 1989 final rule for more information regarding the determination of HC-equivalence (54 FR 14426). These approaches will minimize variations in stringency for different fuel types.
F. Test Procedures
In this final rule we rely on previously established test procedures for land-based diesel engines. Specifically, we require that Category 1 marine engines be tested using the land-based nonroad procedures of 40 CFR Part 89, and that Category 2 marine engines be tested using the locomotive test procedures of 40 CFR Part 92. There are two reasons for using this approach. First, most manufacturers of marine diesel engines also manufacture land-based engines and will be equipped to test engines using these test procedures. Second, marine diesel engines are fundamentally similar to their land-based counterparts, and it is therefore appropriate to measure their emissions in the same way. In addition, the test procedures found in 40 CFR Parts 89 and 92 include flexibility for testing alternative-fuel engines. Some changes are nevertheless necessary. Manufacturers should be aware that the test procedures in MARPOL Annex VI are not equivalent to the test procedures described here and in §94.103 and §94.104. We are including the modifications to these test procedures as described below.
1. Duty Cycles
Testing an engine for emissions typically consists of exercising it over a prescribed duty cycle of speeds and loads, typically using an engine dynamometer. The duty cycle used to measure emissions for determining compliance with emission standards during the certification process is intended to represent operation in the field. The nature of that duty cycle is critical in evaluating the likely emissions performance of engines designed to those standards. To address operational differences between engines, we are specifying different duty cycles for different types of marine diesel propulsion engines. These are summarized here and described further in the Final RIA. Propulsion engines that operate on a fixed-pitch propeller curve must be certified using the International Standards Organization (ISO) E3 duty cycle. This is a four-mode steady-state cycle developed to represent in-use operation of commercial marine diesel engines. The four modes lie on an average propeller curve based on in-use measurements.
Fixed-speed marine propulsion engines with variable-pitch or electrically coupled propellers will be certified on the ISO E2 duty cycle. This duty cycle is also a four-mode steady-state cycle. It uses the same power and weighting factors as the E3 cycle, but the engine is operated in each mode at rated speed.
Constant-speed auxiliary engines must be certified to the ISO D2 duty cycle. Variable-speed auxiliary engines must be certified to the ISO C1 duty cycle. These duty cycles are consistent with the requirements for land-based nonroad diesel engines.
There is another class of propulsion engines that run at variable-speed and use a variable-pitched propeller. These engines are designed to operate near the power curve for the engine to maximize fuel efficiency. In general, these engines will operate at a constant speed near peak torque except when maneuvering in port, where they operate along the lug curve. Because of the expense of the system, variable-speed engines are rarely used with variable-pitched propellers. ISO does not have a test duty cycle specifically designed for these engines. While we proposed to use the E2 duty cycle for these engines, we have since learned the the in-use operation, especially in port areas, is best represented by the C1 duty cycle. This is consistent with MARPOL Annex VI.
For larger marine engines, conventional emission testing on a dynamometer becomes more difficult because of the size of the engine. Often engine mock ups are used for the development of these engines where a single block is used for many years and only the power assembly is changed out. For Category 2 engines, certification tests may be performed on these engine mock-ups, provided that their configuration is the same as that of the production engines.
