We are requiring a similar approach for engines certified using the constant-speed E2 duty cycle. In this case, the "not-to-exceed" zone is at the speed for which the engine is designed to operate for loads ranging from 25 to 100 percent of maximum load at that speed. Because a constant speed can actually operate over a small range of engine speeds in-use, the NTE zone includes this small range of speeds. This zone is also split into subzones above and below 45% of maximum power. More detail on the development of the boundaries and conditions associated with the NTE zones may be found in Chapter 3 of the Final RIA.
We are requiring emissions caps for the NTE zones that represent a multiplier times the weighted test result used for certification for all of the regulated pollutants (HC+NOx, CO, and PM). This is consistent with the concept of a weighted modal emission test such as the steady-state tests included in this rule. The standard itself is intended to represent the average emissions under steady-state conditions. Since it is an average, some points can be higher, some lower, and the manufacturer will design to maximize performance and still meet the engine standard. The NTE limit is on top of this. It is designed to make sure that no part of the engine operation and that no application goes too far from the average level of control.
For propulsion engines certified to the E3, C1, and E2 duty cycles, we believe that a not-to-exceed limit of 1.2 times the emissions standard (or FEL) is appropriate for the subzone at or above 45% of maximum test power. Below 45% of maximum test power, the cap is 1.5. Data presented in Chapter 3 of the Final RIA show that these limits are feasible for marine diesel engines, yet challenging because of variations in emissions at high versus low speeds and loads for some engines. This data show that the 1.2 cap is easily achievable at higher power, but may be more challenging at low powers. We set the cap at 1.5 below 45% of maximum test power for this reason. These subzones and caps apply equally to the Tier 2 emission standards for each regulated pollutant. Manufacturers may alternatively choose to comply with a cap of 1.25 over the whole zone, as we originally proposed. In any future tier of standards, we will review the appropriateness of tailoring the NTE approach to the unique characteristics of the individual exhaust constituents.
When testing the engine within the NTE zone, only nominally steady-state operation will be considered. It is unlikely that transient operation is necessary under the NTE provisions to ensure that emissions reductions are achieved for commercial marine diesel engines. We designed the NTE zones to contain the operation near an assumed propeller curve that the steady-state cycles are intended to represent. We believe that the large majority of commercial marine operation in the NTE zone is steady-state. For planing vessels, we believe the transient operation as a vessel comes to plane generally is along the torque curve and would not be within the NTE zone. However, we don't have enough data to reliably say where under the torque curve marine engines operate during transient operation. Also, we do not believe the NTE zone should include areas where an engine may operate during transients but not in steady-state modes. We therefore don't believe that adding transient operation to the NTE requirements is necessary at this time. This would change if we saw evidence that in-use emissions increase due to insufficient emission control under transient operation.
The NTE standards apply under any ambient air conditions. Within the following air temperature and humidity ranges, no corrections will be allowed to account for the effects of temperature or humidity on emissions: 13-30℃ for ambient air temperature and 7.1-10.7 grams water per kilogram of dry air for humidity. For engines drawing intake air from an enclosed engine room, however, the high end of the air temperature range is 35℃ (measured as intake air temperature). Ambient water temperature must be in the range of 5-27℃ during NTE testing. In addition, the engines must comply with the standards for the full range of test fuel specifications. These ranges for ambient conditions are discussed in more detail in Chapter 3 of the Final RIA.
The defeat device provisions established for highway and nonroad engines apply to marine diesel engines in addition to the NTE requirements. A design in which an engine met the standard at the steady-state test points but was intentionally designed to approach the NTE limit everywhere else would be considered to be defeating the standard, except under limited circumstances discussed below. Electronic controls that recognize when the engine is being tested for emissions and adjust the emissions from the engine would be another example of a defeat device, regardless of the emissions performance of the engine.
We are aware that marine diesel engines may not be able to meet the emissions limit under all conditions. Specifically, there are times when emission control must be compromised for startability or safety. We have excluded engine starting from NTE testing. In addition, our defeat device provisions accommodate the manufacturers potential need to allow emissions to increase to the extent necessary to protect the engine, such as responding to engine overheating.
Manufacturers may ask us to approve an adjusted size or shape of the NTE zone for certain engines if they can show us that the engines will only operate within the revised NTE zone in normal use. This way, manufacturers can avoid testing their engines under operation they would rarely experience in a vessel. However, manufacturers are still responsible for any engine operation seen in normal use. They are also responsible for ensuring that their specified operation is indicative of real-world operation. In addition, if a manufacturer designs an engine for operation at speeds and loads outside of the NTE zone, the manufacturer is responsible for notifying us so their NTE zone can be modified appropriately to include this operation.
We are not in this final rule setting an NTE limit for auxiliary marine engines. We do not yet have enough data on the operating characteristics of auxiliary engines to determine NTE zones and the associated limits for these engines. We expect to pursue similar requirements for land-based nonroad diesel engines. If we adopt NTE requirements for land-based nonroad diesel engines, we expect to extend those provisions to marine auxiliary engines at the same time.
The NTE provisions will go into effect in the 2010 model year for post-manufacture marinizers and in the 2007 model year for other manufacturers for all commercial marine diesel engines. Manufacturers have agreed to collect and show us data on their engines operating in the NTE zone before the NTE standards take effect. We may also choose to require them to give us this data under §208 of the Clean Air Act. This delay in implementation of the NTE provisions for most Category 1 engines will provide reasonable lead time by allowing more time to collect data and assess engine operation in the NTE zone. For larger engines, the early banking program will provide manufacturers with an incentive to produce low-emission engines prior to 2007. This way, if these manufacturers chose to stagger their product line and produce low emission engines early, they will be able to add NTE-type testing to the testing they perform while calibrating their engines.
