5. Determination of Maximum Test Speed
The determination of maximum test speed, where speed is the angular velocity of an engine's crankshaft (usually expressed in revolutions per minute, or rpm) is an important aspect of the duty cycles and "not-to-exceed" (NTE) zones described in this document (see also 40 CFR 94.107). We define the maximum test speed of an engine as the single point on an engine's maximum-power versus speed curve that lies farthest away from the zero-power, zero-speed point on a normalized maximum-power versus speed plot. In other words, consider straight lines drawn between the origin (speed=0, load=0) and each point on an engine's maximum-power versus speed curve (see Figure 1). Maximum test speed is defined as that point where the length of this line reaches its maximum value. Examples of results from this calculation are illustrated by circles superimposed on four maximum-power versus speed curves in Figure 1.
G. Not-to-Exceed Standards and Related Requirements
Our goal is for engines to control emissions over the broad range of in-use speed and load combinations that can occur on a vessel, achieving real-world emission reductions, rather than just controlling emissions under certain laboratory conditions. An important tool for achieving this goal is an in-use program with an objective standard and an easily implemented test procedure. Historically, we have taken the approach of setting a numerical standard on a specified test procedure and relying on the prohibition of defeat devices to ensure in-use control over a broad range of operation not included in the test procedure. 6
6 EPA letter from Jane Armstrong and Bruce Buckheit, October 15, 1998.
No single test procedure can cover all real world applications, operations, or conditions. Yet to ensure that emission standards provide the intended benefits in use, we must have a reasonable expectation that emissions under real world conditions reflect those measured on the test procedure. The defeat device prohibition is designed to ensure that emissions controls are employed during real world operation and not just under laboratory or test procedure conditions. However, the defeat device prohibition is not a quantified standard and does not have an associated test procedure, so it does not have the clear objectivity and ready enforceability of a numerical standard and test procedure. As a result, the current focus on a standardized test procedure makes it harder to ensure that engines will operate with the same level of control in the real world as in the test cell.
Because the E3 duty cycle uses only four modes on an average propeller curve to characterize marine diesel engine operation, we are concerned that an engine designed to the duty cycle would not necessarily perform the same way over the range of speed and load combinations seen on a vessel. The E3 duty cycle is based on an average propeller curve, but a propulsion marine engine may never be fitted with an "average propeller." For instance, a light vessel with a planing hull may operate at lower torques than average while the same engine operated on a heavy vessel with a deep displacement hull may operate at higher torques than average. This can largely be a function of how well the propeller is matched to the engine and vessel. A planing hull vessel can operate at high torques at low speed prior to planing.
To ensure that emissions from propulsion engines are controlled over the full range of speed and load combinations seen on vessels, we are establishing a zone under the engine's power curve where the engine may not exceed a specified emission standard, for any of the regulated pollutants, under the kind of operation that could reasonably be expected to be seen in the real world. In addition, the whole range of real ambient conditions is included in this "not-to-exceed" (NTE) zone testing. The NTE zone, limit, and ambient conditions are described below.
At the time of certification, manufacturers would have to submit a statement that its engines will comply with these requirements under all conditions that may reasonably be expected to occur in normal vehicle operation and use. The manufacturer must provide a detailed description of all testing, engineering analysis, and other information that forms the basis for the statement. This certification statement must be based on testing and/or research reasonably necessary to support such a statement and on good engineering judgment. This supporting information would have to be submitted to us at certification if we request it; manufacturers would not necessarily be required to submit NTE test data for compliance during certification.
We believe there are significant advantages to taking this sort of approach. The test procedure is very flexible so it can represent many in-use speed and load combinations and ambient conditions. Therefore, the NTE approach takes all of the benefits of a numerical standard and test procedure and expands it to cover a broad range of conditions. Also, laboratory testing makes it harder to perform in-use testing since either the engines would have to be removed from the vessel or care would have to be taken that laboratory-type conditions can be achieved on the vessel. With the NTE approach, in-use testing and compliance become much easier since emissions may be sampled during normal vessel use. Because this approach is objective, it makes enforcement easier and provides more certainty to the industry of what is expected in use versus over a fixed laboratory test procedure.
Even with the NTE requirements, we believe it is still important to retain standards based on the steady-state duty cycles. This is the standard that we expect the certified engines to meet on average in use. The NTE testing is more focused on maximum emissions for segments of operation and should not require additional technology beyond what is used to meet the new emission standards. We believe that basing the emissions standards on a distinct cycle and using the NTE zone to ensure in-use control creates a comprehensive program. In addition, the steady-state duty cycles give a basis for calculating credits for use in the averaging, banking, and trading program.
The NTE zone for marine diesel engines certified with the E3 duty cycle is illustrated in Figure 2 and is defined by the power curve of the engine up to rated speed. This zone is based on the range of conditions that a marine diesel propulsion engine typically experiences in use. For variable-speed engines with variable-pitch propellers certified to the C1 duty cycle, this zone is extended to include all torque points between the E3 power curve (between 63 percent and 100 percent speed) and the lug curve. These NTE zones are divided into two subzones above and below 45% of power at maximum test speed.
