Daily Rules, Proposed Rules, and Notices of the Federal Government
Until the effective date of the final guidance and interpretations, manufacturers should continue to refer to the regulations and the existing guidance documents noted below and to work with their certification representatives. We recognize that SCR technology will continue to mature, and we anticipate that appropriate designs
This draft document provides specific examples of how we interpret existing certification regulations and how we intend to apply these regulations to heavy-duty diesel engines using SCR systems, based on the information available to us. These examples are not exclusive and are to be considered examples. Manufacturers remain able to present their own unique strategies that are not the same as the examples we are providing, and such strategies will remain subject to our review and approval under the certification regulations. Manufacturers must still show EPA that they meet all statutory and regulatory requirements when they apply for certification.
In promulgating the 0.20 gram per brake horsepower-hour NO
To comply with the NO
In developing SCR systems, manufacturers consulted with EPA about how SCR systems could be designed and what other steps would be needed (
Manufacturers have also worked to increase DEF availability through infrastructure development. DEF infrastructure and sales volume have continued to grow since introduction of 2010 model year trucks equipped with SCR systems. Initially, DEF availability was concentrated around major truck routes, but has since increased in areas away from these locations. DEF is now available for sale in every state at truck stops and service facilities, and is available for delivery to fleet locations, as well. To assist drivers in finding DEF, multiple Internet-based DEF locator services have also been developed. Sales volumes of DEF are increasing significantly and are believed to correlate with the increased delivery and use of SCR equipped trucks. Increasing demand supported by sales volume should continue to drive the expanding infrastructure.
Under Section 203(a)(1) of the Clean Air Act, engines and/or vehicles must be certified as conforming with all applicable regulations before they may be introduced into commerce. Of particular relevance for on-highway heavy-duty diesel engines using SCR technology are the provisions that govern adjustable parameters at 40 CFR 86.094-22.
It is important for manufacturers to control the emissions performance of an engine or vehicle over the full range of any adjustable parameter in order to ensure that in-use operation is as good as projected at the time of certification. When emission-related parameters can be adjusted, there is a concern that the engine or vehicle can be operated at settings other than the manufacturer's recommended setting, possibly increasing emission levels.
If a parameter is subject to adjustment, the engine may be tested over any point in the range of adjustment and must meet the emissions standard through the range of adjustment. The Administrator determines the range of adjustment for emissions testing based on whether the means used to inhibit improper adjustment (
The emission control efficiency of an SCR system is highly dependent on the presence and quality of the reducing agent. Consequently, it is critical that a SCR-equipped vehicle be designed so that it is highly unlikely that the vehicle will be used without proper reducing agent. Given that most SCR system designs store the required DEF in a tank located on the vehicle and depend on the vehicle operator to refill the tank with DEF, EPA has indicated in previous guidance that manufacturers relying on SCR systems for emission control must incorporate engine design elements that make it highly unlikely the vehicle will operate for any substantial period without the appropriate DEF. In practice, this has meant designing engines or vehicles to alert operators of when the engine will run out of DEF, when the DEF is inadequate, or if the SCR system is not properly operating due to tampering or some malfunction. This has also meant designing engines or vehicles with features that motivate operators to ensure proper use of the SCR system, such as engine derates and vehicle speed inhibitors. Engine derates and vehicle speed inhibitors alter important vehicle performance characteristics, such as acceleration, maximum vehicle speed attainable, and ability to maintain speed under various loads, that are clearly noticeable to a driver.
On March 27, 2007, EPA issued guidance regarding the certification of light-duty and heavy-duty motor vehicles and heavy-duty motor vehicle engines using SCR systems (CISD-07-07).
On February 18, 2009, EPA issued additional guidance (CISD-09-04) to supplement CISD-07-07.
On December 30, 2009, EPA revised CISD-09-04.
EPA has continued to monitor the development of SCR technology and its effectiveness in achieving emission control in use. On July 20, 2010, in conjunction with the California Air Resources Board (CARB), we conducted a public workshop to review existing guidance and policies regarding design and operation of SCR-equipped heavy-duty diesel engines.
For the 2010 and 2011 model years, EPA has certified a total of 71 on-highway heavy-duty diesel engine families with SCR systems produced by 11 engine manufacturers. As part of the certification process, engine manufacturers are required to disclose various aspects of the SCR system designs, including elements of their system that may be adjustable parameters. To date, manufacturers' designs have employed driver warnings and inducements for low reductant level, poor reductant quality, and tampered or malfunctioning SCR systems.
In order to ensure adequate availability of DEF for use with manufacturers' engines, at the time of certification EPA reviews manufacturers' plans for DEF availability and accessibility. EPA expects manufacturers to have DEF available at their dealerships, to encourage DEF availability at third-party locations, and to have an emergency backup plan in case DEF is not readily available.
When manufacturers implement new emission controls, the engine technology generally evolves and the manufacturers make improvements over the course of initial model years as they develop and certify engines and vehicles for each new model year. The process of certification involves interaction between manufacturers and EPA technical staff about the nature and effectiveness of emission controls and often results in manufacturers modifying emission control strategies based on feedback from EPA. In the case of SCR technology, manufacturers have certified only a few model years of engines that incorporate SCR technology, and EPA has seen maturing approaches to implementing the technology. For example, from the 2010 to 2011 model years manufacturers improved or developed new engine/vehicle diagnostic software that provides more or better driver warnings and inducements related to the SCR system. Similarly, manufacturers are also evaluating various sensors that are expected to reduce the amount of time necessary to detect poor quality DEF in future model years. As with other new engine technologies, defects in the operation of SCR system strategies (
The California Air Resources Board (CARB) recently conducted field investigations within the State of California to evaluate implementation of SCR technology for 2010 model year vehicles.
CARB conducted surveys of DEF availability in March 2010 and August 2010. Both surveys indicated that DEF is readily available at major diesel truck stop refueling stations along major interstate highways in California. In the first survey DEF was determined to be available at 85 percent of refueling stations, and in the second survey DEF was determined to be available at 92 percent of refueling stations. In addition, both surveys indicated that 30 percent of retailers that normally supply parts for heavy-duty vehicles have DEF available. CARB noted that as older engines are retired and an increasing number of SCR-equipped engines enter into operation, the availability of DEF should increase with demand. It concluded that DEF is currently being offered in adequate supply for the relatively limited number of vehicles using SCR.
In September 2010, CARB conducted random inspections of 69 trucks equipped with 2010 model year engines to determine whether DEF was being used, whether the DEF was of appropriate quality, and whether driver warning indicators (
In the second half of 2010, CARB conducted an evaluation of SCR inducements on three trucks equipped with 2010 model year engines and SCR systems. The trucks evaluated were a Freightliner Cascadia equipped with a 12.8-liter Detroit Diesel DD13 engine (Test Vehicle 1), a Kenworth T800 equipped with a 14.9-liter Cummins ISX engine (Test Vehicle 2), and a Dodge 5500 equipped with a 6.7-liter Cummins ISB engine (Test Vehicle 3). Each truck was operated under various test conditions to observe the operation of driver inducements and their effectiveness in compelling the driver to take a particular course of action. The conditions under which the trucks were operated included: (1) Operation until the DEF tank was depleted, (2) operation with water in the reductant tank instead of DEF, and (3) operation with a disabled DEF system. CARB staff referenced the vehicle owner's manuals and the February 2009 EPA guidance to ascertain the expected driver warning indicators and inducement strategies that were expected in each condition.
On Test Vehicle 1, the warnings and inducements were implemented as expected. CARB deemed the warnings effective in drawing the driver's attention to the need for SCR-related service. The initial inducement incorporated in Test Vehicle 1 was a 25 percent engine torque derate and a 55 mph speed limitation. CARB concluded that driving the truck with these inducements was neither acceptable nor tolerable, especially when trying to accelerate or driving up-hill, and would
On Test Vehicles 2 and 3, the warnings and some inducements were implemented as expected, but certain inducements were not. Test Vehicle 2 implemented the initial inducement (25 percent engine torque derate) in response to DEF depletion, DEF contamination, and DEF tampering conditions, but failed to implement the severe inducement (5 mph speed limitation) in response to any of these conditions. Test Vehicle 3 incorporates an engine no-restart severe inducement after a 500-mile to no-restart countdown. After the 500-mile countdown reaches zero and a safe harbor event (key-off) is experienced, the truck should not restart. The inducement worked as expected in response to DEF contamination and DEF tampering conditions. In response to the DEF depletion condition, Test Vehicle 3 started the 500-mile to no-restart countdown as expected. However, after the countdown reached zero and the truck was shut off, the truck successfully started the next day and reset the countdown. On a subsequent restart attempt after the countdown reached zero, the truck successfully implemented the no-restart condition.
CARB contacted Cummins, the engine manufacturer for Test Vehicles 2 and 3, about the failures. Cummins was aware of and addressing the issues underlying the failures. In the case of Test Vehicle 2, Cummins in the second quarter of 2010 had implemented a correction on their engine production line and in the third quarter of 2010 had begun a voluntary recall of the engine family to correct the problem.
In 2010, the American Trucking Associations (ATA) through its technical advisory group conducted a survey of 12 trucking fleets operating across the United States regarding their experience operating trucks with SCR-equipped engines.
None of the surveyed fleets reported any problems locating DEF and none reported an engine derate, vehicle speed limitation, or no-restart event caused by operation with an empty DEF tank. Similarly, no fleet reported issues with the quality of DEF. There were six reported instances of an engine derate resulting from circumstances other than an empty DEF tank. Two of these instances were caused by malfunctioning sensors and four were caused by melted DEF supply hoses. None of these instances were associated with the behavior of the operator. Survey respondents also reported a total of five instances of NO
In 2010, Cummins collected information from 47 different customer-owned vehicles that were equipped with Cummins 11.9-liter and 15-liter engines using SCR.
• DEF level was between 5 and 10 percent of tank capacity for less than 0.13 percent of the operating miles (
• DEF level was between 2.5 and 5 percent of tank capacity for less than 0.03 percent of the operating miles (
• DEF level was between zero and 2.5 percent of tank capacity (a condition at which engines experienced derated performance) for less than 0.04 percent of the operating miles (
• DEF level was at zero percent of tank capacity (a condition at which engines experienced derated performance) for less than 0.02 percent of the operating miles (
In addition, DEF quality was unacceptable (
In 2010, Navistar retained EnSIGHT, Inc. to test three 2010 model year SCR-equipped trucks to analyze inducements provided for in EPA certification guidance.
Based on their testing program, EnSIGHT reported the following:
• All trucks physically could be operated for extended periods under an initial inducement. Provided the driver took particular actions, final inducements could be avoided indefinitely. For example, the Freightliner Cascadia was driven over 1,000 miles on an empty DEF tank at a limited speed of 55 mph, which is the initial inducement. As long as no more than 30 percent of the fuel tank capacity (approximately 100 gallons) was added at any single refueling event, the final inducement, a 5 mph vehicle speed limitation was not triggered. The Kenworth T-660 was driven with an empty DEF tank and a 25 percent engine torque derate, which is the initial inducement. As long as the engine was not shut off for more than a few minutes at a time, the 5 mph vehicle speed limitation final inducement was not triggered.
• When DEF tanks were empty and water was added instead of DEF, two trucks were able to run indefinitely. When the Dodge 5500 was low on DEF and began its 500-mile to final inducement (
• SCR system components could be repeatedly disconnected and reconnected to avoid particular inducements. On the Dodge 5500, the driver was able to disconnect the injector electrical connector, which would initiate a 500-mile to final inducement (
• Although the testing program was designed to intentionally operate the trucks until final inducements were encountered, EnSIGHT also provided an assessment of the impact of initial inducements on driver behavior. They concluded that a 25 percent engine torque derate would not induce a corrective response by the drivers, including when the truck was fully loaded. With this level of derate, EnSIGHT's drivers were able to operate the Freightliner Cascadia and the Kenworth T-660 at speeds up to 55 mph and 65 mph, respectively. Of the Kenworth T-660, EnSIGHT's drivers indicated that the truck could easily be operated and was acceptable for typical driving for long periods of time under derate.
The DEF infrastructure and sales volume have continued to grow since introduction of 2010 model year trucks equipped with SCR systems. Initially, DEF availability was concentrated around major truck stops and truck routes and 2.5-gallon jugs represented the common mode of supply. Although very limited, bulk DEF dispensing typically utilized small storage tanks located apart from the fuel islands at truck stops. The refilling of fuel and DEF tanks at truck stops was also more likely to require two separate purchase transactions.
The continually increasing DEF infrastructure and sales volume have resulted in improved DEF availability along major truck routes as well as other locations. “AdBlue and DEF Monitor,” a publication of Integer Research, reports that DEF is available for sale in jug form in every state.
Increasing demand supported by sales volume helps drive the continuing expansion of DEF infrastructure. The same locator service recently reported that more than 100 truck stops in the U.S. and Canada now have DEF available at the pump. Additionally, this service maintains a list of over 3,000 locations that have packaged DEF, and a majority of the locations are in the U.S. As truck stops such as Travel Centers of America roll out on-island DEF dispensers, they usually incorporate technology which allows for single transaction fuel and DEF filling, which makes buying DEF quicker, more efficient, and customer-friendly. On-island DEF dispensing typically requires truck stops to utilize a mini-bulk system with at least 800-gallon above ground storage tanks or even larger underground storage tanks. The transition to larger tanks supports bulk purchases as well as cheaper end-user prices for DEF. This information is consistent with the survey information discussed above.
Regarding DEF quality, ISO 22241-1 sets forth generally accepted industry-wide quality specifications for DEF that were developed by vehicle manufacturers and other affected stakeholders. The American Petroleum Institute (API) Diesel Exhaust Fluid Certification Program (
Considering the developments in SCR-related technologies, DEF infrastructure, and the other available information described above, we believe it is appropriate to further refine our guidance to manufacturers regarding certification of SCR-equipped engines to be compliant with applicable regulations. As discussed in this section of the document, on-highway heavy-duty diesel SCR systems introduced into commerce to date have been highly successful in inducing operators to refill DEF tanks on a timely basis and to avoid interfering with SCR operation, with a few specific exceptions.
As trucks equipped with SCR systems have been introduced into U.S. commerce, drivers have become familiar with this technology. Current information concerning in use operation of SCR-equipped trucks, including all of the studies and other information discussed above, indicates that warning signals work correctly and that drivers do not wait for SCR-related inducements to be triggered to ensure appropriate and continuing operation of the systems. Specifically, the overwhelming majority of drivers surveyed by CARB, ATA, and Cummins did not wait for activation of warning indicators prior to refilling their DEF tanks and, where warnings did occur, generally did not drive distances long enough to lead to activation of inducements. Further, as the infrastructure for making DEF available becomes even more widespread, drivers will have increased and more convenient access to DEF when they need it. As documented in part by CARB's survey, there are currently few availability issues and those appear to stem primarily from limited situations where DEF was not found at the first location at which it was sought. As DEF infrastructure and supply continue to expand, EPA also expects the price of DEF to decrease, in part because of the move to bulk dispensing that is already underway. In addition, EPA expects that the DEF quality assurance programs described above will make it increasingly easy for drivers to find DEF which meets the specifications necessary for proper operation of the SCR systems. The strong indication from all of this evidence is that DEF warning systems are working correctly, and that when warned, drivers have not continued to drive distances long enough to lead to inducements. Inducements appear to be triggered in very few cases.
Navistar's study and CARB's field evaluation provide some evidence indicating that in some cases there have been issues related to SCR-equipped engines and assurance of their proper operation. Navistar's study identifies specific problems associated with the design or manufacture of certain SCR-equipped engines, and outlines the intentional actions taken by drivers employed by Navistar's contractor in conducting the study. The study's findings are properly considered in the context of all the available information on SCR operation. In light of the investigations and surveys conducted by CARB, ATA, and Cummins, EPA does not believe Navistar's findings reflect the overall efficacy of SCR systems on heavy-duty diesel engines currently in operation or the way they are actually used.
Most of Navistar's findings resulted from actions by the contractor's drivers to intentionally circumvent the manufacturer-designed inducements of the three test vehicles. For example, drivers avoided triggering inducements associated with an empty DEF tank by limiting refueling quantities or keeping the truck running when it normally would be turned off. Both ways of circumventing the inducements exact their own costs on drivers in terms of time, convenience, and expense. To illustrate, never refilling above about 30% of the tank leads to approximately three times as many refueling events, and the time and expense associated with this kind of disruption detract from the efficient operation of truck operators, who work in a competitive business. Navistar's contract drivers also disconnected and reconnected various SCR system components as a means of avoiding DEF inducements. Such intentional actions would be considered tampering and are illegal.
We also do not agree with Navistar's view that initial inducements are ineffective to produce corrective responses by drivers. ATA's fleet survey indicates that drivers do not favor inducements involving an engine power derate, especially if it occurs while a truck under heavy load is driving up-hill. Thus, drivers are likely to maintain proper SCR operation to avoid encountering these inducements. CARB's investigation shows that most inducements functioned properly during expected truck operating conditions and their assessment of the effectiveness of initial inducements was contrary to Navistar's findings. CARB determined that the inducements were effective because operating in a way that avoids the inducement strategies and raise the risk of costly repairs would not be worth the downtime and potential financial loss to business. In fact, Cummins' survey, which included some of the same 15-liter engines in Navistar's study, found that surveyed trucks operated with DEF in their tanks for greater than 99.9 percent of their total operation. Cummins' survey also found that trucks operated with unacceptable DEF quality for less than 0.18 percent of their total operation. This strongly indicates that the inducements have the intended effect of motivating appropriate driver behavior.
The report of Navistar's study found that some manufacturers' designs did not adequately detect water in the urea tank and thus did not prevent the driver from refilling the tank with something other than DEF. Navistar and CARB findings on DEF quality detection were not consistent in all cases. For example, Navistar found that initial and final inducements for the Freightliner Cascadia equipped with the 12.8-liter Detroit Diesel DD13 engine were not triggered when the DEF tank was filled with water. During CARB's field investigation, both the initial and final inducements were implemented for Test
EPA's regulatory provisions for adjustable parameters are intended to ensure that manufacturers design their emissions control system in a way that makes it unlikely that they will be operated inappropriately. It appears that manufacturer's past SCR designs and EPA's guidance have resulted in highly effective controls to protect the operation of SCR systems, as evidenced by the surveys and other data which show that drivers are properly operating their SCR-equipped trucks. There have been indications of specific problems with some engines in-use, and the manufactures involved have been addressing them through production and other improvements as the problems are identified. We believe it is appropriate to evaluate the experience gained to date and to make continuing, appropriate adjustments to our certification process for SCR-equipped engines as technology evolves and in-use experience is gained. EPA recognizes that development of even more robust sensors and inducements does not negate past approaches implemented pursuant to existing regulations. Rather, continual improvement is expected given the mounting experience with, and the maturing of, SCR technology, and the greater availability of DEF. As improved strategies and capabilities for proper SCR operation become feasible, EPA may guide their application to provide even further assurance that the technology is operating as intended on SCR-equipped engines.
Several developments in SCR technology allow continuing refinement in SCR design. One area of potential improvement in design involves sensors that can detect poor quality DEF. Current SCR system designs incorporate NO
Since the 2010 model year, manufacturers have also been refining their engine/vehicle system diagnostics software to incorporate additional capabilities for implementing SCR-related inducements. For example, many manufacturers today have developed multiple triggers for triggering inducements, including detection of refueling, extended idling, and engine shutdown events. Incorporation of additional inducement triggers into designs further decreases the likelihood of improper operation of the SCR system. Manufacturers are also improving their diagnostics software to ensure that SCR-related inducements cannot be reset or erased by diagnostic scan tools available to the general public or by disconnecting components in the field.
Many manufacturers are implementing improved designs in their 2011 model year engines/trucks that may be sold in the State of California. After the July 2010 public workshop, CARB and EPA began encouraging manufacturers to adopt the elements of design that were discussed. In order to avoid the need for multiple engine/vehicle production designs, manufacturers have often incorporated the design elements of vehicles sold in California into their 49-state vehicles.
Improving sensor capabilities and inducement strategies should present low risk and little burden for both manufacturers and drivers. Manufacturers are already in the process of improving their SCR designs, and overwhelmingly drivers are not waiting for SCR-related warnings or inducements to be triggered before they refill DEF tanks and otherwise maintain proper operation of SCR systems. Given the importance of reducing NO
This section discusses design criteria for on-highway heavy-duty diesel vehicles or engines using SCR technology. EPA believes that vehicles and engines that meet these design criteria would meet the requirements of the regulations regarding adjustable parameters. EPA will still review each certification application to ensure that the regulatory provisions are met. Likewise, in the case of design criteria that are not fully specified in this guidance, EPA will review the application to ensure that the engine design meets the regulatory requirements. EPA may review and revise this guidance as the technology continues to mature and as EPA receives more information regarding the use of SCR systems. In addition, manufacturers may present other designs for EPA consideration. All designs will remain subject to EPA approval under the existing certification regulations.
As noted above, in determining the adequacy of an engine's means of inhibiting adjustment of a parameter, EPA considers the likelihood that settings other than the manufacturer's recommended setting will occur in use. With this in mind, EPA is providing these draft SCR adjustable parameter design criteria based on our view that an SCR-equipped vehicle that complies with these criteria will be adequately inhibited from use when the SCR system is not operating properly.
EPA is asking for comments on the draft guidance discussed below. The design criteria are divided into four categories. The categories are:
A. Reductant tank level driver warning system.
B. Reductant tank level driver inducement.
C. Identification and correction of incorrect reducing agent.
D. Tamper resistant design.
The emissions performance of SCR-equipped vehicles depends on having an adequate supply of appropriate quality reducing agent in the system. SCR systems require regular user interaction to ensure that the system is operating properly. Therefore, it is critical that the operator both know when reducing agent is needed and have enough time to replace it before it runs out. A properly designed driver warning system should address these concerns.
To achieve this design goal, under our criteria, the manufacturers would use a warning system including the following features:
1. The warning system should incorporate visual and possibly audible alarms informing the vehicle operator that reductant level is low and must soon be replenished. The manufacturer should design the warning system to activate well in advance of the reducing agent running out so that the operator is expected to have one or more refueling opportunities to refill the reductant tank before it is empty.
2. The warning alarm(s) should escalate in intensity as the reducing agent level approaches empty, culminating in driver notification that is difficult to ignore, and cannot be turned off without replenishment of the reducing agent.
3. To provide adequate notice, the visual alarm should, at a minimum, consist of a DEF level indicator, a unique light, reducing agent indicator symbol or message indicating low reducing agent level. The warning light, symbol or message should be different from the “check engine” or “service engine soon” lights used by the On Board Diagnostic (OBD) system or other indicators that maintenance is required. The symbol or message used as the warning indicator should unmistakably indicate to the vehicle operator that the reducing agent level is low. The reducing agent indicator symbol shown below has been generally accepted in the industry and EPA considers it acceptable as an indicator of low reducing agent level.
4. The light, indicator symbol or message should be located on the dashboard or in a vehicle message center. The warning light or message does not initially have to be continuously activated, but as the reducing agent level approaches empty the illumination of the light or message would escalate, culminating with the light being continuously illuminated or the message continuously broadcast in the message center. Many current designs have been found acceptable and EPA does not anticipate requiring changes in the foreseeable future. Unique SCR system warning lights and message designs that deviate from previously approved designs or the design criteria outlined above would need to be approved by EPA.
Manufacturers may also incorporate an audible component of the low DEF warning system. As the reducing agent level approaches empty the audible warning system should escalate.
The warning systems discussed above can play a critical role in achieving vehicle compliance. As noted, a well designed warning system should deter drivers from operating SCR-equipped vehicles without reducing agent. However, we believe an additional, stronger deterrent is necessary and appropriate. Therefore, at some point after the operator receives the initial signal warning that reductant level is low, it is important that the engine design incorporates measures to induce users to replenish the reducing agent.
Under these design criteria, manufacturers would design their engines with a final inducement system that accomplishes the following when the reductant tank is empty or the SCR system is incapable of proper dosing:
1. Maximum vehicle speed is decreased at the quickest safe rate to 5 miles per hour while the vehicle is operating; or
2. The maximum engine fueling and engine speed are decreased at the quickest safe rate while the vehicle is operating, resulting in engine shutdown or limiting operation capability to idle only.
Some manufacturers prefer to trigger the above final inducement only when the vehicle has stopped at a safe location. Under this approach, a vehicle may be assumed to be in a safe location if the engine is purposefully shut off (key turned to the off position), has experienced an extended idle of 60 minutes (as indicated by zero vehicle speed for 60 minutes), or a refueling event has occurred (meaning a volume of fuel has been added equal to or greater than 15 percent of vehicle operating fuel capacity).
If a manufacturer chooses to implement final inducement only when the vehicle is stopped, we believe the engine will need to be designed with the following additional characteristics:
a. Be able to trigger final inducement when the vehicle is stopped at a safe location. The final inducement will consist of limiting the vehicle speed to 5 mph, shutting the engine down, or limiting engine operation to idle only.
b. Prior to triggering final inducement, be able to impose a severe inducement which makes prolonged operation of the vehicle unacceptable to the driver and compels the driver to replenish the reducing agent prior to the SCR system becoming incapable of proper dosing. The severe inducement will consist of an engine derate, a vehicle speed limitation, or a limitation on the number of engine restarts. For example, an engine torque derate of 40 percent may be utilized as a severe inducement for the operator of a Class 8 line-haul truck to replenish the reducing agent. The severe inducement should occur while there is enough reductant in the tank to continue to provide proper SCR dosing for approximately one full day of vehicle operation. For example, it may be appropriate to initiate severe inducement with a 10 percent reserve of reducing agent in the reductant tank.
c. Be able to determine when the vehicle has arrived at a safe location for the purpose of imposing a final inducement. Such a determination will be based upon the vehicle experiencing the next key-off, refueling, or 60-minute idling event after imposing severe inducement. During the course of one day of vehicle operation, EPA believes it sufficiently likely an operator will encounter one of the three events triggering final inducement. In the unlikely scenario that one of the three events is not encountered, the severe inducement should still provide sufficient incentive for the operator to refill the reductant tank.
The above final and severe inducements are not meant to limit the use of other inducements prior to severe or final inducement. EPA encourages the use of additional inducements which would serve to minimize the amount of time either severe or final inducements are encountered.
When developing inducement strategies for review by EPA at the time of certification, manufacturers should be prepared to detail the type and level of inducements chosen and demonstrate how they will sufficiently compel drivers to maintain appropriate reductant levels and ensure vehicle operation is limited only to periods when proper SCR dosing is occurring.
EPA believes that an engine that is designed with warning and inducement strategies consistent with those above will be highly unlikely to be driven with an empty reductant tank, and therefore that such an engine would be adequately protected from operation with an empty tank.
Assuring that an SCR-equipped engine is unlikely to be operated without proper reducing agent calls for an