7-15-2010

Strawman for SCR Workshop Discussion

As we approach the Selective Catalytic Reduction (SCR) public workshop on July 20, 2010 (see 

75 Fed. Reg. 39251, July 8, 2010), EPA would like to present some initial thoughts regarding 

possible outcomes concerning the operation of heavy-duty highway engines equipped with SCR. 

This document is intended to be a strawman to be used as a starting-off point for the workshop 

discussion only. The ideas presented here are based on our experience with SCR to date and do 

not represent final agency decisions.

In order to maximize the productiveness of the workshop, presentations from the public should 

directly respond to the topics and ideas outlined. In addition to comments received at the 

workshop, the agency will accept written comments through August 20, 2010 (see 75 Fed. Reg. 

39251, July 8, 2010 for submission instructions). All input received will be considered in 

evaluating future policies regarding SCR technology.

As always in implementing EPA’s NOx (and all other) standards, certification will require 

engines to comply with applicable regulations. In particular, 40 CFR § 86.004-25 and 40 CFR § 

86.094-25, pertinent to allowable maintenance, 40 CFR § 86.094-22, pertinent to adjustable 

parameters, and 40 CFR § 86.004-2, 40 CFR § 86.082-2 and 40 CFR § 86.004-16, which address 

Auxiliary Emission Control Devices (AECDs), are provisions that are particularly relevant to 

engines using SCR technology.

Applicability

 All complete heavy-duty highway engine certification applications submitted after 

January 1, 2011 (based on normal certification practices)

Reductant Level Monitoring 

 Need some indication of reductant level for the operator

Inducement for Low Level Reductant

 A final inducement should be initiated so the engine/vehicle is limited to 5 mph, no 

power, or idle only when the SCR system is no longer able to dose

 Final inducement (5 mph limit, no power or idle only) to be determined by manufacturer 

should account for safety concerns and allow for diagnostics and restart after refill

 Initiate operator warning prior to any inducement (for example at 2.5% or higher 

reductant level)

 If inducement is phased in, initiate another operator warning prior to final inducement

Reductant Quality 

 Need quality sensor or NOx sensor system with comparable capabilities by January 1, 

2012

 Be able to detect poor reductant quality that causes non-compliance with applicable 

regulations

 Should be able to detect non-compliance with applicable regulations within 1 hour of 

engine restart or change in level of reductant tank 
7-15-2010

Inducement for Poor Quality Reductant

 Notify operator when non-compliance with applicable regulations (or tampering fault –

see below) is detected

 A final inducement should be initiated so the engine/vehicle is limited to 5 mph, no 

power, or idle only within 4 hours of detecting non-compliance with applicable 

regulations

 Final inducement (5 mph limit, no power or idle only) to be determined by manufacturer 

should account for safety concerns and allow for diagnostics and restart

 Initiate operator warning prior to any inducement 

 If inducement is phased in, initiate another operator warning prior to final inducement

 If poor quality reductant (or same fault for tampering – see below) is detected again 

within 40 hours:

o Immediately notify owner

o Ramp to 5 mph limit, no power or idle only within 30 minutes

Indicators of Tampering

 Systems should be designed to be tamper resistant to reduce the likelihood that the SCR 

system will be circumvented

 Manufacturers should be careful to review any element of design that could be tampered 

with and prevent the proper operation of the SCR system

 The following actions should be considered at a minimum:

o Disconnected reductant level sensor

o Blocked reductant line or dosing valve

o Disconnected reductant dosing valve

o Disconnected reductant pump

o Disconnected SCR wiring harness

o Disconnected NOx sensor (that is incorporated with the SCR system)

o Disconnected reductant quality sensor

o Disconnected exhaust temperature sensor

o Disconnected reductant temperature sensor

Inducement for Tampering

 Same as inducement for poor quality reductant

Maintenance Intervals

 Petitions for new maintenance and maintenance intervals shorter than that required by 

regulations (adjustment, cleaning, repair or replacement of the reductant or filter) may be 

supplied by each manufacturer or by a group explicitly representing the manufacturer

 Each petition must address the technological necessity of the proposed maintenance 

intervals

Freeze Protection

 Freeze protection systems will be evaluated as Auxiliary Emission Control Devices 

(AECDs)

 The following test procedure has been offered as an example of a test procedure that 

could be used for ensuring that the AECD is used appropriately 
7-15-2010

 SCR systems that are capable of fully functional dosing at the conclusion of the test 

procedure might be considered acceptable

1. Prior to Procedure: 

 Temperature: Reductant at 20° F (maximum)

2. Soak Conditions:

 Temperature: 0° F (maximum)

 Time: 72 hours or solid reductant (whichever occurs first)

3. Test Duty Cycle:

 Temperature: 0° F (maximum)

 Time: 70 minutes (or 40 minutes) (maximum)

a. Start engine and idle with no engine load for 20 minutes

b. Operate engine at no more than 40% load at rated speed for up to 50 

minutes (or 20 minutes)

 Ensure, by January 1, 2012, that reductant does not refreeze during operation

 Ensure, by January 1, 2012, that dosing occurs within 40 minutes instead of 70 minutes 

outlined in the original test procedure

Unregulated Pollutants

 No emission control device or system shall be used that causes or contributes to an 

unreasonable risk to public health, welfare or safety

 NH3 Slip - Emissions below 10 PPM average over the applicable test cycles would be 

considered acceptable and not require further review (Need to show durability for entire 

useful life)

 Dioxins - Copper zeolite test program at NVFEL 

o Not final

o Based on results to date, there is no indication that the Cu-zeolite catalysts tested 

cause unreasonable risk

o Certification applications with Cu-zeolite catalyst configurations represented by

NVFEL test results can be approved

Infrastructure

 Show that reducing agent will be widely available and readily accessible

 At a minimum, manufacturers should have reducing agent available at dealerships and 

provide a back up plan (such as a toll free number) that operators can use if the are unable 

to obtain it elsewhere

 Manufacturers should also work with 3rd parties to ensure that reductant is widely

available at appropriate locations, in addition to dealerships