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 

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:

Immediately notify owner

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:

Disconnected reductant level sensor

Blocked reductant line or dosing valve

Disconnected reductant dosing valve

Disconnected reductant pump

Disconnected SCR wiring harness

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

Disconnected reductant quality sensor

Disconnected exhaust temperature sensor

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 

SCR systems that are capable of fully functional dosing at the
conclusion of the test procedure might be considered acceptable

Prior to Procedure: 

Temperature: Reductant at 20° F (maximum)

Soak Conditions:

Temperature: 0° F (maximum)

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

Test Duty Cycle:

Temperature: 0° F (maximum)

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

Start engine and idle with no engine load for 20 minutes

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 

Not final

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

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

7-15-2010

