September 28, 2009

Khesha T. Reed

Manager, Heavy-Duty and Nonroad Engine Group

Compliance and Innovative Strategies Division

Office of Transportation and Air Quality

U.S. Environmental Protection Agency

1200 Pennsylvania Ave. N.W.

Washington, D.C. 20460

Via email and overnight mail

Re: Support for EMA’s Request for Adminstrator Approval of New Maintenance Intervals for the Refill of 

Reductant Fluid Tanks Utilized With Heavy-Duty On-Highway SCR-Based Emission Control Systems

Dear Ms. Reed,

Cummins has submitted the first of what will be several certification applications for engine 

families utilizing an emissions control system referred to as a Selective Catalytic Reduction (“SCR”) 

device. These devices require the addition of reductant, being referred to as Diesel Exhaust Fluid 

(“DEF”), into the engine exhaust to accomplish the emission reduction. Typically, the amount of DEF 

required to be added is about 2 to 4 % of the fuel consumed. For Heavy-Heavy and Medium-Heavy Duty 

Diesel Engines, EPA requires that aftertreatment systems, such as SCR devices, not be required to be 

maintained more frequently than 100,000 miles initially and then no more frequently than 150,000 miles 

thereafter (86.094-25). Clearly it is unreasonable to have such a great amount of DEF on board as to 

have a range of 150,000 miles.

Under section 86.094-25(b)(7)(ii) EPA allows manufacturers to petition for reconsideration of the 

minimum maintenance interval. The Engine Manufacturers Association, of which Cummins is a member, 

filed such a petition on June 11, 2009. EPA has not yet acted upon EMA’s request. Cummins needs 

quick turn-around of its applications for certification, and is submitting this letter to provide further 

justification and support for the shorter maintenance interval requested by EMA.

The need for a shorter maintenance interval can be seen by providing a couple of real-world 

examples. At the upper end of real world examples is a line haul truck. In the case of a line haul truck, 

the average fuel economy is approximately 6 mpg. Over 150,000 miles, this line haul truck would 

consume 150,000 miles / 6 miles/gallon, or 25,000 gallons of diesel fuel. At a 3% average DEF 

consumption rate, this would amount to 25,000 gallons x 0.03, or 750 gallons of DEF. Assuming a 

density of 9 lb / gallon, this amount of DEF would weigh 6,750 lbs. A line haul truck is allowed a 

maximum gross vehicle weight of 80,000 lbs. The tare, or empty, weight of a typical line haul truck is 

35,000 lbs, leaving 45,000 lbs for cargo. The requirement to have a DEF tank capable of carrying 750 

gallons or 6,750 lbs of DEF would reduce the cargo-carrying ability to 38,250 lbs, or by 15%. A new line 
haul truck typically runs approximately 120,000 miles a year in the first few years of operation. This 

means that the DEF refill interval would be 1.25 years. 

At the other extreme of real-world examples, Cummins provides engines for use in ‘chassis cabs’. 

We certify these engines as medium heavy-duty diesel engines. If we assume that the average fuel 

economy of engines used in chassis cabs is 12 mpg, then, over 150,000 miles, a chassis cab would 

consume 150,000 miles / 12 miles/gallon, or 12,500 gallons of diesel fuel. At a 3% average DEF 

consumption rate, this would amount to 12,500 gallons x 0.03, or 375 gallons of DEF. Once again 

assuming a density of 9 lb / gallon, this amount of DEF would weigh 3,375 lbs. A typical class 3 chassis 

cab has a carrying capacity of 5000 lbs. The requirement to carry 3,375 lbs of DEF would reduce the 

cargo carrying capacity to 1,625 lbs, or by 68%. A chassis cab typically operates 20,000 miles per year. 

This means that the DEF refill interval would be 7.5 years.

Information about these two examples are summarized on the following table.

Application Minimum 

Maintenance 

Interval

DEF Required 

(gallons)

DEF Required 

(pounds)

Time Between 

DEF Refills

Line Haul Truck 150,000 miles 750 6,750 1.25 year

Chassis Cab 150,000 miles 375 3,375 7.5 years

Paragraph 86.094-25(b)(7)(ii) requires a petitioner to show that the scheduled maintenance is 

new, and that this new scheduled maintenance is a direct result of the implementation of new technology 

not found in production prior to the 1980 model year. Certainly this is the case in this situation where the 

new technology being employed is SCR, and the fact that SCR requires the addition of a reductant in 

order to perform its emission reduction purpose.

Paragraph 86.094-25(b)(7)(ii) goes on to require a petitioner to declare whether the maintenance 

is emission-related or non-emission-related and if it is determined to be emission-related whether the 

maintenance critical or non-critical. As is declared in EMA’s petition, this scheduled maintenance is 

considered to be critical emission-related maintenance.

Finally paragraph 86.094-25(b)(7)(ii) requires the petitioner to suggest a maintenance interval and 

provide evidence that this scheduled maintenance interval is the ‘maximum feasible maintenance 

interval’. 

Cummins would propose that two possible shorter maintenance intervals exist, each of which 

drive decidedly different DEF refilling networks. The first possibility is to demand a DEF refill interval on

the order of magnitude of the lube oil change interval. In the case of the examples provided above, line 

haul trucks typically have a lube oil change interval of 30,000 miles. Chassis cabs typically go 7,500 

miles between oil change intervals. If this were demanded by the Agency, a DEF refilling infrastructure 
would need to be developed around the heavy-duty vehicle lube oil change infrastructure. The following 

table provides information pertinent to this case. The same assumptions are made in calculating these

values as were made in the above analysis of the 150,000 interval.

Application Lube Oil Change 

Interval

DEF if required 

to have sufficient 

DEF on board to 

go an oil change 

interval

(gallons)

DEF if required 

to have sufficient 

DEF on board to 

go an oil change 

interval

(pounds)

Time Between 

DEF Refills

Line Haul Truck 30,000 miles 150 1,350 3 months

Chassis Cab 7,500 miles 18.75 168.75 4.5 months

The second possibility is to demand a DEF refill interval on the order of magnitude of the diesel 

refueling interval. Line haul trucks typically have a fuel tank range of 1620 miles. Chassis cabs typically 

can go a maximum of 624 miles between fuel tank refills. If this were demanded by the Agency, a DEF 

refilling infrastructure would develop around the refueling infrastructure.

Application Max Refueling 

Interval

DEF if required 

to have sufficient 

DEF on board to 

go a fuel change 

interval

(gallons)

DEF if required 

to have sufficient 

DEF on board to 

go a fuel change 

interval

(pounds)

Time Between 

DEF Refills

Line Haul Truck 1620 miles 8.1 72.9 4.9 days

Chassis Cab 624 miles 1.56 14.04 11.4 days

As pointed out above, heavy duty vehicles are purchased to do work, they move either people or

goods or both. Every effort is made to reduce the tare weight to increase cargo-carrying capacity. In 

addition, as the form of the emission standards (g/bhp-hr) shows, as heavy-duty engines do more work, 

they produce more emissions. So, every effort should be made on EPA’s part to keep heavy-duty 
vehicles as efficient as possible, and the DEF tank size practical. Even though having a DEF refill 

infrastructure built around the refueling interval requires more DEF refueling sites than would a DEF 

refilling infrastructure built around the lube oil change infrastructure, the increase in vehicle efficiency 

more than makes up for the cost of doing so.

Cummins believes that the ‘maximum feasible maintenance interval’ is that associated with the 

refueling interval and that the three cases enumerated in EMA’s petition (duplicated below) represent the 

‘maximum feasible maintenance interval’.

...the DEF tank refill intervals for which EMA seeks the Administrator's approval (the 

"Recommended DEF Re-Fill Intervals") are, as follows:

(i) for HDOH vehicles programmed with a driver inducement strategy that derates the engine at a 

rate of 1% per minute up to 40%, the DEF tank refill interval must provide a range of vehicle 

operation that is no less than the range equal to the HDOH vehicle's fuel capacity (i.e., as 1:1 

ratio);

(ii) for all other HDOH vehicles that also have a constant DEF level indicator, the DEF tank re-fill 

interval must provide a range of vehicle operation that is no less than twice the range of the 

HDOH vehicle's fuel capacity (i.e., a 2:1 ratio); and

(iii) for all other HDOH vehicles that do not have a constant DEF level indicator, the DEF tank refill interval must provide a range of vehicle operation that is no less than three times the range of 

the HDOH vehicle's fuel capacity (i.e., a 3:1 ratio).

I hope these examples help EPA see the necessity of granting EMA’s petition, and that EPA will 

do so expeditiously.

Sincerely,

Robert A. Jorgensen

Executive Director – Product Environmental Management

Cummins Inc.