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UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

NATIONAL VEHICLE AND FUEL EMISSIONS LABORATORY

2000 TRAVERWOOD ROAD

ANN ARBOR, MI 48105

 

May 4, 2012

 OFFICE OF

AIR AND RADIATION

MEMORANDUM

SUBJECT: Fuel Use with Dosing for DPF Regeneration

FROM: Lauren Steele, Office of Transportation and Air Quality

TO: Docket EPA-HQ-OAR-2011-1032

Regeneration Frequency

During both active automatic and parked manual diesel particulate filter (DPF) 

regenerations, emission rates may increase for some pollutants, especially nitrogen oxides (NOX)

when NOx-reducing aftertreatment devices are not present downstream of the DPF. Because of 

the potential effect on emissions, engine manufacturers are allowed to provide frequency factors 

that adjust for the average excess emissions during DPF regeneration, as part of the certification

process. During a series of certification tests, the DPF regeneration frequency represents the 

fraction of tests during which an automatic active regeneration occurs. Passive regenerations 

would not be counted in this frequency. Table 1 summarizes some information from EPA 

certification data regarding DPF regeneration frequency factors (FreqDPF), for two model years 

and two types of test cycles.

Table 1: Frequency Factors for Certified Engines

Test Cycle Model Year Low FreqDPF Average FreqDPF High FreqDPF

Urban 2008 Near zero 4.8 % Near 10 %

Highway 2008 Near zero 7.1 % Near 17 %

Urban 2011 Near zero 3.0 % Near 11 %

Highway 2011 Near zero 4.9 % Near 18 % a

a Excluding one outlier in this set with FreqDPF over 60%

It is difficult to translate this information into an over-the-road DPF regeneration 

frequency. We do not have information about the duration in minutes of regenerations that occur 

during test cycles, nor can we translate a typical 40-minute test cycle into an equivalent over-theroad driving distance. However, EPA has information from fire chiefs that indicates many fire 
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trucks are experiencing regeneration intervals of approximately 20-30 engine hours. Further, 

EPA has learned that individual regeneration events on fire trucks are often estimated to have a 

duration of between 20 to 40 minutes: closer to 20 minutes for automatic active regenerations, 

closer to 40 minutes for manual active regenerations. From the available duty cycle data for 

emergency vehicles, we observe that typical annual engine hours range from about 300 hours per 

year for some rural emergency vehicles, to over 1,600 engine hours for some urban emergency

vehicles, with a middle range vehicle running about 1,200 engine hours over a year.1From this 

information, some regeneration frequencies can be derived, though these do not have any

correlation to any frequency factor that may be associated with the engine certification for these 

vehicles.

Table 2 presents some estimates of the number of regeneration events an emergency

vehicle may experience if it had a DPF regeneration interval of 25 engine hours with varying 

annual operating hours. Assuming that an average regeneration event is estimated to last for 30 

minutes, the last row of Table 2 shows this would mean that about two percent of the engine’s 

total annual operating time would be spent regenerating.

Table 2: Estimated In-Use Emergency Vehicle Regeneration Events

Low Engine 

Hours

Middle Engine 

Hours

High Engine 

Hours

Annual Engine Hours 300 1,200 1,600

Annual Regeneration 

Events 12 47 63

Percent Operating Time 

Regenerating 2 % 2 % 2 %

Estimated Effects on Regeneration Frequency from This Action

As a result of this rulemaking, it is possible that some manufacturers will submit 

applications for AECD’s or field modifications with liberalized parameters under which 

automatic active and/or parked manual regenerations may occur, for engines on emergency

vehicles. The frequency of DPF regeneration in use may thus increase for these vehicles. 

If a requested modification does not include any recalibration of engine parameters, this 

simple increase in regeneration frequency would be associated with a decrease in the duration of 

each regeneration event. This would be expected because the shorter time interval would lead to 

a reduced soot loading at the time the regeneration is initiated, which would take less time to 

oxidize.

It is also possible that manufacturers may submit requests for engine recalibrations that 

enable more frequent passive regeneration and rely less on active regeneration, thereby reducing 

the frequency of automatic active and/or manual active regenerations.

 

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See Section IV.C.2(b) of the preamble to the proposed rule, see also Fire Apparatus Manufacturer’s Association, 

Fire Apparatus Duty Cycle White Paper, August 2004, available at 

http://www.deepriverct.us/firehousestudy/reports/Apparatus-Duty-Cycle.pdf
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For purposes of this analysis, EPA is providing an illustrative example of a fire truck that 

typically undergoes an automatic active regeneration every 25 engine hours, and it receives an 

approved field modification so that it may regenerate more frequently. Using this example, we 

illustrate the effect that more frequent manual active regenerations and/or automatic active 

regenerations may have on the number of regeneration events occurring on a truck with 1,200 

annual operating hours. In Table 3, we show the increased number of events if the interval 

between regenerations decreases to 12 engine hours in one case and 8 engine hours in another 

case. In this example, we also consider that the average duration of a single regeneration event 

may decrease from 30 to 25 or 20 minutes.

Table 3: Estimated Change in Emergency Vehicle Regeneration Events

12-Hour Interval 8-hour Interval

Annual Regeneration Events 97 97 143 144

Event Duration 25 min 20 min 25 min 20 min

Percent Operating Time 

Regenerating 3.4 % 2.7 % 5.0 % 4.0 %

From this example, we have shown that some increases in regeneration frequency may

result from this rule. In a vehicle whose active regenerations are enabled with fuel dosing, this 

type of modification could lead to increased fuel use from dosing. However, we do not have 

information about the likelihood of this type of modification, and it is quite possible that some 

engine manufacturers may prefer solutions that increase passive regeneration, or solutions that 

generate the extra heat needed for regeneration by means other than fuel dosing.

Fuel Use from Dosing

Where DPF systems employ fuel dosing to enable active automatic regenerations, the 

active regeneration event can affect the vehicle’s fuel consumption. Some operators have 

reported that vehicle fuel economy is poorer on vehicles with frequent active regenerations than 

on previous vehicle models, though this would vary among makes and models of vehicles. 

As described in the preamble, only some control systems employ fuel dosing as a strategy

to initiate active regeneration. There is very limited information about the amount of fuel used 

during this process. Based on anecdotal information and phone conversations, EPA estimates

that fuel use for an individual active regeneration event with dosing is typically between 0.5 and 

1.0 gallon. In extreme cases such as sub-zero ambient temperatures, the supplemental fuel from 

DPF dosing on some vehicles could easily be in excess of a gallon.

Estimated Effects on Fuel Use from This Action

If a manufacturer requests an AECD or field modification that would increase the number 

of active regenerations during a given operating period, and if the demand for regenerations is 

not reduced through recalibration, then it is uncertain whether or how much fuel consumption 

would increase on a vehicle that uses a fuel dosing strategy for regenerating its DPF. Potential 

increases in fuel use from dosing could be mitigated by the expected decrease in the duration of 
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regeneration events, and by enabling regenerations with other adjustments that could reduce the 

need for supplemental fuel to generate the heat needed for DPF regeneration.

To illustrate a case where an emergency vehicle has increased fuel use from dosing 

related to regenerations, we have estimated the additional fuel use for a truck with a dosing 

strategy where its regeneration interval is decreased from 25 to eight engine hours, due to the 

increased availability of operator-commanded regenerations. In this example, we assume a 

single regeneration consumes approximately half a gallon of supplemental fuel. As presented in 

Table 4, if this truck has average engine operating hours of 1,200 per year, and if it undergoes a 

manual regeneration every 8 engine hours instead of every 25 hours, it would experience an 

increase of 94 regeneration events, under the above assumptions. If the amount of supplemental 

fuel use remained unchanged under the new regime (a conservative assumption) then potentially

this truck could consume an additional 47 gallons of fuel per year from the increased frequency

of regenerations alone.

Table 4: Fuel Use from Dosing with Increased Regeneration Frequency

1,200 Annual Engine Hours

25-Hour Interval

12-Hour 

Interval

8-Hour 

Interval

Annual Regeneration Events 47 96 140

Fuel Dose per Regeneration

(Gallons) 0.5 1.0 0.5 0.5

Annual Fuel Use from Dosing 

(Gallons) 24 47 48 71

Cost Estimates

Table 5 below presents a summary of cost estimates for this exercise. Estimates are 

provided for a vehicle with annual engine operating hours of 300, 1,200, and 1,600. 
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Table 5: Fuel Costs from Dosing with Increased Regeneration Frequency

25-Hour Interval

12-Hour 

Interval

8-Hour 

Interval

Fuel Dose per Regeneration Event 

(Gallons) 0.5 1.0 0.5 0.5

Annual Dosing Fuel with 300 

Engine Hours (Gallons) 6.0 12 12 18

Annual Cost of Dosing (at $4/gal) $ 24 $ 47 $ 48 $ 71

Annual Dosing Fuel with 1,200 

Engine Hours (Gallons) 24 47 48 71

Annual Cost of Dosing (at $4/gal) $ 94 $190 $ 190 $ 280

Annual Dosing Fuel with 1,600 

Engine Hours (Gallons) 31 63 64 94

Annual Cost of Dosing (at $4/gal) $ 130 $250 $ 260 $ 380

As shown in Table 5, estimating that ultra low sulfur diesel fuel costs about four dollars a 

gallon, a vehicle operating 1,200 hours a year with an average regeneration interval of 12 hours

could incur supplemental fuel costs related to dosing of about $190 per year, or an increase of 

almost $100 annually over the base case with the 25 engine hour regeneration interval.

As noted above, EPA believes these estimates are conservative, because the amount of 

fuel used per regeneration event would likely decrease with increasing frequency.