1 **U NITED STA** 

**TES ENVIRONMENTA L PROTECTION A** **GENCY** NATIONAL VEHICLE AND FUEL EMISSIONS LABORATORY

2000 TRAVERWO OD ROAD ANN ARBOR, MI 48105

May 4 , 20 12 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 (NO X ) 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 certificati on tests, the DPF regeneration f requency 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 ty

pes 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 6 0% 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 regeneration s that occur during test cycle s , nor can we translate a typical 40

- minute test cycle int o an equivalent over

- the

road driving distance. However, EPA has information from f ire chiefs that indicates many fire2 trucks are experiencing regeneration intervals of approximately 20
- 30 engine hours. Further, EPA has learned that individual regenerati on 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 ye ar 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. 1 From 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 certificatio n 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, th e last row of Table 2 shows th is would mean that about two percent of the engine’s total annual operating time w ould be spent regenerating.

**Table 2**  **: Estimated In -**  **Use Emergency Vehicl e Regeneration**  **Events**

Low Engine Hours Middle Engine

Hours High Engine

Hours Annual Engine Hours 300 1,200 1,600 Annual Regeneration Events 12 4 7 6 3 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 vehicle s . The frequency

of DPF regeneration in use may thus increase for these vehicles. If a requested modification d oes 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 red uced 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 regeneration s .

1 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.pdf3 For purposes of this analy sis, EPA is provi di ng an illustrative example of a fire truck that ty picall y undergoes an automatic active regeneration every 25 engine hours, and it receives an approved field modification so that it may regenerate more frequentl y . 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, w e show the increase d 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 ty pe of modification could lead to increased fuel use from dosing. However, we do not have information about the likelihood of this ty pe 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 s ys tems employ fuel dosing to enable active automatic regenerations, the active regeneration event can affect the vehicle’s fuel consumption. Some o perators 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 sy stems employ fuel dosing as a strategy to initiate active regeneration. There is very limited information about the amount of fuel used during this process. B ased on anecdotal information and phone conversations, EPA estimate s that fuel use for an individual active regeneration event with dosing is ty pically between 0.5 and 1.0 gallon

. In extreme cases such as sub

- zero ambient temperatures, the supplemental fue l from DPF dosing on some vehicles could easil y be in excess of a gallon. **Estimated Effects on F**  **uel U**  **se from T**  **his A**  **ction** 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 increase s in fuel use from dosing could be mitigated by the expected decrease i n the duration of4 regeneration events, and by enabling regenerations w ith other adjustments that could reduc e the need for supplemental fuel to generate the heat needed for DPF regeneration. To i llustrat e 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 supplem ental fuel. As presented in Table 4, i f th is truck has average engine operating hours of 1,200 per ye ar, 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 , un der 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 ye ar from the increased frequency of regen erations 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 4 7 96 1 4 0 Fuel Dose per Regen eration (Gallons) 0.5 1.0 0.5 0.5 Annual Fuel Use from Dosing (G allons ) 24 4 7 48 7 1 

### 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
.5 **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 w ith 300 Engine Hours (Gallons) 6.0 12 1 2 1 8 Annual Cost of Dosing (at $4/gal) $ 24 $ 4 7 $ 48 $ 7 1 Annual Dosing Fuel with 1,200 Engine Hours (Gallons) 24 4 7 48 7 1 Annual Cost of Dosing (at $4/gal) $ 9 4 $1 90 $ 19 0 $ 280 Annual Dosing Fuel with 1,600 Engine Hours (Gallons) 3 1 6 3 6 4 94 Annual Cost of Dosing (at $4/gal) $ 1 30 $2 5 0 $ 2 60 $ 3 80 As shown in T able 5 , e stimating 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 $ 19 0 per ye ar , or an increase of almost $100 annually

over the base case with the 25 engine hour regeneration interval

. As noted above, EPA believe s these estimates are conservative, because the amount of fuel used per regeneration event would likely decr ease with increasing frequency

.