Re: Evap in MOVES 

Prashanth Gururaja to: James Hyde 07/10/2009 04:54 PM

Jim, here are answers to your evap questions. I hope this helps.

Prashanth Gururaja

U.S. Environmental Protection Agency

Office of Transportation and Air Quality

2000 Traverwood Dr.

Ann Arbor, MI 48105

734.214.4771

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Sec 3.1.2.2

1) Equation (4) contains the terms “t” and “tkeyON”. Neither of these terms are defined. What do they mean?

Equation 4 describes how to calculate tank temperature at time t during vehicle operation . t_keyON is KEY ON 

time. You can also think of this as the time a trip starts .

2) There is no discussion of the rate at which the tank temperature returns to the ambient temperature - the cool down 

rate.

The cool down rate is described in section 3.1.2.1. I am not familiar with the term "cool down", so I used "hot soak". 

The same equations are used to determine fuel tank temperature during cold soak as hot soak ("cool down"). 

Sec 3.2.1

3) Does this mean that in the CRC data which you cite, you have used only the “non-ethanol HC” values?

We used total HC in our permeation rates , not the non-ethanol numbers .

4) Table 1 gives “base permeation rates at 72 F”. Is the 72 ° F referring to the test temperature?

Our base rates were calculated at 72 deg F. This was from the last six hours of the 72-96-72 deg F diurnal test 

cycle, at which point temperatures generally stabilized at 72 deg F. The permeation rates are adjusted 

exponentially with fuel tank temperature as explained , based on the CRC E -65 study that permeation doubles every 

18 deg F. 

5) What are age groups and how were the tabulated values determined?

The age groups are age ranges in years . For example , age group "10-14" would be ages 10 through 14 years old. 

They were determine at the outset of MOVES development , largely based on light -duty exhaust emissions 

deterioration trends .

6) In Table 1 there are rates given for six MY groups for vehicles from MY1971 to MY2003. I am unable to accertain 

the sources from which these data were derived.

These permeation rates were developed not from the E -65 and E-65-3 studies but rather from the E -9 and E-41 

studies, which tested entire vehicles in evaporative SHEDs . We assumed that in the last six hours of the diurnal 

tests, only permeation emissions existed (for non-leaking vehicles ) since temperatures decreased and stabilized 

during that period .

7) Although three MY 2004-2005 vehicles were tested, the MY groups end with MY2003. How does MOVES model 

MY2004 to MY2022?

Since the E -9 and E-41 studies did not contain the more recent model years , we did not have data on those 

vehicles on which to develop those permeation rates . As a result , MOVES assumes for now that MY 2004 and later 

vehicles have the same permeation rates as MY 2003.

8) The vehicles from which the rigs in the CRC tests were produced were California certified vehicles . How have you 

modeled federal vehicles from these data?

Our understanding is that for the most part manufacturers were producing 50-state models for evap emissions .
9) What is the intended purpose of Pnorm and how is it used in MOVES?

Equation 6 is just Equation 5 rewritten in a normalized form (each side divided by P _base, where P_norm= 

P_adj/P_base). As a result , at 72 deg F, P_norm=1 and P_adj=P_base. I will be clearer about this equation in the 

final version of this document .

Sec 3.2.3

10) Are these permeation emissions? (referring to Table 2)

Table 2 addresses permeation emissions . It is in Sec 3.2, which is the permeation section .

11) Why is the 1995 and earlier % increase so different than the results reported in the E-65 study?

The results from E 10 and E6 were combined for the overall ethanol results . We also incorporated E -65-3 data. We 

used only the 65-105-65 deg F diurnal data to compare between E 0 and ethanol. The 1995MY and earlier numbers 

also include post -1995MY vehicles that met only the pre -enhanced evap standards . Different ways of analyzing the 

data will lead to different results .

12) How was the MY1996 value derived?

The MY1996 value was derived from weighting the 1995MY and earlier rates and the enhanced -evaporative rates 

20% and 80%, respectively , to account for the enhanced -evap phase-in percentage for that model year .

13) The MY groups are different from those in Table 1. How were these MY groups selected?

Fuel adjustments are done based on a variable Fuel Model Year , which does not always coordinated exactly with 

Model Year (of the vehicles ). In this particular case , they are different from each other . 

14) why have the E-77 study results not been incorporated into MOVES?

We completed the major evaporative emissions rate analysis in 2008, before the E-77 results became public . We 

are in the process of updating portions of our modeling the E -77 data, time permitting .

"James Hyde" <jdhyde@gw.dec.state.ny.us>

"James Hyde " 

<jdhyde@gw.dec.state.ny.u

s>

06/04/2009 04:50 PM

To Prashanth Gururaja/AA/USEPA/US@EPA

cc

Subject Evap in MOVES

Please see attached.

Thank you,

Jim

James D. Hyde

Chief, Fuels & New Vehicles Section

Bureau of Mobile Sources and Technology Development

Division of Air Resources

New York State
Department of Environmental Conservation

625 Broadway

Albany, New York 12233-3255

Voice: (518) 402-8347

Fax: (518) 402-9035