-18-
Start Emissions (@88muin) = Basic Start Emissions (@12hr) * Soak Function

From Tables 4a, 5a and A-1:
Basic Start Emissions = High_ave * Highs + Norm_ave * Normals

START = 4.829*0.0987 + (1 999 + 0.00683*60)(1.0 - 0.0987) = 2.647 g
HC

Soak Function = California Soak Funct * [Ratiot(1-Ratio)*((SoakTime-10)/(X-
10))]

From Table 6, using the coefficients for catalyst-equipped vehicles:
California Soak Funct = 0.000 + (0.01272)*(88) + (-6.30E-05)*(88)? = 0.63149

Ratio = (Start@10min / Start@12hr) / California Soak Funct@10min
= 1.3234 for HC as given in Section 5.0

SoakTime = 88 minutes
X = 89 minute HC time domain (from Table 6).

Soak Function = 0.63149 * [1.3234 + (1-1.3234) * ((88-10) / (89-10))] =
0.63407

Start Emissions(@90min) = 2.647 * 0.63407 = 1.679g HC

M6 STE.003 March 4, 1999


-12-

Table 5a
Mean START Emissions of High Emitter CARS
Tech
MY Group Group HC Mean CO Mean NOx Mean
1988-93 PFI 4 829 38 06 Same as Normals
1988-93 TBI 3293 2716 Same as Normals
1983-87 FI 5313 6531 Same as Normals
1986-89 Carb 10 520 92 82 Same as Normals
1983-85 Carb 10 520 92 82 Same as Normals
1981-82 FI 5313 92 82 Same as Normals
1981-82 Carb 10 520 92 82 Same as Normals
Table Sb
Mean START Emissions of High Emitter Trucks
Tech
MY Group Group HC Mean CO Mean NOx Mean
1988-93 PFI 5212 83 862 Same as Normals
1988-93 TBI 5212 83 862 Same as Normals
1981-87 FI 5.826 60 319 Same as Normals
1984-93 Carb 9 406 162 115 Same as Normals
1981-83 Carb 17 865 179 549 Same as Normals

The other anomally in the results was the HC and CO high emitter emission
levels for the 1990-93 TBI group. In both of these cases the average start emission
levels of the few cars tested were judged to be unrealistically low. For the case of CO,
the value was -123.84 grams, and for HC it was 0.0356 grams. These low average
levels are the result of small sample size, and the possibility of negative values when the
hot running 505 on a particular car 1s greater than Bag] of the FTP. Rather than insert
negative values in the MOBILE6 model, the HC and CO high emitter emission levels
from the 1988-93 PFI group were substituted in the 1988-93 TBI group. This is a

M6.STE.003 March 4, 1999


-22-

Table A-2
Es Fraction of CO High Emitters in the Fleet
co co co co co co co
| MILEAGE 88-93 PFI 88-93 TBI 83-87 Fl 86-89 Carb 83-85 Carb 81-82 FI 81-82 Carb

2142 0.0093 0 0552 00180 0.0103 0 0130 00119 0.0508
12 823 0.0082 0 0553 00123 00388 0 0093 00511 01102
29 335 00241 0 0553. 0.0357 0.0929 0 0473 0 1334 02441
50 0 0458 0.0554 0.0889 01741 01783 0 2466 0 4138
60 006 0 0566 00555 0 1150 02140 0 2430 0 3024 0 4969
74 239° 00721 00555 0 1496 02715 0 3364 0 3830. 0 6163
87 786 0 0872 0 0556 01765 03270 04271 04614 07312
100 014 0 1010 00556 02012 03778 05102 0 5327 0 8360
112 948 01159 0 0557 02276 0 4323 0 5998 0 6097 0 9479
124 625 0 1296 0 0558. 02518 0 4822 06819 0 6802 1.0000
135 738 0 1429 0 0558 02751 05302 07614 0 7484 41.0000
146 315 0 1556 0 0559 02976 0 5764 0 8381 081414 1.0000
156 38 0 1680 0.0559 03193 06210 09124 0 8775 1.0000
165 96 0 1799 0 0560 0.3402 0 6638 0 9836 0 9387 10000
175 077 01914 0 0560 0.3602 07050 1.0000. 09976 1.0000
183 753 0 2025 0 0561 03795 07445 1.0000 1.0000 1.0000
19201 0 2132 00561 03981 07825 1.0000 10000 1.0000
199 869 0 2235 0 0561 04159 08191 10000 10000 10000
207 349 0 2334 0 0562 0.4330 08541 10000. 1.0000 1.0000
214 466 0 2429 0 0562 04495 0 8877 1.0000 1.0000 1.0000
221 241 0 2521 0 0562 0 4653 0 9200 10000 1.0000 1.0000
227 688 0 2609 0 0563 0 4804 09510 10000 10000 1.0000
233 823 0 2693 0 0563 04949 0.9806 10000 1.0000 1.0000
239 663 02774 0 0563 0 5089 1.0090 1.0000 1.0000 1.0000
245 22 0 2852 0 0564 05222 10363 1.0000 4.0000 1.0000
250 509 0.2927 0 0564, 0 5350 10623 10000 1.0000 1.0000

M6.STE.003 March 4, 1999


MYR

81
82
83
84
85
86
87
88
89
90
1
92
93

ALL

Cars
OPLP

367
1
63

24

538

cL
Carb
657
71
57
30
74
34
17
15
22

977

Distribution of Vehicles by Model Year and Technology*

Cars Cars
TBI PFI
15 29
74 8
127 62
46 (35
5666
60 «92
76 106
69 113
38 = 103
160 250
91 426
57 347
29 (366
898 2003

Cars
ALL

1068
224
309
116
220
193
200
197
163
410
517
404
395

4416

3.

Table 1

MYR

81
82
83
84
85
86
87
88
89
90
91
92
93

ALL

Trucks Trucks Trucks

OPLP

124
45
8
26
33
14

250

cL
Carb

64

TBI

13
23

144
141
92
90

509

Trucks
PFI

1
144
92
93

382

Trucks
ALL

124
45
M1
49
82
87
10

0
0

145

285

184

183

1205

* No entry indicates no data available for that model year/technology type in the FTP dataset used for this analysis

M6 STE 003

March 4, 1999


-19-

Appendix A

Fraction of High and Normal Emitters in the Fleet

The fractions of high and normal emitters in the fleet were calculated based on the
Tunning emission estimates. For consistency, these fractions were also used for start
emissions. The fractions were based on the running estimates, because the running
estimates were corrected to account for the recruitment bias inherent in the FTP data.

A large amount of IM240 data from the Dayton, Ohio I/M program (211,000 mitial
tests) were used to correct the recruitment bias herent in the FTP type data The
recruitment bias 1s believed to exist in the EPA and AAMA FTP samples because of (1)
their relatively small size in comparison to the likelihood of selecting a high emitter, (2) the
belief that motorists with poorly maintained or tampered vehicles will be reluctant to
volunteer them to a government entity like the EPA or even the vehicle manufacturer, and
(3) the relatively low mileage levels of the EPA and AAMA sample (relatively few over
100,000 miles).

Since the Dayton sample contains virtually the entire vehicle fleet (or a randomly
selected 50 percent) of the city these issues of recruitment bias should be minimal. For
example, the sample size is quite large (211,000 vehicles). Even 1f high emitters are just
a few percent of this sample, they should be well charactenzed Also, I/M 1s not a
voluntary program in Ohio; thus, a motorist cannot simply decline to participate. Unless
they have intentionally tampered the vehicle and have an expectation of failure, it is
unlikely that they would seek to avoid the program since the data 1s from the first year of
YM testing in Dayton.

Although the mileage data from Dayton are highly suspect and not useful, the vehicles
of a given model year vintage are older than the vehicles of the same model year vintage
in the EPA and AAMA databases. Thus, they should provide a more representative cross-
section of the in-use fleet. The derivation of the average running emission rates, with the
adjustments based on the Dayton IM240 data, are discussed in EPA document
M6.EXH 001.

Tables A-1 and A-2 show the fraction of HC and CO high emitters in the fleet. The use
of these to develop start emission factors are discussed in Section 4 4 and Section 4.5. The
derivation of these high emitter fractions 1s discussed in detail in EPA document
M6 IM 001. However, a brief description and the mathematical equation 1s shown below.

The number of High and Normal emitters 1s calculated at each age point for each

combination of vehicle type / pollutant / model year / technology group using the following
general equations.

M6.STE.003 March 4, 1999


-21-

Table A-1
Est tion of HC High Emitters in the

HC HC HC HC HC HC HC

MILEAGE | 8803PFi | 88-03TBI | 63-87Fi_ | 86-89Carb | 63-85Carb | 81-e2Fi | 81-82 Carb
2142 | 00184 0.0239 0.0223 0.0052 00232 0.0203 0.0282
12823 | 00227 0.0251 0.0157 00197 00158 0.0654 0.0543
29335 | 00422 0.0270 0.0406 0.0526 0.0047 01613 01580
50 0.0800 0.0386 0 1003 0 1042 0.0917 0.2861 0.2906
60006 _| 00987 0.0458 01298 0 1296 01348 03485 03560
74239 | 01260 0.0561 01723 0 1661 01972 0.4393 0.4503
87 786 | 01525 0.0661 02078 02012 02578 05275 05416
400 01 01770 00753 0.2346 0.2334 03135 0.6094 06253
112948 | _ 02036 0.0851 02634 02678 03737 06986 07152
124 625 |_02280 0.0940 0 2898 0.2902 0.4290 07812 07976
135 738 |_02518 0.1026 03153 03295, 0.4826 0 8620 0772
146 315 |_ 02748 01110 03400 0.3586 05345 09407 09539
156 38 | 02972 01190 0 3638 0 3866 0 5847 1.0000 1.0000
16596 | 03189 01267 0 3868 04135 0.6332 4.0000 1.0000
175 077 |_03398 01341 0.4089 0 4393 0.6801 4.0000 1.0000
183753 | 03601 01412 0.4303 0.4641 07253, 4.0000 1.0000
19201 03798 0 1480 0.4508 04879 07690 1.0000 1.0000
199 869 | 03988 01546 0.4706 05108 08111 10000 1.0000
207 349 |_04171 0 1609 0 4896 0.5327 0.8516 1.0000 1.0000
214 466 | 04348 0 1669 05079 05537 0.8907 1.0000 1.0000
221241 | 04519 01727 0.5255 05738 0.9284 1.0000 1.0000
227 688 |_0 4683 0 1782 05425 0 5931 0.9646 1.0000 1.0000
233 823 | _ 04842 0 1836 0 5587 06116 1.0000 1.0000 1.0000
239 663 |_ 04994 0 1887 05743 06293 1.0000 1.0000 4.0000
24522 | 05141 0 1936 05893 0.6462 1.0000 4.0000 1.0000
250 509 |_0 5283 0 1982 0.6036 0 6624 1.0000 1.0000 4.0000

M6.STE.003 March 4, 1999



-16-
defined as:

Soak Function = California Soak Function
where’

California Soak Function: The values developed by the California Air Resources
Board to adjust the start emissions for soak times other than 12 hours. This 1s a function
of soak time in minutes. The coefficients for catalyst vehicles, non-catalyst vehicles,
and electrically heated catalyst vehicles are given in Table 6. The coefficients for
catalyst-equipped vehicles are for the model year/technology groups examined in this
report. For example, for HC on a catalyst equipped vehicle at a soak time of 100
minutes, the value 1s

0 57130 + 0.00072* 100 + (-1.76E-07)*(100)? = 0.64154

Ratio: This parameter 1s calculated by dividing the EPA ratio of start emissions at 10
minutes to start emissions at 12 hours by the Califorma Soak Function at 10 minutes.
Mathematically, it is given by:

Ratio = (Start @10 minutes / Start @720 minutes) / California Soak Function @10
minutes

The numerator in the above equation (Start @10 minutes/ Start @720 minutes) was
developed from FTP data using the equations in Sections 3.3, and dividing the Start
@10 minutes by the Start @ 720 minutes. One value for each pollutant was developed
that included all technologies and vehicle types These values, used in the numerator of
the equation, are: HC= 0.160, CO = 0.112, and NOx =0 204. The California Soak
Function is the value obtained from the coefficients in Table 6 at a 10 minute soak
point. The California Soak Function values at a 10 minute soak point for catalyst-
equipped vehicles, used in the denominator of the equation, are. HC=0.1209,

CO=0 1147, and NOx=0 3937. Therefore, the Ratios obtained are: HC=1.3234,

CO=0 9765, and NOx=0.5182.

SoakTime: The time duration in minutes of the soak which 1s to be calculated (range
zero minutes to 720 minutes).

X term: This term 1s defined to be zero for soak times from 0-10 minutes. For the range
from 10 minutes to 720 minutes, it 1s set equal to the highest minute in the domain of
the California Soak Function For example, HC emissions from catalyst equipped
vehicles have two time domains in Table 6. These are 0-89 minutes and 90-720

M6 STE.003 March 4, 1999


-8-

Table 2
Mean Estimated Start and FTP Emission Levels by Model Year for Light-Duty Cars

in the FTP Dataset
Basic start (after 12 hour soak) Start (after 10 min soak) Composite FTP
grams grams grams/mile

MYR HC CO NOx MYR HC CO NOx JMYR_ HC co NOx
81 4002 46419 1.373 81 0.610 5115 0.041 81 0706 9667 0897
82 2.445 36378 1237 82 0373 4843 -0045 J 82 0789 8318 0.872
83 2.399 26112 1264 83 0400 3827 0150 § 83 0.431 5073 0.806
84 2.950 34827 1190 84 0513 3418 0047 § 84 0.756 9968 02893
85 3468 30353 1204 § 85 0506 4737 0.095 ff 85 0533 6935 0770
86 2526 26639 1432 86 0298 2082 0.241 86 0926 10.43 0713
87 2.712 20030 1376 87 0597 2.104 0170 § 87 0656 8366 0.790
88 2831 19716 1419 88 0406 1.147 0223 88 0406 4574 0.668
89 2.254 18.610 1434 89 0379 2524 0216 § 89 0311 3.911 0.652
90 2169 18677 1.930 § 90 0.332 2219 0.611 90 0.274 893614 0633
91 2183 19494 1443 91 0275 2132 0530 F 91 0.237 3145 0,525
92 2271 18.878 1645 92 0,304 2595 0485 f 92 0267 4328 0508
93 2312 21.030 1801 93 0.310 2564 0392 § 93 0225 2551 0466

M6 STE 003 March 4, 1999


5.

3.0 DEFINITION OF START EMISSIONS
3.1 Overview of the Federal Test Procedure (FTP)

The Federal Test Procedure (FTP) is a test cycle which is used to certify new
vehicles to emission performance standards (see 40 CFR Part 86, Subpart B, Section
86.144). The FTP consists of a cold start segment (Bag 1), a hot stabilized segment (Bag
2), and a hot start segment (Bag 3). Initially, the vehicle is stored for a mmimum of 12
hours before testing to simulate a 12 hour overnight soak period. The vehicle is then driven
over the cold start segment, which lasts 505 seconds over a length of 3.59 miles, and the
emissions collected as Bag 1 The latter part of the driving in Bag | occurs with the engine
and catalyst na hot stabilized condition. Bag 2 emissions are then immediately collected
from the hot stabilized segment, which lasts 867 seconds over a length of 3 91 miles. After
a 10 minute soak, the 505 seconds of the start segment 1s then repeated and the emissions
collected as Bag 3.

The FTP composite emission rate is a weighted combination of the three measured
bags to represent two tnps. The first trip is a cold start trip after a 12 hour soak, and the
other 1s a hot start trip after a 10 minute soak. Each trp 1s a “LA4" cycle, which is a
combination of the 505 cycle (either Bag | or Bag 3) and the Bag 2 cycle. Ina typical FTP
test, the Bag 2 is only measured once and the results are used for both trips. Since the 505
cycle is 3 59 miles long and the Bag 2 cycle 1s 3.91 miles long, each LA4 tnp is 7 5 miles
long. The cold start trip is weighted at 43% and the hot start tip weighted 57%. Ifthe cold
start trip is 43% of the driving, then the vehicle miles traveled (VMT) in Bag 1! (containing
the cold start) is:

FTP Bag | VMT Weighting = 43% * (3.59 miles / 7.5 miles ) = 0 206

The hot start trip 1s 57% of driving, and the VMT weighting for Bag 3 (containing the hot
start) is:

FTP Bag 3 VMT Weighting = 57% * (3 59 miles / 7.5 miles ) = 0.273

The remaining VMT is from stabilized driving, represented by Bag 2. Since Bag 2 1s used
for both the cold start and hot start trips, 1t uses VMT weighting from both.

FTP Bag 2 VMT Weighting = ( 43% + 57% ) * ( 3.91 miles / 7 5 miles ) = 0 521

The standard VMT weighting of the bags reported in grams per mile for the full FTP are

M6.STE.003 March 4, 1999


-4-

In general, most of the 1990+ model year vehicle data were supplied by AAMA,
and most of the pre-1990 data were supplied by the EPA laboratory testing. The API
sample 1s a relatively small sample (99 cars and trucks). Its chief appeal 1s that the vehicles
all have generally higher mileage readings than the rest of the sample (all over 100,000
miles). The other general trend in the data 1s toward PFI technology, and away from the
others This is seen in the 1990+ vehicles which are predominately PFI with some TBI still
present. The 1981 - 1989 model years start with a high percentage of carbureted and some
open loop, but end with mostly TBI and PFI technology. Although not explicitly shown
in the tables, new catalyst technology was phased slowly into the fleet starting in the mid
1980's.

For analysis, the cars and trucks were placed into the model year/technology groups
shown below Trucks were separated into five different groups by pollutant due to
differences in certification standards.

CARS TRUCKS
MY Group / Technology Type MY Groups / Technology Type
HC/CO/NOX HC/CO/NOX
1988-93 PFI 1988-93 PFI
1988-93 TBI 1988-93 TBI
1983-87 FI 1981-87 FI
1986-93 Carb 1984-93 Carb
1983-85 Carb 1981-83 Carb
1981-82 FI
1981-82 Carb

The technology groups are closed-loop ported fuel injection (PFI), closed-loop throttle body
injection (TBI), and carbureted (CARB). FI refers to a combination of PFI and TBI.
CARB includes both closed-loop and open-loop vehicles which are carbureted. These
model year/technology grouping boundaries were selected on the basis of changes in
emission standards or the development/refinement of new fuel metering or catalyst
technologies. It is assumed that as of 1990, carbureted technology had a very tiny market
share, and are included with the previous carbureted group. Because of the relatively large
amount of 1988-93 fuel injected data, the category was split into PFI technology and TBI
technology for both cars and trucks. This produces separate deterioration functions based
on this fuel delivery technology and allows the modeling of the future penetration of PFI
technology into the in-use fleet.

M6 STE.003 March 4, 1999


-17-

minutes. Thus, for this example, X = 0 for times of 10 minutes or less, and X = 89 for
times from 11 minutes through 89 minutes No soak adjustment 1s applied for the
remaining soak period of 90 minutes through 720 minutes. Only the California Soak
Function 1s used.

For all three pollutants, the difference between the MOBILE6 soak function and
the California soak function will generally be small for the entire range of soak times. If
any difference exists it will reach its highest magnitude in the range of 10 minutes to
about 60 minutes.

6.0 START EMISSION RESULTS

Start emissions are both a function of vehicle deterioration represented by
mileage, and soak time In previous sections the results were shown separately. In this
section, examples of the results are shown with both effects combined.

Shown in the linked EXCEL spreadsheets (CAR_BER.xls and TR_BER.xls) is a
sample calculation of the basic emission start factors for the various model year groups
and pollutants It includes calculations for both start and running emissions The
calculations in the spreadsheet use Equation | in this document, and show the
magnitude of the start emission factors that will be used in MOBILE6.

The statistical results and output are too voluminous to present directly in this
document. However, they are available in the linked document (stat.Ist). The statistical
software SPSS was used to perform the linear regressions and compute the means In
general, the regression correlation coefficients (r-squared) are not high (< 0.10), and
reflect the tremendous scatter in emissions data. However, virtually, all of the
regression coefficients of the normal emitters are significant at least at a 90 percent
confidence level On the other hand, the confidence intervals around the average start
emission levels of the high emitters are quite large due to high scatter and small sample
sizes.

Shown below for illustration purposes 1s a sample calculation of start emissions.
It illustrates the soak function equations and methodology shown in Section 5.

Example: Calculate HC start emissions at a soak time of 88 minutes for a 1991
model year PFI-equipped car with 60,000 miles.

M6.STE.003 March 4, 1999


-7-

For illustration purposes, the average basic start emission rates (in grams) after a
12 hour soak were calculated for each model year and are shown in Tables 2 and 3 for cars
and trucks.

Start emissions after a 10 minute soak can also be estimated from the Bag 3 and
HRS505 emission rates, analogous to the basic start emission rate:

Start Emissions after 10 minute soak (grams) = [Bag 3(g/m1) - HR505(g/m1)] * 3.59 miles

The average start emissions after a 10 minute soak are also shown in Tables 2 and
3 for each model year and for cars and trucks.

For some FTP tests of some cars, the predicted HR505 emissions are higher than
Bag] and/or Bag3 emissions. This causes the start emissions to be negative. This probably
1s due to intermittent emission control system defects. Except in some cases of very small
samples, the negative values were retained in the analysis.

4.0 Basic Start Deterioration with Mileage

41 Definition of Categones

The basic modeling concept behind the start emission factor methodology 1s that
the fleet can be represented as two types of vehicle emitter categories. These two types are
termed “high” emitters, and “normal” emitters. The “high” emitters have FTP average
emission levels which are considerably higher than the overall mean emission levels, and
significantly higher than their FTP standards, indicating that they have problems with their
emission control systems The “normal” emitters are low and average emitting vehicles
with emission control systems which are generally functioning properly. The overall fleet
emission factor 1s a weighted average of the high and normal emitters.

The high/normal emitter modeling concept is also used in the estimation of running
emussions, and is discussed in depth in other reports. For both start and running emissions,
the high/normal concept allows for corrections due to recruitment bias against higher
emitting vehicles, and for more accurate estimates of the effects of I/M programs, fuel
effects, temperatures, etc.

In the data analysis, vehicles were defined as normal emitters for a specific pollutant

if their FTP HC emissions were less than twice the applicable new car certification
standard, or their FTP CO emissions were less than three times the applicable new car

M6.STE.003 March 4, 1999


Ww

EPA

United States Air and Radiation EPA420-P-99-015
Environmental Protection March 1999

Agency M6 STE 003

Determination of Start
Emissions as a Function
of Mileage and Soak Time
for 1981-1993 Model Year
Light-Duty Vehicles

DRAFT

&B Printed on Recycled Paper


-10-

certification standard, or their FTP NOx emissions were less than twice the new car
certification standard,

Vehicles were defined as high emitters for a specific pollutant if ther FTP HC
emissions or FTP CO emissions exceeded twice or three times the applicable new car
certification standard, respectively, or their FTP NOx emissions were two times the new
car certification standard. Because high NOx emissions often occur with low HC and/or
low CO emissions, and sometimes even HC can be high and CO normal, the three
categories were kept separate. Thus, a vehicle could be a high HC emitter, but a normal
CO and NOx emntter.

4.2 Calculation of Start Emission Rates for Normal Emitters

Emission rates for normal emitters were calculated by least squares regression of
the emissions of the normal emntters versus mileage. The regression was done for each
pollutant / model year / technology group. The start emission regression coefficients for
cars are shown in Table 4a and for trucks in Table 4b The column labeled ZML
contains the zero mile coefficients, and the column DET contains the deterioration
coefficients (slope) from the regressions.

Table 4a
Regression Coefficients for START Emissions from Normal Emitter CARS

MY Tech
Group | Group HC Coefficients CO Coefficients | NOx Coefficients

ZML DET ZML DET ZML DET

1988-93 PFI 19987 0.006830 18 972 000703 1444 000220
1988-93, TBI 19019 0 002679 19 233 0.00000 2300 0.00000
1983-87 FI 2 3589 0.001388 19 949 0 00000 1461 000141
1986-89 Carb 1 4934 0.018238 24 698 0 10947 1405 0.00000

1983-85 Carb 15892 0.009408 | 24 442 010577 0748 0.00524

1981-82 FI 2 3543 0 008533 20 038 0 22673 1530 0.00059

1981-82 Carb 21213 0.013610 28 637 0 22673 1601 0.00000

M6.STE.003 March 4, 1999


-9-

Table 3
Mean Estimated Start and FTP Emission Levels by Model Year for Light-DutyTrucks

in the FTP Dataset
Basic start (after 12 hour soak) Start (after 10 min soak) Composite FTP
grams grams grams/muile
MYR HC co NOx | MY HC co NOx MY HC co NOx
R R

81 7342 107501 1.055 § 81 1212 14211 0385 81 1275 = 18.158 1.752
82. 7909 116584 -0119 f 82 1489 14189 0006 82. 1732 16.774 1.732
83 6537 104817 0796 § 83 1577 18657 -0209 83 1361 13.226 1436
84 5219 95.893 0299 § 84 1.098 20.057 0.004 84 0.802 10.633 1405
85 4766 84621 0.457 § 85 0.854 7742 0102 85 1281 14465 1388
86 3.752 41196 0729 f 86 0607 2.148 0128 86 0823 8.789 1.057
87 3352 26635 1266 § 87 0566 1433 0017 87 0401 4610 0.605
88 88 88
89 89 89
90 4705 45331 4683 § 90 0930 7037 0765 90 0800 9510 0885
91 3521 41.128 2761 § 91 0878 7129 0519 1
92 3656 41446 3.054 § 92 0654 5.746 0656 92
93 3644 40557 2736 § 93 0589 4634 0676 93 0420 5363 0.847

M6 STE 003 March 4, 1999


6-
FTP = (Bag 1 * 0.206) + (Bag 2 * 0.521) + (Bag 3 * 0.273)

where the fractions represent the amount of vehicle miles traveled within the three modes
during the FTP tnp, and Bag, Bag2, Bag3 and the FTP emissions are in grams per mile

(g/m1).
3.2. Overview of the Hot Running 505 and Its Use

The FTP testing method outlined above does not allow the precise separation of
start and running emissions, since Bags 1 and 3 contain both start and running emissions.
Bag 2 of the FTP does not conta an engine start; however, the driving cycle used in the
second bag 1s significantly different from the cycle used for Bags 1 and 3. Thus, to
estimate the amount of FTP emissions that can be allocated to engine start, the concept of
the Hot Running 505 (HR505) 1s needed.

The HRSO05 is an extra 505 cycle performed immediately following bag 3 of the
FTP. It uses an identical driving cycle as the first and third bags of the FTP, but does not
include an engine start. For more information, refer to the document “The Determination
of Hot Running Emissions from FTP Bag Emissions”, report number M6.STE 002. With
a HRS505 emission result, it s possible to compare the results obtamed from the HR505 to
the results from Bags 1 and 3 of the FTP to determine the portions of Bags 1 and 3
attributable to start emissions following a 12 hour soak and start emissions following a 10
minute soak, respectively.

Since the HR505 has not historically been included in FTP test programs, a method
of estimating the HR505 was developed, as described in report M6.STE.002. Briefly,
HRS05 emissions were measured from a sample of 77 vehicles tested under EPA contract.
The results from this vehicle sample were used to develop a correlation between the HR505
and FTP bag data. This correlation was then used to estimate HR505 results for the FTP
dataset used for this analysis.

3.3. Basic Start Emission Rate

For MOBILE6, the basic unit of engine start emissions 1s defined as a start after a
12 hour soak. The units for engine start emissions will be grams, instead of grams per mile,
since start emissions will not be allocated by vehicle miles traveled. The engine start basic
emission rate can be determined by subtracting the HR505 emission rate from the Bag 1
emission rate (in grams per mile) using the nomunal distance traveled in the 505 driving
cycle:

Basic Start Emission Rate (grams) = [Bag 1(g/m1) - HR505(g/mi)] * 3.59 miles

M6.STE.003 March 4, 1999


-20-
Where:
Highs is the fraction of High emitters.

Normals is the fraction of Normal emitters.
RLA4 1s the average running emission rate, after adjustment based on IM240 data from

Dayton, OH.
High_ave is the high emitter running emission average estimated from the FTP data.
Norm_ave 1s the normal emitter running emission average estimated from the FTP data.

Highs + Normals = 1 Eqn A-1
and

RLA4 = High ave * Highs + Norm_ave * Normals Eqn A-2

Solving for the variables Highs and Normals produces:

Highs = (RLA4 - Norm_ave) / (Highave - Norm_ave) Eqn A-3

Normals = 1 - Highs Eqn A-4

M6 STE.003 March 4, 1999


1.0 INTRODUCTION

MOBILE will allocate vehicle exhaust emissions to either the “extra” emissions
associated with engine start (start emissions) or the “base” emissions associated with travel
(running emissions). This distinction is to some extent an artifical constramt since in
reality “start” emissions in part will be released while the vehicle is in motion. However,
it1s a useful constraint and not too far from physical reality, in at least summer conditions,
when the extra emissions from a start end after only 1 or 2 mmnutes of driving. This split
allows the separate characterization of start and running emissions for correction factors
such as fuel effects and ambient temperature. It also allows a more precise weighting of
these two aspects of exhaust emissions for particular situations such as morning commute,
parking lots and freeways This document describes the methodology used to calculate start
emissions as a function of mileage and soak time for use n MOBILE6 The results for
model year 1981-1993 light-duty cars and light-duty trucks are presented. The deterioration
of running emissions will be addressed in a separate document (Report Number
Mé6.EXH 001)

This document 1s organized into six sections. The first section 1s the short
introductory section. Section 2 describes the FTP data sources and the model year and
technology groups which are used Section 3 provides a definition of start emissions in
mathematical terms and shows the relationship between start emissions and the Federal
Test Procedure (FTP) emissions. This includes a description of the FTP cycle, the Hot505
cycle, and a definition of cold start and hot start emissions Section 4 describes the
methodology used to predict start emissions as a function of soak time. Section 5 shows
the algorithm used to predict start emissions versus mileage. Section 6 contains an example
of the final start emission results as used in MOBILE6 as a function of both deterioration
and soak time.

2.0 DATA SOURCES USED

The basic datasets used to determine in-use deterioration are based on FTP testing.
(UM data from Dayton, Ohio were also used to correct the results for recruitment bias
which EPA believes affects the FTP test samples - see Appendix A). Three FTP data
sources were used: 1) the test results from the EPA laboratory in Ann Arbor, Michigan, 2)
the data received from AAMA (Amenican Automobile Manufacturers Association) based
on testing conducted in Michigan and Arizona, and 3) the API (American Petroleum
Institute) data collected in Arizona The model years in the dataset range from 1981
through 1993, and contain both cars and trucks. Table 1 gives a breakdown by vehicle type,
model year, and technology for the three datasets combined.

M6.STE.003 March 4, 1999


-13-

reasonable assumption since these vehicles are generally about the same age and model
year vintage, and have reasonably similar emission control technology.

4.4 — Fraction of Hi; Normal Emitters in leet

The basic start emission factor is computed from a weighted average of the highs
and normals. The fraction of high emitters 1n the fleet 1s the weighting factor The
fraction of high start emitters 1s the same fraction as the one used for the running
emissions calculations Appendix A presents the fraction of HC and CO high emitters
in the fleet at selected mileages / ages for each pollutant (see document M6.IM.001 for
further details). The fraction of NOX high emitters is not shown because for NOX the
Normals and Highs are assumed to have the same emission rate (no start NOX highs are
assumed to exist).

4.5 Calculation of Basic Start Emission Rates

The basic start emission rate 1s calculated for each combination of vehicle type /
pollutant / model year group / technology group. The units are start emissions in grams
Equation 1 1s used to calculate the basic (mean) start emission rate from the high and
normal emitter emission values and the rate of high emitters in the fleet For NOX
emissions a special case of this equation is used where the normal and high emission
rates are set equal to each other.

START = ST_High_ave * Highs + ST_Norm_ave * Normals Eqn tl
Where:
Highs = fraction of High emitters
Normals = fraction of Normal emitters
START is the basic (mean) emission rate
ST_High_ave 1s the high emitter start emission average
ST_Norm_ave 1s the normal emitter start emission average

Where:

Highs + Normals = 1 Eqn 2

M6.STE.003 March 4, 1999


-15-

Table 6

Coefficients for Adjusting Engine Start Emissions for Soak

Time

(from “Methodology for Calculating and Redefining Cold and Hot Start Emissions”, CARB)

Non-Catalyst Vehicles
HC HC co co NOX NOX Curve 2
Curve 1 Curve 2 Curve 1 Curve 2 Curve 1
Constant 0 38067 0 43628 0 43803 -0 08541 131568 2 48061
minutes -0 00163 0.00078 -0 00998 000303 002752 -0 00018
minutes? 6 64E-05 0 701E-05 | -211E-06 | -000015 -2 6E-06
domain(min) 0-52 53-720 0-119 120-720 0-119 120-720
Catalyst Equipped Vehicles
HC HC co co Nox NOx Curve 2
Curve 1 Curve 2 Curve 1 Curve 2 Curve 1
Constant 0 057130 0 0 70641 0 11796 112983
minutes 001272 0 00072 001195 0.00033 0 02967 2 216-05
minutes? -6 30E-05 | -1 76E-07 ~476E-05 | 100E-07 | -000021 -3 04E-07
domain(min) 0-89 90-720 0-116 117-720 0-61 62-720
Electrically Heated Catalyst Equipped Vehicles
HC HC co co Nox NOx Curve 2
Curve 1 Curve 2 Curve 1 Curve 2 Curve 1
Constant (a) 0 0 50641 0 0 44733 105017 137178
minutes (b) 0 00561 0 00069 000707 0.00162 0 00362 0.00027
minutes? (c) -5 O9E-06 0 -1336-05 | -118E-06 | -557E-06 -1 09E-06
domain(min) 0-117 118-720 0-107 108-720 0-113 114-720

California Soak Function = a + b * minutes + c * minutes? (where minutes !s time since last engine
operation (Ie , soak time))
The Soak Function is the grams per soak time | divided by the grams per overnight soak (720
minutes or 12 hours

M6.STE.003

March 4, 1999



EPA420-P-99-015

- Draft -

Determination of Start Emissions
as a Function of Mileage and Soak Time
for 1981-1993 Model Year Light-Duty Vehicles

Report Number M6.STE.003

March 4, 1999

Ed Glover
Penny Carey

U.S.EPA Assessment and Modeling Division

NOTICE

This technical report does not necessanily represent final EPA decisions or positions It 1s intended to present
technical analysis of issues using data which are currently available The purpose in the release of such
reports 1s to facilitate the exchange of technical information and to inform the public of technical
developments which may form the basis for a final EPA decision, position, or regulatory action

M6.STE.003 March 4, 1999


EPA420-P-99-01
March 196

Determination of Start Emissions as a Function of Mileage and
Soak Time for 1981-1993 Model Year Light-Duty Vehicles

M6.STE.003

DRAFT

Ed Glover
Penny Carey

Assessment and Modeling Division
Office of Mobile Sources
US. Environmental Protection Agency

NOTICE

This technical report does not necessarily represent final EPA decisions or positions
It 1s intended to present technical analysis of issues using data which are currently available
The purpose in the release of such reports 1s to facilitate the exchange of
technical information and to inform the public of technical developments which
may form the basis for a final EPA decision, position, or regulatory action


-ll-

Table 4b

Regression Coefficients for START Emissions from
Normal Emitter Light Trucks

MY Tech
Group | Group HC Coefficients CO Coefficients | NOx Coefficients

ZML DET ZML DET ZML DET

1988-93 PFI 2873 0 00000 32 178 00168 1597 0.00000
1988-93 TBI 4073 001309 42 456 01411 4294 0 00324
1981-87 FI 2599 000964 23 497 00613 1384 0.00000
1984-93 Carb 3916 0 00854 78.286 02564 0 143 0 00436

1981-83 Carb 6817 000154 98 432 03240 1082 0.00000

4.3 Calculation of Start Emission Rates for High Emitters

High emitters are the vehicles in the fleet which likely have problems with their
emission control systems, as evidenced by emission levels which are considerably
higher than the FTP standards. In the analysis they were defined as those vehicles
exceeding either twice FTP standards for HC or NOX or three times FTP standards for
CO. The emissions line is a flat horizontal line because the emissions of a high emitter
were not a statistically significant function of mileage In addition, the relatively small
sample sizes of high emitters make regression determined mileage coefficients
unreliable indicators of actual behavior Table 5a shows the average emissions of the
high emitters (cars only) for the pollutant / model year / tech groups, and Table Sb
shows the analogous results for light trucks.

For NOX start emissions, the normals and the highs were combined together,
and the emissions were regressed versus mileage This has the effect of eliminating the
NOX high emitter group for start emissions. This combination was done for two
reasons. First, for many of the model year / tech groups the average NOX start
emissions were found to not be statistically significantly different from start emissions
from the normals This was found to be the case even when different definitions of a
high emitter were tried (1X FTP NOX, 1.5X FTP NOX, and 2X FTP NOX). This
phenomenon is consistent with the mechanisms of NOX formation - higher emissions
under lean high temperature / load FTP conditions, and lower during rich and cooler
start conditions. Second, the sample sizes for NOX high emitters were smaller in both
an absolute sense, and in comparison to the HC and CO high emitter sample.

M6 STE.003 March 4, 1999


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5.0 Start Emissions Versus Soak Time

Start emissions will be a function of soak time so that MOBILE6 will be able to
account for the entire distribution of soak trmes observed 1n the fleet. This ranges from
a minimum soak time of zero minutes up to a 12 hour soak period (720 minutes). Soak
periods exceeding 12 hours will be assumed to be the same as for a 12 hour soak.

To develop the relationship between start emissions and soak time, the FTP
database was used only to determine the engine start emissions after a 10 minute soak
and a 12 hour (720 minute) soak (these are the only data points available). To predict
start emissions for the entire range of soak duration, a model was developed from the
two FTP points, and from testing done by California of the effect of soak time on engine
start emissions (see CARB report “Methodology for Calculating and Redefining Cold
and Hot Start Emissions”)

The model which was developed uses the FTP start emission data from the two
FTP soak times to adjust the curves presented in the Califorma report. The start
emission data points at 10 minutes and 720 minutes are derived from the FTP dataset
described earlier and are a function of pollutant, technology, model year group, and
mileage. The California interpolation curves (California Soak Function) is a function of
pollutant and catalyst type

Mathematically, the start emissions of a given pollutant (in grams) as a function
of soak time 1s shown as:

Start Emissions (@ soak time) = Basic Start Emissions (@ 12 hour soak) * Soak
Function

where the Soak Function 1s a multiplicative factor used to calculate start emissions for
other soak times. The Soak Function is calculated by dividing the grams for the soak
time of interest by the grams for a soak time of 12 hours. Therefore, at a 12 hour (720
minute) soak time, the Soak Function 1s equal to 1.0.

Mathematically, for the first domain of the California Soak Function (see Table 6 for the
two domains for each pollutant and catalyst type) the Soak Function is defined as:

Soak Function = California Soak Function * [Ratio+(1-Ratio)*((SoakTime-10)/(X-10))]

For the second domain of the California Soak Function (1 e., HC for catalyst equipped
vehicles the second domain 1s 90 minutes through 720 minutes) the Soak Function is

M6.STE.003 March 4, 1999