CO Soak Function (Ratio)

100

090 }
080 |
070
060
050 :

040 |}

0.30

020 |

010 |,

000

Figure 5
CO Soak Function vs Soak Time for 1981+ Vehicles

0 60 120 180 240 300 360 420 480 540 600 660 720

Soak Time (in Minutes)

——Califomia

——CO Soak Func
toe =


Table 3c
Basic Start Deterioration with Mileage for Light-Duty Open Loop and Closed Loop Carbureted Vehicles*

Cars Trucks
Pollutant MY Group Tech Number ZML Det Pollutant MY Group = Tech Number ZML Det
HC 1990-93 CLCarb HC 1990-93. CL Carb
HC 1986-89 CL Carb 88 1 532 0017 HC 1986-89 CLCarb 9 6 480 0 000
HC 1983-85 CL Carb 161 0 486 0070 HC 1983-85 CL Carb 54 1 338 0072
HC 1981-82 CL Carb 728 2825 0 046 HC 1981-82 CL Carb “ 2 825 0046
HC 1981+ OPLP 538 1194 0044 HC 1981+ OPLP 250 6 469 0 008
Pollutant MY Group Tech Number ZML Det Pollutant MY Group Tech Number ZML Det
co 1990-93. CL Carb co 1990-93 CLCarb
co 1986-89 CL Carb 88 24 300 0 089 co 1986-89 CLCarb 9 4111 1415
co 1983-85 CL Carb 161 19 495 0 496 co 1983-85 CLCarb 54 56 604 0 830
co 1981-82 CL Carb 728 30 953 0 483 co 1981-82 CLCarb ” 30 953 0 483
co 1981+ OPLP 536 19 350 0 582 co 1981+ OPLP 250 96 418 0231
Pollutant MY Group Tech Number ZML Det Pollutant MY Group Tech Number ZML Det
NOx 1990-93 CL Carb NOx 1990-93 CLCarb
NOx 1986-89 CL Carb 88 1377 0 000 NOx 1986-89 CLCarb 9 0700 0 000
NOx 1983-85 CL Carb 161 1189 0 000 NOx 1983-85 CLCarb 54 0700 0 000
NOx 1981-82 CL Carb 728 1 684 0.000 NOx 1981-82 CLCarb ” 1684 0.000
NOx 1981+ OPLP 538 0704 0 000 NOx 1981+ OPLP 250 0753 0000

* — The basic unit of engine start emissions 1s defined as a start after a 12 hour soak ZML and Det are the regression coefficients for the zero mile level
(intercept) and the deterioration rate (slope) per one thousand miles, respectively The confidence levels shown are the upper and lower 95% confidence
intervals Significance values less than 0 05 are considered statistically significant at the 95% confidence level

** Due to lack of data for the 1981-82 CL Carb truck category, the deterioration functions for the 1981-82 CL Carb cars were used to represent this category


Figure 9
NOx Start Emissions vs Soak Time for 1990-93 PFI Cars

—0 miles
— 50 miles
—— 100 miles

200 .

180 +

160 +

4
2

0

80 |. ff:
060 }-

o eo 8 @
= - + 0

(swei6) suoissiw 3 ye}S XON

040 +

000

180 240 300 360 420 480 540 600 660 720
Soak Time (in Minutes)

120

60


-5-
3.2 Basic Start Deterioration with Mileage

This section describes the methodology used to estimate start emission deterioration, and
presents the basic deterioration rates versus mileage The basic start (1 e , following a 12 hour soak)
deterioration rates were obtained from simple linear regression of the Basic Start Emission Rate data
(expressed as grams) versus mileage. The results are shown in Tables 3a, 3b, and 3c. Table 3a
includes the deterioration rates for the fuel injected cars and Table 3b shows the rates for the fuel
injected trucks. Table 3c shows the deterioration rates for the closed-loop carbureted and open-loop
cars and trucks.

Separate deterioration rates were calculated for both cars and trucks, for each of the three
pollutants, and for each model year/technology group. The exception is the 1981-82 fuel injected
and closed-loop carbureted truck categories, which had zero data Because of the lack of 1981-82
FI and CL Carb truck data, the deterioration functions for the corresponding 1981-82 car categories
were used. The effect of this substitution in the MOBILE6 model should be negligible due to the
scarcity of older model year fuel injected trucks in the in-use fleet.

Selected results from Table 3a (cars only) are also shown graphically in Figures 1 through
3 for HC, CO, and NO, for each model year/ technology group. For HC, the results are generally
as expected with the new model years having lower start emission levels and deterioration rates than
the older model years. However, comparing PFI and TBI for the 1990-93 cars shows TBI cars
having slightly lower emission levels than PF] cars. This 1s somewhat of an anomaly since it is
believed that PFI is a superior technology to TBI. However, both regressions were generally
statistically significant at least at a 90% confidence level, and further analysis of the sample using
scatter plots (not shown) revealed that the differences were not the result of outliers greatly
influencing the sample Thus, the 1990-93 TBI vehicles will be projected to have slightly lower HC
start emissions than the corresponding PFI vehicles.

Again for CO, the 1990-93 TBI category 1s slightly lower than the PFI category because of
a lower ZML. Also, in this case, the 1986-89 model year group has slightly lower CO emissions
than the 1990-93 PFI group. However, in this case, the deterioration rate is not statistically
significant for the TBI or 1986-89 model year groups Finally, the 1981-82 group 1s considerably
higher than the other two groups with CO emissions at the 100,000 mile level almost twice as high
as the other model year groups This is not unexpected since much of the 1981-82 fuel injection
technology was in early stages of development.

For NOx, the emission levels and deterioration rates for all model year groups are generally
the same The principal exception is the 1990-93 TBI group. For the 1990-93 TBI group, the

deterioration rate 1s similar to the others, but the intercept is considerably higher.

3.3. Start Emissions Versus Soak Time


NOx Soak Function (Ratio)

120

100 |
090 |

080 |

070

o6o |
050 |
040 |.
030 |
020 |
o10 |

000 |

Figure 6
NOx Soak Function vs Soak Time for 1981+ Vehicles

0 60 120 180 240 300 360 420 480 540 600 660 720
Soak Time (in Minutes)

—Califomia
—— NOx Soak Func!


Figure 8
CO Start Emissions vs Soak Time for 1990-93 PFI Cars

—0 miles
—50 miles
—— 100 miles

250

(swes6) suoissiwy weg OD

120 180 240 300 360 420 480 540 600 660 720
Soak Time (in Minutes)

60


NOx Start Emissions (grams)

NOx Basic Start Emissions for Fl Cars by Model Year Group

Figure 3

400
350 |
300
250 SS aa
- —e— 90-93 PFI
. —a— 90-93 TBI
—
200 a} _o- 86-89 FI
eee 4 83-85 FI
SS —— $ |» 81-82 FI
150
100
050
0.00

50

100

150 200
Mileage (in thousands)

250

300



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

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 MYR HC co NOx
81 4002 46.419 = 1.373 81 0.610 5.115 0.041 81 0706 9.667 0.897
82 2.445 36.378 1237 82 0.373 4.843 -0.045 82 0789 8318 0 872
83 2.399 26.112 1.264 83 0.400 3 827 0 150 83 0.431 5.073 0.806
84 2.950 34 827 1.190 84 0513 3.418 0 047 84 0 756 9.968 0 893
85 3468 30.353 1.204 85 0.506 = 4.737 0.095 85 0.533 6.935 0.770
86 2.526 26.639 1432 86 0.298 2.082 0.241 86 0926 10432 0713
87 2.712 20030 1.376 87 0597 2104 0170 87 0.656 8.366 0.790
88 2.831 19.716 1419 88 0 406 1.147 0.223 88 0406 4.574 0 668
89 2.254 18.610 1434 89 0.379 = 2.524 0.216 89 0311 3911 0.652
90 2169 18.677 = 1.930 90 0.332 2219 0611 90 0.274 = 3.614 0.633
91 2.183 19.494 1.443 91 0275 2.132 0.530 91 0 237 3.145 0 525
92 2.271 18878 1645 92 0304 2.595 0.485 92 0.267 4328 0.508
93 2.312 21.030 1801 93 0.310 2564 0.392 93 0225 2.551 0 466

In some isolated instances, a negative number for a start emissions estimate was obtained. This 1s possible when the simulated
HR505 value is greater than the Bag 1 or Bag 2 value from the FTP.


-7-

Ratio This parameter 1s calculated by dividing the EPA ratio of start emissions at 10 minutes to start
emissions at 12 hours by the California 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 3.1.3, 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
= 0204. The Califorma Soak Function is the value obtained from the coefficients in Table 4 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=0.9718, and NOx=0 5182.

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

The operation of the multiplicative Soak Function 1s illustrated in Figures 4, 5, and 6 for HC,
CO, and NOx respectively The Y-axis is the Soak Function (a unitless ratio) and the X-axis is the
soak time in minutes The California Soak Function 1s also shown for comparison.

For HC and NOx, the difference between the MOBILE6 soak function and the California
soak function will be moderate for soak times between 30 minutes and 600 minutes For CO, the
two soak functions are very similar.

4.0 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. For example, Figures 7 through 9 show the
HC, CO, and NOx start emissions as a function of soak time for three odometer levels (0, 50,000,
and 100,000 miles) of 1990-93 PFI cars. For all three pollutants, the figures show low
deterioration rates as mileage is increased at short soak times, and larger but constant
deterioration rates at soak times after 120 minutes.

Shown below for illustration purposes is a sample calculation of start emissions. It

illustrates the equations shown in Section 3.

Example: Calculate HC start emissions at a soak time of 90 minutes for a 1991 model year
PFI-equipped car with 50,000 miles.


-6-

Start emissions will be a function of soak time so that MOBILE6 will be able to account for
the entire distribution of soak times observed in 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 mode! 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 California 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) 1s a function of pollutant and catalyst type.

Mathematically, the start emissions of a given pollutant (1n 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 is a multiplicative factor used to calculate start emissions for other soak
times. The Soak Function is the grams for the soak time of interest divided by the grams for a soak
time of 12 hours. At a 12 hour (720 minute) soak time, the Soak Function 1s equal to 1.

Mathematically, the Soak Function is defined as.

Soak Function = California Soak Function * [Ratio+(1-Ratio)*((SoakTime-10)/(720-10))]

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 is a function of soak time in minutes.
The coefficients for catalyst vehicles, non-catalyst vehicles, and electrically heated catalyst vehicles
are given in Table 4 The coefficients for catalyst-equpped vehicles are for the model
year/technology groups examined 1n this report For example, for HC on a catalyst equipped vehicle
at a soak time of 100 minutes, the value is

0 57130 + 0 00072* 100 + (-1.76E-07)*(100)? = 0 64154


Figure 4
HC Soak Function vs Soak Time for 1981+ Vehicles

— Califomia
——HC Soak Func

1.00

S i=] o o ° i=] i=] i=} °o i=3
fo) © 8 o wo vt ) nN 7 fs)
°o o o Oo o i=) o o to} oO

(oney) uojouny yeog OH

120 180 240 300 360 420 480 540 600 660 720
Soak Time (in Minutes)

60


Table 1
Distribution of Vehicles by Model Year and Technology*

Cars Cars Cars Cars Cars Trucks Trucks Trucks Trucks Trucks
MYR OPLP CL TBI PFI ALL MYR OPLP CL TBI PFI ALL
CARB CARB

81 367 657 15 29 = =1068 81 124 124
82 71 71 74 8 224 82 45 45
83 63 57 127 62 309 83 8 3 1
84 5 30 46 35116 84 26 22 1 49
85 24 74 56 66 220 85 33 30 13 6 82
86 7 34 60 92 193 86 14 9 23 41 87
87 1 17 16 106 200 87 6 4 10
88 15 69 113 197 88 0
89 22 38 103163 89 0
90 160 250 410 90 144 1 145
91 91 426 517 91 141 144 285
92 57 347 404 92 92 92 184
93 29 366 =. 395 93 90 93 183
ALL 538 977 898 2003 4416 ALL 250 64 509 382 1205

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


EPA-420-D-97-005

- 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

October, 1997

Ed Glover
Penny Carey
Phil Enns
David J. Brzezinski

U.S.EPA Assessment and Modeling Division

1.0 INTRODUCTION

MOBILE6 will allocate vehicle exhaust emissions to either those associated with engine start
(start emissions) or those associated with travel (running emissions). 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 in
MOBILES. 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
M6.STE.004)

Section 2 describes the FTP data sources and the model year and technology groups which
are used. Section 3 describes the methodology and models for determining start emissions. It is
divided into three sub-sections The first sub-section describes the FTP cycle, the Hot505 cycle, and
defines the basic unit of start emissions. The second sub-section describes the analysis of start
emissions deterioration with mileage. The third sub-section describes the methodology used to
predict start emissions as a function of soak time Section 4 illustrates how start emissions will be
estimated in MOBILE6 as a function of both deterioration and soak time

2.0 DATA SOURCES USED

The datasets used to determine in-use deterioration are all based on FTP testing No IM240
data or data collected by a state I/M program were used. Three data sources were used: 1) the test
-- results from the EPA laboratory in Ann Arbor, Michigan, 2) the data received from AAMA


Table 3a
Basic Start Deterioration with Mileage for Light-Duty FI Cars*

Sample Coefficients ZML Confidence Level Det Confidence Level Significance

Pollutant MY Group Tech Size ZML Det Lower Upper Lower Upper ZML Det
HC 1990-93 PFI 1389 2016 0.0074 1 885 2148 00042 00105 0000 0000
HC 1990-93 TBI 337 1835 00041 1635 2035 0 0000 0 00856 0000 0074
HC 1986-89 FI 657 2145 0 0067 1 856 2 433 00029 00104 0000 0001
HC 1983-85 FI 392 2476 00119 1500 3451 00000 00299 0000 0191
HC 1981-82 FI 126 2435 00133 1859 3011 00022 00244 0000 0019
Sample Coefficients ZML Confidence Level Det Confidence Level Significance

Pollutant MY Group Tech Size ZML Det Lower Upper Lower Upper ZML Det
co 1990-93 PFI 1389 17 987 00572 16 292 19 682 00169 0 0975 0000 0005
co 1990-93 TBI 337 15 649 00376 9 360 21 938 0 0000 0 1782 0000 0599
co 1986-89 FI 657 19 443 00071 15 713 23.174 00000 0 0553 0000 0772
co 1983-85 FI 392 23 378 00720 16 360 30 396 0 0000 0201 0000 0274
co 1981-82 FI 126 23 311 0 3489 10 345 36 275 0 0989 0 5989 0000 0007
Sample Coefficients ZML Confidence Level Det Confidence Levei Significance

Pollutant MY Group Tech Size ZML Det Lower Upper Lower Upper ZML Det
NOx 1990-93 PFI 1389 1 484 00020 1381 1588 00000 000448 0000 0107
NOx 1990-93 TBI 337 2142 00020 1 854 2431 00000 0.0085 0000 0541
NOx 1986-89 FI 657 1 268 00023 1090 1445 00000 0 0046 0000 0050
NOx 1983-85 FI 392 1 333 0 0028 1119 1545 0 0000 0 00676 0000 0155
NOx 1981-82 Fl 126 1679 0 0000 1229 2129 00000 0 0021 0000 0134

The basic unit of engine start emissions 1s defined as a start after a 12 hour soak

ZML and Det are the regression coefficients for the zero mile level (intercept) and the deterioration rate (slope) per one thousand miles, respectively

The confidence levels shown are the upper and lower 95% confidence intervals Significance values less than 0 05 are considered statistically significant at
the 95% confidence level


Table 2b
Mean Start and FTP Emission Levels by Model Year for Light-DutyTrucks*

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 MYR HC co NOx
81 7.342 107501 1055 81 1.212 14.211 0385 81 1275 18.158 1752
82 7909 116584 -0.119 82 1489 = 14.189 0.006 82 1.732 16.774 1.732
83 6537 104.817 0.796 83 1577 18.657 — -0.209 83 1.361 13226 1.436
84 5219 95.893 0.299 84 1098 20.057 0.004 84 0 802 10.633 1405
85 4766 84 621 0457 85 0.854 7742 0 102 85 1281 14.465 1.388
86 3752 41.196 0.729 86 0607 2148 0.128 86 0.823 8.789 1.057
87 3.352 26.635 1 266 87 0566 = 1.433 0.017 87 0401 4610 0605
88 88 88
89 89 89
90 4705 45331 4683 90 0.930 7037 0 765 90 0 800 9510 0885
91 3521 41128 2761 91 0878 = =7.129 0.519 91
92 3656 41446 3054 92 0654 5.746 0 656 92
93 3644 40.557 2.736 93 0.589 4.634 - 0.676 93 0 420 5363 0847

No FTP data are available for 1988 and 1989 model year light-duty trucks.

In some isolated instances, a negative number for a start emissions estimate was obtained This 1s possible when the simulated
HRS05 value is greater than the Bag 1 or Bag 2 value from the FTP.


-8-
Start Emissions (@90mun) = Basic Start Emissions (@12hr) * Soak Function

From Table 3a:
Basic Start Emissions = 2.0163 + (0.0074/1000 miles) * 50,000 miles = 2.3863g

Soak Function = California Soak Funct * [Ratio+(1-Ratio)*((SoakTime-10)/(720-10))]

From Table 4, using the coefficients for catalyst-equipped vehicles:
California Soak Funct = 0 57130 + (0 00072)*(90) + (-1.76E-07)*(90)? = 0 63467

Ratio = (Start@10min / Start@12hr) / Califorma Soak Funct@10min
= 1 3234 for HC as given in Section 3 3

SoakTime = 90 minutes
Soak Function = 0 63467 * [1.3234 + (1-1 3234) * ((90-10) / (720-10))] = 0.81680

Start Emissions(@90min) = 2.3863 * 0.81680 = 1.9491g HC


Figure 7
HC Start Emissions vs Soak Time for 1990-93 PFI Cars

——0 miles
— 50 miles
—— 100 miles

3.00

200 +
150 4
100

(swes6) suoissiwy 1e}S$ DH

000 -

120 180 240 300 360 420 480 540 600 660 £720
Soak Time (in Minutes)

60


4

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 contain an engine start; however, the driving cycle used in the second bag is significantly
different from the cycle used for Bags | and3 Thus, to estimate the amount of FTP emissions that
can be allocated to engine start, the concept of the Hot Running 505 (HR505) is needed.

The HRS05 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 HR505 emission result, it is possible to
compare the results obtained 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, HR505
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 HR505S and FTP bag data This
correlation was then used to estimate HR505 results for the FTP dataset used for this analysis.

3.1.3 Basic Start Emission Rate

For MOBILES, the basic unit of engine start emissions is 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 | emission rate (in grams per
mile) using the nominal distance traveled in the 505 driving cycle.

Basic Start Emission Rate (grams) = [Bag 1(g/mi) - HR505(g/mi)] * 3 59 miles

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 2a and 2b

Start emissions after a 10 minute soak can also be estimated from the Bag 3 and HRS05
emission rates, analogous to the basic start emission rate:

Start Emissions after 10 minute soak (grams) = [Bag 3(g/mi) - HR505(g/mi)] * 3 59 miles

The average start emissions after a 10 minute soak are also shown in Table 2a and 2b for each
model year


Table 4

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 Curve | | HCCurve2 | COCurve! | COCurve2 | NOX Curve | NOX Curve
I 2

Constant 0 38067 0 43628 0 43803 -0 08541 131568 2 48061
minutes 0.00163 0 00078 -0 00998 0.00303 0.02752 -0 00018
minutes* 6 64E-05 0 7O1E-05 -2 11E-06 -0 00015 -2 6E-06
domain(min) 0-52 53-720 0-119 120-720 0-119 120-720
Catalyst Equipped Vehicles

HC Curve | | HCCurve2 | COCurve! | COCurve2 | NOx Curve lt | NOx Curve 2
Constant 0 057130 0 0 70641 011796 1 12983
minutes 001272 0.00072 001195 0 00033 0 02967 2 21E-05
minutes? -6 30E-05 -1 76E-07 -4 76E-05 1 0OE-07 -0 00021 -3 04E-07
domain(min) 0-89 90-720 0-116 117-720 0-61 62-720
Electrically Heated Catalyst Equipped Vehicles

HC Curve | | HCCurve2 | COCurve l | COCurve2 | NOx Curve | | NOx Curve 2
Constant (a) 0 0 50641 0 0 44733 105017 137178
minutes (b) 0 00561 0 00069 0.00707 0.00162 0 00362 0 00027
minutes? (c) -5 09E-06 0 -1 33E-05 -1 18E-06 -5 57E-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 1s time since last engine operation (1 e , soak time))

The Soak Function 1s the grams per soak time 1 divided by the grams per overnight soak (720 minutes or 12 hours)



CO Start Emissions (grams)

150
140

130 |.
120 |
110
100 |
90 4

80
70

60 |.
50 |
40 |

30
20
10

Figure 2

CO Basic Start Emissions for Fl Cars by Model Year Group

90-93 PFI

—a— 90-93 TBI

86-89 FI
a 83-85 Fi

—~e— 81-82 FI

0 50

100 150
Mileage (in thousands)

200

250 300


3-
3.1 Background
3.1.1 Overview of the Federal Test Procedure (FTP)

The Federal Test Procedure (FTP) 1s 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 minimum of 12 hours before testing to simulate a 12 hour
overnight soak period. The vehicle 1s 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 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 trips The first trip is a cold start after a 12 hour soak, and the other is a hot start after
a 10 minute soak Each trip is a “LA4" cycle, which 1s a combination of the 505 cycle (either Bag
1 or Bag 3) and the Bag 2 cycle. In a typical FTP test, the Bag 2 is only measured once and the
results are used for both trips Since the 505 cycle 1s 3 59 miles long and the Bag 2 cycle is 3.91
miles long, each LA4 trip is 7.5 miles long. The cold start trip 1s weighted at 43% and the hot start
trip 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 1 VMT Weighting = 43% * (3 59 miles /7 5 miles ) = 0 206
The hot start trip is 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 1s from stabilized driving, represented by Bag 2. Since Bag 2 is used for both
the cold start and hot start trips, it 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:
FTP = (Bag | * 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 trip in grams per mile (g/mi).

3.1.2 Overview of the Hot Running 505 and Its Use


-2-

(American Automobile Manufacturers Association) based on testing conducted in Michigan and
Arizona, and 3) the API (American Petroleum Institute) data collected in Anzona. 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

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 is a relatively
small sample (99 cars and trucks) Its chief appeal 1s that the vehicles all have generally higher
mileage readings that the rest of the sample (all over 100,000 miles) The other general trend in the
data is 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

MY Group / Technology Type
1990-93 PFI

1990-93 TBI
1986-89 FI
1986-89 CL Carb
1983-85 FI
1983-85 CL Carb
1981-82 FI
1981-82 CL Carb
1981+ OPLP

The technology groups are closed-loop ported fuel injection (PFI), closed-loop throttle body injection
(TBD), closed-loop carbureted (CARB), and open loop (OPLP). FI refers to a combination of PFI
and TBI. These model year/technology grouping boundaries were selected in conjunction with the
FACA In-Use Deterioration Workgroup on the basis of changes in emission standards or the
development/refinement of new fuel metering or catalyst technologies Itis assumed that as of 1990,
carbureted technology had negligible market share, and will not be modeled. Because of the
relatively large amount of 1990-93 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

3.0 | DETERMINATION OF START EMISSIONS


Table 3b
Basic Start Deterioration with Mileage for Light-Duty FI Trucks*

Sample Coefficients ZML Confidence Level Det Confidence Level Significance

Pollutant +MY Group Tech Size ZML Det Lower Upper Lower Upper ZML Det
HC 1990-93 PFI 330 2709 0 0000 2 482 3 308 0 0000 0 00432 0000 0334
HC 1990-93 TBI 467 4112 00118 3 809 4416 0 0046 00188 0000 0001
HC 1986-89 FI 74 2312 00221 1 330 3.295 0 0052 0 0369 0000 0010
HC 1983-85 FI 20 0 834 0 0387 0000 6 827 0 0000 0 104 0773 0227
HC 1981-82 FI “ 2435 0 0133 1859 3011 0.0022 00244 0000 0019
Sample Coefficients ZML Confidence Level Det Confidence Level Significance

Pollutant MY Group Tech Size ZML Det Lower Upper Lower Upper ZML Det
co 1990-93 PFI 330 32 237 00223 26 950 37 524 0 0000 0 1308 0000 0687
co 1990-93 TBI 467 42 204 0 1490 37 695 46712 0 0438 0 2536 0000 0006
co 1986-89 FI 74 16 314 02145 2427 30 200 00000 0 439 0022 0061
co 1983-85 FI 20 4421 0 2844 0 000 57 334 0.0000 0 858 0863 0311
co 1981-82 Fl ” 23 311 0 3489 10 345 36 275 0 0989 0 5989 0000 0007

Sample Coefficients ZML Confidence Level Det Confidence Level Significance

Pollutant MY Group Tech Size ZML Det Lower Upper Lower Upper ZML Det
NOx 1990-93 PFI 330 1411 0 0000 1366 1 958 0 0000 0 0004 0000 0067
NOx 1990-93 TBI 467 4293 0 0033 3 836 4750 0.0000 00139 0000 0548
NOx 1986-89 Fl 74 1245 0 0000 0 800 1691 00000 0 00288 0000 0235
NOx 1983-85 FI 20 1754 0 0000 0000 3 529 0 0000 0 0060 0052 0166
NOx 1981-82 FI ” 1679 0 0000 1229 2129 0 0000 00021 0000 0134

* The basic unit of engine start emissions 1s defined as a start after a 12 hour soak ZML and Det are the regression coefficients for the zero mile level
(intercept) and the deterioration rate (slope) per one thousand miles, respectively The confidence levels shown are the upper and lower 95% confidence
intervals Significance values less than 0 05 are considered statistically significant at the 95% confidence level

** Due to lack of data for the 1981-82 FI truck category, the deterioration functions for the 1981-82 FI cars were used to represent this category


HC Start Emissions (grams)

10 00

900

800

700 |

600

500

400

300

200

100

000

Figure 1
HC Basic Start Emissions for Fl Cars by Model Year Group

90-93 PFI
—=— 90-93 TBI
—o— 86-89 Fl
4 83-85 FI
eo 81-82 Fl

0 50 100 150 200 250 300
Mileage (in thousands)