Report No. EPA 460/3-88-004
Analytical Support for
Emission Factors Development
and Air Quality Assessment
Work Assignment No. 0-01:
Analysis of California
I/M Review Committee Data
Task 4 Report
Analysis of Loaded Mode Testing
on the Potential Effectiveness of
Vehicle Inspection and Maintenance
prepared for
U.S. Environmental Protection Agency
September 30, 1988
prepared by:
Sierra Research, Inc.
1521 I Street
Sacramento, California 95814
(916) 444-6666
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EPA 460/3-88-004
ANALYTICAL SUPPORT FOR
EMISSION FACTORS DEVELOPMENT
AND AIR QUALITY ASSESSMENT
EPA Contract No. 68-03-3474
Work Assignment No. 0-01:
Analysis of California
I/M Review Committee Data
Task 4 Report:
Analysis of Loaded Mode Testing
on the Potential Effectiveness of
Vehicle Inspection and Maintenance
prepared for:
U.S. Environmental Protection Agency
September 30, 1988
prepared by:
Thomas C. Austin
Thomas R. Carlson
Kathryn A. Gianolini
Sierra Research, Inc.
1521 I Street
Sacramento, CA 95814
(916) 444-6666
-------
ANALYTICAL SUPPORT FOR
EMISSION FACTORS DEVELOPMENT
AND AIR QUALITY ASSESSMENT
Task 4 Report:
Analysis of Loaded Mode Testing
on the Potential Effectiveness of
Vehicle Inspection and Maintenance
Table of Contents
page
1. Summary 1
2. Introduction and Methodology 7
3. Results 18
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1. SUMMARY
During a recent evaluation of the California vehicle inspection and
maintenance program, an analysis of California surveillance data was
conducted to determine the ability of loaded mode testing to increase
the identification of "excess emissions" in the motor vehicle fleet.
The analysis was possible because steady-state loaded mode tests had
been conducted on most of the surveillance vehicles. Because NOx
emission control is given high priority in California, NOx emission
cutpoints were included in the evaluation. In addition, the idle
emission cutpoints used in conjunction with the loaded modes were the
California cutpoints. The California idle cutpoints are generally
more stringent than the federal "207(b)" cutpoints, especially for
hydrocarbons.
In order to determine potential benefits of loaded mode testing in
other I/M programs, EPA requested further analysis of the California
data using loaded mode cutpoints for HC and CO only, and the federal
207(b) idle cutpoints. Since only the 1980 and later model California
models represent vehicles subject to the 207(b) cutpoints, the
if
analysis was restricted to that model year range.
* However, it should be noted that the federal 207(b) cutpoints apply
only to 1981 and later models. By expanding the data base with the
1980 model California vehicles, some uncertainty in the results is
introduced by that fact that the performance of the earlier generation
3-way catalyst systems may not represent 1981 and later models.
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The results of the analysis indicate that steady-state loaded mode
testing would increase the excess HC and CO emissions identified. As
illustrated in Figure 1, using the most stringent loaded mode
outpoints considered, the percent of excess emissions identified
increases from 41.4% HC and 45.8% CO to 60.1% HC and 69.3% CO.
CD
CO
O
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CO
CD
O
X
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CD
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Figure 1
Effect of Test Type
and Loaded Mode Stringency
on Excess Emissions Identified
(207(b) Idle Outpoints)
100
•o
CD Qrt
H= 90
80
70
60
50
40
30
20
10
0
69.3
63.8
54.8
45.8
/y//.
60.1
10.9
16.5
207(b)
Idle Only
207(b) Idle
+ Loaded A
Test Type
207(b) Idle
+ Loaded B
HC
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However, as shown in Figure 2, more detailed analysis of the data
indicates that the benefits of loaded mode testing may decrease in the
future. Much of the benefit of loaded mode testing for the current
fleet results from big increases in the detection rate for carbureted
vehicles, especially those with closed-loop, 3-way catalyst systems.
Figure 2
Effect of Emission Control System Design
on Excess Emissions Identification
(207(b) Idle vs. Idle + Loaded Mode)
TJ
0
H=
I
CO
g
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LJJ
CO
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In contrast, the incremental benefits for fuel injected, 3-way
catalyst equipped vehicles are relatively small. As pointed out by
EPA staff, some uncertainty is introduced by the fact that most of the
carbureted, 3-way catalyst vehicles included in the sample were 1980
model California models.
As Figure 2 shows, the 207(b) idle cutpoints are ineffective in
identifying carbureted, closed-loop, 3-way catalyst equipped vehicles
with excess emissions. Only 5.3% of the excess HC emissions and none
of the excess CO emissions were identified when these cutpoints were
applied to 24 vehicles that failed the FTP standards. Steady-state
loaded mode testing was capable of identifying 76.9% of the excess HC
and 86.4% of the excess CO.
In the case of fuel injected, 3-way catalyst equipped vehicles, the
207(b) idle cutpoints identified 69.6% of the excess HC and 77.5% of
the excess CO from 68 vehicles that failed the FTP. Steady-state
A
loaded mode testing increased the excess emissions identification rate
to 76.9% for HC and 86.4% for CO. If the trends shown in Figure 2
hold up, the excess emission detection for 207(b) idle cutpoints will
improve as the fraction of fuel injected vehicles grows. Steady-state
loaded mode testing will further increase the detection of excess
emissions, but the increase may be smaller than it is when a large
fraction of the fleet is made up of carbureted vehicles.
The conclusions of this study should be considered preliminary because
they are based on the analysis of one particular loaded mode test (the
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"High Cruise" mode from the Clayton Key-Mode test) that may not be
optimum. Sierra never determined the reason for the high error of
commission rate that its subcontractor reported when the cutpoints
developed for the High Cruise mode were applied to the 50 mph cruise
data obtained under EPA surveillance testing. There appears to be
either an unexpectedly sensitive relationship between the loaded test
type and the optimum cutpoints, or there are unexplained differences
between the EPA and California surveillance fleets. This issue needs
further study.
It would also be useful to consider the incremental effects of loaded
mode testing as a supplement to idle plus 2500 rpm no load testing.
Under Task 3 of our Work Assignment, it was demonstrated that the
addition of 2500 rpm testing increases the failure rate of the I/M
test. Because that earlier analysis was based on Test Analyzer System
data only (from the I/M test), information was not available on the
percent of excess emissions identified by the addition of 2500 rpm
>
testing. In addition, under Task 1 of the Work Assignment, it was
demonstrated that the inclusion of 2500 rpm failures had a slightly
positive impact on the emission reductions currently being achieved
under the California I/M program.
As discussed in Section 3, it appears that 2500 rpm testing is much
less effective than the Clayton "high cruise" mode. However, further
analysis of California I/M evaluation data and the latest available
surveillance data could provide an estimate of how much the
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theoretical benefits of loaded mode testing are reduced by the
addition of a 2500 rpm test mode.
It tt U
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2. INTRODUCTION AND METHODOLOGY
Under a contract with the U.S. Environmental Protection Agency (EPA)
for "Analytical Support for Emission Factors Development and Air
Quality Assessment," Sierra Research, Inc. (Sierra) performs a variety
of Work Assignments for the Emission Control Technology Division
(ECTD) of EPA's Motor Vehicle Emissions Laboratory in Ann Arbor,
Michigan. Work Assignment 0-01 directed Sierra to perform analysis of
California I/M data for the ECTD Technical Support Staff (TSS). Task
number 4 of that Work Assignment required an evaluation of how steady-
state loaded mode testing could affect the identification of excess
emissions.
The general direction provided by TSS was as follows:
The discussion and analysis of steady-state loaded mode tests
on pages 193-210 of the Technical Appendix (to Sierra's
previous report on the California I/M Evaluation Program)
assumes that NOx is a target for identification and repair.
The contractor shall repeat the analysis with appropriate
modifications, but assuming no NOx inspection cutpoint and no
interest in NOx identification or reduction. The contractor
shall assess the incremental effect of loaded mode HC and CO
testing over idle-only testing. The analysis shall be
performed using both California and Federal (207(b))
cutpoints.
Background
The reason that visual and functional inspections are an important
element of I/M programs is that the "no-load" (idle and 2500 rpm)
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testing procedures used to measure emissions are incapable of
detecting certain emissions related defects. However, Sierra's
evaluation of the California I/M program indicated that
visual/functional checks are performed correctly only about 25 percent
of the time.
The alternative to many of the visual and functional checks is "loaded
mode" testing using chassis dynamometers to simulate actual driving
i
conditions. Loaded mode testing can reveal defects that are not
apparent at idle or 2500 rpm no-load. The accuracy of defect
correction depends on the sophistication of the testing procedures
employed.
Loaded mode testing has been considered particularly important in
detecting excessive NOx emissions because high NOx emissions do not
occur until the vehicle is under load and because certain NOx control
devices (such as EGR) are non-functional at idle. However, certain
types of HC and CO related defects are also difficult to detect during
no-load testing. For example, partially poisoned catalysts are more
effective at reducing emissions under no-load conditions than when the
exhaust gas volume increases during actual driving.
Loaded mode tests are of two types -- steady-state tests, where
vehicles are operated at a fixed speed/load condition and transient
tests where vehicles are driven at varying speeds to include
acceleration, deceleration and cruise modes. The type of dynamometer
instrumentation required to measure emissions and the time required to
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perform the two types of tests are different, and the transient test
requires considerably more expensive equipment than the steady-state
test. During Sierra's earlier evaluation of potential improvements to
the California I/M program, both steady-state and transient loaded
mode testing were evaluated.
The conclusions of the earlier analysis are summarized in Figure 3.
As the figure shows, loaded mode testing was shown to be capable of
substantially increasing the detection of excess emissions. Using
California's idle and 2500 rpm emission cutpoints, only 54% of the
excess HC and CO emissions were detected. Vehicles which failed the
test were responsible for 19.8% of the excess NOx emissions. The
earlier analysis showed that steady-state loaded mode testing could
increase the detection of excess emissions into the range of 68-78%
for all three pollutants. Using the more complicated transient test,
90-95% of the excess emission were detected.
Modifications to the Earlier Analysis Requested by EPA
The analysis conducted for the California I/M Review Committee cannot
be directly applied to I/M programs where NOx emission reductions are
of no interest. There was no attempt in that analysis to isolate the
benefits of loaded mode testing on HC and CO only since some of the
excess HC and CO emissions identified could have resulted from
vehicles that only failed the NOx cutpoints. Exclusion of the NOx
testing would also be expected to affect the overall failure rate and
the error of commission rate. In addition, the idle cutpoints used in
the analysis are unique to California.
-9-
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by
Figure 3
Excess Emissions Identified
Various Emission Measurement Options
CO
o
'at
CO
1
CO
CO
CD
o
X
LU
**•«
O
3*
100
90
80
70
60
50
40
30
20
10
0
Ide Only
92.5
94.8
Steady State
Loaded
Transient
Loaded
To evaluate the potential benefits of loaded mode testing in other
areas of the country, the Technical Support Staff requested that the
analysis be repeated using the federal 207(b) cutpoints for idle-only
and without the consideration of NOx testing. In addition, TSS
requested that Sierra focus on the less expensive, steady-state
testing mode.
Methodology
Test Procedure Selection - Sierra's analysis of loaded mode testing
for the California I/M Evaluation Committee was based primarily on the
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surveillance data collected by ARB (Series 1-8). The data were
supplemented with EPA Emission Factor test data for a 50 mph steady-
state loaded mode and the corresponding FTP- However, differences in
the test methods limited the extent to which the data sets could be
combined. The loaded-mode steady-state test conducted by the ARB was
the "Clayton Key-Mode" test (where the test speed and horsepower
setting of the dynamometer is a function of the weight of the
vehicle). 1980 and later model vehicles also received the "MVIP
Loaded Mode" test (where the test speed is 40 mph and the horsepower
setting of the dynamometer is a function of the number of cylinders
and weight of the vehicle). The test used during the EPA surveillance
programs was performed at 50 mph cruise using the certification
horsepower setting for each vehicle.
Table 1 summarizes the loaded mode test procedures that have been used
in the California Air Resources Board's surveillance testing programs.
The Series 1-3 programs cover model years through 1978. 1980 and
;>
later models began showing up in the Series 5 program. As the table
shows, there are several loaded modes available for 1980 and later
models. (It should be noted that all tests specified in the table
were not consistently performed on all vehicles.)
The 40 mph cruise mode added during the "Series 4" surveillance
testing program does not appear to be ideal because the test mode is
influenced more by the number of cylinders of the engine than the
weight of the vehicle. It would be counter-intuitive if this were
proven to be the optimum approach. The weight of the vehicle would
-11-
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Table 1
GARB Surveillance Program
Test Routines
Speed Load
Test Series Test Modes (mph) (horsepower')
1-3 Idle 0 0
Low Cruise
2000-2800 Ibs 22-25 4-6
2801-3800 Ibs 29-32 8-10
>3801 Ibs 32-35 10-12
High Cruise
2000-2800 Ibs 36-38 13-15
2801-3800 Ibs 44-46 21-24
>3801 Ibs 48-50 27-30
4-6 As in 1-3, plus:
40 MPH Cruise Mode
<4 cylinders 39-41 9.0-11.0
5-6 cylinders 39-41 13.5-16.5
>7 cyl., <3250 Ibs 39-41 16.0-19.0
>7 cyl., >3250 Ibs 39-41 18.5-22.5
7-8 As in 4-6, plus:
2500 rpm
appear to be a more effective parameter for determining the
dynamometer load which best simulates a typical vehicle load during
actual driving. The 40 mph cruise mode was ignored and the analysis
of steady-state loaded mode testing was based exclusively on the "High
Cruise" mode of the Clayton Key-Mode.
12-
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Cutpoints - The loaded mode emission cutpoints used in the earlier
analysis were based on an error of commission rate analysis. CARS
staff had specified that two sets of cutpoints be utilized, one that
results in an error of commission rate of 2 percent and a second that
results in a rate of 5 percent. Error of commission (E ) rates were
calculated from the formula:
E = Number of vehicles failing short test + passing FTP
Total sample of vehicles
Analysis of the surveillance data to derive cutpoints conforming to
the 2 and 5 percent E rates was performed by calculating a mean and
C
variance of loaded mode emissions for vehicles passing FTP standards
in each technology type/model year group. Assuming a normal
distribution, the one-sided "tail" representing 2 percent and 5
percent of the population respectively was translated to a cutpoint.
The method provided cutpoints that were highly variable between
technology and model year groups and, in most cases, were numerically
very low. To account for instrumentation accuracy and variability
between technology groups, somewhat higher (i.e., less stringent)
cutpoints than indicated by the error of commission analysis were
developed. As shown in Table 2, two different levels of HC and CO
stringency were used. Values labeled "A" are the less stringent
cutpoints and values labeled "B" are the more stringent cutpoints.
Using these cutpoints, the actual EC values for the current California
I/M cutpoints for idle (or idle + 2500 RPM for 1980+ vehicles), as
well as the values of E resulting from the addition of the loaded
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Table 2
Loaded Mode Cutpoints
Used in the California I/M Evaluation Program
Model Year
1975-1979
1980
1981+
(A)
(B)
(A)
(B)
(A)
(B)
HC (ppm)
100
50
100
50
100
50
CO (%)
1.0
0.5
1.0
0.5
1.0
0.5
NOx (ppm)
1600
1600
1000
1000
750
750
mode test were computed. For 1980 and later models, the error of
commission rate for the idle and 2500 rpm cutpoints was 0.0%. i.e.,
all of the vehicles that failed the no-load cutpoints also failed the
FTP standards.
The error of commission rate for the less stringent loaded mode
cutpoints ranged from 0-4.6%, depending on the technology category.
For the more stringent cutpoints, the error of commission rate ranged
from 0-8.8%. Although NOx testing affected the error of commission
rate, Sierra estimated (and subsequent analysis confirmed) that the
same HC and CO cutpoints could be used in the analysis requested by
EPA. Maximum error of commission rates were still in the target
ranges when NOx cutpoints were excluded. (Note that these are not the
207(b) cutpoints.)
Using the same HC and CO cutpoints and less stringent NOx cutpoints
(1000 ppm for all model years), Sierra's previous analysis indicated
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much higher error of commission rates for the EPA data base. Since
there were no significant differences associated with the no-load
testing, it appeared that the 50 mph cruise mode used on the EPA
surveillance fleet produced significantly different results than the
Clayton Key-Mode test used on the California surveillance fleet. As a
result, the two fleets could not be combined and the analysis was
restricted to the use of Clayton Key-Mode tests on the California
fleet.
Computation of Excess Emissions Identified and Other Statistics - The
effectiveness of any short test has always been gauged by several
measures. The most important measures are:
O Error of Commission Rate - or the percentage of the vehicles
that fail the short test when they should not, and
O Excess Emissions Identification Rate - or the percent of
emissions in excess of standards identified.
In addition to these two measures, the overall failure rate is often a
factor related to the public acceptability of an I/M program. Errors
of Omission (vehicles that pass the I/M test but fail the FTP) are
also of some interest. The "high emitter" identification rate is of
special interest as Sierra's prior analysis found that most of the
emission benefits of repair are from high emitters (defined as
vehicles emitting in excess of 5 times California FTP standards).
Using two stringency levels of loaded mode HC and CO cutpoints, a
total of six different sets of emission cutpoints were needed to
perform the analysis requested by EPA:
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1. 207(b) idle outpoints only;
2. California idle outpoints only;
3. 207(b) idle outpoints plus less stringent loaded mode
outpoints;
4. 207(b) idle outpoints plus more stringent loaded mode
outpoints;
5. California idle outpoints plus less stringent loaded mode
outpoints;
6. California idle outpoints plus more stringent loaded mode
outpoints.
As discussed above, the loaded mode outpoints used in the analysis
were the same for all 1980 and later models (see Table 2). However,
the California idle outpoints are a function of technology. The
California outpoints are compared to the federal 207(b) outpoints in
Table 3.
Table 3
Idle Emission Cutpoints for I/M Programs
California vs. Federal 207(b)
California Federal 207(b)
Technology HC CO HC CO
No Catalyst 150 ppm 2.5% 220 ppm 1.2%
Oxidation Catalyst/no AIR 150 ppm 2.5% 220 ppm 1.2%
Oxidation Catalyst w/AIR 150 ppm 1.2% 220 ppm 1.2%
3-Way Catalyst 100 ppm 1.0% 220 ppm 1.2%
For 2500 rpm testing (not included in the analysis), the federal
207(b) outpoints are the same as the outpoints used at idle. In
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addition, California also uses the federal 207(b) outpoints for 2500
rpm testing.
For each of the six sets of outpoints, Sierra determined which 1980
and later vehicles in the surveillance data set would have failed an
I/M test using those cutpoints. Sierra then calculated the fraction
of emissions in excess of the FTP standards for the surveillance
fleet that were captured by each set of cutpoints. The error of
commission rate, the error of omission rate, the failure rate, and the
fraction of "high emitters" identified were also computed. (High
emitters were defined as vehicles 5 or more times the FTP standards
for one or more pollutants.) All of these calculations were done for
the 1980 and later fleet as a whole and for each of five technology
categories. Those categories were:
1. Carbureted vehicles equipped with oxidation catalysts and
air injection (Carb/OC/Air);
2. Carbureted vehicles equipped with open-loop, 3-way
catalysts (Carb/30L);
3. Carbureted vehicles equipped with closed-loop, 3-way
catalysts (Carb/3CL);
4. Carbureted vehicles equipped with closed-loop, 3-way
catalysts and clean up oxidation catalysts (Carb/3CL+OC);
and
5. Fuel injected vehicles equipped with closed-loop, 3-way
catalysts (FI/3CL).
41 II j£
* excluding vehicles for which loaded mode test results were not
available
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3. RESULTS
The analysis conducted indicates that a substantially higher
percentage of excess emissions can be identified when a steady-state
loaded mode is added to the federal 207(b) idle test. Figure 4
summarizes how the addition of steady-state loaded mode testing to the
California idle cutpoints increases the excess emissions identified in
the California surveillance fleet for less- and more stringent levels
of loaded mode testing (loaded A and B, respectively). For the more
stringent loaded mode test cutpoints, excess emissions identified
increase from 45.5% HC, 48.2% CO, and 10.7% NOx to 62.5% HC, 70.7% CO,
and 18.8% NOx.
Figure 5 shows a very similar trend when the loaded mode tests are
r>
added to the federal 207(b) cutpoints. For the more stringent loaded
mode test cutpoints, excess emissions identified increase from 41.4%
HC, 45.8% CO, and 8.4% NOx to 60.1% HC, 69.3% CO, and 16.5% NOx.
Figure 6 shows the effect of loaded mode addition when both the
California idle and federal 207(b) idle baselines are plotted on the
same chart. As the figure shows, the incremental benefits of the more
stringent idle cutpoints are maintained when loaded mode testing is
added.
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Figure 4
Effect of Test Type
and Loaded Mode Stringency
on Excess Emissions Identified
(California Idle Outpoints)
100
California
Idle Only
California Idle
+ Loaded A
Test Type
California Idle
+ Loaded B
HC
CO
NOx
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0)
CO
o
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.CO
LJJ
CO
CO
o
o
X
LU
(D
O
0)
Q_
Figure 5
Effect of Test Type
and Loaded Mode Stringency
on Excess Emissions Identified
(207(b) Idle Outpoints)
100
90
80
70
60
50
40
30
20
10
0
69.3
63.8
54.8
207(b)
Idle Only
60.1
10.9
207(b) Idle
+ Loaded A
Test Type
16.5
207(b) Idle
+ Loaded B
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Figure 6
.a>
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Table 4 contains the data plotted in Figures 4, 5, and 6. In
addition, Table 4 shows the differences in excess emissions identified
for each of the five technology categories that were evaluated. As
the table shows, there are large differences in how the different
categories are affected by loaded mode testing. These differences are
also illustrated in Figures 7 and 8. The number of vehicles in each
Table 4
Excess Emissions Identified by Short Tests
GARB Surveillance Data - 1980 and Later Vehicles
Idle Stringency: California
Sample
Group
All Vehicles
CARB/OC/AIR
CARB/30L
CARB/3CL
CARB/3CL+OC
FI/3CL
Idle
CO NOx
45.5 48.2 10.7
45.4 40.8 8.8
39.9 56.1 4.9
5.3 0.0 27.8
42.8 41.7 9.8
70.8 77.5 15.4
Excess Emissions (%)
Idle + Loaded A
HC CO NOx
59.0 66.1 13.2
Idle + Loaded B
HC CO NOx
62.5 70.7 18.8
59
62
76
51
79
.9
.4
.9
.2
.8
64
74
86
54
86
.2
.5
.4
.5
.6
15
6
27
10
..15
.0
.3
.8
.8
.4
65
77
76
52
79
.9
.0
.9
.4
.9
78
84
86
54
86
.4
.6
.4
.7
.6
21
17
35
16
18
.4
.1
.1
.3
.4
Idle Stringency: Federal 207(b)
Sample
Group
HC
Idle
CO
NOx
All Vehicles 41.4 45.8 8.4
CARB/OC/AIR
CARB/30L
CARB/3CL
CARB/3CL+OC
FI/3CL
45.0
34.1
5.3
35.0
69.6
40.0
56.1
0.0
36.4
77.5
8.8
4.9
24.4
4.3
14.4
59.5
56.6
76.9
43.4
78.6
Excess Emissions (%)
Idle + Loaded A
HC CO NOx
54.8 63.8 10.9
63.4
74.5
86.4
49.2
86.6
Idle + Loaded B
HC CO NOx
60.1 69.3 16.5
15.0
6.3
24.4
5.3
14.4
65.5
77.0
76.9
47.6
78.7
77.6
84.6
86.4
51.8
86.6
21.4
17.1
31.7
10.8
17.4
Legend: OC = oxidation catalyst, 30L = open-loop 3-way catalyst,
3CL = closed-loop 3-way catalyst, GARB = carburetor,
FI = fuel injection
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of the technology categories is given later in Table 5 (page 26). The
dramatic increase in excess emission for the CARB/3CL category may be
partially due to the relatively small size of that category (29
vehicles).
With California idle cutpoints as the baseline, Figure 7 shows that
there are large differences in the effect of adding loaded mode
testing between technology categories. The incremental effect of
adding loaded mode testing on excess emissions identified for fuel
injected, closed-loop vehicles is relatively minor (see the right-most
group of bars in each chart). However, the percentage of excess
emissions identified is greatly increased by the addition of loaded
mode testing for carbureted, closed-loop vehicles (see the center
grouping of bars).
Figure 8 shows that the effect of adding loaded mode testing to the
federal 207(b) idle test is very similar. There is no significant
difference in the percent of excess emissions identified for fuel
injected, closed-loop vehicles and there is a substantial increase in
excess emissions identified with loaded mode testing for carbureted,
closed-loop vehicles. None of the excess CO emissions from
carbureted, closed-loop vehicles is identified with the idle test but
86.4% is identified with loaded mode testing. The effect on the
identification of excess HC emissions is similar. Only 5.3% of the
excess HC is identified in carbureted, closed-loop vehicles with idle-
only testing, but 76.9% of the excess HC is identified with loaded
mode testing.
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Rgure 7
Effect of Emission Control System Design
on Excess Emissions Identification
(California Idle Outpoints)
100
80
CO
8 70
(0
m
60
50
o 40
m
•5 30
"1 20
-7-
[Z]HC
CO
NOx
Carb/OC/Air Carb/3CL F1/3CL
Carb/3OL Carb/3CL+OC
(California Idle + Steady State Loaded Mode)
100
co
to
111
CO
CO
CD
o
X
LLJ
1
HC
CO
NOx
Carb/OC/Air Carb/3CL F1/3CL
Carb/3OL Carb/3CL+OC
Emission Control System
Note: OC = oxidation catalyst
SOL = 3-way catalyst, open loop
3CL - 3-way catalyst closed loop
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Figure 8
Effect of Emissions Control System Design
on Excess Emissions Identification
(207(b) Idle Outpoints)
IUU
TJ
£ so
1 80
1 70
CO
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NOx
Carb/OC/Air Carb/3CL FI/3CL
Carb/3OL Carb/3CL+OC
(207(b) Idle + Steady State Loaded Mode)
J HC
1 CO
I NOx
Carb/OC/Air Carb/3CL FI/3CL
Carb/3OL Carb/3CL+OC
Emission Control System
Note: OC - oxidation catalyst
SOL = 3-way catalyst open loop
3CL = 3-way catalyst, closed loop
-25-
-------
For other carbureted vehicles, the benefits of loaded mode testing are
significant, but not nearly as dramatic.
Table 5 presents the error of commission rates and sample sizes for
the 1980 and later models in the surveillance fleet. (Note that
although the excess emissions identification rate for the idle testing
of carbureted, closed-loop vehicles was extremely low, there were 24
of these vehicles in the sample that failed the FTP standards.) Error
Table 5
Error of Commission Rates (%)
Computed From GARB Surveillance Data
1980 and Later Vehicles
Idle Test Stringency: California
Error of Commission Rates (%)
Sample
Group
All Vehicles
CARB/OC/AIR
CARB/30L
CARB/3CL
CARB/3CL+OC
FI/3CL
Sample
Size
659
155
85
29
254
106
Passing
FTP
194
36
31
5
77
38
Idle
Cutpoints
0.0
0.0
0.0
0.0
0.0
0.0
Idle+Loaded
Cutpoint A
0.8
0.0
1.2
0.0
1.2
0.9
Idle+Loaded
Cutpoint B
2.4
1.3
5.9
0.0
2.4
2.8
Idle Test Stringency: Federal 207(b)
Error of Commission Rates (%)
Sample
Group
All Vehicles
CARB/OC/AIR
CARB/30L
CARB/3CL
CARB/3CL+OC
FI/3CL
Sample
Size
659
155
85
29
254
106
Passing
FTP
194
36
31
5
77
38
Idle
Cutpoints
0.0
0.0
0.0
0.0
0.0
0.0
Idle+Loaded
Cutpoint A
0.8
0.0
1.2
0.0
1.2
0.9
Idle+Loaded
Cutpoint B
2.4
1.3
5.9
0.0
2.4
2.8
-26-
-------
of commission rates were extremely low for all outpoints and
technology categories and there is no difference between the error of
commission rates for the California idle cutpoints plus loaded mode
and the federal idle cutpoints plus loaded mode. Only the carbureted,
3-way, open-loop vehicles exceeded an error of commission rate of more
than 3%, but even this group was only just over 5% using the most
stringent loaded mode test.
Table 6 presents the failure rate, error of omission rate and "high
emitter identification rate" for the surveillance vehicles based on
different test types. Errors of omission are vehicles that fail the
FTP standards but pass the I/M test. "High emitters" are defined as
vehicles with either HC or CO emissions equal to or greater than five
times the California standard. As the table shows, loaded mode
testing significantly increases the I/M failure rate, reduces the
error of omission rate, and increases the percent of "high emitters"
identified. However, the sample sizes for the various technology
categories was low. The number of "High Emitters" identified was:
All Vehicles 42
CARB/OC/AIR 13
CARB/30L 3
CARB/3CL 1
CARB/3CL+OC 18
FI/3CL 7
-27-
-------
Table 6
Failure Rate (F), Errors of Omission (0) and
High Emitter Identification Rate (H)
GARB Surveillance Data - 1980 and Later Vehicles
I/M Stringency: California
Sample Idle
Group
Idle + Loaded A
All Vehicles
6.8 63.7 52.4
12.1 59.2 71.4
I/M Stringency: Federal 207(b)
Idle
Sample
Group
All Vehicles
5.1 65.4 47.6
Idle + Loaded A
10.5 60.8 66.7
Idle + Loaded B
19.3 53.7 73.8
CARB/OC/AIR
CARB/30L
CARB/3CL
CARB/3CL+OC
FI/3CL
9.0
4.7
6.9
6.3
8.5
67.7
58.8
75.9
63.4
57.6
46
66
0
50
71
.2
.7
.0
.0
.4
18.7
14.1
13.8
9.4
10.4
58.1
50.6
69.0
61.4
56.6
69
100
100
61
85
.2
.0
.0
.1
.7
25.2
30.6
17.2
15.4
16.0
52.9
38.8
65.5
56.7
52.8
76.9
100.0
100.0
61.1
85.7
17.9 55.1 71.4
CARB/OC/AIR
CARB/30L
CARB/3CL
CARB/3CL+OC
FI/3CL
8.4
3.5
3.4
3.9
6.6
68.4
60.0
79.3
65.8
55.7
46
66
0
38
71
.2
.7
.0
.9
.4
18.1
12.9
10.3
7.1
8.5
58.7
51.8
72.4
63.8
54.7
69
100
100
50
85
.2
.0
.0
.0
.7
24.5
30.6
13.8
13.4
14.2
53.6
38.8
69.0
58.7
50.9
76.9
100.0
100.0
55.6
85.7
The effect on I/M failure rates is illustrated in Figure 9. As the
figure shows, the idle-only failure rate increases by about a factor
of two when the less stringent loaded mode test cutpoints are added,
and by a factor of three when the more stringent loaded mode test
cutpoints are used.
-28-
-------
o
•«
DC
O
"CO
LL
50
40
30
20
10
Figure 9
Effect of Test Type
on Failure Rate
California Idle
207(b) Idle
19.3
17.9
6.8
Idle Only Idle + Loaded A Idle + Loaded B
Test Type
Although not addressed in the task description, it seems that it would
be useful to consider the incremental effects of loaded mode testing
as a supplement to idle plus 2500 rpm no load testing. Under Task 3
of our Work Assignment, it was demonstrated that the addition of 2500
rpm testing increases the failure rate of the I/M test. Because that
earlier analysis was based on Test Analyzer System data obtained from
I/M stations, information was not available on the percent of excess
-29-
-------
emissions identified by the addition of 2500 rpm test. In addition,
under Task 1 of the Work Assignment, it was demonstrated that the
inclusion of 2500 rpm failures had a slightly positive impact on the
emission reductions currently being achieved under the California I/M
program.
Figure 10 provides a sense of how 2500 rpm testing would affect the
incremental benefits of loaded mode testing. Based on our Task 3
report ("Incremental Effects of 2500 RPM Testing and Alternative Idle
Outpoints on I/M Results," December 1, 1987), the I/M failure rate for
1980 and later models increased by 56% when 2500 rpm testing was added
to the federal 207(b) idle test. In contrast, the failure rate
increases by 251% when loaded mode testing is added. The available
data seem to indicate that loaded mode testing is much more effective
in identifying defective vehicles than the 2500 rpm test. (It should
be noted that the difference in idle failure rates for surveillance
data and Test Analyzer System data reflect the higher average mileage
for the 1980 and later models recently tested in the I/M program
compared to the average mileage for vehicles tested in the
surveillance program.)
Further analysis of California I/M evaluation data and the latest
available surveillance data could provide a more refined estimate of
how much the theoretical benefits of loaded mode testing are reduced
by the addition of a 2500 rpm test mode.
-30-
-------
Figure 10
Effect on Failure Rate
of Adding Loaded and 2500 RPM Tests
to the 207(b) Idle Test
Idle-Only Idle + Loaded
Surveillance Data
Data Source
Idle-Only Idle + 2500
TAS Data
-31-
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