IMS-009/ST-1
Light Duty Vehicle and
Light Duty Truck Emission Performance
Warranty; Short Tests and Standards
December, 1979
NOTICE
Technical Reports do not necessarily represent final EPA decisions or posi-
tions. They are intended to present technical analysis of issues using data
which are currently available. The purpose in the release of such reports
is 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.
Inspection/Maintenance Staff
Emission Control Technology Division
Office of Mobile Source Air Pollution Control
Office of Air, Noise, and Radiation
U.S. Environmental Protection Agency
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Abstract
This report addresses the relationship between short test emission results
and emissions as measured on the "complete" or certification test (hydro-
carbons and carbon monoxide) for 1981 and later model year light duty vehi-
cles and light duty trucks. Several jurisdictions are now using idle and
loaded mode short tests as methods for evaluating emissions from in-use
motor vehicles. As provided in section 207(b) of the Clean Air Act, EPA
must establish an Emissions Performance Warranty if a short test can be
developed which is: 1. available, 2. in accordance with good engineering
practice, and 3. reasonably capable of being correlated with the Federal
certification test (known as the Federal Test Procedure or FTP). The pur-
pose of this report is to evaluate the correlation of idle and loaded short
test emissions to results which will be obtained on the certification test
for 1981 model year and later passenger cars and light trucks.
In proceeding with this work, a less common definition of correlation was
adopted. While it is not possible for the short tests to predict on-road
mass emissions with mathematical certainty, they can detect malfunctioning
vehicles with their attendant high emissions. This functional definition of
correlation is advanced in this paper as the only practicable approach which
satisfies the statutory requirement.
This report addresses the issue of correlation for 1981 and later model year
vehicles. For this purpose, data from 1975-77 model year federal cars was
examined. This group represents the most advanced automotive emission
control technology in service for which adequate data is available. (Cali-
fornia cars would be more appropriate for some purposes but, unfortunately,
sufficient data does not exist.)
Three short tests are recommended: idle, two speed idle and two mode loaded.
These procedures, necessary equipment and short test standards are all
described in Section XI of this report. These short tests and associated
standards give approximately the same error of commission rate as the FTP
(comparing single test results to average emission levels) while identifying
a substantial part of the excess emissions. This result is obtained because
the short test tends to ignore marginal failures, i.e. those vehicles only
slightly above FTP standards.
Further information regarding 207(b) short tests may be obtained from United
States Environmental Protection Agency, Inspection/Maintenance Staff, 2565
Plymouth Road, Ann Arbor, MI 48105, (313)668-4367.
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Table of Contents
Items Page
I. Background, Statutory Requirements 1
II. Rulemaking Activities, Direction of Program 2
III. Approach 4
IV. Data 6
V. Reasonable Correlation 8
VI. Standard Selection 11
VII. Two Speed Idle Test 12
VIII. Idle Test 16
IX. Two Mode Loaded Test 17
X. Geographical Effects, Light Duty Trucks 20
XI. Optional Standards 22
XII. Recommendations, Summary 22
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I. Background, Statutory Requirements
The purpose of this paper is to examine the relationship between short test
emissions and actual emissions observed on the EPA certification test pro-
cedure. (The EPA certification test, or Federal Test Procedure, is commonly
referred to as the FTP). Many states will be inspecting motor vehicles for
exhaust emissions using various short tests; repairs will be required if
emissions exceed limits established by the states. These Inspection/ Main-
tenance (I/M) programs are mandated by the Clean Air Act for areas with
severe air quality problems.
As an element of consumer protection, the Congress provided for an emission
control performance warranty, Section 207(b) of the Clean Air Act. Under
certain conditions, the manufacturer will be required to remedy emission
failures. However, before this warranty can become effective, EPA must
promulgate an "approved" short test;
If the Administrator determines that
(i) there are available testing methods and procedures to as-
certain whether, when in actual use...each vehicle...complies with
emission standards,
(ii) such methods and procedures are in accordance with good
engineering practices, and
(iii) such methods and procedures are reasonable capable of being
correlated with...(certification tests)...then
he shall establish such methods and procedures by regulation. (Clean
Air Act Section 207(b).)
The first two requirements have already been satisfied. As several juris-
dictions are currently using idle and/or loaded testing for inspection
purposes, these tests are certainly "available". (The last half of the
first requirement, ability to ascertain compliance with emission standards,
is shown by satisfying the third requirement, correlation with the certifi-
cation test.) The criterion of good engineering practice is met because
these tests can be conducted with reasonable demands of test personnel and
equipment, and they yield reasonably accurate and reproducible results.
The term "reasonably capable of being correlated" is not defined in the
Clean Air Act. Correlation implies a mutual relationship; two quantitites
which can be mathematically related are said to be correlated. Also, two
methods of ranking objects are correlated if they put the objects in the
same order or class. For example, if eggs are normally graded by weight, a
method of measuring the length and width which achieves the same result can
be said to be "correlated." The degree of error which can be tolerated
before "correlation" is lost is subjective.
Correlation is the most difficult, and consequently the most crucial, ele-
ment in establishing an approved short test. Before they can be sold, car
and light truck exhaust emissions are measured (using prototype vehicles) on
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the Federal Test Procedure (FTP). It is an expensive, time consuming and
complicated method designed to duplicate urban driving. This test takes a
minimum of 12 hours, has a specific preconditioning sequence and requires
sophisticated gas metering and analytical equipment. If emission standards
are met, a certificate of conformity is issued by EPA and sales can begin.
While the FTP is totally unsuited for inspection purposes, its intended
functions, prototype vehicle certification, selective enforcement audit and
recall, are served well. The test begins with a cold start after a simu-
lated overnight "soak"; many different driving modes are tested, including
some highway operation. All of this is performed under controlled labora-
tory conditions using a chassis dynamometer to duplicate vehicle inertia,
wind resistance and tire losses.
It should be obvious that correlating a short, simple inspection test to the
FTP is a significant task. Compounding this problem is the FTP's cold start
which yields a substantial part of the total hydrocarbon (HC) and carbon
monoxide (CO) emissions. The cold start also tends to be quite variable.
During cold starts, a gasoline engine requires a significantly richer fuel/
air mixture to insure that enough fuel is vaporized. For most vehicles this
is provided by a "choke" on the air supply. It is this rich mixture and
choke operation which cause the increased cold start emissions. (Without
enough air for complete combustion high emissions are inevitable) For warm
starts and normal operation a choke is not needed. Practical considerations
prevent any I/M short test from including a cold start; therefore, it is
impossible to fully characterize a vehicle's true FTP emissions. (A car
with a faulty choke might have very high FTP emissions and still be "clean"
on any short test.) Since classical correlation requires some sort of
mathematical relationship, [e.g. FTP emissions = function(Short Test)] no
short test can ever achieve classical correlation. However, the short test
can be used to correctly identify a substantial number of the high emitting
vehicles; this will be developed below.
The position taken in this report is that a short test which accurately
predicts FTP failure satisfies the correlation requirement of the Clean Air
Act; strict mathematical correlation is not necessary.
A short test should be acceptable if it satisfies two goals. First, it
should identify a substantial portion of "excess" emissions, i.e. emission
above the appropriate standard. Second, the number of false short test
failures, (called errors of commission on EC'S), should be as low as pos-
sible. This is necessary so that manufacturers (and owners whose vehicles
don't meet warranty requirements) will not be burdened by having to make
unnecessary repairs. It is unfortunate, but not pertinent, that a short
test will not identify all non-complying vehicles. These errors of omission
(Eo's) have no impact on the manufacturers' warranty claims. In addition,
the omitted vehicles tend to exceed standards only by a moderate amount; the
potential for air quality improvement is not as large as with the correctly
failed vehicles.
II. Rulemaking Activities, Direction of Program
On 25 May 1977 the Environmental Protection Agency issued a Notice of Pro-
posed Rulemaking (NPRM) on the Emission Performance Warranty, 42 Federal
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Register 26742 and 26747. This rulemaking consisted of two parts: proposed
alternate short tests (and associated standard setting methods) and regula-
tions to actually implement the warranty. For various reasons, the imple-
mentation regulations were withdrawn and were reproposed on 20 April 1979,
44 Federal Register 23784. Before the Emission Performance Warranty can
become effective, both sets of rules must be promulgated in final form.
Originally, five alternative short tests were proposed. These tests fell
into three classes; unloaded, steady state loaded (constant speed) and
transient (varying speed). Unloaded testing includes the high and low speed
idle modes, with exhaust concentrations measured by simple "garage" analy-
zers. Oxides of nitrogen (NOx) cannot be determined by the unloaded tests.
For steady state testing, a chassis dynamometer is employed to impose a
power requirement on the engine ("load") for specific vehicle speeds;
garage analyzers are also used for determining exhaust concentrations. As
proposed, neither the unloaded or steady state loaded procedures would
determine the actual mass of emissions produced, only the concentration of
exhaust pollutants would be measured. However, the transient tests proposed
in the NPRM do determine true mass emissions at the price of using equipment
very similar to the FTP. The three types of tests represent increasing
levels of sophistication with corresponding cost and complexity.
Along with the various short tests, several methods were proposed for sel-
ecting short test standards. These methods applied various statistical
tools to determine appropriate standards. At the beginning of each model
year, the new vehicle population was to be divided into groups by make,
engine size, vehicle size and technology. Vehicles from each group would be
tested to establish correlation between the FTP and the various approved
short tests. Use of many specific groups was promoted to maximize the
correlation obtained. (If sufficient commonality existed, groups of vehi-
cles would be combined to minimize testing.) One of the proposed metho-
dologies would be applied to the data from each group to obtain standards.
It would require testing many cars each year at considerable expense; short
test standards would not be available until many months after the start of
the model year.
In response to comments received, new data, a revision to the Clean Air Act
which shortened the warranty, and internal policy decisions, EPA's position
has been revised. Initially, only three tests are recommended for promul-
gation (idle, two speed idle, two mode loaded). This results because,
subsequent to the NPRM, EPA acquired data revealing that the idle tests have
higher than anticipated correlation for the latest technology vehicles.
Also, the idle tests are much more widely accepted and "available". For
those jurisdictions which wish to use loaded testing, a simplified version
of the Federal Three Mode has been developed. For each test, a single set
of standards will apply to the entire vehicle population. This approach
will sacrifice some potential accuracy while significantly simplifying the
program. As will be shown later, a relatively small number of "gross emit-
ting" vehicles contribute the majority of all excess emissions. These
vehicles are detected by the short tests and standards in this report. So,
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even if a more sophisticated procedure will detect a larger number of excess
emitters, its additional air quality impact will not be substantially great-
er.
In this report, loaded mode testing of NOx emissions will not be addressed.
III. Approach
By statute, the emission performance warranty is tied to state (or local)
vehicle inspection programs. Only when a car or truck fails inspection (and
some sanction will be imposed) can the warranty be invoked. Even then,
certain mileage and maintenance restrictions apply. It is anticipated that
many states will use the emission performance warranty standards as a lower
limit for their inspection standards; this will achieve the greatest possi-
ble air quality improvement without failing vehicles for which the warranty
is not available. Actual I/M standards must be set after considering the
amount of air quality improvement needed, alternate approaches, etc.
It would be possible to develop short test warranty standards by evaluating
vehicles which meet all the warranty requirements (i.e., age and mileage
limits, proper maintenance). Unfortunately, such a data set does not exist.
Further, since these standards may have wider application, a group of as-
received in-use light duty vehicles will be the basis for setting standards.
It should be noted that a portion of those vehicles failing the state I/M
short test will not qualify for warranty coverage because of tampering, high
mileage and lack of required maintenance.
EPA plans to have the emission performance warranty effective beginning with
the 1981 model year. Promulgation of the warranty regulations, short tests
and standards (or procedures to set standards) must occur prior to the start
of that model year; this is a specific requirement of The Clean Air Act.
Quite obviously, it is impossible to test in-use vehicles before their
introduction. Instead, the standards will be derived by testing the highest
technology vehicles for which data is available. Under the NPRM, this
dilemma was to be solved by collecting data on early production vehicles.
But, with the enactment of the 1977 Clean Air Act amendments, the warranty
period was significantly reduced making the proposed approach less attrac-
tive; data gathering would consume a major part of the time available for
warranty coverage.
A comparison reveals that 1975 through 1977 California vehicles have the
closest emission standards to the forthcoming 1981 and later Federal limits.
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Emission Standards (FTP) - g/miles
HC_ CO NOx
California - car
1975-6 0.9 9.0 2.0
1977 0.41 9.0 1.5
Federal - car
1975-6 1.5 15 3.1
1977-9 1.5 15 2.0
1980 0.41 7.0 2.0
1981 and later 0.41 3.4* 1.0
* Possible waiver to 7.0 for 1981 and 1982.
Unfortunately, 1975-7 California vehicles have not been tested in adequate
numbers and under appropriate conditions to establish nationwide short test
standards. Instead, this paper will use EPA's Portland, Oregon data base.
Over 2200 (1975 through 1977) cars have been tested at an actual I/M lane.
Subsequent FTP's and short tests were performed by EPA's contractor. An
evaluation of these results will produce short test standards for which
correlation with the FTP can be established.
Future Federal standards are more stringent than current levels. With the
lower emission standards in the future, one can reasonably expect lower
short test emissions. Therefore, short test standards developed using
1975-7 Federal vehicles can be applied to 1981 and later model year vehicles
without prejudicing the manufacturers rights. However, if unforseen tech-
nology is developed for which the standards are not appropriate, the manu-
facturer could be allowed to apply for a separate short test standard for
the effected vehicles.
Short test standards developed in this paper will apply to light duty trucks
(LOT) as well as passenger cars. Certification standards for light duty
trucks for 1979 and later models were derived from the 1977 passenger car
levels. Adjustments were made to account for the higher weights and larger
frontal areas; the same degree of emission control is required from 1979
light duty trucks as from 1977 light duty vehicles (passenger cars).
Emission Standards (FTP) - g/mile
HC_ C0_ NOx
1977 LDV 1.5 15 2.0
1979 LDT 1.7 18 2.3
Light trucks have used, and will continue to use, the same emission control
technology as passenger cars. Most light trucks also use engines derived
from passenger cars. The same certification test (FTP) is also used for
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light trucks. For these reasons, light trucks will respond to the short
tests in a manner similar to light duty vehicles. Therefore, short test
standards derived from 1975-7 cars can be directly applied to 1980 and later
light trucks.
For a full discussion of the light truck standards, test procedure, emission
control equipment and related issues, see the rulemaking docket for the 1979
light truck regulations.
IV. Data
Information for this paper came from EPA's Portland study. Results from
over two thousand 1975 through 1977 in-use passenger cars were evaluated.
These particular vehicles were tested from September 1977 through January
1979 and were selected to represent various types of emission control tech-
nology and not the general vehicle population. For purposes of 207(b) this
is rather fortunate; any lack of correlation for a low sales group will be
more evident than if the sample were sales weighted. All testing was
carried out at an elevation of approximately 50 feet.
No effort was made to screen out maladjusted or tampered vehicles. The
sample represents vehicles as they would be presented to an inspection
station. As it is expected that some jurisdictions may use the warranty
standards as limits to their I/M cutpoints, this approach will give an
estimate of the potential benefits of an I/M program.
Each vehicle received an idle test by the Oregon Department of Environmental
Quality (DEO). It was then taken to Hamilton Test Systems (HTS), EPA's
contractor, where it received a second idle test, a Federal Three Mode (F3M)
and a Federal Test Procedure (FTP). DEQ uses a three-step idle procedure;
idle - 2500 rpm - idle; the lowest of the two idle readings is used to
determine compliance with Oregon's standards. The Federal Three Mode is a
loaded test simulating steady state driving; it has high and low speed
cruises followed by an idle. In order to determine compliance with Federal
Emission standards, an FTP was also run. A summary of the data set appears
in Figure 1.
Figure 1
Data Summary
Mean Mean FTP (g/mile)
Model Year No. Mileage HC_ CO NOx
1975 636 39174 1.96 25.30
1976 828 28663 1.64 20.30
1977 734 17787. 1.61 22.06
Overall 2207 28030. 1.72 22.33 2.3R
Presented in Figure 2 is the distribution of FTP emission values for HC and
CO. Each "contour" line on the graph indicates the percent of vehicles
which would fail the FTP at any combination of HC and CO standards on the
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Figure 2
FTP Failure Rate-(%)
75 65 45 35 25 15
10.0 —I
6.0 .
4.0
s 2.0
00
o
EC
1.0
0.6
0.4
Standard - 15
I
6
I I
10
I
20
I
40
I
60
f I
100
CO - g/mile
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line. For example, 53% of the sample exceed the emission standards of 1.5
g/mile HC and 15 g/mile CO. This is indicated by the 45% and 65% "contours"
which bracket the point representing these standards. While a large number
of vehicles exceed new car certification levels, many of these are fairly
close to the standards. Only 35% are over 1.5 times either standard; at
twice either standard this falls to 26%. But these 26% of all vehicles
account for over 85% of all excess HC and CO emissions, i.e. emissions over
the standards. Fortunately these vehicles are easiest to detect using the
short test.
V. "Reasonable" Correlation
Any emission performance warranty short test must be "reasonably capable of
being correlated" with the Federal Test Procedure as required by section
207(b). But what is "reasonable"? Certainly, the best possible short test
could do no better than the FTP. Since any test has some inherent varia-
bility, even the FTP will occasionally fail a vehicle incorrectly. Such
errors of commission (Ec's) are unavoidable. The purpose of this section is
to investigate the correlation of FTP results to subsequent FTP tests. By
this means, we will be able to estimate the number of Ecs which an "ideally"
correlating test will yield. Intuitively a "reasonably" correlating short
test will be permitted a greater number of Ecs. Compliance with the stat-
utory correlation requirement will be made on this basis.
FTP variability has been characterized in "Survey of Sources of Test Varia-
bility in the 1975 Federal Test Procedure," August, 1978, by Douglas Berg
of EPA's Motor Vehicle Emissions Laboratory. In Table B, Mr. Berg makes the
following estimates for total FTP variability on the same vehicle:
Percent Coefficients of Variation*
HC: 10-25%
CO: 15-30%
*Sample standard deviation/sample mean.
These coefficients of variation can be used to estimate the percentage of
error of commissions if the FTP were used as a short test.
In order to evaluate these errors of commission, two assumptions must be
made. First, it is assumed that test variability follows the normal (or
bell shaped) distribution curve. Second, the Portland data (FTP results) is
assumed to be representative of the true emissions of the general popula-
tion. It is acknowledged that these assumptions are not precisely correct.
However, their whole function is to help estimate how well the FTP would
function as a short test. Given the range of the estimated coefficients of
variation, these assumptions are adequate.
Cars. from the Portland data base were segregated into groups which passed
FTP standards. All of these vehicles were assumed to have "true" FTP valves
equal to the test results observed. For any given car this would not be
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Figure 3
FTP Errors of Commission
.1%
T
0.10
0.20
0.30
CO - Coefficient of Variation
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Figure 4
Comparison of I/M Idle Standards
I/M Standards for late model
large displacement cars
300
o New Jersey
200 _
0)'
I
ex
i
o
100 __
o California
Portland
Proposed 207(b) ~ Two sPeed idle
"Standard Locus"
o Arizona
1.0
I
2.0
CO - %
I
3.0
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correct; however, for the entire population this assumption should be rea-
sonable. It is expected that if a subsequent FTP were administered, the
results observed would be similar to the first set; variations for indivi-
dual vehicles would average out.
To determine the FTP's error of commission rate, coefficients of variation
for HC and CO were assumed. For each vehicle passing the FTP a probability
of failing was calculated. This probability is a function of how close the
FTP results were to be standards. Various coefficients of variation for HC
and CO were assumed. (Probability of failure was calculated by determining
how many standard deviations a particular vehicle was below the standards
and looking up the probability in a normal distribution table. For example;
at an assumed HC coefficient of variation of 0.20, a vehicle whose emissions
are 1.25 g/mile would be 1.0 standard deviation below the 1.5 g/mile stan-
dard: 1.5 g/mile - 1.25 g/mile = 0.25 which is 0.20 of that vehicles emis-
sions of 1.25 g/mile; or one standardized deviation. At 1.0 standard devia-
tion below the standard the vehicle would have a 16% chance of failing a
subsequent FTP. This process was then performed for CO, and a total EC
probability determined). This process was repeated for each passing vehicle
to determine its probability of being an error of commission (Ec) on a
subsequent FTP. The sum of these probabilities divided by the total number
of vehicles is the estimated FTP EC rate. Results are indicated in Figure 3
for a range of HC and CO coefficients of variation.
Assuming coefficients of variation of 20% and 25% for HC and CO, the FTP
will give approximately 5.3% errors of commission. (Using the range of
estimates for coefficients of variation, EC'S will be between 3 and 6%).
This statement is derived from the Portland data sample where only 47% of
the vehicles pass FTP HC and CO standards. If a "cleaner" population (more
passing cars) were tested, errors of commission would increase because more
cars would be subject to the random test variability. (As a convention,
errors of commission are expressed as a percent of the entire population,
not just those below emission standards.)
Since the FTP, used as a "short" test, yields approximately 5% errors of
commission, this is a criteria against which the short tests can be evalu-
ated.
VI. Standard Selection
Figure 4 indicates idle HC and CO I/M standards for late model, large dis-
placement cars in several jurisdictions. Also shown is a general rela-
tionship between the two constituents, developed from earlier work. This
relationship, or "standard locus", represents EPA's best judgment (as of
September, 1979) of the best relationship between HC and CO standards for
typical I/M programs. In developing this relationship, test results from
approximately 300 1975-77 California cars were briefly evaluated. Items
investigated were failure rate, errors of commission and excess emissions
identified. Results of this investigation indicate that the "standard
locus" is the center of a region where errors of commission and excess
emissions identified are constant for a given failure rate. Farther away
from the standard locus, the test loses some effectiveness and errors of
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12
commission increase. For these reasons, short test standards will be de-
veloped from this relationship. (A more thorough study on the topic of I/M
standards is now underway; results should be available in early 1980).
As of September, 1979 the most stringent I/M program had idle standards of
1.0% CO and 225 ppm HC (Portland, Oregon for catalyst vehicles). The corre-
sponding standard on the locus is 1.0% CO and 200 ppm HC. If errors of
commission are low enough, such a standard for the emission performance
warranty would be desireable.
It is expected that many future vehicles will be designed for low idle
emissions, even after some key parts of the control system have failed. For
these types of failures an additional short test will be needed. To be
effective, such a short test must exercise the fuel and emission control
systems so as to detect component failures. Either a high speed idle or
loaded mode should accomplish this end.
Standards will be developed for three separate, but related, short tests.
All tests include an idle mode. Different standards are necessary because
of the way results are calculated and because of potential preconditioning
differences. The three tests are briefly described below; all modes except
the 30 mph cruise are performed with transmissions in neutral.
Idle - ° Idle
Two Speed Idle - ° Idle
- ° 2500 rpm idle
- ° Idle
Two Mode Loaded - ° 30 mph cruise
- ° Idle
The two speed idle will be addressed first. This test is used in the Port-
land I/M program. Standards of approximately equal stringency will then be
developed for the other procedures.
VII. Two Speed Idle Test
An analysis was performed on the Portland data using an idle standard of
1.0% CO and 200 ppm HC. The two speed idle test consists of two idle por-
tions separated by a high speed segment (idle - 2500 rpm - idle); the lowest
HC and CO levels of the two low speed idles is used to compare with the
standards. This is the procedure used in Portland.
Idle Portion only
Failures - 37%
EC'S - 4.0%
Excess HC identified - 81%
Excess CO identified - 83%
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This test satisfies the requirement of reasonable correlation and is an
acceptable emission performance warranty standard. Effects of other pos-
sible standards are shown in Figure 5. Comparison of the two speed idle
test (idle portion only) to the FTP is shown in Figure 6.
However, as with any sampling process, predicting the number of Ecs (like an
election result) is not an exact process. For idle standards of 1.0% CO and
200 ppm HC an estimate taking into account the impact of test variability
was made. The sample of 2207 vehicles was randomly divided into 22 subsam-
pies of 100 cars each. For each subsample the number of Ecs was computed.
Considering this to be a sample of 22 programs, nonparametric tolerance
intervals based upon the distribution of order statistics were derived to
estimate expected programmatic effects. The following statements can be
made with 90% confidence:
- 89% of the I/M programs will have EC'S less than 5%
- 92% of the I/M program will have EC'S less than 6%
Of course, these error of commission rates were derived by an analysis of
the idle standard applied to groups of 1975 to 1977 model cars. The emis-
sion performance warranty will apply to 1981 and later vehicles. For pas-
senger cars, idle emissions and errors of commission should be much lower
since the newer vehicles will be certified to lower emission standards.
Light trucks will experience about the same EC rate, they use the same
emission control systems as the earlier cars.
The emission performance warranty can also be applied to the high speed
(2500 rpm) segment. For 1975 through 1977 model cars the low speed idle is
an effective test. But, with changing technology the high speed segment
(2500 rpm) may be needed to identify high emitters. (EPA has obtained test
results verifying this occurance. For some future technology cars, the 2500
rpm segment identifies certain failure modes where the normal idle does
not.) Results of the idle test are summarized below, standards of 1.0%
CO/200 ppm HC were used. A summary of these results is as follows; they all
meet the statutory requirement of reasonable correlation:
Two Speed Idle Test Summary
Failure
Rate
Excess Emissions Identified
Ecs HC CO
Idle (minimum of 37%
two idles)
2500 rpm
Combined
22%
42%
4.0%
2.8%
6.0%
81%
60%
87%
83%
59%
90%
Note: Test sequence is: idle - 2500 rpm - idle. Idle results are
the lowest of the two HC and two CO values observed. Standards of
1.0% C0/200ppm HC were used for both idle and 2500 rpm.
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100 _
Figure 5
Impacts of Possible Standards
(Two Speed Idle Test — Idle portion only)
U-l
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01
CO
O
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CO
CO
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s
CO
co
0)
0
X
w
80 -
60 ..
40 -
20 >
HC
I
10
20
I
30
I
40
I
50
. 10
% Ecs
- 5
Failure Rate %
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Figure 6
Comparison of Two Speed Idle Test to FTP
(Idle portion only)
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4-1
c
0)
CO
CO
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16
While the two speed idle test is a specified sequence (idle - 2500 rpm -
idle), three ways exist to take emission results. (See Section XI for a
full test description). These methods are as follows:
1. Idle mode only. Emissions from the two idle sequences are measured.
The lowest HC and CO readings observed are compared against the stan-
dards. Emissions from the 2500 rpm mode are either not measured or
their results are disregarded. (This mode is preconditioning for the
second idle). Of course, if the vehicle passes on the first idle
sequence, the remainder of the test need not be run. (The standard is
1.0% CO/200 ppm HC).
2. 2500 rpm mode only. The vehicle is briefly idled prior to the 2500
rpm mode. Emission measurements need only be taken at 2500 rpm, the
second idle is deleted. (The standard is 1.0% CO/200 ppm HC).
3. Combination of idle and 2500 rpm. The full test sequence, idle-
2500 rpm-idle, is run with emissions measured under all modes. To
pass, a vehicle must be under the standards at both idle and 2500 rpm.
As with the "Idle mode only" procedure described above, the lowest HC
and CO readings from the two idle sequences are compared against the
standard. If the vehicle passes the first idle, the second idle se-
quence may be deleted. (Standards for both modes are 1.0% CO/200 ppm
in HC).
VIII. Idle Test
This is the simplest short test; exhaust concentrations are measured with
the vehicle idling in neutral. (This procedure is followed in New Jersey
and other locations.) To achieve the same level of stringency as the two
speed idle (idle mode only), slightly higher standards will be necessary.
(The two speed idle uses the lowest of two observed idle measurements, any
single measurement procedure will require higher numerical standards at the
same level of stringency).
For standards of 1.2% CO and 220 ppm HC (hexane) the idle test yields the
following results:
Idle Test Summary
Failure Excess Emissions Identified
Rate Ecs HC CO
39.4% 5.6% 82% 84%
These compare quite closely with those for the idle mode of the two speed
idle. This test meets the statutory requirement of reasonable correlation,
i.e. it results in low Ecs and a high fraction of excess emissions identi-
fied.
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17
IX. Two Mode Loaded Test
This paper presents a simplified loaded test for use with the emission per-
formance warranty. Derived from the Federal 3 Mode, the simplified two mode
test has identical test conditions for all vehicles: 30 mph cruise at 9.0
hp load followed by an idle in neutral. Following is a history of its
derivation and an estimate of its effectiveness.
As an alternative to the idle test, 1/M jurisdictions may employ loaded mode
testing. Currently, Arizona uses a loaded mode preconditioning for its idle
test, other states and localities are considering loaded tests. To the
extent possible, the emission performance warranty should accomodate these
procedures.
Unfortunately, previously there was no standard loaded mode test in which
the test parameters are the same for all cars.
In the NPRM, EPA proposed the "Federal 3 Mode" (F3M), consisting of 50 and
30 mph cruises followed by an idle in neutral. Vehicles were divided into
four weight categories for the purpose of setting dynamometer load. This
test was subsequently modified before the Portland program to provide many
more categories of dynamometer adjustment as well as an idle in Drive for
automatic transmission cars. EPA's experience with this test revealed the
virtues of a procedure with fixed test conditions. In performing a proce-
dure with multiple test conditions, much time is spent determining the
proper classifications for a particular vehicle; errors can occur. Any
possible increase in correlation from the multiple classification will not
be great enough to offset the extra complexity.
For this reason a simplified loaded procedure with one test condition will
be evaluated.
As specified in the NPRM, the Federal 3 Mode low speed cruise for vehicles
up to 2500 pounds was 30 mph with a 9.0 hp load. This will be adopted for
all vehicles. The high speed cruise will be deleted to reduce test length.
(An optional high speed cruise will be permitted, but warranty standards
will not apply). For safety reasons, the idle mode will be run in neutral
instead of Drive for automatic transmission vehicles.
For heavier vehicles, this test condition is less severe than the original
F3M. This power level is equivalent to a modest acceleration for small
vehicles and a very low acceleration for a larger car, see Figure 7.
(During the FTP, a vehicle will see acceleration rates of up to 3 mph/sec.)
In order to achieve the same general level of stringency it is necessary
that slightly higher standards be employed for the idle portion of the
simplified loaded test than for the idle test. During the Portland program,
idle exhaust emissions averaged approximately 0.2% CO and 25 ppm higher on
the F3M than the idle test (idle portion of two speed idle). These results
were obtained from manual transmission cars, thus avoiding any increase due
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18
Figure 7
Loaded Mode Power Settings
10 -
ex
I
I-
o
CO
rt
n
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to automatic transmissions being idled in "Drive" (F3M) as opposed to neu-
tral (idle test). This offset is probably caused in part by the loaded-mode
"preconditioning" under the F3M procedure and, in part, by the use of the
lower of the two idles in the two speed idle test. Consequently, idle
standards for the loaded test will be set at 1.2% CO and 220 ppm HC.
To set standards for the loaded mode it is necessary to calculate a theore-
tical exhaust concentration. One must assume both an exhaust emission level
(grams/mile) and fuel economy (miles/gallon). (Several additional facts and
assumptions enter in the calculation; fuel density, fuel composition,
stoichiometric combustion, standard temperatures and pressures, etc. Minor
discrepancies in these ancillary facts will not upset the approximate out-
come). From this point one can apply the standard combustion equations to
predict an exhaust concentration. For example, a car traveling 30 mph,
emitting 7.0 g/mile CO and 0.41 g/mile HC (1980 standards), and getting 50
miles/gallon will have exhaust concentrations of approximately 1.0% CO and
180 ppm HC. Vehicles with fuel economies less than 50 miles/gallon will
consume more fuel and have corresponding higher exhaust flows. For the same
mass emissions (g/mile), exhaust concentrations (%, ppm) will have to be
lower. Air pumps, employed on some vehicles, will increase exhaust flow
with the same effect on concentration.
A very conservative example was used in the paragraph above; a vehicle
getting 50 miles/gallon at 30 mph while its engine produces over 9.0 horse-
power. (Tire and drive train losses are not considered in setting the
dynamometer to 9.0 hp.) Such a vehicle would have to have a very efficient
engine, less than 0.4 Ib fuel/horsepower - hr. It is doubtful that any real
vehicle would consume less fuel and have a lower exhaust flow. Also, it was
assumed that HC and CO were being emitted at the level of the standards.
Again, this is very conservative; a vehicle which meets emission standards
will be very clean at a steady cruise under low power levels when fully
warmed up. (These conditions describe the loaded mode test condition.) To
pass the FTP, such clean operation is essential to balance inherently high
cold start emissions. The same standards used for the idle portion, 1.2%
CO/220 ppm HC, will pass the hypothetical example in the previous paragraph;
this is a conservative standard and will have very few errors of commission
when applied to 1981 and later passenger cars.
These same standards can also be used for light trucks even though their
1980 standards are significantly higher, (1.7 g/mile HC; 18 g/mile CO).
However, light trucks consume significantly more fuel with resulting larger
exhaust flows. The appropriateness of these standards for light trucks can
be verified by examining how 1975-7 cars in the Portland data base respond.
As explained previously, these vehicles are technologically similar to 1981
and later model light trucks and should respond similarly to the same short
tests. This comparison will also serve as an "upper limit" for 1981 and
later passenger cars; their cleaner emissions will give lower Ecs with
expected decreases in failure rate and excess emissions identified. Results
are stated below (Test conditions were the same or more severe than the two
mode test recommended. Results here are estimates only for the loaded
mode).
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20
Loaded Test Summary
Failure Excess Emissions Identified
Rate Ecs H£ C0_
Loaded (Estimates) 24% 4.3% 59% 54%
Idle 40% 5.2% 83% 85%
Combined 46% 7.0% 93% 93%
Note: Test sequence is 30 mph at 9.0 hp load followed by an idle in
neutral; standards are 1.2% CO/220 ppm HC for each mode.
The two mode loaded test is a specified sequence. However, as with the two
speed idle test, three ways exist to take emission measurements.
1. Loaded Mode only. Standards of 1.2% CO/220 ppm HC are used for the
loaded mode, the concluding idle may be disregarded.
2. Idle Mode only. The vehicle undergoes the 30 mph cruise for a
brief period, 10-30 seconds. An emission measurement need only be
taken for the idle mode. Standards are 1.2% CO/220 ppm HC.
3. Combination of Loaded and Idle. The full test sequence is run with
standards of 1.2% CO/220 ppm HC applied to both modes. If these stan-
dards are exceeded on either mode, the vehicle fails.
As indicated above, the loaded test and associated standards comply with the
requirements of Section 207(b). Errors of commission are within acceptable
limits and a substantial part of the excess emissions are identified. Light
trucks (1981 model year) should respond in a similar manner to the above
table. Actual EC'S for 1981 passenger cars will be lower due to more strin-
gent Federal Standards.
X. Geographical Effects, Light Duty Trucks
To gain additional confidence in the application of the short test standard
to other geographic areas, a similar analysis using EPA emission factor data
was performed. All currently available EPA emission factors and restorative
maintenance test data on 1975 through 1979 models was used. (Analysis was
done in October 1979, test results on 3706 cars and light trucks were avail-
able). This data has been collected over a number of years in 8 different
cities; it represents the best cross section available. For this analysis,
results from the idle test (using the recommended standards, 1.2% CO/220 ppm
C,) were compared with FTP emissions; failure rates and percent errors of
commission were calculated. As can be seen in Figure 8, the results compare
closely to those observed in Portland. It is also evident that light trucks
are treated slightly less stringently than automobiles.
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22
XI. Optional Standards
The short test standards developed above are appropriate for anticipated
future vehicles. It is possible, but unlikely, that control technology will
be developed for which these standards are not appropriate. Under these
circumstances specific standards or modified procedures should be esta-
blished for the effected vehicles.
XII. Recommendations Summary
Three short tests can be used for the Emission Performance Warranty; idle,
two-speed idle and two-mode loaded. Initial standards for 1981 and later
model light trucks and passenger cars should be as set forth in Figure 9.
Figure 9
Short Test Summary
Name
Description
(test modes)
Standards
Equipment
1.2% CO
220 ppm HC
Garage
Analyzer
Two Speed Idle
1.
2.
3.
Idle
2500 RPM
Idle
lr.0% CO*
200 ppm HC*
Garage Analyzer
Tachometer
Two Mode Loaded
1. 30 mph/9.0 hp
2. Idle
1.2% CO**
220 ppm HC**
Garage Analyzer
Dynamometer
* Standards apply to the lowest HC and lowest CO emissions observed
during the two idle portions of the test. Standards also apply to the
2500 rpm mode either independently or in conjunction with the idle
portions.
** Standards apply to the loaded mode and idle, either In combination
or independently.
Note: All idles are in neutral
As experience Is gained with both the warranty program and the later tech-
nology vehicles, data can be collected and more stringent standards, if
appropriate, proposed in future rulemakings.
Standards have been set so that the error of commission rate is approxi-
mately the same as for the FTP. As a result, the short test concentrates on
vehicles with very high emissions. Failure rates are much lower than for
the FTP. Because of the heavy contributions from these "gross emitters", a
substantial portion of the total excess emissions is identified.
U£. GOVERNMENT PRINTING OFFICE: 1979- 651-112/0131
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21
Figure 8
Idle Test Comparison For Various Cities
City
Chicago
Denver
Houston
Los Angeles
St. Louis
Washington
Detroit*
Phoenix
Composite
Type
LDV
LOT
Total
LDV
LOT
Total
LDV
LOT
Total
LDV
LDT
Total
LDV
LDT
Total
LDV
LDT
Total
LDV
LDV
LDT
Total
LDV
LDT
Total
Vehicles
792
27
819
416
27
443
321
27
348
371
27
398
625
23
648
339
27
366
100
574
10
584
3538
168
3706
Number
Failures
332
3
335
207
13
220
168
13
181
115
8
123
199
7
206
136
5
141
35
202
3
205
1394
52
1446
Percent
EC
42
1
43
8
1
9
23
0
23
23
2
25
27
1
28
22
1
23
5
42
0
42
192
6
198
Fail
42
11
41
50
48
50
52
48
52
31
30
31
32
30
32
40
19
34
35
35
30
35
39
31
39
EC
5.3
3.7
5.3
2.0
3.7
2.0
7.2
0.0
6.6
6.2
7.4
6.3
4.3
4.3
4.3
6.5
3.7
6.3
5.0
7.3
0.0
7.2
5.4
3.6
5.4
Portland * LDV 39 5.6
LDV = Passenger car (Light duty vehicle)
LDT = Light duty truck
* No LDT's tested
Source: EPA test programs through October 1979 for 1975-79 model vehicles.
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