EPA-AA-IMS-81-22
Technical Report
The Effect of Gasohol on I/M Programs
by
R-. Bruce Michael
November, 1981
Inspection and 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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Introduction
The use of gasohol (10% ethanol and 90% gasoline by volume) can significantly
reduce FTP mass exhaust emissions of HC and CO. Test projects in Denver and
in the EPA Ann Arbor lab (MVEL) reported average reductions of about 10% in
FTP HC emissions and 30% in FTP CO emissions [ 1,2] .* Increases in NOx and
evaporative HC emissions were also noted. Neither of these programs studied
the effect on idle emissions, however.
A later test program was therefore run at MVEL to investigate the effects of
gasohol on idle emissions(3). Two catalyst vehicles had decreases in idle
emissions of 1.1% CO and 200 ppm HC when they were operated close to the New
Jersey I/M standards of 3.0% CO and 300 ppm HC. This showed that there was
reason for concern that the use of gasohol may allow vehicles to pass an I/M
test which would normally fail the test on gasoline.
I/M staff decided to study the matter further. An appropriate and inexpensive
way to test a large number of vehicles was to add gasohol short tests to an
already planned test program. The test program chosen was a study in Portland
which would be testing about 200 vehicles from Portland and Vancouver[4]. The
vehicles were 1976 and 1978 model years, representing an emission technology
which would comprise the majority of vehicles tested in most I/M programs in
the 1980's.
Summary
The idle emission changes with gasohol varied with the different short tests.
Using the first idle readings of the Two-Speed Idle Test, average idle HC
emissions increased by 19% while CO emissions decreased by 13% with gasohol.
Using the second idle readings, HC increased by 8% and CO decreased by 9%.
These results — the HC increases and the small CO decreases — conflict with
the earlier study which showed large reductions in both idle HC and CO with
gasohol. The earlier study only tested two vehicles, however.
Gasohol .generally caused a change in failure rate. The change varied
depending on the test used, however. For the 207(b) Emission Performance
Warranty cutpoints, the failure rate using the first idle portion of the
Two-Speed Idle Test increased with gasohol from 39% to 46%. The failure rate
using the second idle portion decreased with gasohol, however, from 27% to
23%. The failure rate using the full Two-Speed Idle Test (testing at both
idle and 2500 rpm) remained essentially unchanged at 35%.
The change in failure rate was almost entirely due to CO emission changes, not
HC. For example, using the second idle portion of the Two-Speed Idle Test,
the number of vehicles failing a 2% idle CO cutpoint decreases from 17.5% to
11% with gasohol, whereas the number of vehicles failing a 300 ppm HC cutpoint
remains unchanged at 11.5%.
*Numbers in brackets indicate references listed at the end of the report.
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Importance of the Results to I/M Programs
The use of gasohol does not appear to be a significant problem for I/M pro-
grams. Results indicate that some vehicles will have higher emissions with
gasohol and some lower. The fact that failure rate changes in this study
varied with the type of test, sometimes increasing and sometimes decreasing,
indicates that the I/M failure rate may not noticeably change for a large
fleet of vehicles if gasohol usage suddenly increased.
The extent to which gasohol use becomes even a slight problem in I/M programs
depends on the degree of its usage in general and the manner of its usage by
individual owners. For example, if owners who normally use gasoline use
gasohol only in order to try to pass the I/M test, the program effectiveness
may decline due to the slight reduction in effective failure rate. EPA
expects that this would not be a widespread problem, however, due to the
majority of the public either being disinterested in trying to pass the test
with just a fuel change or being unaware of the possibility. The fact that
many vehicles will have higher emissions with gasohol may also discourage
people from trying.
General usage of gasohol does not appear to be increasing and interest in it
has declined. The economics of gasohol usage is heavily influenced by
federal and state subsidies and other incentives for its production and use.
In the absence of subsidies, gasohol is generally not competitive and would be
unavailable in most areas. .
Test Results
Each vehicle was tested on the Four-Mode Idle Test with normal unleaded test
fuel and with gasohol. This test is the same as the Two-Speed Idle Test with
the addition of an idle emissions reading in Drive for vehicles with automatic
transmissions. Emissions for the simple Idle Test can be taken from the first
idle Neutral reading.
A total of 212 vehicles were tested. Their average short test emissions are
shown in Table 1. On the average, all HC emissions increased with gasohol and
all CO emissions decreased. Table 2 presents the results for only the
vehicles which failed the Portland I/M test at a State lane. Directional
changes and some of the percent differences were similar for the groups in
both tables.
Table 1
Average Short Test Emissions
For All Vehicles (N=212)
2500 rpm Second Idle
HC CO HC CO
Gasoline 206 1.12 76 0.27 142 0.77
Gasohol 246 0.97 104 0.21 153 0.56
% Difference + 19% -13% *37% -22% +8% -9%
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Table 2
Average Short Test Emissions For
Vehicles Failing Portland I/M Test (N=71)
First Idle 2500 rpm Second Idle
HC CO HC CO HC CO
Gasoline 357 2.20 105 0.52 295
Gasohol 387 1.91 151 0.32 288
% Difference +8% -13% +44% -38% -2% -26%
A major concern for I/M programs is the effect on idle test failure rate that
the use of gasohol has. Because the failure rate depends on the cutpoints
used, which will vary from state to state, idle emissions of HC and CO were
separated into several categories. These categories reflect some of the
cutpoint strategies different states may use. Table 3 shows the number of
vehicles within five categories for idle HC and CO. Idle emissions were taken
from the second idle portion of the Four-Mode Idle test. The way to use this
table is to count up the number of vehicles above a certain cutpoint for
gasoline and gasohol and compare the difference. For example, the number of
vehicles above 2% idle CO is 16-|-9-t-7+3 = 35 vehicles with gasoline and
ll-|-4-(-5-t-2 = 22 vehicles with gasohol. Since Table 3 uses the matched sample of
200 vehicles in the study (100 Portland vehicles matching 100 Vancouver
vehicles by make, model year, etc.) the idle CO failure rates for this example
are 17.5% and 11% respectively for gasoline and gasohol, showing a reduction
of 6.5 percentage points in idle CO failure rate with the use of gasohol.
There is essentially no effect on the idle HC failure rate with the use of
gasohol.
Table 3
Numbers of Vehicles Within Certain Categories
of Idle Emissions for Gasohol
Versus Gasoline (N=200)
Idle CO
1-2% 2-3% 3-4% 4-5% 5%
Gasoline 15 16 9 73
Gasohol 17 11 4 52
Idle HC (ppm)
225-300 300-400 400-500 500-600 600-1
Gasoline 8 8 645
Gasohol 6 8 527
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For a second example, the specific cutpoints called for in the 207(b) Emission
Performance Warranty were used. These cutpoints are very similar to the
Portland I/M cutpoints for most of the vehicles in the study. The simple Idle
test was evaluated in two ways: using the first idle readings from the
Two-Speed Idle Test and using the second idle readings. This was done because
some states will specify a preconditioning before the idle measurements
similar to the 2500 rpm engine operation prior to the second idle readings in
the Two-Speed Idle Test. The failure rates for the Idle Tests and the
Two-Speed Idle Test are shown in Table 4.
The use of only the first idle readings gives the highest failure rates and,
surprisingly, more vehicles fail using gasohol than gasoline. Nine vehicles
(4.3%) fail on gasohol and pass on gasoline, whereas 24 vehicles (11.4%) fail
on gasoline and pass on gasohol. These trends are reversed using the second
idle emissions. More total vehicles failed with gasoline than gasohol and 14
vehicles (6.6%) failed with gasoline and passed with gasohol versus only 6
vehicles (2.8%) failed with gasohol and passed with gasoline. The second idle
readings give more consistent results also, i.e. fewer vehicles fail on only
one fuel than in the first idle. The Two-Speed Idle Test shows nearly the
same fail rates with both gasoline and gasohol and also compares well with the
Portland I/M fail rate.
Table 4
Failure Rates With Gasoline and Gasohol
Using 207(b) Cutpoints
Test
First Idle
Second Idle
Two-Speed Idle
Portland I/M Program
Gasoline
Failure Rate
39%
27%
35%
33%
Gasohol
Failure Rate
46%
23%
36%
Cutpoints
HC CO
220 ppm 1.2%
220ppm 1.2%
200 ppm 1.0% (at both speeds)
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REFERENCES
1. "Exhaust Emissions and Fuel Economy From Automobiles Using
Alcohol/Gasoline Blends Under High Altitude Conditions", EPA report 79-1,
October, 1978.
2. "Gasohol Test Program", EPA-AA-TAEB-79-4B, February 1980.
3. "Effects of Gasohol on Idle HC and CO Emissions", EPA-AA-IMS/ST-80-4,
March 1980.
4. "Vancouver Versus Portland Vehicle Emissions", Test Group Technical
Direction No. 9 to EPA Contract No. 68-03-2829.
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