EPA-AA-TSS-PA-86-02
Technical Report
Vehicle Driveability with Gasoline/Alcohol Blends
By
Jonathan Adler
and
Craig A. Harvey
May, 1987
NOTICE
Technical Reports do not necessarily represent final EPA
decisions or positions. 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.
Technical Support Staff
Emission Control Technology Division
Office of Mobile Sources
Office of Air and Radiation
U. S. Environmental Protection Agency
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VEHICLE DRIVEABILITY WITH GASOLINE/ALCOHOL BLENDS
1.0 INTRODUCTION
Gasoline/alcohol blends such as gasohol (90% unleaded
gasoline/10% ethanol) and ARCO's Oxinol blend (unleaded
gasoline with a maximum of 4.75% methanol and 4.75% tertiary
butyl alcohol [TEA]) have been successfully marketed for a
number of years now. Also, EPA has approved a waiver from the
requirements in section 211 of the Clean Air Act for a blend
prepared by DuPont. This blend includes 5% methanol with 2.5%
cosolvent alcohols such as ethyl, propyl, or butyl alcohols.
It has not been commercially marketed yet because of industry's
apparent concern about the feasibility of economically meeting
the volatility restrictions associated with the waiver
approval. These volatility restrictions are designed to help
assure that the evaporative emissions of vehicles using the
blend do not increase compared to those of the same vehicles
using the gasoline it would displace.
Many oxygenated blends have been evaluated in a variety of
test programs conducted by oil companies, other fuel
developers,' vehicle manufacturers, EPA, DOE, and .other
interested parties. While there are many issues involved in
the decisions about the desirability of such fuels (economics,
alcohol supply, octane enhancement, vehicle driveability,
emissions, fuel volatility levels, etc.), this paper addresses
only the issue of vehicle driveability with gasoline/ethanol
and gasoline/methanol/cosolvent blends. This paper does not
.examine driveability with gasoline/MTBE blends because there is
less data available. There is current research in the area of
gasoline/MTBE blends which has been sparked by recent interest
in the fuels, and more data may be forthcoming.
Various programs have been conducted evaluating vehicle
driveability with these blends and comparing it to that
obtained with gasoline. Some of these programs include
subjective evaluations of the performance of fleets of in-use
vehicles. These evaluations provide information about the
performance of the fuels under many driving situations. Other
programs have been run with limited numbers of vehicles using
more objective driveability tests with trained observers over
controlled conditions. These tests do not cover all of the
driving conditions encountered during in-use driving. This
report summarizes the results of several testing programs. No
attempt is made to reevaluate the conclusions of the individual
studies.
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1.1 Oxygen Content
Probably the most important factor in determining
driveability of oxygenated fuels is the oxygen content of the
fuel. This is usually expressed in weight percent of oxygen.
Neat methanol has an oxygen content of 50% by weight, while
that of ethanol is 35%. The maximum oxygen content of methanol
blends is limited to 3.5% and 3.7% by weight under the EPA
waiver decisions for Oxinol and the DuPont waiver blend,
respectively. Gasohol contains 3.7% oxygen by weight, because
the ethanol content is specified at 10%. Thus, the volume
percent of methanol is limited to 7.0% and ethanol 10%.
However, in the case of Oxinol and the DuPont waiver blend, the
methanol content is limited to 4.75% and 5% respectively, due
to the addition of cosolvent alcohols. Cosolvent alcohols
reduce the possibility of phase separation in the blend, and
they help prevent problems related to materials compatibility.
They are required for gasoline/methanol blends (in at least a
1:1 ratio for Oxinol and a 1:2 cosolvent/methanol ratio for the
DuPont blend) for these and other reasons. Including the
oxygen content of the cosolvent alcohols, the oxygen content of
the gasoline/alcohol blend will frequently be close to if not
equal to the 3.5% or 3.7% by weight limit.
Oxygen content is an important driveability factor because
the presence of oxygen in the fuel makes the air/fuel mixture
leaner than if the fuel consisted only of hydrocarbons. With
oxygenated fuels there is more oxygen available to burn a given
quantity of carbon and hydrogen. Also, the oxygen displaces
some of the carbon and hydrogen in a given volume of the fuel.
Since fuel metering systems are generally volumetric, less
hydrogen and carbon are delivered to the cylinders during a
given cycle, and the mixture is enleaned. Since an engine
usually operates best within a certain narrow range of air/fuel
mixtures, anything that puts the air/fuel mixture outside that
range (especially on the lean side) will tend to degrade the
driveability. Therefore, the greater the oxygen content of the
fuel, the leaner the mixture will be and the more likely it
becomes that the mixture will be outside of the optimal range.
As the mixture moves away from this optimal range, the
driveability worsens. This phenomenon is especially important
for older cars without closed loop control systems which adjust
the air/fuel ratios to within the desired range. Many newer
cars with closed loop control systems adjust air/fuel ratio for
optimal operation of the engine and the catalytic converter.
Driveability changes due to use of gasoline/alcohol blends
should be less significant with these vehicles.
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1.2 Volatility
Another fuel property that can influence driveability is
volatility. Volatility affects the tendency of the fuel to
evaporate enough to start a cold engine, its ability to
vaporize fully and be distributed uniformly to all cylinders
during and after warm-up, and the possibility during hot
operation of producing vapor in the fuel metering system so
that vapor lock occurs. Standard tests have been developed to
measure properties which are related to these fuel qualities.
Reid Vapor Pressure (RVP) is a measure of the vapor pressure at
100°F; the ASTM D-86 distillation procedure provides a
temperature versus percent evaporated curve; and vapor/liquid
ratio is measured as a function of fuel temperature. In
addition, the heat of vaporization of a fuel provides an
additional indication as to effects that are heat transfer
dependent as opposed to equilibrium dependent.
A motor fuel with optimized volatility should evaporate
just after it is metered into the intake stream. If it
evaporates too early, then it may cause vapor lock or sluggish
performance. If it evaporates too late, then it may cause
uneven distribution among the cylinders and other conditions
which would adversely affect driveability. Also, highly
volatile fuel can excessively load the carbon canister, which
can cause hot-starting problems when the canister is purged.
Since different vehicles handle fuel in different ways, there
is no single measure of volatility which correlates directly
with the way fuel behaves in fuel systems.
Since the addition of alcohol to gasoline normally changes
the fuel's volatility characteristics, it can have an effect on
.driveability. If blended with ordinary gasoline (splash
blended), both ethanol and methanol will raise the RVP and
increase the percent evaporated in the 140 - 200°F range. The
effect on RVP is more pronounced with methanol blends. If the
RVP of the base gasoline is adjusted to compensate for this
increase by removing or leaving out light ends (those
hydrocarbons which evaporate at lower temperatures, such as
butanes and possibly pentanes), then the blend RVP can be held
constant or increase only slightly. The addition of cosolvents
can also reduce the effect of ethanol and methanol on RVP.
However, the higher temperature volatility characteristics will
still be different from those of typical gasoline because most
of the alcohol evaporates within a relatively narrow
temperature range. Special formulation of the base gasoline
can negate this effect, but that is not considered necessary or
economically feasible for most purposes. The type and quantity
of alcohol in the blend dictates the effort and expense that
would be necessary to adjust the volatility in a given way.
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1.3 Heat of Vaporization
The heat of vaporization is the quantity of heat required
to vaporize a given quantity of fuel. This heat is absorbed
from the surrounding air and engine components thus having a
cooling effect on them. Alcohols have a higher heat of
vaporization than gasoline and, therefore, require more heat to
vaporize as shown by the figures below.
Heat of Vaporization: Gasoline 940 BTU/gallon
Ethanol 2600 BTU/gallon
Methanol 3320 BTU/gallon
Any possible problems related to this difference would most
likely show up as difficulties in starting a cold engine or
keeping it running once it is started. The standard ASTM fuel
volatility tests mentioned above do not address this fuel
property since they simply provide as much heat as necessary to
achieve the required temperatures for fuel distillation or
vapor formation.
1. 4 Oc'tane
Another driveability-related fuel property that is
affected by alcohols is octane. Alcohols raise octane when
added to gasoline, so the degree of engine knock experienced
with gasoline/alcohol blends will tend to be less than that
with a base gasoline of lower octane. However, some concern
has been expressed1 that the difference between research and
motor octanes (known as the sensitivity of a fuel) may be
larger for alcohols than for hydrocarbon compounds typically
present in gasoline. Gasoline is frequently blended for an
acceptable average of research and motor octanes (the "pump"
octane, which equals [research + motor octane]/2), so the motor
octane of the gasoline/alcohol blend may be lower than that of
a hydrocarbon only fuel of the same pump octane rating. A low
motor octane can result in engine knock especially under high
speed or load conditions. Thus, use of gasoline/alcohol blends
could result in some engine knock not experienced with
gasoline. Knocking under conditions of high speed and load can
lead to catastrophic failure of the engine2. However, other
components commonly used in gasoline, such as toluene and
xylene, have sensitivities as high as alcohols3. Some data
are. available indicating that the sensitivity of
gasoline/alcohol blends may be somewhat more than that of
gasoline itself" and other data indicate3 that this
situation may not occur.
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1. 5 Intake System Deposits
Deposits in the intake system can affect driveability, as
well as fuel economy and emissions. Their formation is
affected by fuel composition, engine condition, and vehicle use
pattern. Deposits can accumulate anywhere from the carburetor
to the intake valves, and they can restrict air flow, clog
vacuum hoses, change swirl patterns, and otherwise interfere
with devices in the intake system.
Some gasolines include detergent additives in order to
minimize the accumulation of these deposits near the beginning
of the intake system. These additives may not inhibit deposits
forming farther downstream near the EGR duct or the intake
valves. Other additives, such as carrier oils may serve to
carry the deposit-forming materials into the cylinder, where
they may be burned or exhausted. Of interest in this report is
how the use of blended fuels can affect the formation of
deposits in the intake system.
1.6 Other Parameters
There are many other factors which can affect the outcome
of driveability tests, such as base gasoline composition,
additives to prevent corrosion and phase separation (other than
cosolvent alcohols), and specific points on the distillation
curve of fuels. These parameters are useful in interpreting
the results of individual test programs. However, it is beyond
the scope of this report to examine them in detail for each
study.
2.0 DRIVEABILITY TESTING PROGRAMS
Many organizations have conducted driveability testing
programs. This section will summarize some of these programs.
The smallest of the programs evaluated the performance of five
vehicles, while the largest included several hundred. The
programs generally did not evaluate driveability in the same
way. Some of the smaller programs included controlled tests
that were developed by the Coordinating Research Council, Inc.
These tests involve drivers trained in the evaluation of
driveability problems, as well as specified driving
procedures. The larger programs were conducted with in-use
fleets, so they were generally not able to conduct the
controlled driveability tests. The evaluations that were
produced by these programs are the result of longer term use
under normal operating conditions, often over the course of
more than a year.
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2.1 Fleet Testing Programs
Southwest Research Institute conducted a variety of fleet
tests over five and a half years as part of the U.S. Department
of Energy's Project for Reliability Fleet Testing of Alcohol/
Gasoline Blends5. Most of the individual fleets participated
in this program for approximately one year. These fleet tests
were conducted in several geographic locations using four
different gasoline/alcohol blends. The fuels were gasohol
(apparently a splash blend with 10% by volume of anhydrous
ethanol), a volatility controlled ethanol blend (10% by
volume), Oxinol, and a 4.2% methanol blend which included 2.1%
ethanol and 2.1% tertiary butyl alcohol as cosolvents. The
tests were conducted under normal operating conditions with
established fleet operators. A total of 552 vehicles
accumulated 6,643,936 miles over the course of the program. Of
these, 218 vehicles were operated on unleaded gasoline as
experimental controls. The following fleets with a total of
264 vehicles participated in the driveability portion of this
project: Contra Costa County, CA; Tennessee Valley Authority
(two separate fleets); the State of New Jersey; the State of
Minnesota; U.S. Border Patrol in El Paso, TX; and Southwest
Research Institute. Vehicles in Contra Costa County were
tested with two blended fuels (gasohol and a gasoline/methanol/
TEA blend); the other fleets were tested with only one blend.
The report includes analyses of the differences in
driveability between the cars that were operated with blended
fuels and the control vehicles in each fleet, as well as a
composite analysis of the effects of gasohol on three of the
fleets. The following problem areas were examined; starting,
stalls during warmup, stalls in traffic, rough idling,
hesitation, loss of power, pinging, and dieseling. Performance
problems are rated in terms of the number of driver complaints
divided by the number of total reports. In five of these
areas, the blended fuels performed significantly worse than
regular unleaded gasoline. Table 1 (reproduced from page 6-5
of the report) shows the results of significance tests of the
measured differences in performance between the test and
control vehicles within each fleet. Table 2 (reproduced from
page 7-6 of the report) summarizes for three of the fleets the
differences in performance between the vehicles which used
gasohol and the vehicles which used gasoline.
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Table 1. Summary of Driveability Tests Using Blends
Department of Energy/Southwest Research Institute
Table reproduced from page 6-5 of Reference 5.
FLEET
CONTRA COSTA
COUNTY
TVA 1 & i
FUEL TYPE
Gasoliol
Gasoliol
NEW JERSEY Gasolt*!
CA. ENERGY COMM.
Sacramento M94.S Vs EIOII
Los Angeles Melllanol (M94.5)
MINNESOTA
UORDER PATROL
CONTRA COSTA
COUNTY
SWRI
ET-2
ET-2
Oxinol 50
MeOII/EIOII/TDA
CRANKING
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Table 2. Comparison of Driveability with Gasoline and Gasohol
Department of Energy/Southwest Research Institute
(Table reproduced from page 7-6 of Reference 5.)
COMPOSITE ANALYSIS - TENNESSEE VALLEY AUTHORITY,
STATE OF NEW JERSEY AND CONTRA COSTA COUNTY
PERFORMANCE PROBLEMS
CRANKING
STALLS WHILE STARTING
STALLS IN TRAFFIC
ROUGH IDLING
HESITATION
LOSS OF POWER
PINGING
DIESELING
FREQUENCY* OF OCCURRENCE
GASOLINE
.0165
.0151
.0039
0.065
.0106
.0099
.0091
.0047
GASOHOL
.0443
.0373
.0209
.0156
.0406
.0254
.0065
.0017
SIGNIFICANCE**
<0
<0
<0
<0
<0
<0
<0
<0
.001
.001
.001
.001
.001
.001
.025
.001
Frequency = Total complaints/total reports, where gasohol
total reports = 12,846 and gasohol total report = 11,743
Value indicates significance level of test.
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Gasohol performed significantly better than gasoline in
the areas of rough idling, pinging, and dieseling, and
significantly worse than gasoline in the other problem areas.
Three fleets were used for the analysis listed in Table 2
(Contra Costa County, New Jersey, and the TVA fleets) totaling
108 vehicles from model years 1974-1981. Table 1 includes
these fleets, as well as the Minnesota fleet, which had 60
1980-82 vehicles, the El Paso fleet, which had 52 1980-83
vehicles, the Contra Costa fleet operating on Oxinol, which had
30 1975-78 vehicles, and the Southwest Research Institute
fleet, which had 14 1984 Ford Escorts. There were no reported
incidences of vapor lock or problems with cold weather
operation which were attributable to the use of the
gasoline/alcohol blended fuels. These reports indicated that
the differences in driveability with the gasoline/alcohol
blends were statistically significant and definitely
perceptible. But the reports did not necessarily indicate that
the differences were large.
The Tennessee Valley Authority (TVA), in cooperation with
ARCO, conducted a separate fleet test of 140 vehicles during
1983 and part of 19846. This program tested a base fuel and
three blended fuels. The blends included varying amounts of
methanol and tertiary butyl alcohol to achieve oxygen contents
of 3.5%, 4%, and 5% by weight (4.75%, 6.0%, and 8.2% by volume
of methano-1) . The volatility of these blends was not
controlled. The fleet was divided into four groups, one for
each fuel. One of the sub-fleets used gasoline during the
entire test period. The other fleets used blended fuels
roughly half of the time; gasoline was used the rest of the
time to allow evaluation of the drivers' responses with the
same vehicles. Drivers recorded performance information on a
.daily basis during the test. Driveability was observed by
recording the number and severity of occurrences of specific
driveability problems. These were hard starting, rough idle,
stalls during idle, stalls during driving, hesitation,
backfire, dieseling, and knock. The data were analyzed
separately for the four seasons. The analyses of these data
showed no significant differences between the test and base
phase for any of the fuels tested, except for the 3.5% and 5%
oxygen blends during the spring phase of the program. However,
in the case of the 3.5% oxygen blend, the report concludes that
the observed differences are the result of factors other than
oxygenate content. A few of the vehicles showed exceptional
susceptibility to problems when fueled with the 5% oxygen fuel
in the spring phase. The report concludes that the 3.5% and 4
oxygen fuels provide driveability equivalent to that of
hydrocarbon-only fuels, and that the 5% oxygen fuel provides
driveability equal to that of hydrocarbon-only fuels for most
but not all vehicles.
•6
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Alberta Gas Chemicals, Ltd., the Ontario Ministry of
Transportation and Communications, and Suncor Sunoco Group
conducted tests beginning in 1982 on a fleet of 34 in-use
vehicles in Canada7. The fuels used in this program
contained 7% methanol and 3% isobutanol. These fuels were
blended to meet the seasonal volatility specifications used by
the supplier. The driveability testing portion of this program
was conducted in four phases, using test criteria adapted from
various CRC reports. The tests evaluated cold start, cold
drive, warm start, and warm drive performance. The blended
fuel gave worse driveability, but the report states that this
difference is not statistically significant, and that the test
drivers rated the fuel performance as acceptable.
In support of its waiver application for Oxinol, ARCO
provided a wide range of driveability test data for Oxinol and
other alcohol blends8. One program involved fleet testing of
150 employee-owned vehicles with fifty operating on each of a
base gasoline, Oxinol, or gasohol. Results indicated that
driveability of an Oxinol blend was equivalent to that of
gasohol, and cold-engine performance was the only operating
mode where these blends showed more operational problems than
the base gasoline. A similar test program was conducted to
evaluate cold weather operation using the same blends as well
as a blend of 16% TEA. In this program all four fuels yielded
equivalent driveability. A smaller scale testing program9
examined vehicles in two fleets which had been using Oxinol for
at least a year. One of these fleets consisted of eleven
vehicles that were owned and operated by ARCO employees, while
the other consisted of five matched pairs of vehicles (half of
which used gasoline). The program examined the condition of
the intake systems at the end of the period of Oxinol use, and
found that the deposits in the Oxinol fueled vehicles'
carburetors were typical of those which would be found in
gasoline fueled vehicles of the same mileage.
American Methyl Corporation submitted some driveability
test data along with its waiver application for Methyl-1010.
This fuel consists of methanol, cosolvent alcohols and a
proprietary additive blended with unleaded gasoline such that
the final oxygen content is no more than 5.0% by weight.
Fifteen 1974 - 1981 model year vehicles were evaluated by their
owners over a six month period of operation on the test fuel.
In general, it ,was found that older vehicles had less tolerance
for oxygenates, and closed loop emission control systems on
newer vehicles were found to alleviate most driveability
concerns.
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Ashland Oil Company conducted two short duration fleet
tests (approximately 90 days each) of 1% and 2% methanol
blends11. Eighteen vehicles were evaluated with the 1%
blend, and four vehicles were evaluated with the 2% blend. For
the 1% blend each of the drivers of the test vehicles were
interviewed regarding their experience with the fuel. Comments
ranged from neutral to positive. The comment most heard was a
decrease in pinging when the cars began the test. Other
comments noted improved fuel economy or improved acceleration.
One vehicle with electronic fuel injection experienced hot
start problems early in the test. No other problems were
noted. For the 2% blend one vehicle experienced no significant
change in startability, but there was a slight intermittent
change in hot startability. A decrease in part-throttle knock
intensity was the only significant difference noted with this
vehicle using the test fuel. Another vehicle experienced more
significant hot start problems, which may have been related to
the use of fuel injection.
The Bank of America has conducted fleet tests with a
variety of blends12. One program involved testing 67
unmodified vehicles fueled with blends of up to 8% methanol.
Driveability was measured on the basis of starting, warm-up,
idling, cruise, power (acceleration), and shutdown performance
with drivers who did not know which fuel they were using.
Vehicles without closed loop control systems experienced
decreasing driveability with increasing oxygen content, but
vehicles with closed loop systems maintained comparable
driveability to gasoline even with 8% methanol fuel.
The TVA has also participated in a program of more
controlled driveability testing, using the Driveability Test
Procedure developed by the Coordinating Research Council
(CRC) ' 3 . The tests were conducted on sixteen 1983 and 1984
model year vehicles which were leased from local car rental
agencies. These cars had odometer mileages in the range of 500
to 15,000. The program tested five fuels; a base fuel from
which the blends were developed, a splash blend of 10% Oxinol,
a blend of 10% Oxinol with the RVP adjusted to within 0.5 psi
of that of the base gasoline, a blend of 10% Oxinol with a
reformate added to match the distillation curve of the base
gasoline as closely as practical, and a splash blend of 10%
ethanol. The report notes that the last of these reflected the
characteristics of many commercially available gasohol blends.
The report concludes that the different fuels did not affect
cold-start driveability of the vehicles either as a group or
when they are stratified by fuel system or emission control
system.
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The Coordinating Research Council conducted extensive
tests on fourteen cars from the 1980 model year1"'15. The
driveability portion of these tests consisted of the CRC
Intermediate Temperature Cold Start and Driveability Test, and
the CRC Vapor Lock Test. These tests were conducted in two
phases; phase one included ethanol blends, and phase two
included methanol and methanol/cosolvent blends. The vehicles
tested in this program represented a mix of emission control
and fuel systems available in 1980; two had fuel injection, the
rest had carburetors; seven had closed loop emission control
systems calibrated to 1980 California emission standards, and
seven had open loop systems calibrated to 1980 Federal emission
standards. Only ten of the vehicles were tested in phase two,
due to funding constraints. The following fuels were included
in phase one of the program; a base fuel, a splash blend of 10%
ethanol, a blend of 10% ethanol adjusted to match the RVP of
the base fuel, and a blend of 10% ethanol adjusted to match the
RVP and percent evaporated at 158°F of the base fuel. The
blends had significantly worse driveability than the base
fuel. In its discussion of the driveability data, the report
states that the driveability is probably adversely affected by
the leaning effect of the blends, and that increased volatility
seems to improve driveability. The blends also showed a higher
tendency to vapor lock than the base fuel. The tendency to
vapor lock increased as the percent evaporated at 158°F
increased. In the second Phase of the program, six fuels were
tested; a base fuel (not the same as, but very similar to that
in the first phase), a blend of 3.8% methanol, a blend of 3.3%
methanol and 1.1% isobutanol, a blend of 10.0% methanol, a
blend of 8.8% methanol and 2.9% isobutanol, and a blend of
14.0% methanol and 2.0% isobutanol. As with the phase one
fuels, driveability with the blends was significantly worse
than that with the base fuel. The report states that the
driveability degradation seems to be related to the oxygen
content of the fuel, and that the presence of cosolvent had no
effect.
Mobil Research and Development Corporation conducted a
number of driveability test programs comparing Oxinol blends to
gasolines16. The first of these involved six 1983 cars
tested with gasoline, a matched distillation Oxinol blend, and
a lower volatility gasoline. Tests were conducted under
temperature controlled conditions, at 60, 45, and 25°F. The
cold start and driveability demerits for the Oxinol blend were
50 - 100% greater than the matched gasoline and roughly
equivalent to the lower volatility gasoline. A second program
using fifteen 1981-1983 cars and a consumer-type driveability
test determined the cold start driveability at temperatures
ranging from 0 - 60°F. A 12.5 psi RVP gasoline was best with
6% unacceptable trips, followed by a 14.8 RVP Oxinol blend with
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9%, and a 9.8 RVP gasoline with 10% unacceptable trips. It is
interesting to note that the blend averaged only half as many
stalls on start-up as the 12.5 RVP gasoline. A similar study
used ten 1984 cars at 60 - 95°F with both cold and hot start
evaluations. The Oxinol blend fuel had RVP and distillation
properties between those of the two test gasolines (11.3 and
11.8 psi RVP). The cold start results showed the percent of
unacceptable trips with the blend to fall between the two
gasolines. Under hot start conditions, however, the blend had
a much greater percentage of stalls on start-up than either of
the gasolines, and therefore, a greater percentage of
unacceptable driveability (14% versus 0-4%).
Esso Petroleum Canada conducted a program in the summer of
1984 to compare a base gasoline with an Oxinol blend17. In
this program two similar 30 car fleets represented the
1977-1984 model year Canadian car population. The program was
followed in winter/spring 1985 with another program which
included two 25 car fleets to represent 1980-1985 Canadian cars
fueled with a winter grade gasoline, Oxinol blend or 10% MTBE
blend. The summer Oxinol blend resulted in roughly twice as
many complaints as the corresponding gasoline, including hard
starting, rough idling, and sluggishness. For the winter fuels
the Oxinol blend did not have any significant effect on
start-up or idling, but there were roughly three times as many
complaints of sluggishness relative to the gasoline. The MTBE
had no significant effect on driveability.
From September 1983 to September 1984, Texaco conducted a
one year test using 200 1976-1983 model year domestic vehicles
with gasoline and two blends of 6% methanol and 2% TEA; one
with RVP equal to the gasoline and one with RVP of 1.0-1.5 psi
higher. The volatility of the base gasoline used to prepare
the blends was adjusted to provide good warming-up performance
when blended with the alcohols. The pump octane ratings of the
blends were slightly higher than that of the gasoline.
Vehicles operated 1/3 of the time on each of the three fuels.
The program was designed to allow analysis of the effects of
ambient temperature, warming-up driveability, warmed-up
driveability, and knock. The warming-up driveability of all
three fuels was roughly equivalent; the warmed-up driveability
of the blends was lower. The report states that midrange
volatility might be a factor which caused this degradation. No
cases of vapor lock occurred, even with the higher RVP blend.
The knock performance of the alcohol blends was slightly better
than that of the gasoline, reflecting their slightly higher
octane ratings.
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3.0 SMALLER TESTING PROGRAMS (10 or Fewer Vehicles)
General Motors Research Laboratories conducted
driveability tests using methanol and methanol/cosolvent
blends19. Six 1983 and 1984 GM cars chosen to represent a
mix of fuel systems were tested on five different fuel blends;
a base fuel, a blend with 9.5% Oxinol, a blend with 8.2%
methanol and 2.7% TEA, a blend with 3% methanol, and a blend
with 7% methanol. Two versions of each of these blends were
used, one to fit ASTM class C specifications, and one for class
D. The fuels were tested with a modified version of the CRC
hot-weather driveability and vapor lock procedure. Statistical
analysis of the driveability data showed that the volatility
class of the fuel was the most significant fuel-related factor
in determining the driveability of these cars, and that the
alcohol content was not as important. It was noted though that
an isolated problem with fuel foaming occurred on one of the
carbureted vehicles with a blended fuel containing 8.2%
methanol and 2.7% TEA. Fuel foaming is apparently an unusual
phenomenon involving formation of a gasoline foam in the
carburetor bowl which results in excessively rich operation
(less than 11.7:1 air:fuel ratio). It is not evaluated in
conventional driveability tests. Formation of the gasoline
foam is caused in part by excess fuel volatility. Intuitively,
most fuel injected vehicles should be less susceptible to the
problems of foaming and vapor lock, because the high pressures
in the metering system prevent the fuel from vaporizing before
it is added to the intake stream. Low pressure systems, which
are less common than the high pressure systems, would have less
of this resistance.
General Motors also conducted tests on five 1980 - 1981
model year GM cars, using three different fuels; a base
(Indolene), a splash blend of 10% alcohol, and another with 18%
alcohol20. The alcohol used was a 2:1 mix of methanol and
butanol. The study showed that driveability with the 10% blend
was much worse than that with the base fuel. Driveability with
the 18% blend was not evaluated. The report cites the leaning
effect of the alcohol, and the cooling of the intake manifold
by the alcohol as reasons for the diminished driveability.
A presentation given by Sun Tech in 1983 shows a graph of
total average demerits versus fuel oxygen content for eight
1980 vehicles using the CRC cold start and driveaway procedure
with hydrocarbon-only, ethanol blend, and Oxinol blend
fuels21. The curve has a significant, nearly linear positive
slope indicating roughly equivalent deterioration of
driveability for ethanol and methanol blends of equal oxygen
content.
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As part of the Tennessee Valley Authority program to
evaluate gasoline/alcohol blends, seven 1983-1984 model year
vehicles were evaluated for driveability using a cold start
followed by 3.6 miles of driving through various
maneuvers22. Five of the test vehicles were carbureted and
two had throttle body fuel injection, and all vehicles were
tested by a single trained driver. The fuels included a base
gasoline, a 10% methanol blend, a 5% methanol/3.2% ethanol
blend, and a 5% methanol/6.6% ethanol blend. Each vehicle/fuel
combination was tested in duplicate. The tests indicated that
the driveability of methanol blends was independent of the
cosolvent used. The vehicle-to-vehicle variation was greater
than any variation associated with different oxygen levels.
While some vehicles performed poorly with methanol blends, they
also performed relatively poorly with the base gasoline.
Texaco conducted a 50,000 mile testing program with six
vehicles from the 1982 model year2'1. Three of these used a
blend of 6%/2% methanol/TBA blend, while the others used
gasoline only. Both fuels contained a detergent additive; the
blended fuel contained 50% more. The only substantial
difference found on examination of the two groups was the
cleanliness of the intake valves. The cars which used blended
fuel had heavy deposits on the intake valves, while those which
used gasoline had much cleaner valves. The quantity of the
deposits va'ried from cylinder to cylinder within each of the
cars that used the blend. The report makes no determination as
to whether the greater concentration of detergent in the
blended fuel affected the formation of deposits.
VW has reported that greater detergent levels are needed
to ensure that deposits do not build up in the intake manifold
.and carburetor2''. Also, greater alcohol levels require
greater amounts of detergent. The report does not discuss
deposits on the intake valves, and it only discusses results of
testing with gasoline/methanol blends.
Ashland Petroleum Company examined gasohol performance in
dynamometer and in-use tests25. Three pairs of cars and some
light trucks were used. One pair of vehicles was run on
dynamometers for a 50000 mile test which examined lubricant
performance, emissions, driveability, and other performance
criteria. One vehicle was fueled with regular unleaded
gasoline, and the other with a 10% ethanol blend. This test
found little or no difference between the two vehicles in the
fuel-related areas of comparison, including fuel economy,
driveability, and deposits in the intake and combustion
chamber. The other vehicles used in this testing program were
tested in-use under less controlled conditions. Driveability
was evaluated in formal reports by the drivers. The report
concludes, based on the results of all of these tests, that
driveability is not affected by the addition of ethanol.
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4.0 Conclusions
As a general observation, the driveability of many
vehicles on low level alcohol blends appears to be roughly
equivalent to that of gasoline. However, there are indications
of problems with some vehicles and certain operating
conditions. These problems seem to occur less on vehicles with
fuel injection and closed-loop fuel control systems which are
more prevalent in recent model years. These problems seem to
occur somewhat more on vehicles with carburetors especially
those without feed-back to control air:fuel ratio. While
driveability problems of the type discussed below are noted
more with blends than with gasoline, it is not clear that the
problems would be serious and/or objectionable, just that they
would be perceptible to some degree. Nevertheless, the
possibility of some increased driveability complaints due to
increased use of gasoline/alcohol blends cannot be ruled out,
although such complaints may not be numerous.
4.1 Oxygen Content
The closer a vehicle is to its lean operating limit with
gasoline, the less fuel oxygen it will be able to tolerate
before experiencing lean mixture driveability problems such as
hesitation and s'ome loss of power as noted in the Department of
Energy project.
It appears that the richer a vehicle operates on gasoline
(whether due to carburetor adjustment or high altitude
operation, although no driveability tests have been run with
gasoline/alcohol blends at high altitude) the more fuel oxygen
it should be able to tolerate before experiencing any
deterioration of driveability. (Any vehicles which operate
excessively rich on gasoline may even experience improvements
in driveability with oxygenated fuels.)
As mentioned above, closed loop fuel metering systems can
alleviate most if not all of the normal driveability problems
that can be associated with the mixture enleanment of
oxygenated fuels, up to the adjustment limits of the system.
Without closed loop systems, increasing fuel oxygen
content can be expected to increase the incidence of
driveability problems.
4 . 2 Excessive Fuel Volatility
For blends the higher volatility in the 140 - 200°F range
can result in increased driveability problems due to increased
cases of vapor lock, fuel foaming, and hot-starting problems.
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Also, a loss of power in traffic is often noted before vapor
lock occurs. Such problems would be more likely to occur in
high altitude areas. Blends showed an increased tendency to
vapor lock in the CRC vapor lock procedure than gasoline, but
vapor lock was not specifically found to be a problem in the
studies of in-use vehicles. Some of the in-use studies did
find increased hot-starting problems.
These problems can be mitigated somewhat by keeping blends
in compliance with ASTM volatility recommendations. Additional
control of volatility, such as maintaining the percent
evaporated at some midrange point in the distillation curve
equal to that of typical gasolines or additional reductions in
RVP, might help more. Adjusting the entire distillation curve
to be equal to that of typical gasolines would help quite a
bit. It is not known, however, how such an adjustment would
interact with the high heat of vaporization (of alcohols) or
other parameters to affect driveability under other conditions,
such as cold starting. The high cost of an adjustment such as
this, as well as other factors, would make it unlikely to occur
in actual practice.
4.3 Heat of Vaporization (cold starting)
Ethanol and methanol require approximately three times as
much heat' to vaporize as does gasoline. Under certain
conditions this can make it a little harder to start and keep a
cold engine running with blends that contain these alcohols.
However, a high heat of vaporization might reduce somewhat the
likelihood of vapor lock by cooling the fuel system.
4.4 Octane (knock, dieseling)
Since methanol and ethanol increase the pump octane rating
of blended fuels, there is a tendency for blends to reduce
incidences of knock and dieseling (run-on) relative to the base
gasoline. Research octane may benefit more from alcohols than
motor octane, so under certain operating conditions where motor
octane is important (e.g., high load) there may be no effective
octane benefit from the alcohol. However, the data available
on this point do not conclusively indicate whether the
increased sensitivity of the blended fuels over gasoline would
pose a problem.
4.5 Intake System Deposits
Increased amounts of deposits, especially on the intake
valves, have been reported in some studies26, while others
have indicated that there is no such increase. It is possible
that the differences may be due to variations in the quantity
of detergents used in the fuels. Evidence is not available to
conclusively resolve this issue.
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4.6 Other Parameters
Fuel additives are mentioned in many of the reports as
being crucial to the successful operation of a vehicle with a
gasoline/alcohol blend. These additives are formulated to
inhibit corrosion, prevent the gasoline and alcohol from
separating, and help clean fuel system parts. Their effect on
driveability is less direct than the other fuel properties, and
their value becomes more apparent when examining the.issue of
materials compatibility.
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REFERENCES
1. United Nations Economic and Social Council, "Use of
Replacement Fuels and Fuel Components in Europe",
TRANS/SC1/WP29/R.328, May 2, 1984.
2. "Alcohol Blend Operational Problems of Concern to Chrysler
Corporation", part of a presentation by Gordon Allardyce,
Chrysler Corporation to EPA Workshop on the Effects of
Gasoline/Alcohol Blends on Vehicles and Vehicle Emissions at
High Altitudes, Aug 20, 1986.
3. James M. Dejovine, Edward G. Guetens, Jr., George J.
Yogis, Brian C. Davis, Walter H. Douthit, Paul E. Hagstrom,
"Use of Oxinol and Other Alcohol Blending Components in
Gasoline", National Petroleum Refiner's Association, November,
1982.
4. N. D. Brinkman, N.E. Gallopoulos, "Exhaust Emissions, Fuel
Economy, and Driveability of Vehicles Fueled with
Alcohol-Gasoline Blends", SAE paper 750120, 1975
5. John D. Tosh, Anna F. Stulgas, Janet P. Buckingham, John
A. Russell/ and John P. Cuellar, Jr., "Project for Reliability
Fleet Testing of Alcohol/Gasoline Blends", Contract report
prepared for U.S. Department of Energy, April 1985.
6. John R. Morgan, "Recent TVA Experience with Methanol Blend
Fleet Testing", Alcohol Week Conference, Washington D.C.,
November, 1984 .
7. K. Taylor, "Methanol/Gasoline Blend Vehicle Fleet
Demonstration - A Joint Project of Alberta Gas Chemicals Ltd.,
Ontario Ministry of Transportation and Communications, and
Suncor Sunoco Group", presented by Brian Davis at the 6th
International Symposium on Alcohol Fuels Technology, May 1984.
8. ARCO fuel waiver application for Oxinol, April 27, 1981.
9. David J. Miller, David A. Drake, and James M. Dejovine,
"Material Compatibility and Durability of Vehicles with
Methanol/Gasoline Grade Tertiary Butyl Alcohol Gasoline
Blends", SAE paper 841383, 1984.
10. American Methyl Corporation waiver application for
Methyl-10, June 3, 1983.
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11. Comments submitted by Ashland Oil Company concerning the
first DuPont waiver application, December 3, 1982.
12. Comments submitted by Bank of America concerning the first
DuPont waiver application, November 18, 1982.
13. John R. Morgan and Uwe Zitzow, "Effects of Alcohol
Blending Procedures on 1983-1984 Vehicle Driveability",
presented at The U.S. Blend Methanol Experience - and Outlook,
May 17-18, 1984.
14. "Performance Evaluation of Alcohol-Gasoline Blends in 1980
Model Automobiles", Coordinating Research Council Report #527,
July 1982.
15. "Performance Evaluation of Alcohol-Gasoline Blends in 1980
Model Automobiles Phase II - Methanol-Gasoline Blends",
Coordinating Research Council Report prepared for the
Department of Energy, January, 1984.
16. Letter from R.H. Perry, Mobil Research and Development
Corporation to A. M. Biervio, Chrysler Corporation, with
attachments on fuel properties and driveability, November 2,
1984.
17. Esso Petroleum Canada, summary of oxygenate driveability
test program at its Sarnia Research Centre conducted in summer
1984 and winter/spring 1985.
18. Texaco, Inc., "Consumer Reaction Program", 200 employee
owned cars, conducted September 1983 - September 1984.
19. Philip A. Yaccarino, "Hot Weather Driveability and
Vapor-Lock Performance with Alcohol-Gasoline Blends", SAE Paper
852117, 1985
20. Robert L. Furey and Jack B. King, "Emissions, Fuel
Economy, and Driveability Effects of Methanol/Butanol/Gasoline
Fuel Blends", SAE Paper 821188, 1982.
21. B. Davis, "Methanol/Gasoline Blends Cosolvent Needs and
Content Control", Sun Tech, Inc., slides of a presentation
given in Arlington, VA, October 17-18, 1983.
22. J. Morgan, "Driveability Characteristics of Blends Using
Methanol With Ethanol Cosolvent", Tennessee Valley Authority,
1984 .
23. Texaco, Inc., "Evaluation of 6/2 MeOH/TBA Gasoline-Alcohol
Blend Performance", Road Simulator Test No. 30, Presented to
Chrysler.
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24. Holger Menrad, Bernd Nierhauve, "Engine and Vehicle
Concepts for Methanol-Gasoline Blends", SAE paper 831686, 1983.
25. Estel M. Hobbs, Victor L. Kersey, "Test Vehicle Experience
with Ethanol Extended Fuels - Driveability and Corrosion",
Ashland Petroleum Company, presented at American Petroleum
Institute's 51st Midyear Refining Meeting, 1986.
26. Letter from Charles L. Gray, Jr., Director, Emission
Control Technology Division, EPA, to Wilhelm Hall, BMW
Corporation, discussing BMW's examination of intake valve
deposits in in-use vehicles, March 27, 1986.
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