75-28 JLB
Octane Requirements of 1975 Model Year
Automobiles Fueled with Unleaded Gasoline
August 1975
Technology Assessment and Evaluation Branch
Emission Control Technology Division
Office of Mobile Source Air Pollution Control
Environmental Protection Agency
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TABLE OF CONTENTS
Section Page
1. Summary and Conclusions, as of August 1975 1-L
2. Introduction 2-1
3. Fundamentals Concerning Knock and Octane Requirements 3-1
3.A. Knock and the Variables which affect it 3-1
3.B. Knock Rating of Gasolines 3-2
3.C. Octane Requirements of Automobiles. ... 3-2
3.D. The Octane Requirement Increase (OR!) 3-3
3.E. The Distribution of Octane Number Requirements 3-4
3.F. Effects of Light-Knock on Emissions, Performance,and
Durability. . 3-5
4. Octane Number Requirements for a Sample of 138 1975 Model
Year Cars 4-1
4.A. Summary of the Analysis of the Data 4-1
4.B. Summary of the Data Submitted by the Participating
Laboratories 4-2
5. Effects of Spark Retard 5-1
5.A. Effect of Spark Retard on Gasoline Consumption. ..... 5-1
5.B. Effect of Spark Retard on Exhaust Emissions 5-2
5.C. Effects of Large Spark Retardations 5-3
6. Specific Documentation. 6-1
7. References. . 7-1
Appendixes
I. Plots A.I-1
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1-1
Octane Requirements of 1975 Model Year
Automobiles Fueled with Unleaded Gasoline
1. Summary and Conclusions, as of August 1975
Some concern has been voiced-mainly by petroleum companies and fuel
additive manufacturers—that a large portion of 1975 model year auto-
mobiles will have engine knock problems when operating with unleaded
gasoline of 91 RON/83 MON.
The majority of the petroleum refiners maintain that the per-
centage of 1975 cars satisfied with the available unleaded gasoline
will be much lower than the percentages of past years (which ranged
between 85 and 95% throughout the automotive industry). The con-
cerned groups point out that too many cars will have to resort to spark
retard for elimination of knock, and that this will result in a sub-
stantial loss in 'fuel economy. On the other hand, some petroleum
companies indicate that the situation will not be much different
than that of previous years, and all the major U.S. auto manufacturers
affirm that there will be no serious problem.
The deposits which accumulate in the combustion chamber of the
vehicles result in octane requirement increases (ORI), up to the
point when the deposits reach a stabilized level. The ORI is one
of the most important items for determining whether there will or will
not be a problem with the octane requirements of the 1975 model year
cars.
Another important point regarding octane requirements is the
difference between the ratings by trained raters and ordinary drivers.
It has become apparent that there is an urgent need to document and
define what difference can actually be considered or tolerated between
the "technical" and "customer" requirements.
On the basis of the available information, it is estimated that
the percentages of 1975 model year cars satisfied with 91 RON/83 MON
unleaded gasoline would be:
For ORI =4, approximately 78% cars satisfied
For ORI = 6, approximately 62% cars satisfied
For ORI = 8, approximately 44% cars satisfied.*
These estimates are based on data obtained through the Coordinating
Research Council Informal Data Exchange Program and submitted, on
December 13, 1974, to the EPA by the National Petroleum Refiners
Association. However, the analysis of interim results from the CRC—
dated May 14, 1975—for more recent data indicates that the percentage of
cars satisfied will be higher. For these interim results, the TAEB
of the EPA estimates that, for ORI = 6 and ORI = 8, the cars satisfied
would be about 79% and 65%, respectively.
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2-1
2. Introduction
Some concern has been voiced—mainly by petroleum companies and fuel
additive manufacturers—that a large portion of 1975 model year auto-
mobiles will have engine knock problems when operating with unleaded
gasoline of 91 RON/83 MON.
In this regard it has been pointed out that unleaded fuel of 91 RON/
83 MON is the only unleaded gasoline that will be available at most
of the retail pump outlets. This will occur because most of the gasoline
companies will limit their production to satisfying only the minimum
requirements of the current EPA regulations. These regulations require
availability of unleaded gasoline of "not less than 91 Research Octane
Number."
The concerned groups indicate that the percentage of cars satisfied
with this unleaded gasoline will be much lower than the percentages of
past years.* These concerned groups point out that too many cars
will have to resort to spark retard for elimination of knock, and that
this will result in a substantial loss in fuel economy.
The purpose of this report is to document and discuss, concisely,
that information which is relevant to this potential problem concerning
engine knock.
* It appears that in the past, the percentage of cars satisfied with
the fuels specified by the car manufacturers has ranged between 85 and
95% throughout the automotive industry.
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1-2
These estimates should be considered with caution since the
data is limited. To refine the prediction, more conclusive infor-
mation is needed.
If the ignition timing were retarded as needed, up to a maximum
of 4°, it is estimated that the percentages of 1975 model year cars
satisfied with 91 RON/83 MON unleaded gasoline would be:
For OKI = 4, approximately 95% cars satisfied
For OKI = 6, approximately 89% cars satisfied
For ORI = 8, approximately 78% cars satisfied.
In this case it is estimated that the increase in gasoline fuel
consumption for the 1975 model year car population would be:
For ORI = 4, approximately 0.5%
For ORI'= 6, approximately 0.8%
For ORI = 8, approximately 1.6%.
These fuel consumption increases of 0.5%, 0.8%, or 1.6% (for
spark retard up to a maximum of 4° and ORI = 4, 6, or 8) for the
1975 model year car population would mean increases of approximately
0.05%, 0.08%, or 0.16%, respectively, in the total gasoline consumption
of the overall car population in the USA.
Of the several oil companies contacted for this analysis, only
one has reported an increase to date in customer complaints of engine
knock over previous years. The company has only this year instituted
a system of record keeping for customer complaints and they have no
quantitative basis for comparison with previous years but the feeling
was expressed that there is some increase. The increase is not judged by the
company to be of major significance. Nevertheless, there is still a
possibility that accumulation of miles and dry hot weather would develop
audible knock in a relatively high number of cars. Certainty that
this will not materialize cannot exist until enough time for mileage
accumulation has passed.
Independently of the outcome of this eventual problem, the concern
for the relationship between knock and octane for 1975 cars will result
in some improvement of the technical evaluation of that relationship.
Spokesmen from the government and the industry have pointed out the
need for improving the procedure for determining the octane requirements
of automobiles. Some steps are already being taken to study how
this procedure can be improved. Improvements of the procedure should
result in a more efficient use of engines and gasoline in the future.
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3-1
3. Fundamentals Concerning Knock and Octane Requirements
3.A. Knock and the Variables which affect it.
In the automotive field, "knock" is the term generally used to
signify the noise associated with the autoignition of a portion of the
fuel-air mixture .ahead of the normal flame front. More specifically,
"spark knock" is a recurrent knock which can be controlled in intensity
by adjusting the spark timing. Advancing the spark increases the
knock intensity and retarding the spark reduces the intensity.
While slight knock may be desirable because it hastens the
combustion process and increases the power output and efficiency, knock
of high enough intensity can cause engine failure. The more likely
explanation of the mechanism causing the damage is that the pressure
waves associated with knock increase the rate of heat transfer to—and
hence the temperature of—the susceptible parts, which causes either
local melting of the material or softening to such an extent that the
high local pressure causes erosion.
To understand the circumstances that cause knock, it is important
to know that the most significant variables that control autoignition
are the composition of the fuel and the following factors affecting
the combustible mixture:
Temperature
Density
Ignition delay
Fuel-air ratio.
Thus, because of the effects of these variables, knock in the
spark ignition engine:
9
Increases with a lower octane rating of the fuel
Increases with the compression ratio
Increases with engine load
Increases with lower engine speed
Increases with inlet air temperature
Increases with engine coolant temperature
Decreases with spark retard
Decreases with higher inlet air humidity
Decreases for either rich or lean mixtures
Depends on the combustion chamber design.
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3-2
3.B. Knock Rating of Gasolines
The knock rating of a gasoline is found by comparing its knock
response with that of a blend of "primary reference fuels" (PRF). These
fuels are n-heptane with an "octane number" (ON) of 0, and isooctane
with an octane number of 100. A blend containing x percent (by volume)
isooctane is defined as an x octane primary reference fuel.
Several methods of knock rating of gasoline are encountered. In
each of these methods a special standard engine must be run under pre-
scribed operating conditions (of speed, temperature, etc.). The octane
rating of a gasoline may have different values for different tests.
Some fuels are relatively insensitive to such changes while others are
quite sensitive. The two most common octane rating tests are known
as the Research and Motor methods, and their corresponding ratings are
indicated as Research Octane Number (RON) and Motor Octane Number
(MON). The difference between RON and MON is called the "sensitivity"
of the fuel. Although the RON rating is the one indicated most
commonly, it has increasingly been reported that the MON rating is more
representative for the octane requirements of cars of recent years.
3.C. Octane Requirements of Automobiles
Of particular interest is the octane number requirement (ONR)
of vehicles on the road. A direct method for obtaining octane require-
ment data from cars under normal service was developed by the Coordinating
Research Council (CRC), for use by all participants in its periodic
new-car Octane Requirements Surveys. This is referred to as the CRC
E-15 method, and it measures maximum octane requirements in terms of
both primary reference fuels (PRF) and full-boiling reference fuels
(FBR and FBRU for leaded and unleaded fuels, respectively) that are
typical of current commercial gasolines. The ONR is determined for
full-throttle accelerations, as well as for the most critical part-
throttle conditions.
Although the CRC E-15 method is representative of normal vehicle
operation, this method nonetheless has some vague test conditions
which may yield differences in the results. The following are examples
of these unspecified conditions:
a) Although the temperature and humidity of the atmosphere
are known to have a major effect on the octane number require-
ment, the CRC E-15 method only requires that the "tests will
be conducted on moderately dry days, preferably at ambient
temperatures above 60°F, and should not be conducted during
periods of high humidity such as prevail when rain is
threatening or during or immediately after a rain storm."
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3-3
b) The position of the rater is not defined completely. This
can lead to differences in rating since the knock is judged by
ear.
c) The procedure allows simulation of the road test on chassis
dynamometers. Currently, less than half of the participant
laboratories carry on the tests actually on the road. However,
it is known that significant differences exist between the
results from chassis dynamometer tests and actual road test.
For example, E.S. Corner has reported that for large samples
of 1971 cars, in the region from 70 to 90% cars satisfied,
the average RON for unleaded fuel was about two units higher
for dynamometer tests than for actual road tests.
Time schedules and other constraints probably explain the
looseness of some details of the CRC E-15 method. None the less,
the method should be improved to eliminate as much uncertainty as
possible, and means should be found for correcting the effect of
those variables which cannot be maintained within proper limits.
The CRC octane number rating is determined on the basis of
borderline knock as judged by trained raters. This is referred to as
the "technical" rating. However, customer satisfaction occurs at
lower octane numbers than those determined by the CRC procedure.
Generally, the "customer" requirements are estimated to be two
or three units lower than the "technical" requirements. This point
is very significant and there is an urgent need to document and define
what difference can actually be considered or tolerated between the
"technical" and "customer" requirements.
The CRC is aware of the need for improving and complementing the
CRC E-15 procedure. A CRC ad hoc committee has been formed to study
what should be done regarding these matters.
3.D. The Octane Requirement Increase (ORI)
As a new vehicle goes through its normal break-in process,
deposits accumulate in the combustion chamber and eventually reach
a stabilized level. The sources of these deposits are the fuel, the
lubricant, and the air which enter the combustion chamber. The
composition of the deposits depend on: a) the physical and chemical
natures of the fuel and the lubricant, b) the additives in fuel and
lubricant, c) the operating conditions of the engine, d) the weather
and climate, and e) the location in the combustion chamber.
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3-4
The deposits increase the octane .requirements of the engines.
The most significant reasons for this increase are the higher end-gas
temperatures caused by the insulating effect of the deposits and the
increase in compression ratio caused by the volume of the deposits.
The "octane requirement increase" is defined as:
ORI = (octane requirement of engine with stabilized deposits) -
(octane requirement of clean engine).
There is limited information on the ORI for automobiles operated
with unleaded gasoline. However, the available data indicates that
while cars operated with leaded fuel reach stabilized octane require-
ments before accumulating 5,000 miles, cars operated with unleaded
fuel require more miles to reach stabilized requirements. Also, the
ORI for cars operated with unleaded gasoline appears to be higher
than the ORI for leaded-fuel cars. The CRC 1971 ORI Survey indicated,
for 47 matched pairs of cars, that the average stabilized ORI was 3.8
RON for cars operated with leaded gasoline and 5.8 RON for cars operated
with unleaded gasoline. The CRC 1973 ORI Survey determined, using
unleaded full-boiling reference fuels, an average ORI of 8.4. 54%
of the 1973 unleaded fuel cars had their ORI stabilized below 12,000 miles;
the rest of the cars had stabilized octane requirements at a mileage
of 12,000 miles or more.
The ORI is one of the most important items for determining
whether there will or will not be a problem with the octane require-
ments of the 1975 model year cars. Therefore, to provide a well
qualified answer to this question, ORI data for 1975 model cars is
needed.
3.E. The Distribution of Octane Number Requirements
Because of the many factors which affect the octane number require-
ments, even identical cars may have large differences in octane number
requirements. Typically, the distribution of octane number require-
ments of identical cars show, when operated with FBRU fuels, a variation
of about 10 research octane units between the 5 and 95 percentiles.
Naturally, the variability of the octane requirements for the whole
car population of a given model year is even higher.
In automotive literature the percentiles of the distribution for
octane number requirements are designated as "percent cars satisfied".
Individual manufacturers vary in the conservatism of the design target
which they use to assure that excessive customer complaints will not be
received concerning knocking under operation with the specified fuel.
It appears that traditionally, the design target—for cars with
stabilized deposits—varied from 85 to 95% cars satisfied throughout
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the automotive industry. Of course, when the unleaded fuel requirement
was not a constraint, the unsatisfied cars could be satisfied, in
general, by using other fuels normally available with higher lead
content.
3.F. Effects of Light-Knock on Emissions, Performance, and Durability
The current concern for both fuel economy and engine knock makes
it particularly appropriate to consider the potential benefits and
dangers associated with light-knock operation. These matters are
discussed in the following paragraphs.
The literature concerning the effect of knock on emissions is
scarce. Some data is available, at steady state conditions, from
two single cylinder engines and from four cars (one 1969 and three
1970 model cars) 3»4>5. In generaj_j comparing the results under
light-knock and no-knock, these data indicate that:
a) The variations of the CO and HC emissions were not
significant.
b) Light-knock operation increased the NO emissions.
It is difficult to quantify the increases in NOx emissions.
The data from the four cars showed that the maximum increase was
approximately 10% under heavy knock; therefore, with light-knock
the percentage of NOx increase would be below 10%. Accordingly,
the increases of NOx in these cars under the LA-4 driving cycle of the
Federal test procedure should be small, since in this test knock
would occur only during certain driving modes. To have accurate
values of the increases of NOx in 1975 model cars which knock, it
would be necessary to measure the NOx from some 1975 cars under
operation with and without knock. For this purpose, the cars
should be tested with unleaded gasoline of 91 RON/83 MON and with
unleaded gasoline of higher octane number as required for operation
without knock.
When an engine knocks slightly, retarding the spark will
eliminate the knock. However, the spark retard will decrease the
power output and the fuel economy. On the other hand, an increase
in spark advance beyond a certain point will increase the knock and
decrease the power output and fuel economy. Thus, the maximum
output and fuel economy are obtained under some light-knock
conditions.* This is because under knocking the gases in the
combustion chamber vibrate, with heat losses as a result, but
at some level of light-knock the gain from the faster combustion
is greater than the heat loss caused by the vibrating gases.
*
Supporting evidence for this statement is found in reference 6,
page 298.
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3-6
Whereas a certain level of light-knock is beneficial from the
very important viewpoint of fuel economy, there are some questions
about the feasibility of an extended use of light-knock operation.
The first difficulty associated with permitting light-knock**
operation is rating the level of knock. Currently, the only practical
method of measuring knock is by ear; therefore, the intensity of
knock may vary according to the particular observer. Rating the
level of knock is much more difficult than simply distinguishing
the following cases included in the CRC E-15 octane rating procedure:
1) no knock
2) borderline knock
3) above borderline knock.
Also, if some level of light knock is permitted within the normal
ranges of speed, load, and weather, it must be considered that the
knock will be higher under other conditions of operation which are
more prone to induce knock. Furthermore, even if the knock would always
be within a certain limit, there is a lack of information about
the effect that this knock could have on engine durability and
performance if it would occur for substantial periods of time.
There are differences in opinion of whether the effects of such a
substantial occurrence would be serious or not.
Therefore, it appears that to allow for the general use of
light-knock operation with confidence that it will not cause serious
hardship, two precautions should be taken. First, it would be
necessary to establish a procedure to properly measure the level of
light-knock. Second, it would be required to determine what level of
light-knock would be permissible without penalizing performance or
durability. However, the determination of a feasible level of
light-knock is further complicated by the fact that different engines
may be able to tolerate different levels of knock.
Supposedly, if light-knock was permitted for 1975 cars or future
model years cars, it would be the responsibility of the automotive
manufacturers to verify that such knock would not impair the durability
or the performance of the engines. As was indicated before,the CRC
has set up an ad hoc committee that will study what sort of program
should be started to define the relationship between "technical" and
"customer" octane number requirements. However, it is doubtful if this
CRC committee will address the issue of the effects of light-knock
on durability and performance.
** The expression "light-knock" is used in this report to indicate
the region of knock intensity immediately above the borderline of
knock. Some literature uses expressions such as "audible knock" to
refer to the first portion of the knock region beyond "trace" or
"borderline knock".
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4. Octane Number Requirements for a Sample of 138 1975 Model Year Cars
The National Petroleum Refiners Association (NPRA) and, separately,
the Mobil Research and Development Corporation, expressed their concern
about the octane number requirements of the 1975 cars. They submitted
to the EPA (on December 13, 1974, and January 6, 1975, respectively)
data on the RON requirements for a sample of 138 cars. This data was
obtained through the Coordinating Research Council Informal Data
Exchange Program, on clean engines, following the CRC E-15 octane rating
method, and using 1974 CRC FBRU or CSU-8* unleaded reference fuels.
This CRC data is the largest sample of data that has been made
available to the EPA in octane requirements for 1975 model year cars.
An analysis of this data is summarized in the following section 4.A.
Some details on the data gathered and submitted by the participant
laboratories are presented in Section 4.B.
4.A. Summary of .the Analysis of the Data
**
For this specific data, on the basis of:
a) weighting the data according to the new car production
figures projected for the 1975 model year,
b) assuming that the "customer" RON requirements are two and
a half units lower than the "technical" RON requirements, and
c) decreasing the RON requirements by one unit, to compensate
for the fact that actual road knock ratings are somewhat lower
than chassis dynamometer ratings,
the TAEB of the EPA has estimated that the percentages of cars
satisfied with the 91 RON/83 MON unleaded gasoline would be as
follows:
For ORI = 4, approximately 78% cars satisfied
For ORI = 6, approximately 62% cars satisfied ^
For ORI = 8, approximately 44% cars satisfied.
1974 FBRU designates full-boiling range unleaded reference fuels
which approximate the characteristics of commercially available
unleaded gasoline in 1974. The sensitivity (that is, RON minus MON)
of the FBRU fuels increases progressively with the RON, ranging from
about 6 at 84 to 10 at 100 with a value of about 8 for 91 RON.
CSU-8 designates full-boiling range unleaded reference fuels which
maintain about 8 sensitivity throughout the range. These CSU-8
fuels were used by some laboratories in some low octane requirement
cars.
**
Details of the analysis can be found in reference 7.
***
However, the analysis of the CRC interim results obtained more recently
indicates that the percentage of cars satisfied will be higher, see
note in page 1-1.
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It must be pointed out that the 1975 model year car population may
have RON requirements different from those indicated by the CRC sample
of 138 cars. According to the production data submitted to the EPA for
certifying the 1975 model year cars, this CRC sample included models
which represented only about five and a half million out of the
total ten million cars that were projected for the 1975 model year
domestic car population.
If: 1) the difference between "technical" and "customer" octane
requirements is taken as two units, 2) the difference between chassis
dynamometer and actual road ratings is neglected, and 3) a value of 8
units is considered for the ORI, then the percentage of cars satisfied
with the 91 RON/83 MON unleaded gasoline would only be about 30%. This
is approximately the percentage of cars that would be satisfied
according to the estimate indicated by the Mobil Research and Develop-
ment Corporation in its letter of January 6, 1975.
The National Petroleum Refiners Association was less specific
in its estimate of the percentage of cars satisfied. In its letter
of December 13, 1974, it indicated that "over one-half of the 1975
model vehicles can be expected to experience knock on 91 RON
gasoline".
Analysis from others consider that the ORI for unleaded gasoline
will be not too different from the ORI for leaded gasoline and estimate
that higher percentages of cars will be satisfied. The Exxon Research
and Engineering Company, for instance, indicated, on January 29, 1975,
at the public hearings on the application for suspension of the 1977
LDV emission standards, that the unleaded gasoline on the market will
satisfy something on the order of 88 percent of the 1975 vehicles.
To summarize, the accuracy of the prediction of the percentage of
cars that will be satisfied with 91 RON/83 MON unleaded gasoline
depends basically on: 1) what difference can actually be considered
or tolerated between "technical" and "customer" RON requirements, 2)
what is the actual ORI in customer use for stabilized engines, and 3)
how representative of the new 1975 car population is the sample of
cars used for determining the RON requirements. Therefore, to
refine the prediction, more conclusive information on these three
items is needed.
4.B. Summary of the Data Submitted by the Participating Laboratories
In responding to the NPRA's letter of December 13, 1975, Mr. Stork,
DAA for the MSAPC of the EPA, requested that the companies which had
contributed in obtaining information on the ONR provide their data,
in detail, directly to the EPA. A summary of the data that has been
received by the EPA in response to this request follows.
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Amoco Oil Company
In a letter dated January 16, 1975, Amoco indicated that they had
tested thirty-nine 1975 model cars. These cars had less than 1,000 miles
on the road when tested. In this group of 39 cars, the "technical"
RON requirements—using 1974 FBRU fuels—were:
1 car (i.e., 3%) required 89.5 RON
5 cars (i.e., 13%) required5?87 RON
7 cars (i.e., 18%) required ^85 RON
32 cars (i.e., 82%) required*:85.RON.
For 11 of the cars, data was also obtained when they reached
4,000 miles. The ORI ranged from 0 to 7 units and averaged 2.8.
The maximum requirement was 95 RON.
Ethyl Corporation
In a letter dated January 14, 1975, the Ethyl Corporation
informed the EPA that they had contributed data from nine 1975 vehicles.
These cars were tested, in their "controlled weather" chassis dyna-
mometer rooms, when they had less than 1,000 miles. For these nine cars,
the "technical" RON requirements—using 1974 CSU-8 fuels—were:
1 car (i.e., 11%) required 91 RON
2 cars (i.e., 22%) required^89 RON
7 cars (i.e., 78%) required <89 RON.
Gulf Research and Development Co.
On November 15, 1974, Gulf sent data from seven 1975 cars.
The data was taken in its "all weather" chassis dynamometer. With
less than 1,000 miles, using 1974 FBRU fuels, the "technical" RON
requirements of these seven cars were:
2 cars (i.e., 29%) required 87 RON
5 cars (i.e., 71%) required< 87 RON.
Sun Oil Company
On January 29, 1975, Sunoco sent to the EPA the data from fifteen
1975 model cars. Only four of these cars had been included in the NPRA
list of 138 cars, since the other eleven cars were tested at a later
time. The cars were tested at less than 1,000 miles, on the chassis
dynamometer. Using 1974 FBRU fuels, the "technical" RON
requirements of these fifteen cars were:
1 car (i.e., 7%) required 92 RON
2 cars (i.e., 13%) required?90 RON
5 cars (i.,e., 33%) required ?89 RON
10 cars (i.e., 67%) required< 89 RON.
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4-4
Cities Service Oil Company
Cities Service sent to the EPA, on February 18, 1975, ONR data
from eight 1975 cars. This data had been obtained using 1973 FBRU
fuels and had not been included in the NPRA data from 138 cars. The
data from these eight cars had been taken at substantially different
mileages. The highest "technical" octane requirements were 91 and
90 RON for two vehicles with 5,666 and 11,120 miles, respectively.
The other six cars had lower mileages, and their requirements were
equal or less than 85 RON.
Ashland Oil, Inc.
Ashland sent to the EPA, on January 13, 1975, ONR data from
29 low mileage 1975 model year cars. This information was taken using
PRF instead of FBRU fuels, and was not obtained by the CRC E-15
method, but with the Modified Uniontown technique. It was not
included in the data submitted by the NPRA. No meaningful conclusions
can be extrapolated from these data regarding satisfaction when using
FBRU fuels and the CRC E-15 method.
Phillips Petroleum Company
Phillips submitted, on March 5, 1975, to the participants
of the CRC 1975 Informal ONR Survey, data from fifteen 1975 cars.
This data is not included in the data from the 138 car sample since
it was obtained later, in January and February of 1975. This data
is from low mileage cars (ranging from 89 to 3,505 miles) and was
taken using a chassis dynamometer, at 75°F and low relative humidity.
Using CRC 1974 CSU-8 fuels, the "technical" RON requirements were:
1 car (i.e., 7%) required 90.5 RON
4 cars (i.e., 27%) required =;89 RON
11 cars (i.e., 73%) required<89 RON.
E. I. DuPont de Nemours & Co.
DuPont submitted to the EPA, on January 22, 1975, data from
fifty 1975 cars. This data was from low mileage cars (below 400
miles) and was taken using a chassis dynamometer. The data was
obtained using a DuPont prepared series of full-boiling range
unleaded reference fuels instead of the CRC 1974 FBRU fuels.
This data was not included in the NPRA data from 138 cars. From
its data, DuPont has estimated the "technical" RON requirements
of these 50 cars for the CRC 1974 FBRU fuels; in summary, these
requirements would be:
1 car (i.e., 2%) would require 97.4 RON
2 cars (i.e., 4%) would require ^95 RON
9 cars (i.e., 18%) would require ?90 RON
20 cars (i.e., 40%) would require?88 RON
30 cars (i.e., 60%) would require<88 RON.
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5. Effects of Spark Retard
To decrease or eliminate engine knock when there is not the
possibility of using a higher octane gasoline, the simplest solution
is to retard the spark timing. Thus, spark knock can be decreased
or eliminated by spark retard; but this action also has other effects
which are considered in the following sections.
5.A. Effect of Spark Retard on Gasoline Consumption
The fuel economy of automobiles depends very significantly on
the timing of the ignition. Therefore, even though spark retard reduces
octane number requirements, it also reduces fuel economy. It is
shown in Figures 1-1 through 1-3 that while one degree of spark
retard will reduce the octane requirements about one number,more 4
than 4-5 degrees of retard will cause the fuel economy to degrade
drastically. Therefore, spark retard is considered a reasonable
approach to octane requirement reduction only within the range of
1° to 5°, where one degree of spark retard causes only about 1%
deterioration in fuel economy.
EPA technical staff have estimated* the nationwide fuel economy
losses that would result if the spark were retarded up to a maximum
of 4° to satisfy a greater fraction of the 1975 model year cars with
91 RON/83 MON unleaded gasoline. Using the clean engine RON require-
ments of the 138 1975 model year cars tested under the CRC Informal
Data Exchange Program, and on the basis of:
a) weighting the data according to the new car production
figures projected for the!975 model year,
b) assuming that the "customer" RON requirements are two and
a half units lower than the "technical" RON requirements,
c) decreasing the RON requirements by one unit to compensate
for the fact that actual road knock ratings are somewhat lower
than chassis dynamometer ratings,
d) estimating that fuel economy (mpg) deteriorates 1% per unit
of octane number gained (by spark retard), up to 5 RON units of
gain**, and
* Details on the analysis can be found in reference 8.
** The EPA does not have much data available on the percentage of fuel
economy lost per unit of octane number gained by spark retard. The
values used in the analysis are the averages from a few available
data, and are consistent with the values quoted by the auto industry.
For accuracy, more data is needed. Furthermore, the actual percentage
of the decrease in the mpg will also vary upon whether the spark
retard is achieved by simply changing the distributor timing—which
will provide a constant spark retard—, or by the more sophisticated
method of modifying the ignition timing mechanisms for load and speed
as required for minimum fuel economy losses.
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5-2
e) assuming that, as a first approximation, the aggregate con-
sumption of gasoline is proportional to the number of cars, i.e.,
approximately independent of the type of cars,
the, estimated increase in gasoline fuel consumption for the 1975 car
population is:
For OKI = 4, approximately 0.5%
For ORI = 6, approximately 0.8%
For ORI = 8, approximately 1.6%.
Actually, the corresponding percentage of increase in gasoline
fuel consumption would be somewhat less because: 1) not all the 1975
model year cars use catalysts, and 2) some cars will use available
unleaded gasoline of higher than 91 RON.
It can be assumed that the 1975 model cars will constitute
approximately 10% of the overall car population. Therefore, these
fuel consumption increases of 0.5%, 0.8%, or 1.6% (for ORI = 4,
6, or 8, respectively) for the 1975 model year car population would
mean increases of 0.05%, 0.08%, or 0.16%, respectively, in the total
gasoline consumption of the overall car population in the USA.
If this case (i.e., if the ignition timing were retarded as needed,
up to a maximumof 4°),it is estimated that the percentages of cars
satisfied with 91 RON/83 MON unleaded gasoline would be:
For ORI = 4, approximately 95% cars satisfied
For ORI = 6, approximately 89% cars satisfied
For ORI = 8, approximately 78% cars satisfied .
5.B. Effect of Spark Retard on Exhaust Emissions
It is well known that spark retard decreases the emissions of
NOx. Therefore, in this regard, the retarding of the ignition timing
is beneficial (see Figure 1-4).
Also, in general, the exhaust emissions of HC decrease with spark
retard. The limited data obtained with the spark timing retarded
(specifically to decrease the octane requirements) show that this
is the general trend (See Figure 1-5). In some cases the data indicated
increases of HC, but even in these instances the absolute values of
HC were several times lower than the 1975 standards for HC.
-------
5-3
The concentration of CO at the outlet of the cylinders of the
spark ignition engine is known to depend almost exclusively on the
air-fuel ratio of the mixture fed to the cylinders. Accordingly,
unless the higher exhaust temperatures associated with spark retard
result in a higher oxidation of CO, some increase in the mass emissions
of CO could be expected. This increase would occur because of the
larger exhaust flow caused by the increased fuel consumption associated
with spark retard. However, the increases in mass emission of CO
appear to be much larger than what could be expected on the basis
of fuel economy deterioration. The limited data which is available
(Figure 1-6) shows variations of CO mass emissions ranging approximately
from -15% to +300%. Possibly, the high increases in CO emissions can
be explained by the increased operation under enriched carburetion,
which might result from the increased throttle opening associated
with retarding the ignition timing. Nevertheless, if no more than
4°-5° of spark retard are permitted, to minimize impact on fuel
economy, the absolute increases in CO emissions do not appear large.
Therefore, if this data on CO emissions is representative of the general
situation, it appears that spark retard would not impede fulfillment
of the 1975 emission regulations.
5.C. Effects of Large Spark Retards
Normally, a few degrees of spark retard would have no noticable
adverse effects other than those on fuel economy and on some emissions,
as indicated before. However, large retardations in the spark timing
will not only result in large fuel economy losses and increased emissions
of some pollutants, but will also cause a loss in power and driveability
of the vehicle. In addition, since spark retard increases the exhaust
gas temperature, large retardations in the spark timing can result
in such problems as engine overheating, burned valves, shortened
spark plug life, and preignition.
-------
6-1
6. Specific Documentation
A few comments concerning some of the more significant documents
which were reviewed for preparing this report are presented in this
section.
"Summary of Responses to EPA Request for Information on ORI for 1975
Model Automobiles"
This document is dated September 11, 1974. Briefly, it shows that
the four major U.S. auto manufacturers did not expect serious diffi-
culties with the ON requirements of the 1975 cars.. Also, the manu-
facturers indicated that any problems in the field will be easily
corrected by spark retard.
Public Hearings on the Application for Suspension of the 1977 LDV
Emission Standards
The records of these hearings, which were held on January of
1975, indicate that each of the U.S. auto manufactures testified that
they had not received unusual complaints concerning knocking with 1975
model cars.
These records were consistent with the findings of a small survey
made in January of 1975 by the TAEB of the EPA. Car dealers of
all the major U.S. auto manufacturers were contacted by telephone in
the Ann Arbor (Michigan) area, and none indicated that they had
received any complaints about knocking.
It must be noted, however, that these records do not guarantee
that there will not be complaints in the future, if the hot weather
and the accumulation of mileage expose audible knock.
SAE Panel Discussion on Octane Number Requirements of 1975 Model Year
Cars
The SAE panel discussion on ONR of the 1975 cars (held in Detroit,
on February 27, 1975) provided an account of the views on the subject.
In general, the U.S. auto manufacturers restated that there will be
no serious problems, and that the unsatisfied cars will be taken care
°f with a few degrees of spark retard.
-------
6-2
On the other hand, the participating petroleum and fuel additive
companies indicated that unusually high numbers of 1975 cars will not
be satisfied with the 91 RON/83 MON unleaded gasoline. Their estimates
of 1975 satisfied cars ranged from 30 to 80%, approximately.
Panelists of both automotive and fuel companies pointed out the
need to improve the procedure for determining the "customer" octane
number requirements of automobiles.
In addition, Chrysler and Ford spokesmen suggested that greater
attention should be paid to increasing the availability of higher
octane unleaded gasolines. Specifically, Ford's spokesman indicated
that unleaded gasolines of 95 or 96 RON should be made generally
available in the future to maximize the energy availability from
petroleum.
-------
7-1
8. References
1. "Octanes on the Road-Leaded and Unleaded", E. S. Corner, API pre-
print No. 02-72, May 9, 1972.
2. "February Meetings of the CRC Groups Related to Octane Number
Requirements", memo by J. L. Bascunana, EPA, March 6, 1975.
3. "The Relation Between Knock and Exhaust Emissions of .a Spark
Ignition Engine", L. C. Duke et al., SAE paper No. 700062.
4. "The Effects of Knock on the HC Emissions of a Spark-Ignition
Engine", H. P. Dayis et al., SAE paper No. 690085.
5. "Effect of Knock on Exhaust Emissions", W. Brown, September 10,
1970, MPR 8-70 memo from Ethyl Corporation.
6. "Internal Combustion Engines", E. F. Obert, International
Textbook Company, 3rd edition, 1968.
7. "Analysis of the RON Requirement Data from 138 Cars of the 1975
Model Year", memo by J. L. Bascunana, EPA, February 11, 1975.
8. "Estimated Fuel Economy Losses for Elimination of Knocking in
1975 Model Cars by Spark Retard", memo by J. L. Bascunana, EPA,
January 21, 1975, updated on April 2, 1975.
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