MMT 77 -4
Technical Support for Regulatory Action
A summary of Industry Comments
Received on Manganese Fuel
Additive (MMT)
February 1977
Thomas M. Baines
Notice
Technical support reports for regulatory action do not
necessarily represent the final EPA decision on regulatory issues.
They are intended to present a technical analysis of an issue
and recommendations resulting from the assumptions and constraints
of that analysis. Agency policy considerations or data received
subsequent to the date of release of this report may alter the
recommendations reached. Readers are cautioned to seek the latest
analysis from EPA before using the information contained herein.
Technology Assessment and Evaluation Branch
Emission Control Technology Division
Office of Mobile Source Air Pollution Control
U.S. Environmental Protection Agency
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Manganese Fuel Additive (MMT)
The recent Supreme Court decision affirming the legality of the lead
phase down has renewed interest in using the octane-improving fuel
additive Methylcyclopentadienyl Manganese Tricarbonyl (MMT). The
industrial segments most interested in use of MMT appear to be the
manufacturers of it and the oil companies that are using it. According
to the principal manufacturer of MMT (Ethyl Corporation) crude oil
savings with MMT would amount to 1% of the crude run if all gasoline in
the run were unleaded. It is apparent that the principal motivating
force for the use of MMT is to improve the octane rating of the gasoline
with MMT rather than with additional refining steps. The cost of MMT is
traded off against a savings in crude required for the additional refining
as well as refinery capital and operating costs.
MMT is currently in use as an octane "trimming" agent. The Environmental
Monitoring and Support Laboratory (EMSL) of EPA is currently monitoring
manganese (Mn) levels of gasolines sampled from service stations through-
out the United States. The results of this survey have shown that an
increasing percentage of the samples taken contain sufficient Mn to
indicate MMT has been used to "trim" the octane of that sample. The
latest sampling report (September, 1976) indicated 10% of the samples
taken during the first half of 1976 contained significant Mn levels.
This coupled with predictions of much greater use by the oil companies
necessitated EPA requiring MMT be present in Certification service ac-
cumulation fuel beginning with the 1979 model year.
I. Summary of Submissions
EPA has been very interested in the MMT developments, especially because
of the results of a number of EPA and industry studies that have recently
been completed or are currently in progress. Some of the results from
these studies show a potential negative influence of MMT on exhaust
emissions. In order to more fully evaluate the research results of
these industry studies, the Emission Control Technology Division of the
EPA Office of Mobile Source Air Pollution Control invited the submission
of MMT/emission control related data that has been developed by various
companies. These following firms were contacted and supplied information
to EPA.
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Company Date Information Received Comments
American Motors Corp. July 9, 1976 . No data to report
Ford Motor Company July 21, 1976
Chrysler Corporation July 26, 1976
Shell Oil Company August 10, 1976
Gulf Oil Company August 16, 1976
September 9, 1976
British Leyland UK Ltd. August 19, 1976 No data to report
Saab-Scania AB August 25, 1976 No data to report
Ethyl Corporation August 27, 1976 Main comments
September 15, 1976 Additional data
General Motors Corp. August 31, 1976
Exxon Research & Engin. Co. September 9, 1976
A summary of these comments, by issue, is given in the following sections:
A. Effect of MMT on Octane Ratings
Gulf Research and Development submitted a set of data concerning the
effect of MMT on octane ratings. A summary of this data is shown in
Graph 1. This graph shows how octane numbers initially increase quite
rapidly with the addition of MMT to gasoline. However, after the addition
of about 0.125 gm Mn/gal the rate of increase in octane number is not as
great.
The GM submission contained limited information concerning MMT effects
on octane ratings. GM mentioned that the addition of 0.13 gm Mn/gal
raised the Research Octane Number from 91.4 to 94.0 (an increase of 2.6)
and raised the Motor Octane Number from 83.3 to 84.7 (an increase of
1.4).
Ethyl stated that "on the average 0.125 g Mn per gallon as MMT in un-
leaded gasoline gives an increase of about 2 road octane numbers".
Ethyl has presented other data showing that the addition of 0.125 g
Mn/gal increases RON by 2.4 and MON by 1.4. The data presented by GM
and Ethyl tend to agree with that.presented by Gulf, except that Gulf's
Road Octane Number curve appears to be about one number low throughout
its range relative to the data presented by Ethyl.
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6.0K
Graph 1
Effect of MMT on Octane Ratings -
Gulf Data (submitted to EPA Aug. 16, 1976)
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3
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5.0
4.0
3.0
2.0
1.0
0.0
Research Octane Number
Motor Octane Number
Road Octane Number
I
0.0 0.10 0.20 0.30 0.40
MMT Added to Fuel (grams manganese/galIon)
0.50
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With regards to expected usage levels and octane ratings, Shell seated
the following: "It is our belief, after a review of all relevant data
available to us, that the use of up to 0.1 gram of manganese per gallon
(as MMT) in unleaded gasoline is a socially acceptable move which can be
of benefit both to gasoline manufacturers and consumers. In general,
this quantity of MMT in unleaded gasoline confers an octane improvement
of 1.0 and 2.0 units (MON and RON respectively) thus permitting the
production of a higher percentage of unleaded gasoline in a given re-
finery gasoline pool."
B. Effect on Gaseous Emissions
Shell Oil Company tested four 1975 vehicles designed to meet the 1975
Federal Standards (two Chevrolets 350 CID and two Fords 351 CID) at
various intervals over 50,000 miles. The vehicles ran on lead-free
gasoline containing 0.0625 gm Mn/gal. Shell concluded that HC, CO and
NOx emissions did not deteriorate more rapidly than would be expected
with MMT-free unleaded fuel.
Gulf Oil Company has reported the results of three studies that tested
the effect of MMT on gaseous emissions. In the first study, three fuels
were each run in the same three non-catalyst vehicles and the emissions
were measured by the 1972 FTP. The fuels were 1) "base" fuel (without
MMT or lead), 2) "base" fuel plus 0.125 gm Mn/gal, and 3) "base" fuel
plus 0.125 gm Mn/gal plus 0.5 gm lead/gal. The results showed no significant
difference in HC, CO and NOx emissions among the three fuels.
The second Gulf study involved operating four 1974 non-catalyst vehicles
for 20,000 miles (91 RON unleaded gasoline) followed by operating che
vehicle for another 20,000 miles with the same gasoline but with 0.125
gm Mn/gal added to it. The emissions were determined at various intervals.
The results indicated that, whereas there was an appreciable fluctuation
in the data, there was no significant deterioration in the emission
levels for any of the vehicles.
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The third Gulf study involves investigating the effect of MMT on catalyst
activity and durability and at the time of the report was still an on-
going study. Two pairs of comparison vehicles are accumulating 50,000
miles in normal customer service. These are 1975 vehicles, one pair of
which are Chevrolets (350 CID engines, 2 barrel carburetors) and the
others are Fords (351 CID engines, 2 barrel carburetors). One vehicle
of each pair is using 91 RON unleaded gasoline whereas the other is
using the same type fuel plus 0.125 gm Mn/gal. After 30,000 miles of
operation, Gulf sees no significant differences in overall emissions
between the two Chevrolets. However, the Ford operating on MMT is
producing significantly lower CO emissions than the Ford operating on
non-MMT fuel. This result may be due to vehicle variability rather
than a direct effect of MMT use.
Chrysler tested a U.O.P. oxidation catalyst (70% Pt/30% Pd) in a tube
furnace and on a single cylinder engine using both unleaded fuel and un-
leaded fuel with 0.12 gm Mn/gal. On a short-term basis, they found no
significant reduction in catalyst efficiency.
Exxon reported an engine dynamometer test which was run under steady-
state conditions simulating a 40 mph cruise, with catalyst temperatures
of 1200-1250°F. Two fuel Mn levels of 0.0625 and 0.125 g/gal. were
used. Under these conditions, no evidence of catalyst plugging was
found after 700 hours or 28,000 miles "of operation. No adverse effect
of MMT was found on either catalyst conversions or engine HC emissions.
Exxon also tested four 1975 California cars which were run for 30,000
miles under simulated urban driving conditions. Three of these vehicles
used fuel containing 0.125 gm Mn/gal, while the fourth vehicle (the
control) used Mn sterile fuel. Exxon's comparison of the emissions
results indicated that MMT does not adversely affect either the gaseous
exhaust emissions or sulfate emissions. However, non-sulfate parti-
culates may have been increased by MMT usage.
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Ford's laboratory tests of MMT on PTX catalysts showed no adverse effect
under normal oxidizing conditions. Definite poisoning was noted under
reducing conditions, the effects of which could be reversed by an oxidizing
treatment above 500 C. Dynamometer testing with 0.25 gm Mn/gal over 96
hours (about 6,000 mi) showed no loss in catalyst efficiency. However,
the test was terminated because of excessive back pressure caused by Mn
deposits on the catalyst.
The GM submission reports some results from a program that was in progress
wherein GM was evaluating 1) "current" (1976) and 2) "future" (1977)
engine and emission control systems for compatibility with the MMT fuel
additive. Two 1976 production Federal Oldsmobile Cutlasses with beaded
underfloor converters and three 1977 prototype California Chevrolet
Novas with monolithic manifold converters in addition to beaded underfloor
converters were accumulating mileage on chassis dynamometers using a
driving schedule which is considered more severe than the certification
schedule. One Cutlass and one Nova were using Chevron UL77CQ unleaded
gasoline which is normally used for mileage accumulation during exhaust
emission certification tests. The other three cars were using Chevron
UL77CQ fuel containing 0.13 grams of manganese per gallon. This program
was planned to accumulate 50,000 miles on each car without changing
spark plugs.
In evaluating the results from the "current" vehicle program, GM found
that both Cutlasses completed 50,000 miles without any severe operational
or emission control problems. Exhaust emissions from the tailpipe never
exceeded the 1976 Federal standards for hydrocarbons, carbon monoxide,
or nitrogen oxides. There was no apparent effect of MMT on tailpipe
emissions. However, MMT appeared to increase the engine emissions of
hydrocarbons. Engine back pressure increased by about 50% at full
throttle on the car using MMT fuelV which probably indicates some plugging
of the underfloor converter. However, emissions or performance with
this car were not affected. "~ - ,..
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The "fucure" vehicle part of the GM program had not been completed at
the time of the GM submission. The three Novas had accumulated mileages
ranging from 20,000 to 40,000 miles. GM experienced many problems with
one of the vehicles using MMT as the start catalyst plugged repeatedly.
The other two vehicles (one with MMT fuel and one without) showed no
significant deterioration in catalyst activity.
The first Ethyl Corporation submission (August 27) contained comments on
the GM results showing higher engine-out HC emissions and stated that 1)
this result was from one vehicle only, which could be atypical, and 2)
regulated HC emissions were not adversely affected as the catalyst
brought the emission down to within the applicable standards. Ethyl
goes on to say "Our experience indicates that MMT actually helps in this
regard by enhancing the activity of the catalyst."
Ethyl submissions described some work done with four non-catalyst cars.
Two 1971 Plymouth 360-CID V-8 cars, a 1974 Buick 455-CID V-8 California
car and a 1975 Ford 400-CID California car were operated for 50,000
miles of EPA-type durability driving. A 1972 Buick 350-CID V-8 was
operated for 25,000 miles in continuous freeway service. Ethyl states
that the data indicates some cars may show an increase in HC emission
while others will show a decrease.
The CO data from the Ethyl experiments generally show a downward trend
when manganese is added to the fuel. However, Ethyl did not report an
improvement in CO emission except in cars equipped with catalysts where
CO is generally lower with MMT than comparison cars which have not
operated on MMT.
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None of the Ethyl data showed any benefit for MMT in terms of NOx control
since, in nearly all Ethyl tests regardless of whether MMT is used,
NOx generally decreases with increasing mileage.
Ethyl also reported results of a fleet test of 22 vehicles operated on
an EPA-type durability route for 50,000 miles (two vehicles failed to
make the entire test). The fleet was paired such that one of the pair
ran on 0.125 gm Mn/gal and the other ran on MMT sterile fuel. The over-
all conclusion was that the emissions at the end of the testing were
essentially the same for both the MMT fueled vehicles and those run
without MMT. Ethyl reports some other tests wherein plugging was ob-
served on both dynamometer and road tests done on close-coupled mono-
lithic catalysts run on MMT fuel. The testing employed a duty cycle
that raises the catalyst temperatures in excess of 1500 F.
C. Physical Effect (such as plugging) on Catalysts
In the Shell study of four 1975 vehicles (50,000 miles with unleaded
fuel, 0.0625 gm Mn/gal), no plugging of either the pelletized or monolithic
catalysts was observed. Gulf's study of two pairs of comparison vehicles
(50,000 miles customer service, '75 Chevrolets 350 CID, '75 Fords 351
CID, one vehicle of each pair without and the other with 0.125 gm Mn/gal)
includes testing exhaust pressures. As of 30,000 miles, Gulf found no
evidence of catalyst plugging in any of the four vehicles. As mentioned
in the previous section, Ford's engine dynamometer test showed PTX
catalyst plugging at 96 hours (about 6,000 miles) using 0.25 gm Mn/gal.
No temperatures were given for this data. Exxon's engine dynamometer
testing showed no such plugging of the PTX catalyst after 700 hours
(28,000 miles) of operation at lower MMT concentrations. They ran under
steady.state conditions (40 mph cruise simulation) with catalyst tempera-
tures of 1200°-1250°F and used 0.0625 and 0.125 g Mn/gal.
The GM experiments have yielded information on the physical effects of
MMT on catalysts. The GM program that was designed to evaluate MMT in
1976 production vehicles used two 1976 Oldsmobile Cutlasses with beaded
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underfloor converters. They were tested at various intervals over
50,000 miles of heavy-duty chassis-dynamometer accumulation, one without
and one with MMT in the fuel. The engine back pressure increased by
about 50% at full throttle on the car using MMT fuel, which GM reports
as indicative of some plugging of the underfloor converter. However,
emissions or performance of this car were not affected.
The other GM program involved evaluations of 1977 California vehicles.
GM used three Novas with monolithic manifold converters in addition to
beaded underfloor converters, one of which used MMT sterile fuel and the
other two used MMT fuel. The Nova that used MMT sterile fuel experienced
no problems. One of the Novas using MMT fuel experienced very poor
vehicle performance (it could not follow the driving cycle) at 8,000
miles. Upon removal of the monolithic converter, it was observed that
the converter inlet was 80 to 90 percent plugged with deposits of man-
ganese oxide, which had caused a doubling of engine back pressure. A
new manifold converter was installed and the accumulation resumed. At
20,000 miles, HC emissions exceeded the standard and at 22,500 miles the
second monolithic converter plugged. GM states that this plugging was
probably due to higher exhaust gas temperatures, which exceed 1500 F by
as much as 150°F during 70 mph cruising. The other Nova that used MMT
fuel had no converter plugging in 40,000 miles, the probable principal
reason being exhaust temperature si:
temperature" for catalyst plugging.
reason being exhaust temperature slightly below the 1500 F "critical
Ethyl commented on the Nova catalyst plugging problems in their first
submission. Ethyl, too, states that the plugging is due to "the extra-
ordinarily high temperature of the exhaust feed gas to the catalyst
(1600 F-t-)". They also state that neither they nor GM can explain why
the vehicle is operating at such high temperatures. One explanation
that Ethyl gives as a possibility is that the higher test loading keeps
the carburetor power jet open and the resultant rich mixture yields ad-
ditional CO that is oxidized ahead of the catalyst thereby increasing
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the temperature. Ethyl data show exhaust temperatures of vehicles
operated on mileage accumulation «
than road operation temperatures.
operated on mileage accumulation dynamometers to be about 200 F higher
With regard to the effect of MMT on catalysts, Ethyl states in their
first submission that "We have accumulated many hundreds of thousands of
test miles on monolithic and on pelleted exhaust catalysts with no
adverse effects attributable to the use of MMT. There is good evidence
from these tests that MMT enhances the conversion efficiency of exhaust
catalysts". However, they later submitted to EPA a second letter de-
tailing some plugging problems in an in-use fleet. Ethyl has "been
operating a fleet of eight, cars since about April of 1975 in field
service using MMT in the gasoline. Four of these cars are General
Motors, two are Fords and two are Chryslers. All were equipped with
emission control systems designed to meet California emission standards.
Four of these cars were assigned to personnel in Ethyl's Detroit Labora-
tories and four were assigned to field personnel in Ethyl's Petroleum
Chemicals Division."
Ethyl made the following comments about these vehicles.
The four cars being operated by personnel in (the) Detroit
Laboratories are being fueled by unleaded gasoline to which
MMT has beten added in an amount equal to 0.125 g Mn/gal of
gasoline. All of these cars use monolithic catalysts and
no problems have been encountered in their operation.
However, in the case of the four General Motors cars operated
by (Ethyl) field personnel the salemen were to add, through
small cans which they used to pour into the gas tank, MMT
which was supposed to result in a concentration of MMT
equivalent to 0.125 g Mn/gal gasoline. (Ethyl) now recognize(s)
that the addition of MMT in this manner, if not done properly,
could have resulted in some stratification and, in addition,
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there is no way to know whether the amount of MMT was added
to gasoline which may already have contained MMT when the
gasoline was purchased. Much of the purchased gasoline was
bought from oil companies who are MMT customers. If the
particular purchased gasoline did in fact contain MMT, the
Mn concentration in the tanks could have been as high as
0.25 g/gallon at times. Therefore, the exact concentration
of MMT in the four field cars is now known.
Ethyl reported data indicating that two of these eight cars have developed
some back pressure in the exhaust system at about 32,000 miles. A third
car may have done so at 16,000 miles. All three were General Motors
cars with pelletized catalysts. Ethyl's data indicate that this is
caused by overheating of the catalyst to such an extent that the alumina
in the pellets is converted from the usual gamma to the theta or alpha
form, with concurrent shrinkage so that the shrunken pellets fall into
the shallow depressions in which the exit louvers of the catalyst con-
tainers are located and partially block the louvers, thus reducing gas
flow.
Ethyl also reported high back pressure problems on a police car after
25,000 miles of operation on 0.125 gm Mn/gal. They found a plugging
situation similar to that discussed above. They go on to state that "We
have been told that high back pressure is a problem in a high percentage
of police cars equipped with pelleted catalysts using clear fuel".
Therefore, in summary, it appears that under many operating conditions
MMT produces no measurable negative effects on either monolith or pel-
leted catalysts. However, there appear to be several operating con-
ditions that could lead to temperatures high enough to not only destroy
the catalyst's effectiveness but to also significantly impair the vehicle's
performance. It is clear that the small amount of data presented does
not resolve this issue.
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D. Effect on Spark Plugs
The Shell submission reports that spark plug performance either measured
directly in terms of misfire or indirectly in terms of emissions and
fuel economy performance was not measurably affected by the presence of
manganese, although distinct manganese deposits were very evident on
used plugs.
Gulf notes that spark plug fouling has been encountered in two of the
test cars. In the 1974 Mustang, fouling occurred at 15,000 miles.
However, for this model car, the manufacturer recommends that spark
plugs be changed at 12,000 mile intervals. In the 1975 Ford, fouling
was also detected at 15,000 miles. This fouling occurred right at the
recommended interval for spark plug change. There have been no spark
plug failures in the other cars operating on manganese fuels.
General Motors data indicates MMT may cause plug fouling at high mileages.
Exxon reports vehicle tests of four 1975 California cars which were run
for 30,000 miles under simulated urban driving conditions. Three of
these cars used fuel containing 1/8 g Mn/gal., while the fourth car,
which served as a control, used Mn sterile fuel. There were no adverse
effects of MMT found on spark plug life in this service.
In general, it appears that at low mileages MMT has no effect (other
than reddish deposits) on spark plugs. However, small amounts of data
indicate a potential problem at higher mileages.
E. Effect on Octane Requirement Increase
Shell reported that octane requirement increase characteristics were
similar to those determined during unleaded gasoline service. Gulf came
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to essentially the same conclusion. No other data was reported on this
subject.
F. Effect on Engine
Both Shell and Gulf tests indicated that engine wear rates are normal
when the engine operates on MMT fuel. GM is studying this issue and has
no results to report yet. Shell reported the observation that MMT "pro-
duced a very distinctive red-brown deposit layer covering the surfaces
of the combustion chambers, spark plugs, and exhaust system including
internal surfaces of the catalytic converter". They did not mention
whether or not these deposits were harmful. Shell also studied the
effect of MMT on lubricants and stated that "apart from an accumulation
of manganese in the crankcase lubricant, there was no apparent effect on
the lubricant and its ability to control sludge and varnish deposits".
General Motors has stated that they are continuing to study some of
these issues.
G. Effects on Gasoline Properties
Gulf reported that, except for octane ratings, no significant differences
in fuel properties can be attributed to the addition of MMT to fuels.
H. Anticipated Future Usage
Shell has stated that their usage will be at concentrations up to 0.1 gm
Mn/gal. They state that such levels will be needed initially by August,
1977 in some of their unleaded fuel production. This could grow to as
much as 55% of their unleaded production over the next few years. In
the remaining 45%, "it is questionable whether the use of MMT will ever
prove desirable".
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Gulf has commented on overall MMT usage stating that if all automotive
gasoline is eventually unleaded, and if MMT is used at the maximum con-
centration recommended by Ethyl Corporation, then Gulf estimates that
14,000 tons of manganese per year will be consumed by the U.S. oil
industry. Gulf also stated that in the foreseeable future, lead will be
used in a significant portion of automotive gasoline, and the average
concentration of manganese in unleaded gasoline will be lower than 0.125
gm/gal. Gulf forecasts that manganese consumption will reach 8,000 to
10,000 tons/year, and it should take about 10 years to reach that level
of consumption.
With regard to industry and Exxon's MMT plans, Exxon stated the following:
We cannot, of course, speak for other gasoline producers with
regard to usage of manganese. However, we could expect other
companies also faced with octane capacity limitations resulting
from the lead phasedown regulations to make use of as much MMT (up
to the recommended maximum 0.125 g/gal.) as is available. There-
fore, in the near term, its usage will probably be limited by the
availability of raw materials and/or production capacity.
Exxon is currently using MMT at our Gulf/East Coast refineries and
expect to begin its use at our California refinery in the near
future. Initially, we expect our unleaded gasoline will average
about 1/16 gram of manganese per gallon (0.0625 gm Mn/gal), with a
maximum concentration of 1/8 gram per gallon (0.125 gm Mn/gal) on a
continuing basis, subject to supply availability.
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Preliminary Conclusions
The following preliminary conclusions can be drawn from the data sub-
mitted by the respondents:
1. Addition of about 0.125 gm Mn/gal of MMT increases the Research
Octane Number by about 2.6 and the Motor Octane Number by about
1.3. The increase in Road Octane Number is uncertain as the data
conflict.
2. Providing the catalyst does not plug or otherwise fail, the
tailpipe emissions performance over time does not seem to deteriorate
any more rapidly with MMT fuel than with MMT sterile fuel. Ethyl
seems to think that catalyst HC efficiency may actually be improved
by MMT because of limited data indicating increased engine-out HC
emissions.
3. Limited testing indicates no adverse effects on sulfate emis-
sions but a possible increase in non-sulfate particulate emissions.
4. Under many operating conditions (e.g. certification mileage
accumulation), MMT appears to have no physical effect on catalysts
other than coating the surface with a reddish-brown layer of man-
ganese compound. However, operating conditions such as a heavy
load cycle that elevate the catalyst to temperatures in excess of
about 1500 F appear to result in severe plugging of monolith
catalysts. Also, limited data from GM indicate a plugging problem
with pelleted, underfloor catalysts. The data presented are some-
what preliminary and more work is being done to confirm these
findings.
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5. Spark plug performance appears to be unaffected by MMT over the
commonly recommended plug change intervals. However, some data
indicate potential fouling problems at high mileages approaching
50,000 miles.
6. MMT appears to have no effect on octane requirement increase.
7. MMT appears to have no effect on engine wear rates, lubricant,
or gasoline properties (other than octane number).
8. In the short term, MMT usage will be limited by the availability
of raw materials and/or MMT production capability. During this
short term, fuel concentrations of MMT will be at about 0.0625 gm
Mn/gal and will be used in more than one half of the U.S. crude
refining capacity.
9. In the long term, nearly all gasoline refiners and/or suppliers
will probably be using MMT in much of their unleaded fuel frequently
at concentrations of 0.125 gm Mn/gal. However, there are some
companies (such as Shell) that indicate they will probably never
use MMT in some portion of their fuels.
10. Projections of MMT usage appear to be generally independent of
lead phase down. The oil companies that commented on this indicated
that the lead phase down will tend to accelerate the introduction
of MMT somewhat.
11. Projections of MMT usage were made implicitly assuming a lack
of EPA regulation of MMT. Such regulation could markedly alter MMT
usage patterns.
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