420-S-77-001
MMT 77-2 " ' I
Technical Support for Regulatory Action
A Summary of Industry Work on
Manganese Fuel Additive (MMT)
March 9, 1977
I
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)
I Introduction and Background
s
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. A recent
sampling report (September, 1976) indicated 10% of the samples taken
during the first half of 1976 contained significant Mn levels. Ethyl
has stated that by the end of 1976 MMT was being used in 40% of unleaded
gasoline at an average level of 0.04 g Mn/gallon in this 40% fraction. .
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 as directed in
Advisory Circular 26B issued January 7, 1977.
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
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of MMT/emission control related data thc.t has been developed by various
companies. The following firms were contacted and supplied information
to EPA.
Company
American Motors Corp.
Ford Motor Company
Chrysler Corporation
Shell Oil Company
Gulf Oil Company -
British Leyland UK Ltd.
Saab-Sca'nia AB
Ethyl Corporation
General Motors Corp.
Exxon Research & Engin. Co.
Date Information Received
July 9, 1976
July 21, 1976
July 26, 1976
August 10, 1976
August 16, 1976
September 9, 1976
August 19, 1976
August 25, 1976
August 27, 1976
September 15, 1976
August 31, 1976
September 9, 1976
Comments
No data to report
No data to report
No data to report
Main comments
Additional data
On January 20, 1977, EPA held a public meeting at their Ann Arbor laboratory
to update this information. A number .of companies, including Ford, GM,
and Ethyl had done significant work since their submissions. In addition
to this meeting, some companies such as Ford have presented extensive
information to EPA. The information obtained from these sources is
summarized, by issue, 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).
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Graph 1
Effect of MMT on Octane Ratings -
Gulf Data (submitted to EPA Aug. 16, 1976)
6.0h-
a)
c
(T)
u
o
o
03
3
•O
01
U)
o
c
Research Octane Number
Motor Octane Number
Road Octane Number
.0.10 0.20 0.30 0.40
MMT Added to Fuel (grams manganese/gallon)
0,50
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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.
With regards to expected usage levels and octane ratings, Shell stated
Che 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
The major effect of MMT on gaseous emissions appears to be a potential
increase in engine-out hydrocarbon emissions. It is generally accepted
that MMT forms combustion chamber deposits. It is possible that these
MMT-related deposits increase quenching of hydrocarbon oxidation thus
causing higher engine-out hydrocarbon emissions. -The effect of MMT
would be similar to that found with lead additives which also increase
engine-out hydrocarbon emissions. Since the catalyst is, roughly speaking,
a percentage reduction device, an increase in engine-out emissions may
also result in an increase in tailpipe emissions. Some, but not all, of
.the available data show an increase in hydrocarbon emissions due to use
of MMT.
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5
Another potential effect of MMT, which currently appears minor, is
actual poisoning of the catalyst causing an increase in gaseous emissions.
Very little mention of.this phenomenon is made in any information submitted
to EPA. It should be noted that a catalyst poisoning phenomena (such as
occurs with lead compounds) is different from the catalyst plugging
phenomenon discussed in the next section.
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 the
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.
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
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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 resultjnay 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.
Ford has run some vehicles showing a significant increase in tailpipe
hydrocarbon emissions that is probably (but not definitely) due to MMT.
These vehicles are 12 medium duty trucks being run for 1978-79 certification.
Ford is using MMT service accumulation fuel in their 1978 medium duty
truck certification program so they can carry the data over to 1979 when
MMT is required (at 0.125 gm Mn/gal.) in the certification fuel.
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7
Ten of these vehicles showed a large increase in tailpipe hydrocarbon
emissions from zero to 15,000 miles. The average increase at 15,000
miles is 0.51 gpm or 111% over the zero mile values. By contrast, the
hydrocarbon emissions for the 1977 light duty trucks (which are similar
to the 1978 certification vehicles) increased only 0.13 gpm or 31% in
this interval. Ford has measured only the tailpipe emissions on these
trucks since they are not permitted to measure engine-out emissions on
certification vehicles.
Two trucks of the original 12 have been removed from the certification
program. Engine-out hydrocarbon emissions increased 49% in 18,000 miles
compared to a 28% decrease in hydrocarbon emissions for 1975 non-catalyst
systems. Ford feels that increased combustion chamber deposits due to
MMT are responsible for this increase.
Ford is running 7 of a fleet of 17 3-way catalyst vehicles on fuel
containing 0.125 gm Mn/gal. Engine-out hydrocarbons have increased 30%
for the vehicles using MMT versus a 19% decrease for the vehicles not
using MMT over a zero, to 10,000 mile interval; Tailpipe hydrocarbon
',;» '- •
emissions increased 165% for the cars using MMT versus 32% for the cars
not using MMT in this interval. Ford noted that the oxygen sensors
appear to still be functioning in these vehicles even though considerable
deposits have accumulated on them.
Ford's laboratory tests of MMT on Engelhard 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.
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8
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 by about 100% over 50,000 miles. There was no increase in
engine emissions of hydrocarbons for the Cutlass not using MMT. Engine
back pressure increased by about 50% at full throttle on the car using
MMT fuel, which probably indicates some plugging of the underfloor
converter. However, emissions or performance with this car were not
affected.
The "future" vehicle part of the GM program also indicated that MMT had
no effect on the tailpipe emissions over 50,000 miles. However, the
hydrocarbon engine emissions for the Nova using MMT increased from
1.2 gpm to about 2.2 gpm (a 83% increase) while there was only a slight
increase (about 10%) for the car not using MMT. The combustion chamber
deposits were removed from the Nova that had used MMT fuel for 50,000
miles. A subsequent emissions test showed engine hydrocarbon emissions
to decrease to about 1.6 gpm.
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9
GM tests on four 1979 prototypes using fuel with 0.125 gm Mn/gal. MMT
showed an increase in engine hydrocarbon emissions from 1.8 to about 2.8
gpm in 15,000 miles. Tailpipe hydrocarbon emissions also increased from
about 0.3 to 0.6 gpm in this interval. Additional tests on eight 1979
Chevrolet prototypes showed about a 50% increase in engine hydrocarbon
emissions compared to two cars not using MMT. The mileage on these cars
ranged from 10,000 to 25,000 miles. Similar tests on 5 Pontiacs using
MMT and 6 Pontiacs not using MMT showed about an 80% increase for the
former category and a 10% decrease for the latter category after 50,000
miles. All of the cars using MMT were run on ^.125 gm Mn/gal.
GM concludes the following as a result of their tests:
"The adverse effects of MMT on engine-out HC emissions may
affect initial engine calibration to the extent that the
0.41 g/mi. HC standard may not be achievable."
The first Ethyl Corporation submission (August 27) contained comments on
the early 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.
TITO 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, Efchyl did not report an
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10
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.
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 designed for
the 1975 California standards 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 overall 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 observed on both dynamometer and road
tests done on close-coupled monolithic catalysts run on MMT fuel. The
testing employed a duty cycle that raises the catalyst temperatures in
excess of 1500°F.
Ethyl ran some very recent tests on two 1977 non-catalyst AMC Pacers for
20,000 miles. These cars were run for 20,000 miles on an AMA type
schedule with fuel containing 0.125 g Mn/gal for one car and no MMT for
the other car. The hydrocarbon emissions did increase for the car with
MMT but the increase was attributed to the carburetor rather than to
MMT. These data were just obtained and are being evaluated.
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 MnAgal)
includes testing exhaust pressures. As of 30,000 miles, Gulf found no
evidence of catalyst plugging in any of the four vehicles. As mentioned
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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
MITT on catalysts. The GM program that was designed to evaluate MMT in
1976 production vehicles used two 1976 Oldsmobile Cutlasses with beaded
underfloo.r converters. They were tested .at various intervals over
50,000 miles of heavy-duty chassis-dynamometer accumulation, (GM ORI
cycle) 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. A new converter was placed on
this car which also plugged 22,000 miles later. The other Nova that
used MMT fuel also had converter plugging but not until 50,000 miles.
The probable principal reason for the later plugging is that the exhaust
temperature on this car was slightly below the 1500 F "critical temperature"
for catalyst plugging.
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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+)". 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
the temperature. Ethyl data show exhaust temperatures of vehicles
operated.on mileage accumulation <
than road operation temperatures.
operated.on mileage accumulation dynamometers can be about 200 F higher
Ethyl attempted to repeat the GM studies by running five 1977 California
Novas'for 50,000 miles using the GM-ORI cycle on a test track. Two cars
operating on 0.125 gm Mn/gal. of MMT developed severe exhaust backpressure
at 45,000 miles while the two cars operating at 0.0625 gm Mn/gal experienced
no problem. Ethyl stated the plugging occurred due to a build-up of
manganese oxide dust blocking the louvres on the pelleted catalyst.
These cars were run 24 hours/day while Ethyl stated that cars operating
under less severe conditions (e.g. 18 hours/day) would not build up this
dust. Ethyl did not find any plugging of the start catalyst. Ethyl finds
that the catalyst temperatures on these five Novas and five other Novas
are below 1500°F.
With regard to the effect of MMT on catalyst activity, 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-r
tories and four were assigned to field personnel in Ethyl's Petroleum
Chemicals Division."
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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 been 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 salesmen weie 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,
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 not 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.
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Ethyl also reported high back pressure problems on a police car after
25,000 miles of operation on 0.125 gin 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".
Ethyl also ran 10 monolith catalyst cars and 6 pelleted catalyst cars on
0.125 gm Mn/gal for 50,000 miles of AMA mileage accumulation. These
cars were part of the 22-car fleet Ethyl ran. All of the vehicles were
designed to meet 1975 California standards. No catalyst plugging was
found for-any of these vehicles.
Ethyl also reported that Clark Oil Company has been using MMT in their
commercial unleaded fuel for several years. Clark reports no catalyst
plugging problems for a 94-car' salesman fleet they own. This fleet
contains 60 monolith and 34 pelleted catalyst cars which accumulate an
average of 22,000 miles per year. Some of the cars have up to 60,000
miles.
Ethyl also reports that monolith catalysts can plug under very severe
conditions such as heavily loaded small cars operated continuously at 70
mph. However, Ethyl stated such plugging would not occur under more
typical conditions.
Ford reported catalyst plugging in one of their certification trucks
after 15,000 miles. A 300 CID truck catalyst was found to be 90% plugged
with manganese-containing deposits. Visual inspection showed that
manganese deposits were building up on the exit face of some of the
other catalysts of trucks in this fleet.
Ethyl Corporation states that the catalyst plugging may be due to a
large void Volume in the canister before the catalyst. Ethyl further
states that a different catalyst configuration should alleviate this
problem. This possible solution has not been evaluated yet.
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Ford also reported that the oxidation catalyst following the 3-way
catalyst of one of their prototypes was observed to be partially plugged
after 10,000 miles of operation on AMA driving with fuel containing
0.125 gm Mn/gal.
The New York State Department of Environmental Conservation reports a
case of a police car (a 1975 Plymouth .Fury with 69,000 miles) having a
catalyst plugged due to MMT. Further inspection revealed that the
center core of the catalyst had melted. It is not known whether MMT was
responsible for the problems with this vehicle. This car had high oil
consumption. Additional work by New York Sta_5 and Ford has shown that
high oil consumption alone can result in plugged catalysts under severe
operating conditions.
In summary, it appears that use of MMT can result in plugged catalysts.
This plugging occurs generally under severe driving conditions when the
catalyst may fail due to higher temperatures. However, there are also
cases where catalyst plugging has been reported under less severe
conditions (e.g. AMA). The available data do not completely resolve
this issue. •' .
D. Effect on Spark Plugs
The Shell submission reports tbat 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.
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General Motors data indicates MMT may cause plug fouling at high mileage
*
(.approaching 50,000 miles).
Ford reported a slight misfire condition at 19,000 miles on one of their
certification trucks that may be' due to heavy manganese deposits on the
.-spark plugs. Ford has also found deposits forming on the spark plugs
from other vehicles but found no misfiring.
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
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.
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G. 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".
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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Conclusions
The following conclusions can be made from the currently available data
on MMT.
1. Addition of about 0.125 gm Mn/gal 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. Available data generally show that MMT increases engine-out hydro-
carbon emissions. Extensive tests run by GM and Ford show a marked
increase in engine-out hydrocarbon emissions. However, other data by
Ethyl show that engine-out emissions may either increase or decrease due
to use of MMT. The tailpipe hydrocarbon emissions are generally affected
much less than the engine-out emissions.
3. Catalyst plugging due to MMT occurs generally only under more
severe driving conditions, probably those conditions associated with
higher catalyst temperatures-. There have Been .some limited cases of
catalyst plugging in some less severe driving modes such as the Ford
certification trucks over the AMA schedule. More data are needed to
determine if catalyst plugging from MMT will be ,a problem.
4. The effect of MMT on 3-way catalyst systems, including both the
catalyst itself and the oxygen sensor, is not known. Additional work
must be done in this area to clarify this question.
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).
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8. In the short terra, 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. 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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