EPA-AA-SDSB-82-1
Technical Report
A Brief Summary of the Technical Feasibility,
Emissions and Fuel Economy of
Pure Methanol Engines
by
Jeff Alson
December 1981
NOTICE
Technical Reports do not necessarily represent final EPA decisions
or positions. They are intended to present technical analysis of
issues using data which are currently available. The purpose in
the release of such reports is to facilitate the exchange of tech-
nical information and to inform the public of technical develop-
ments which may form the basis for a final EPA decision, position
or regulatory action.
Standards Development and Support Branch
Emission Control Technology Division
Office of Mobile Source Air Pollution Control
Office of Air, Noise and Radiation
U.S. Environmental Protection Agency
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I. Introduction
Because of the general perception that our country cannot
afford to continue to rely on foreign sources for nearly half of
our petroleum supply, considerable resources both in the private
and public sectors are being expended to develop alternative
liquid fuels which could power future automotive vehicles. Fuels
under consideration include alcohol fuels such as methanol, which
can be synthesized from coal, natural gas, wood or other biomass
feedstocks, and ethanol, which is produced by the fermentation of
sugars and starches, as well as synthetic gasolines, diesel fuels,
and broad-cut fuels from coal and oil shale. Because of their
strong dependency on fuel type, tl».; environmental and energy
characteristics of the various alternative fuels are of primary
concern. Clearly, the emissions and efficiency capabilities of
the various alternative fuels, which often have very different
physical and chemical properties, should be important determinants
in the selections of acceptable alternative fuels.
This report deals with just one of the fuels under study —
methanol. In the last decade considerable research has been
undertaken to evaluate methanol as an automotive fuel and this
report will attempt to summarize the emissions and fuel efficiency
data from the many studies. Because there is a general consensus
that pure methanol is preferable to methanol/gasoline or methanol/
diesel fuel blends (as opposed to ethanol which is very satis-
factory in blends such as gasohol), and because the emissions and
efficiencies of vehicles operating on pure methanol are sometimes
much different from those operating on methanol blends, this paper
will generally limit itself to data involving pure methanol com-
bustion. A notable exception will be the sections dealing with
methanol combustion in compression-ignited diesel engines.
Because of the paucity of data on pure methanol combustion in such
engines, much of the data will involve the use of pilot fuels (to
aid ignition) in addition to methanol.
The first section of this report will consider the important
physical and chemical properties of methanol which define Its
characteristics as a motor fuel, and will compare its properties
to those of gasoline and diesel fuels. The report will then
briefly summarize the state-of-the-art of the technical feasi-
bility of .pure methanol vehicles. Next, it will examine the emis"
sions of various pollutants from methanol-fueled vehicles, both in
terms of what would be theoretically expected and what has been
experimentally determined. Finally, it will summarize the fuel
efficiency results of studies of methanol-fueled vehicles.
Recent motor vehicles have utilized internal combustion
engines which can be divided into two general groups. One group
of engines combust a homogeneous mixture with a precisely con-
trolled air/fuel mixture, utilizing throttled intake air, fuel
induction, and spark ignition, and generally utilizing gasoline as
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fuel. A second group of engines combust a heterogeneous mixture
containing excess air at high compression, utilizing direct-
cylinder fuel injection and compression ignition, and generally
utilizing diesel fuel. These two engine types are often referred
to as spark-ignited and compression-ignited engines, or, more
popularly outside the industry, as "gasoline" and "diesel"
engines. The distinctions between these two engine types have
blurred in recent years, however, as engines have been developed
which utilize characteristics of both engine types. For example,
stratified-charge engines (such is Ford's PROCO) combust a hetero-
geneous mixture and utilize dij ect-cylinder fuel injection which
are characteristics of the compression-ignited diesel engine, but
also employ spark ignition and sometimes throttling which are
characteristics of the spark-ignited gasoline engine. Moreover,
many stratified-charge engines exhibit multifuel capability.
These engine-type distinctions are blurred even more with
methanol combustion. As discussed above, the two engine types
have been designed and optimized for gasoline and diesel fuel com-
bustion, respectively. Neither has been designed or optimized for
methanol combustion. Not surprisingly, methanol's properties are
such that the "ideal" methanol engine would utilize some of the
characteristics of the spark-ignited gasoline engine as well as
some of the characteristics of the compression-ignited diesel
engine. The question then becomes how to classify the basic
engine types in a discussion involving comparisons with methanol
combustion. Of course, with methanol as a fuel the gasoline/
diesel classification is meaningless. Because methanol's proper-
ties make autoignition very difficult, it is not anticipated that
' any methanol engines would be able to rely solely on compression
for ignition, so the spark-ignited/compression-ignited distinction
is also not accurate. I have decided that for the purposes of
this paper I will rely on a cylinder fuel-inducted/cylinder
fuel-injected classification scheme. Basically, cylinder
fuel-injected engines include all compression-ignited diesel
engines (which, for methanol, will generally utilize some form of
ignition assistance) as well as most stratified-charge engines,
while cylinder fuel-inducted engines include all spark-ignited
gasoline engines except for the stratified-charge engines. Since
at this time there is little reported data involving methanol com-
bustion in stratified-charge engines, this classification scheme
will result in discussion which will parallel that which would
have resulted using a gasoline/diesel breakdown. In the future,
however, this cylinder fuel-inducted/cylinder fuel-injected
classification scheme should be quite helpful.
It must be emphasized that the development of pure methanol
vehicles is very much in a state of flux. Meaningful investiga-
tions of pure methanol (or nearly pure methanol) in cylinder
fuel-injected engines have only recently begun and much optimiza-
tion work is still possible even for the more studied fuel-induc-
ted engines. Also important, only this year will the first
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multi-vehicle pure methsaol fleets go into operation which will
provide important data in future years with respect to the poss-
ible deterioration of emissions and fuel efficiency in use. Thus,
it can be expected that the data base on pure methanol vehicles
will greatly expand in the next few years.
II. Properties of 'Methanol as a Vehicle Fuel
Methanol, whose chemical formula is CH30H, is the simplest
alcohol. It is generally synthesized by the addition of two mole-
cules of hydrogen to o le molecule of carbon monoxide. Accor-
dingly, its combustion properties are similar to these gases and
distinct from the large hydrocarbon molecules which comprise gaso-
line and diesel fuels. The oxygen constitutes one-half of the
methanol molecule's weight and forms a hydroxyl group making it
strongly polar as compared with the nonpolar hydrocarbon fuels.
These basic differences result in quite different vehicle fuel
properties for methanol compared to gasoline and diesel fuels.
The most important fuel combustion properties are summarized in
Table 1.
From Table 1 it is apparent that methanol is quite distinct
from gasoline and diesel fuels in many ways. The much lower
energy density of methanol requires much larger fuel delivery and
storage systems than those in use in current vehicles. Its much
larger heat of vaporization means that methanol requires much
greater amounts of heat to vaporize it. This has positive
results, allowing increased cooling of intake air and engine parts
(and thus greater efficiency), but can also cause mechanical prob-
lems and ignition delay. MethanolTs lower vapor pressure (com-
pared to gasoline) and lack of any low-boiling point components
make it more difficult to cold-start. Methanol's higher octane
number allows the use of greater compression ratios resulting in
higher thermodynamic efficiencies, while its lower cetane number
makes it more difficult to ignite in compression-ignition
engines. Finally, methanol has a higher flame speed and corres-
pondingly wider misfire limits. This allows methanol combustion
to be leaner resulting in efficiency improvements. These distinct
combustion properties are the primary determinants of the emis--
sions and efficiency differences between methanol and petroleum
(gasoline and diesel) fuels.
The following discussion will separate the use of neat meth-
anol in cylinder fuel-inducted engines from use in cylinder
fuel-injected engines. Because of its high.octane and low cetane
numbers, methanol has been studied in fuel-inducted engines much
more so than in fuel-injected engines. This historical tendency
is now changing- somewhat as the emphasis on optimizing energy
efficiency has encouraged researchers to experiment with the high
compression, fuel-injected engine as a methanol powerplant and as
new methods of facilitating such use become apparent. Much of the
discussion below will report data from vehicles using both meth-
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anol and diesel fuels, with the former being used as the predomi-
nant fuel and the latter being used as a pilot fuel to initiate
ignition.
III. Technical Feasibility
A. Cylinder Fuel-Inducted Engines
Methanol has been recognized as a fine fuel for fuel-inducted
engines. Many i.-f its most distinctive properties, such as its
high heat of viporization, high .flame speed, and high octane
number, are ideal for combustion in a fuel-inducted Otto-cycle
engine. These properties strongly suggest the possibility of the
development of a low emission, high energy economy and high per-
formance power system with methanol usage in a fuel-inducted
engine. In fact, conclusions from earlier experimental studies
are now being coordinated and implemented into complete vehicle
systems. It is now possible to build a fuel-inducted engine
powered by methanol, and future work will likely involve optimiza-
tion of emissions, fuel economy, and durability.
Of course, certain changes are necessary and/or desirable in
changing from gasoline to methanol combustion in a fuel-inducted
engine. These modifications revolve around three parameters —
maximizing engine thermal efficiency, minimizing cold-start diffi-
culties, and resolving any corrosion or durability problems asso-
ciated with methanol combustion.
The primary vehicle modification involved in increasing
engine efficiency is an increase in the combustion chamber com-
pression ratio. Such a change is easily accomplished at the manu-
facturing level. Most researchers have concluded that compression
ratios in the 12:1 to 13:1 range are preferable for methanol com-
bustion, as compared to the 8:1 to 9:1 ratios typical of current
fuel-inducted engines operating on lower octane gasolines. Slight
combustion chamber modifications will also likely be desirable to
optimize efficiency at the higher compression ratios. Finally,
because of methanol's much lower heating value and wide flamma-
bility limits, methanol engines would utilize a much different
air/fuel ratio than current gasoline-inducted engines and thus
relatively simple carburetibn or fuel metering changes are neces-
sary. The issue of energy efficiency will be quantitatively dis-
cussed later in this report.
Without special modifications, methanol-inducted engines
experience cold-start difficulties at temperatures around
40°F.[5] Several possible solutions have been proposed and are
being investigated. These include the blending of volatile, low
boiling point components into the methanol (for example, isopen-
tane), the use of electrical fuel preheaters, much better fuel
nebulization, and even dissociation of methanol into gaseous car-
bon monoxide and hydrogen. Volkswagen was able to achieve good
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cold-stai ting capability at temperatures as low as -7°F with the
addition of 5 to 10 percent of highly volatile substances to the
methanol fuel.[5] Obviously, all of these would require some car-
buretion or fuel system modifications. Also suggested is the use
of high-energy ignition systems to satisfy the demands of the
higher compression ratios and to improve driveability after cold
starting.[6]
Finally, there is the issue of durability of methanol
engines. Because methanol contains no carbon-carbon bonds, there
should b> no soot deposit buildups in methanol engines. Volks-
wagen inspected the combustion chambers, valves, and pistons of a
methanol-fueled Rabbit after 35,000 kilometers of operation and
found them to be clean.[5] There is legitimate concern about
methanol's corrosive nature. For example, methanol attacks the
terne plate (lead-tin alloy coating) in fuel tanks, some alloys
(especially zinc and aluminum) used in carburetor castings, and
some nonmetallic parts. In addition, research at the Southwest
Research Institute has indicated that pure methanol can cause up
to 6 times more engine wear (cylinder bores, piston rings, engine
bearings, etc.) during cold starts than unleaded gasoline, due
primarily to the formic acid and formaldehyde produced during
methanol combustion.[7] However, the same researchers have
developed an additive which cuts methanol's engine wear rate in
half, and it seems reasonable to expect that further materials and
additives research will solve these corrosion and wear problems.
Manufacturers around the world have begun to produce or are
developing the capability to produce fuel-inducted engines speci-
fically designed for methanol. Volkswagen has had an active
methanol development program since at least 1974. It is producing
100 pure methanol passenger cars for West Germany's Alcohol Fuels
Project which will provide significant in-use data from 1980
through 1982. Volkswagen is also providing 15 to 20 methanol-
inducted vehicles (Rabbits and pickup trucks utilizing manifold
port injection upstream of the intake valve) to the State of Cali-
fornia for the latter's three-year fleet test.[8] These vehicles
are basically assembly-line vehicles and indicate that Volkswagen
could likely mass produce methanol vehicles in the near future.
Ford is supplying California with 40 methanol-powered Escorts
which will have some modifications made off the assembly line.[8]
Of course, Volkswagen, Ford, and many other world manufacturers
have gained experience with designing and manufacturing alcohol
vehicles as part of Brazil's ethanol program. By agreement
between Brazil and the auto manufacturers, • 200,000 neat ethanol
cars were to be produced during 1980 and 900,000 by the end of
1982[9]. The experience of the manufacturers in mass producing
ethanol vehicles 'will be of great value should they decide to mass
produce methanol vehicles. This experience, along with the rather
minor technical problems addressed above, indicates that there is
very little question that methanol-inducted engines could be mass
produced if that becomes desirable.
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B. Cylinder Fuel-Injected Engines
Cylinder fuel-injected engines can be divided into two
general types. The first type is what has come to be known as the
stratified-charge fuel-injected engine. This type of engine
shares some characteristics of both the spark-ignited gasoline
engine and the compression-ignited diesel engine. As such, some
have theorized that the stratified-charge fuel-injected engine
might be very well suited for methanol combustion. Although
several such designs are known, such as the Ford PROCO and' the
W lite TCCS engines, there is no data base available for either of
t;iese engines utilizing methanol as a fuel.
The second type of cylinder fuel-injected engine is the com-
pression-ignited diesel engine. While methanol has always been
recognized as a fine fuel for spark-ignited fuel-inducted, Otto-
cycle engines, it has typically been characterized as a poor
fuel-injected, diesel-cycle fuel. The primary problem is meth-
anol's very low cetane number, which makes autoignition due to
compression alone very difficult. This ignition problem in com-
pression-ignited fuel-injected engines is much more serious than
in spark-ignited fuel-inducted engines, where serious problems
generally occur only during low ambient temperatures. Because of
this serious ignition difficulty, very little research has been
done concerning the use of pure methanol in cylinder fuel-injected
engines. But as fuel conservation has become of ever greater
importance, the possibility of combining an efficient fuel —
methanol — with an efficient engine — the high compression,
cylinder fuel-injected diesel cycle — has received renewed atten-
tion.
Many possible solutions have been proposed for pure meth-
anol's autoignition problems in the cylinder fuel-injected diesel-
cycle engine, making it, in effect, an ignition-assisted diesel
engine. These include intake air preheating, turbocharging,
higher compression ratios, glow plugs, and spark ignition. The
latter two methods have been receiving greater attention.
Researchers in Brazil have successfully operated a 3.9-liter,
4-cylinder engine with glow plugs to initiate surface ignition, a
design concept which takes advantage of the high detonation
("knocking") resistance and low surface (or "hot spot") pre-
ignition resistance of methanol.[10] While methanol requires
higher air-fuel mixture temperatures to self-ignite, the presence
of a hot surface has been shown to trigger pre-ignition of meth-
anol to a greater extent than for other fuels; this is likely due
in part to the dissociation of methanol at high temperatures to
carbon monoxide and hydrogen, with the latter breaking down into
various radicals triggering pre-ignition.[11] While this surface
ignition phenomenon would be of some concern in a gasoline engine
because of the possibility of the center electrode of the spark
plug promoting pre-ignition in advance of the spark, it might be
advantageously utilized in a diesel engine to initiate combus-
tion.
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MAN of West Germany has recently modified a direct-injection
diesel engine for pure "methanol combustion. The two key aspects
of the modification were the addition of spark ignition and the
functional separation of fuel injection and mixture formation
through the application of wall deposition of the methanol. MAN
reports promising initial test results for the concept, including
improved acceleration, better torque at full load, and no cold
start difficulties. MAN has equipped an urban bus with one of
their methanol-injected engines and it is being used as part of
the German Alcohol Fuels Project.[12,13]
The use of cetane improving additives like amyl or hexyl
nitrate or the use of dual-fuel injection systems (with a high
cetane fuel used as pilot injection) have received considerable
attention, though these methods cannot be said to utilize pure
methanol. The German company KHD is providing 2 buses and 10 com-
mercial vehicles utilizing the dual-fuel system for the German
Alcohol Fuels Project.[12] Volvo has performed extensive testing
investigating the possibilities for utilizing alcohol fuels in
fuel-injected turbocharged diesel-cycle engines and has concluded
that the most promising concept is the dual-fuel engine with two
separate injection systems, one for small amounts of diesel pilot
fuel and one for large amounts, of methanol. [32] One can only
speculate about the outcome of these projects, but it is clear
that there are several possible solutions to methanol's auto-
ignition difficulties in the diesel engine.
Other expected vehicle modifications would be similar to
those discussed for fuel-inducted engines. Methanol's much lower
heating value would require much larger injection pump flow
rates. The fact that methanol combustion produces no soot would
be beneficial, but the corrosion and wear problems mentioned in
the previous section would likely apply to fuel-injected engines
as well, and could be exascerbated by the fact that diesel-cycle
engines typically have longer lives than Otto-cycle engines. One
special problem for methanol combustion in diesel engines concerns
its poor lubricity. Since diesel fuel is a good lubricant, it is
used to lubricate parts of the injection pump. Pure methanol
would likely cause accelerated wear of the injection pump com-
ponents. Two possible solutions are the use of an oil lubricated
pump (already available on the market) or the use of small amounts
of castor oil blended directly into the methanol (though the side
effects of the use of castor oil are unknown). Once again, this
problem appears solvable in the near future.
One advantage of methanol-injection compared to diesel-
injection is that the former appears capable of producing specific
power outputs equal to, or greater than, those achieved by the
latter. Apart from the possibility that methanol-injection might
well result in higher thermodynamic efficiencies, there is also
the fact that because of the very low (and possibly zero) smoke
levels of pure methanol operation, higher fueling rates can be
used without reaching the smoke limit.[14]
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In conclusion, the development of pure methanol cylinder
fuel-injected engines is not as far along as that of fuel-inducted
engines. Research and development work should be expanded and
expedited so that a reasoned decision can be made with respect to
whether methanol should be encouraged for fuel-inducted or fuel-
injected engines or both.
IV. Emissions
A. Cylinder Fuel-Inducted Engines
1. Organic (Unburned Fuel and Aldehyde Emissions)
Although gasoline-inducted engines emit measurable amounts of
nonhydrocarbon organic compounds (for example, oxygenated species
such as aldehydes and alcohols), the vast majority of organic
emissions from gasoline-inducted engines are unburned fuel and the
custom has been to focus attention on hydrocarbons as the most
important class of organic emissions. Such a description would
not be proper for emissions from methanol exhaust since oxygenated
compounds predominate. Thus, the term "organic" emissions has
been used to account for all of the unburned fuel, hydrocarbon,
and aldehyde emissions from gasoline and methanol exhaust.
Most organic emissions in gasoline engine exhaust are the
result of incomplete combustion. The primary cause of incomplete
combustion is wall quenching, where the relatively cool combustion
chamber wall prevents ideal propagation of the flame all the way
to the wall. Other sources of incomplete combustion include poor
condition of the ignition system such as fouled spark plugs, low
charge temperature, too rich or too lean air-fuel ratios, and
large exhaust residuals in the cylinder. One would expect these
same phenomena to be the primary sources of incomplete combustion
and organic emissions in methanol engine exhaust. Some of meth-
anol 's fuel properties such as its high octane number, high flame
speed, and wider flammability limits (resulting, as we will show
later, in a higher thermal efficiency for methanol as compared to
gasoline) would tend to decrease incomplete combustion, while
other properties such as its high heat of vaporization and low
vapor pressure would tend to increase incomplete combustion. In
terms of engine-out organic mass emissions it is not theoretically
apparent whether methanol would be better or worse than gasoline.
Empirical research must be relied upon to help us analyze these
organic emissions questions.
Though several researchers have studied the issue of organic
emissions from methanol exhaust as compared to gasoline exhaust,
there has not been a consensus with respect to overall environ-
mental impact of organic emissions. Even the structure of the
discussion has varied among researchers. Some have compared total
organic emissions, others have broken organic emissions down
between unburned fuel (methanol in methanol exhaust, hydrocarbons
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in gasoline exhaust) and aldehydes. This latter breakdown makes
the most sense, because aldehydes are generally only a relatively
minor component of organic emissions on a mass basis, because
aldehydes are of special concern from an air quality/public health
basis, and because aldehydes are generally measured in a
completely different way than are unburned fuel emissions.
Unburned fuel emissions from gasoline-inducted engines are
typically measured by a flame ionization detector (FID), which
measures the amount of ionizable carbon present in the exhaust
sample, or, when condensation is a concern, by a heated FID
(HFID). Because unburned methanol is water soluble, it is most
appropriately measured by a HFID. Both the speed and magnitude of
the HFID response are affected by the type of hydrocarbon in the
sample. For unburned fuel measurement from gasoline-inducted
engines, propane is used as the analyzer calibration gas. But the
HFID detects the carbon atom in methanol with less sensitivity
than it does the carbon atom in propane. Thus, two basic options
are available for measuring unburned methanol emissions in a
HFID. One, a specific concentration of methanol in a diluent gas
can be used in calibration. Two, the analyzer can be calibrated
with propane and corrected for the relative response to methanol
as compared to propane. The relative response to methanol as com-
pared to propane can be experimentally determined, and has .been
found to range from 0.73 to 0.85.[15,16,17,18] Obviously,
unburned methanol emissions data from a HFID calibrated with pro-
pane must be corrected in order to be meaningful.
A second issue with respect to unburned methanol emissions
concerns its oxygen component. The unburned fuel emissions from
gasoline-inducted engines are composed almost exclusively of car-
bon and hydrogen, and thus the hydrocarbon mass can be determined
by simply using the H/C ratio of the gasoline. Methanol, however,
is half oxygen by weight and the question arises as to.whether the
emissions measurements should be reported as total grams per mile
unburned methanol (which would include the oxygen component) or
grams per mile ionizable carbon or grams per mile ionizable carbon
plus associated hydrogen (both of which would not include the
oxygen component). Researchers have reported results in all of
these ways, and it is important to identify the methodology used
in reporting such results since the inclusion of the oxygen com-
ponent of unburned methanol will produce twice the mass measure-
ment compared to excluding the oxygen component.
The situation is somewhat more straightforward with respect
to aldehyde mass emissions measurement and reporting. ' Determina-
tion of total aldehydes is nearly universally performed by using
the 3-methyl-2-benzothiazolone hydrazone hydrochloride (MBTH)
technique. Measurements of aldehyde emissions from both gasoline
and methanol-fueled vehicles are generally reported as formal-
dehyde, which is the predominant aldehyde in both types of
exhausts.[19
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Keeping in mind the above remarks, the following results have
been reported in the literature for unburned fuel and aldehyde
emissions from methanol-inducted and gasoline-inducted engines.
Ingamells and Lindquist modified a 1971 compact car and found
unburned fuel emissions to be twice as high with methanol without
a catalytic converter but approximately equal with a converter
(total methanol mass basis); aldehyde emissions were approximately
equal without the converter.[1] Hilden and Parks used a single-
cylinder engine without catalytic reduction but with "standard"
and "improved" vaporization. With standard vaporization, unburned
fuel emissions were four times greater with methanol but with
improved vaporization the unburned fuel emissions were approxi-
mately equal (total methanol mass basis). Aldehyde emissions were
10 times and 3 to 4 times greater with methanol for standard and
improved vaporization, respectively.[15] Menrad, Lee, and Bern-
hardt modified a VW Rabbit without a catalytic converter. They
found unburned fuel emissions to be 4 times lower with methanol
(on a total methanol mass basis) and aldehyde emissions to be
somewhat higher.[17] Brinkman modified a 1975 car utilizing mani-
fold port injection upstream of the intake valve and tested it
with and without a catalytic converter. Engine-out unburned fuel
emissions were 3.5 times greater and tailpipe (with catalyst)
unburned fuel emissions were 5 times greater with methanol (total
methanol mass basis) under near-stoichiometric conditions.[20]
Pischinger and Kramer performed a series of tests on a single-
cylinder engine without an oxidation catalyst and found aldehyde
emissions to generally be 2 to 3 times greater with methanol.[21]
Bechtold and Pullman tested a 1976 full-size Dodge vehicle at two
air/fuel ratios (stoichiometric and 20 percent lean) and two com-
pression ratios (8.5:1 and 13:1). All their unburned fuel data
were reported as ionizable carbon only. At the .standard (i.e.,
gasoline) compression ratio and stoichiometry, unburned fuel emis-
sions were twice as great with methanol without the oxidation
catalyst but only one-half as much with the catalyst. Under lean
operation the unburned fuel emissions with methanol were 40 per-
cent greater without the catalyst and 20 percent less with the
catalyst. Under the higher compression ratio only the catalyst
condition was tested. Unburned fuel emissions with methanol were
approximately one-half as great as those with gasoline under both
stoichiometric and lean conditions. The same researchers also
tested three 1978 Ford Pintos equipped with three-way-catalysts at
the standard 8.5:1 compression ratio and stoichiometry. Unburned
fuel emissons were about half for methanol compared to gasoline.
Aldehydes were 6 times greater from methanol.[16] Finally,
Baisley and Edwards also tested some 1978 Pintos with three-way-
catalysts. Unburned fuel emissions with methanol were one-half of
those with gasoline (on an ionizable carbon basis) while aldehydes
were 3 times greater with methanol.[19]
What tentative conclusions can be drawn from the above
results? The first five studies all reported unburned methanol on
a mass basis. Except for the Rabbit data, all the results showed
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unburned methanol.,-emissions to be equal to or up to 5 times
greater than unburned gasoline emissions. The final two studies
reported unburned fuel emissions on the basis of ionizable car-
bon. Per carbon atom, the actual mass of unburned methanol is 2.3
times that of gasoline (methanol's molecular weight of 32 divided
by a typical weight of 13.85 for gasoline). Thus, one would
expect the final two sets of data to be more promising for meth-
anol,'and they are, with the catalyst data consistently less for
methanol than for gasoline. If we were to multiply the final two
sets of data by 2.3, however, the methanol data would be equal to
or somewhat greater than the gasoline data and thus would be in
fair agreement with the earlier studies. The aldehyde data
clearly indicate that methanol-fueled engines emit greater amounts
of aldehydes, generally on the order of 2 to 6 times as many as
gasoline-fueled vehicles.
Besides the conflicting test results and reporting methodolo-
gies, other factors also make a comparison of the organic emis-
sions from gasoline and methanol exhausts very difficult. Many of
the early comparative studies used single-cylinder engines or
vehicles which did not utilize any type of exhaust aftertreat-
ment. It has been demonstrated that catalytic converters are very
efficient at reducing methanol and aldehyde emissions.[20,21,22]
Even more importantly, it must be emphasized that the past com-
parisons between methanol-inducted and gasoline-inducted single-
cylinder engines and vehicles have clearly by necessity been some-
what biased in favor of the gasoline-fueled vehicles. After all,
the study of organic (hydrocarbon) emissions from gasoline-induc-
ted vehicles has been a central concern for automotive engineers
for over a decade and engine design, fuel system delivery design,
and converter technology have all been optimized for low organic
emissions from gasoline-fueled engines. Certainly, organic emis-
sions from methanol combustion, which involve completely different
species, have not been subjected to the same degree of analysis or
controls, and it seems likely that a reasonable amount of progress
could be achieved if the necessary resources were expended. A few
studies have appeared which justify such optimism. For example,
it has been demonstrated that part of the reason for discrepancies
in the measurements of unburned fuel emissions .in methanol exhaust
is due to the preparation of the air/fuel mixture; methanol is
much more difficult to vaporize than gasoline and those
researchers who have made extra efforts to improve methanol
vaporization have generally reported lower relative emissions of
unburned methanol. [15] Studies of aldehyde formation in methanol
engines should facilitate the development of designs to lower
aldehyde emissions.[11,23]
The above discussion indicates that it is not now possible to
determine whether organic emissions, on a mass basis, will be
greater or less for a methanol-inducted engine relative to a gaso-
line-inducted engine. It must be remembered, however, that the
most serious environmental problem associated with organic emis-
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sions in general is their role as oxidant precursors in urban
atmospheres. As such, the relative masses of organic emissions in
gasoline and methanol exhausts are not as important as the rela-
tive reactivities of the organic emissions. Though;aldehydes (and
particularly formaldehyde), which are generally emitted in greater
amounts by methanol-inducted engines, are known to be reactive,
methanol combustion produces almost no alkenes, aromatics, or non-
methane alkanes which are the most reactive components of gasoline
exhaust. Thus, it is not immediately clear whether methanol
exhaust would be more or less reactive than gasoline exhaust.
Recently published research by Bechtold and Pullman has shed
additional light on the relative reactivities of methanol and
gasoline exhausts.[16] They performed two different types of smog
chamber experiments to determine relative gasoline and methanol
exhaust reactivities, in both cases using surrogate organic com-
pounds to represent the organic compounds in the actual exhausts.
In the first set of experiments, the initial NOx concentration in
the smog chamber was held constant at 0.40 parts per million,
regardless of the NOx concentration in the vehicle exhaust. The
various measures of reactivity, such as the maximum ozone and
nitrogen dioxide concentrations and the time it takes to reach
them, were comparable for gasoline and methanol exhausts for all
vehicles and operating conditions tested. In the second set of
experiments, the initial NOx concentrations in the smog chamber
were varied in proportion to the NOx emissions concentrations in
the gasoline-fueled and methanol-fueled vehicles' exhausts. Under
stoichiometric conditions, the methanol exhaust was less reactive
in terms of every parameter examined. At lean engine operation,
the results were mixed with methanol exhaust yielding the higher
maximum ozone concentration but gasoline exhaust yielding the
higher nitrogen dioxide concentration. Of considerable relevance
was the finding that the maximum formaldehyde concentrations in
many of the smog chamber tests with gasoline exhaust exceeded
those from the tests with methanol exhaust. Even though the
initial formaldehyde concentrations were much greater in the meth-
anol exhaust, much more formaldehyde was formed (probably from
alkene oxidation) during the photochemical process from the gaso-
line exhaust. This is a very important consideration since for-
maldehyde is a suspected carcinogen.
In addition, it must be noted that the use of neat methanol
fuel is expected to greatly reduce evaporative organic emissions.
As noted above, the vapor pressure of methanol is considerably
lower than that of gasoline, and for pure fuels vapor pressure is.
a good indicator of evaporative emissions. This property is very
important since as exhaust organic emissions levels have been
lowered the evaporative component has become more important. For
example, EPA's emission factors indicate that by the mid-1980's
evaporative emissions will account for as much as one-fifth of all
zero-mile gasoline-powered vehicle organic emissions, though the
relative percentage from the evaporative component lessens with
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-13-
vehicle age. Since evaporative emissions contain no met'iane com-
ponent, they are of considerable interest with respect to reac-
tivity. Thus, less evaporative emissions from methanol will also
decrease the reactivities of urban atmospheres.
2. Carbon Monoxide Emissions
Very little discussion of the effect of methanol's usage in
fuel-inducted engines on carbon monoxide levels is necessary. CO
levels are primarily a function of the air/fuel ratio, vdth more
CO formed as the mixture becomes richer. Practically a.'i 1 of the
published studies agree that at stoichiometric air/fuel condi-
tions, CO levels in methanol exhaust are very similar to those in
gasoline exhaust.[1,15,17,20] Because methanol can be operated
at leaner air/fuel ratios, there is a good possibility of even
lower CO levels. One study reported CO emissions from a methanol-
fueled vehicle operating 14 percent lean to be 30 percent less
than the same vehicle operating at 5 percent lean (the maximum
leanness for good driveability) on gasoline.[1] Another study
showed engine CO emissions from a methanol-fueled vehicle to drop
from 23 grams per mile (gpm) at 4 percent lean to 10 gpm at 17
percent lean to 7 gpm at 38 percent lean. Similarly, tailpipe CO
emissions (including aftertreatment) were 5.5 gpm, 3.9 gpm, and
1.6 gpm, respectively.[20]
3. NOx Emissions
Nitric oxide is formed from the reaction of atomic oxygen or
nitrogen with molecules of nitrogen or oxygen. The reactions are
very slow, with half-lives on the same order as the expansion
stroke in an engine. The formation of NO is thus primarily
governed by the kinetics rather than the equilibrium considera-
tions , and as a result, has a very strong exponential temperature
dependence.[4] As methanol combusts at a lower flame temperature
compared to gasoline, and because methanol can operate at leaner
air/fuel ratios as well (also lowering peak temperatures), NOx
emissions are inherently lower in a methanol-fueled engine. In
fact, this characteristic of methanol combustion provided some of
the impetus for early methanol studies.
A search of the literature shows a general consensus that
methanol-inducted engines produce approximately one-half of the
NOx emissions of gasoline-inducted engines at similar operating
conditions, with individual studies showing reductions of from 30
percent to 65 percent.[1,20,21,24,25] One .of the major engine
design changes expected with methanol-inducted engines is th'e use
of higher compression ratios to increase engine effficiency.
Experiments have confirmed the theoretical expectation that higher
compression ratios, with no other design changes, increase NOx
emissions considerably due to the higher combustion tempera-
tures. [17,26] But, due to the high compression ratio, less spark
timing advance is needed. Retarding spark timing is known to
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-14-
reduce both NOx emissions and engine efficiency. Fortunately, it
has been shown that the combination of a much larger compression
ratio with a few degrees of spark timing retard can both increase
thermal efficiency and decrease NOx emissions.[26] Thus, the use
of methanol might make it possible for vehicles to meet the cur-
rent 1.0 gpm NOx standard without the need for a NOx-reducing
catalyst.
The lower NOx emissions from methanol-inducted vehicles would
have two major beneficial environmental impacts. First, as dis-
cussed in the section on organic emissions, the lower NOx emis-
sions would decrease the reactivity of methanol exhaust in urban
atmospheres. Second, lower NOx vehicle emissions would help
alleviate the serious acid rain problems which are of paramount
concern in certain areas of the country.
4. Sulfur Emissions
It is anticipated that the sulfur levels in methanol fuel
will be zero or near zero because of requirements in the methanol
production synthesis process. Thus, there will be no possibility
of any consequential amounts of sulfur-containing pollutants.
This will again be an advantage compared to gasoline-fueled vehi-
cles which, because of the catalyst material in the converter and
small amounts of sulfur in the fuel, emit small amounts of sul-
furic acid mist.
B. Cylinder Fuel-Injected Engines
As stated above, cylinder fuel-injected engines include both
the spark-ignited stratified-charge engine and the compression-
ignited diesel engine. Although the former is thought to be a
promising powerplant for methanol-injection, there is not much of
a data base in the literature on the emissions or fuel efficiency
of methanol-injected stratified-charge engines. Therefore, the
discussions of the emissions and fuel efficiencies of methanol-
injected engines will necessarily concentrate on diesel-cycle
engines, generally with some sort of ignition assistance.
1. Particulate Emissions
From a welfare standpoint, diesel particulate has long been
considered both an aesthetic problem (as "smoke," the visible com-
ponent of particulate, which does not always correlate with parti-
culate mass emissions) and as a contributor to urban visibility
problems. It has also been well established that particulate mat-
ter can increase the prevalence of chronic respiratory disease in
healthy adults and the aggravation of bronchitis, emphysema, and
asthma in susceptible persons. In the last few years, diesel
particulate has become of much more concern, due to its small
size, its greater relative impact on air quality where people live
and work (compared to other large sources of particulate emis-
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-15-
sions), and the' finding that its extractsble organic fraction is
mutagenic in short-term bioassays.[27] EPA, other government
agencies, and private industry are spending millions of dollars to
determine the carcinogenic risk of diesel particulate to public
health. Even absent an absolute finding on the cancer issue,
particulate emissions have become of such concern that EPA has
promulgated standards for diesel passenger cars and light trucks
and proposed standards for heavy diesel trucks.[28,29]
Diesel particulate consists of sol?'?' carbonaceous particles
(soot) and liquid aerosols. The former ace generally formed when
fuel-rich mixture pockets burn and form solid particulate. This
solid particulate can then serve as a nuclei for more harmful
organic species to adsorb onto and as a "vehicle" for such com-
pounds to reach (and possibly lodge in) the lung's bronchial
region. Although large reductions in engine-out particulate have
been reported, particulate matter seems to be an inherent pollu-
tant in diesel-injected compression-ignition engines.
Methanol has no carbon-carbon bonds and has not been observed
to form carbonaceous particles.[14j In addition, methanol does
not contain inorganic materials like sulfur or lead which can also
be sources of solid particulate. Accordingly, with pure methanol
there would be no nuclei for liquid aerosols to adsorb onto-and
total particulate emissions would be expected to be zero.[30]
Unfortunately, there appear to be no studies which have measured
particulate emissions from diesel-injected engines burning neat
methanol. There is a small data base in the literature on the
effect of methanol injection on smoke levels in diesel-cycle
engines. Smoke levels are a measure of the visible fraction of
particulate matter. As such, smoke levels do not correlate per-
fectly with particulate emission levels but are generally direc-
tionally consistent. The MAN spark-ignited pure methanol-injected
engine reportedly exhibited no exhaust discoloration whatsoever in
initial tests under full load conditions. A similar MAN compres-
sion-ignited diesel-injected engine exhibited smoke levels of
between 1 and 3 Bosch smoke units over the same full load condi-
tions. [13] Several studies have reported lower smoke levels for
dual-fuel engines using diesel pilot fuel and methanol as the pri-
mary combustion fuel, both in single-cylinder tests and in tests
of the Volvo dual-fuel engine.[10,31,32] Recently EPA confirmed
these results for the Volvo dual-fuel engine, finding that smoke
levels for the dual-fuel engine when using methanol as the primary
fuel were consistently lower than smoke levels for the baseline
diesel-injected engine, especially under transient and power curve
testing. Particulate emission levels were approximately one-half
as high with the methanol/diesel dual-fuel Volvo engine compared
to the baseline diesel-injected engine.[36] Although the 50 per-
cent particulate reduction is significant, particulate emissions
were not zero. It must be noted that the Volvo dual-fuel engine
utilized approximately 20 percent diesel fuel by weight and it
seems likely that it was this diesel combustion that produced the
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-16-
particulate emissions. There seems to be very little question
that neat methanol combustion in cylinder fuel-injected engines
would result in very low (and possibly zero) particulate emis-
sions, which would provide a very important environmental advan-
tage compared to diesel fuel combustion.
2. Organic (Unburned Fuel and Aldehyde) Emissions
There is very little data or the relative organic emission
levels of fuel-injected engines using methanol and diesel fuels,
and what data there are generally involve dual-fuel engines which
combust meaningful amounts of diessl fuel. Such engines would not
be expected to have the same organic emissions as pure meth-
anol-injected engines. One study using methanol with diesel pilot
fuel in a single-cylinder engine reported considerably higher
organic emissions while another study under similar conditions
reported equal or somewhat lower organic emissions.[33,31] Volvo
reported that in very limited testing their dual-fuel-injected,
turbocharged engine emitted equal or slightly less organic
emissions with methanol depending on the load range.[32] Recent
EPA testing of the Volvo dual-fuel engine showed higher organic
emissions compared to the baseline diesel-injected engine.[36] In
an independent review of the literature, Ricardo recently con-
cluded that alcohol-injected engines would likely produce more
organic emissions than diesel-injected engines, especially at
lower loads.[14] Conclusions with respect to this issue are dif-
ficult because of the scarce data base for pure methanol-injected
combustion (compared to dual-fuel injection) as well as confusion
over how to measure and report organic emission levels (see the
discussion under fuel-inducted engines). Much more work is neces-
sary with respect to the measurement and characterization of
organic emissions from methanol-injected engines.
There is no data base with respect to aldehyde emission
levels from pure methanol-injected engines. The only data avail-
able involved dual-fuel engines. One researcher reported less
aldehydes with a dual-fuel engine than with pure diesel fuel
combustion.[31] EPA testing of the Volvo dual-fuel engine
resulted in much higher aldehyde emissions—4.5 times more alde-
hydes for the methanol/diesel dual-fuel engine than for the base-
line diesel-injected engine during steady-state testing and 18
times more aldehydes during transient testing.[36] Aldehyde emis-
sions are a serious concern from methanol-injected engines, parti-
cularly since formaldehyde, the principal aldehyde from methanol
combustion, has been shown to be carcinogenic. One possible solu-
tion for unburned methanol and aldehydes is aftertreatment, as
catalytic converters have been found to be effective at oxidizing
these compounds. The two reasons why it has been difficult to
design an effective diesel catalytic converter are the lower
diesel exhaust gas temperatures and the high particulate emission
rates (which tend to clog up the converter). Methanol usage would
exascerbate the first problem as it appears to produce 'even
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-17-
lower exhaust gas temperatares (which is positive from an effi-
ciency standpoint) but methanol's particulate-free combustion
would remove the second obstacle to diesel converter develop-
ment. [10] MAN reports promising results with catalytic after-
treatment on their spark-ignited, methanol-injected bus
engine.[13] EPA tested the Volvo dual-fuel engine with an oxida-
tion catalyst which was not optimized for the Volvo engine. It
lowered hydrocarbon emissions by approximately 90 percent and
unburned methanol emissions by from 57 to 82 percent, but actually
increased aldehyde emissions somewhat.[36] Catalyst development
for unburned methanol and aldehyde emissions reduction is an area
where improvements can be expected.
Of course, as discussed in a previous section, it is not the
mass of organic emissions but rather the emissions' reactivity
that is of the greatest importance. No diesel-injected engine
organics versus methanol-injected engine organics smog chamber
studies have been reported. Given that diesel exhaust organics
are generally thought to be more reactive than gasoline exhaust
organics (especially for gasoline engines with catalytic conver-
ters where a significant portion of the organics is nonreactive
methane) and that we previously concluded that methanol exhaust
organics (at least in fuel-inducted engines) would likely be less
reactive than gasoline exhaust organics, it would appear plausible
that methanol exhaust organics may well be less reactive than
diesel exhaust organics.
Finally, as was discussed in the previous section, it is
thought that methanol will avoid the particulate/cancer problems
of the diesel-injected engine. One reason is that there are not
the solid particulate nuclei for organics to adsorb onto and which
can carry the organics deep into the lung. Also critical is that
methanol exhaust will not contain significant amounts of the
long-chain and multi-ring hydrocarbons which are of the greatest
public health concern, although recent studies on formaldehyde
would certainly indicate that the carcinogenic risk from methanol
exhaust is not zero.
3. Carbon Monoxide Emissions
Again the data is very sketchy but theoretically one would
expect methanol-injected engines to produce similar levels of CO
as diesel-injected engines.[30] Two different single-cylinder,
dual-fuel studies did show comparable CO emissions.[31,33] EPA
found that the Volvo dual-fuel engine produced 2 to 3 times more
CO than its diesel-injected counterpart.[36] The unthrottled
fuel-injected engine's inherent lean combustion combined with
methanol's lean combustion and good efficiency ensure that CO
levels would be reasonably low on a pure methanol-injected engine.
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-18-
4. NOx Emissions
As with fuel-inducted engines, methanol's lower flame
temperature should facilitate lower NOx emission levels from meth-
anol-injected engines than from diesel-injected engines. Again,
the single-cylinder, dual-fuel tests support this hypothesis, with
one of the tests reporting NOx levels one-half as high as those
from pure diesel operation. [31,33] EPA testing of the Volvo
dual-fuel engine produced NOx reductions of from 35 to 56 percent
as compared to i.'->e diesel-injected baseline engine. [36] MAN
reports that thei." spark-ignited methanol-injected bus engine
emitted 3.0 grams of NOx per horsepower-hour over the 13-mode
test, a level approximately one-half of the best NOx levels of
current diesel-injected engines. Methanol combustion would not
only help alleviate acid rain and ambient N02 problems, but
would also provide a long-term solution to the problem of reducing
NOx levels from heavy-duty diesel engines which are currently
unable to meet the Clean Air Act mandate for NOx emissions. As
with fuel-inducted engines, lower NOx emissions would be one of
the most important environmental advantages of methanol combustion
in fuel-injected engines.
5. Sulfur Emissions
Diesel fuel contains from 0.1 to 0.5 percent sulfur. The
major sulfur product in diesel exhaust is sulfur dioxide which can
be converted to sulfuric acid in the atmosphere. Since methanol
would not contain any sulfur because of production requirements,
it would not produce any sulfur pollutants. This would again
reduce the acid rain burden slightly.
V. Fuel Efficiency
A. Cylinder Fuel-Inducted Engines
As shown in a previous section, methanol has a very low heat-
ing value, approximately one-half that of gasoline on a volumetric
basis. But it is energy (such as Btu's) which is to be conserved,
not volume of fuel, and so to be meaningful methanol and gasoline
should be compared not on a mpg basis, but rather on an energy
efficiency basis (for example, miles per million Btu). This dis-
cussion will limit itself to comparisons on an energy efficiency
basis. In addition, the following efficiency comparisons will be
on a relative basis and not on an absolute basis. In other words,
if engine A is 10 percent more efficient than engine B that does
not mean that engine A has a thermodynamic efficiency which is 10
percentage points greater than engine B, rather it means that
engine A is, say, 33 percent efficient compared to engine B's 30
percent efficiency.
There is general agreement among researchers that methanol is
a more energy efficient vehicle fuel than gasoline. There are
theoretical reasons why this is so. Methanol's lower flame
temperature reduces the amount of heat transfer from the combus-
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-19-
tion chamber to the vehicle coolant system. Its high heat of
vaporization acts as an internal coolant and reduces the mixture
temperature during the compression stroke. These characteristics
increase methanol's thermodynamic efficiency, and are realized in
experiments without having to make any major design changes from
current vehicles. Studies have shown these inherent properties of
methanol to increase the relative energy efficiency of a fuel-
inducted passenger vehicle by from 3 to 10 percent with a middle
range of about 5 percent.[17,20,25]
Other properties of neat methanol combustion allow even
greater efficiency improvements. Its wider flammability limits
and higher flame speeds relative to gasoline allow methanol to be
combusted at leaner conditions while still providing good engine
performance. This lean burning capability allows more complete
combirstion and improves energy efficiency. Early testing on a
single-cylinder fuel-inducted engine yielded estimated energy
efficiency improvements of 10 percent due to leaning of the meth-
anol mixture as compared to gasoline tests; subsequent vehicle
testing has shown relative efficiency improvements of lean meth-
anol combustion of 6 to 8 percent, and 14 percent, respec-
tively. [34, 1,20] Given these results, it would seem that meth-
anol's lean burning capability may yield as much as a 10 percent
relative efficiency improvement.
Methanol's higher octane number allows the usage of higher
compression ratios with correspondingly higher thermal efficien-
cies. Of course, there is a practical limit to compression ratio
increases due to increased friction losses. Early single-cylinder
testing estimated the relative thermal energy efficiency improve-
ments of the higher compression ratios to be in the range of 16 to
20 percent.[26,34] Unfortunately, little vehicle data exists to
confirm these figures, but it must be expected that improvements
of up to 10 percent are likely.
Adding up the possible improvements indicates that methanol-
inducted engines may well be as much as 25 percent more energy
efficient than their gasoline counterparts. Volkswagen has
reported energy efficiency improvements of approximately 15 per-
cent for its mid-1970's methanol vehicles, with a corresponding
power output increase of approximately 20 percent.[35] While it
Is true that emissions concerns may force some tradeoffs (the
TOx/efficiency tradeoff has already been discussed) in terms of
efficiency, it is also true that so far methanol energy efficiency
iata have been obtained using vehicles which were designed and
optimized for gasoline-fueling and not for methanol combustion.
^s with emissions, time and resources will allow much methanol-
specific optimization which should improve the energy efficiency
)f methanol-inducted engines even more.
B. Cylinder Fuel-Injected Engines
It has already been stated that there are several reasons why
aethanol is much more efficient than gasoline in fuel-inducted
-------
-20-
engines; the improvement has been estimated to be as much as 25
percent on an energy basis which is similar to the efficiency
advantage often quoted for current diesel-fueled vehicles compared
to current gasoline-fueled vehicles. Some of those characteris-
tics which make methanol efficient in the fuel-inducted engine,
such as its low flame temperature and low exhaust gas temperature,
also are advantageous in the high compression, fuel-injected
engine. Some of its other properties are not of much help, how-
ever, such as its high heat of vaporization (which simply makes it
that much more difficult to ignite), lean combustion (which is
inherent in diesel-cycle operation anyway) and high octane number.
Again, there is a dearth of information on pure methanol com-
bustion in high compression, fuel-injected engines. One set of
data involving pure methanol (with 1 to 2 percent castor oil for
lubricity) utilized a 3.9-liter, 4-cylinder engine with glow plugs
to initiate surface ignition. Steady-state tests with this engine
showed significantly higher brake thermal efficiencies for meth-
anol compared to diesel fuel above 30 percent load, ranging as
high as 22 percent greater, while diesel fuel was more efficient
at lower loads.[10] A second set of data involving pure methanol
involves the MAN spark-ignited methanol-injected concept. Ini-
tially a non-commercial air-cooled 4-cylinder engine was modified
and installed in a small 2-ton cross-country vehicle; methanol
operation resulted in 12 percent better fuel economy than the
diesel counterpart (test procedures unknown). More recently, in a
simulation of urban traffic conditions, the MAN bus engine
described earlier gave 5 percent better fuel economy than the cor-
responding diesel-injected engine.[13] One other single-cylinder,
dual-fuel study reported slightly higher efficiency for methanol,
while two other dual-fuel studies, one with a single-cylinder
engine and the other the Volvo dual-fuel turbocharged engine, also
showed methanol to be somewhat more efficient at higher loads but
similar to diesel fuel at lower loads. [31,32,33] EPA found the
Volvo dual-fuel engine to be approximately 5 percent less energy
efficient than the diesel-injected baseline engine over the new
transient test procedure, though most and probably all of the
difference can be attributed to the fact that the injection timing
of the dual-fuel engine was retarded five degrees from the
diesel-injected baseline engine.[36]
It cannot be overstated that much work needs to be done in
the area of methanol use in cylinder fuel-injected engines. The
primary problem has been the initiation of combustion, and
researchers continue to examine several solutions including pilot
fuels (usually diesel fuel), glow plugs, spark ignition, cetane-
improving additives, etc. Once a preferred design can be identi-
fied, serious optimization work can begin. Based on the early
engine results reported above and the huge opportunity for basic
improvements in this area, it seems likely that, should methanol
prove feasible in high compression, fuel-injected engines, it will
actually be a slightly more energy efficient fuel. Even if it
should only match diesel fuel in energy efficiency, it would pro-
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-21-
vide many environmental benefits (primarily particulate and NOx
emissions reductions) as compared to diesel fuel.
VI. Conclusions
A. Cylinder Fuel-Inducted Engines
There is little question about the technical feasibility of
methanol combustion in fuel-inducted engines and several manufac-
turers (most notably Ford and Volkswagen) are now involved in the
development of prototype and experimental fleet vehicles. Meth-
anol use in fuel-inducted engines. would reduce NOx emissions by
approximately one-half, would result in similar or somewhat lower
CO emissions, and would reduce sulfur emissions to zero. At this
time, the data suggest that methanol combustion would reduce the
total reactivities of the organic components of fuel-inducted
engine exhaust, but this thesis is preliminary and more research
must be undertaken. Particular emphasis must be placed on the
control of formaldehyde emissions which are very reactive and
likely carcinogenic. Methanol-inducted engines would definitely
be more energy efficient than their gasoline-inducted counter-
parts, possibly by as much as 25 percent. Further research and
optimization may allow additional improvements, but even absent
further progress it now appears that methanol-inducted engines
will be preferable to gasoline-inducted engines both in terms of
energy efficiency and environmental pollution.
B. Cylinder Fuel-Injected Engines
Methanol has always been considered a poor compression-
ignition, fuel-injected engine fuel .because of its poor auto-
ignition. Thus, while greater emphasis has recently been placed
on methanol combustion in fuel-injected engines, this .development
is not as far along as that with fuel-inducted engines and any
conclusions are much more tentative. Methanol use in fuel-injec-
ted engines would likely result in zero or near-zero particulate
emissions, considerably lower NOx emissions, zero sulfur emis-
sions, and approximately equal CO emissions. Again, the data base
is very sketchy with respect to organic emissions. On a mass
basis, methanol-injected engines may produce greater amounts of
organic emissions than diesel-injected engines. But it is impos-
sible at this time to predict the effect of pure methanol-injec-
tion on the reactivity of fuel-injected engine exhaust. Given
that current diesel-injected engine exhaust prganics are generally
considered more reactive than current gasoline-inducted 'engine
(with catalytic converter) exhaust organics and that we have pre-
viously concluded that methanol exhaust organics (at least in
fuel-inducted engines) would likely be less reactive than gasoline
exhaust organics, it appears possible that methanol exhaust might
well be. less reactive than diesel exhaust. Research must be
expedited in this area, especially with respect to the charac-
terization and control of formaldehyde emissions. Methanol-injec-
ted engines would likely result in similar or somewhat greater
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-22-
energy efficiencies than diesel-injected engines, though research
could produce greater improvements. The primary benefits of
methanol usage in fuel-injected engines would be the significant
particulate and NOx emission reductions.
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-23-
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-------
-24-
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22. "Alcohol Engine Emissions - Emphasis on Unregulated
Compounds," M. Matsuno et al., Paper 111-64, Third International
Symposium on Alcohol Fuels Technology, May 29-31, 1979, Published
by DOE in April 1980.
23. "Formaldehyde Emissions From a Spark ,Ignition Engine
Using Methanol," Kenichi Ito and Toshiaki Yano, Paper 111-66,
Third International Symposium on Alcohol Fuels Technology, May
29-31, 1979, Published by DOE in April 1980.
24. "Research and Development - Alcohol Fuel Usage in Auto-
mobiles," University of Santa Clara, DOE Automotive Technology
Development Contractor Coordination Meeting, November 13, 1980.
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-25-
25. "A Motor Vehicle Powerplant for Ethanol and Methanol
Operation," H. Menrad, Paper 11-26, Third International Symposium
on Alcohol Fuels Technology, May 29-31, 1979, Published by DOE in
April 1980.
26. "Effect of Compression Ratio on Exhaust Emissions and
Performance of a Methanol-Fueled Single-Cylinder Engine," Norman
D. Brinkman, SAE Paper No. 770791.
27. "Application of Bioassay to the Characterization of
Diesel Particulate Emissions," Huisingh, J. ,. et al., Presented at
the Symposium on Application of Short-Term Bioassays in the Frac-
tionation and Analysis of Complex Environmental Mixtures," Wil-
liamsburg, Virginia, February 21-23, 1978.
28. Federal Register, March 5, 1980, p. 14496.
29. Federal Register. January 7, 1981, p. 1910.
30. "Alcohols in Diesel Engines - A Review," Henry Adelman,
SAE Paper No. 790956.
31. "A New Way of Direct Injection of Methanol in a Diesel
Engine," Franz F. Pischinger and Cornelis Havenith, Paper 11-28,
Third International Symposium on Alcohol Fuels Technology, May
29-31, 1979, Published by DOE in April 1980.
32. "The Utilization of Different Fuels in a Diesel Engine
with Two Separate Injection Systems," P. S. Berg, E. Holmer, and
B. I. Bertilsson, Paper 11-29, Third Symposium on Alcohol Fuels
Technology, May 29-31, 1979, Published by DOE in April 1980.
33. "Alternative Diesel Engine Fuels: An Experimental
Investigation of Methanol, Ethanol, Methane, and Ammonia in a D.I.
Diesel Engine with Pilot Injection," Klaus Bro and Peter Sunn
Pedersen, SAE Paper No. 770794.
34. "Single-Cylinder Engine Evaluation of . Methanol—
Improved Energy Economy and Reduced NOx," W. J. Most and J. P.
Longwell, SAE Paper No. 750119.
35. "The Alternatives and How to Apply Them to the World
Transport Industry," Dr. Winfried Bernhardt, Volkswagen, Second
Montreux Energy Forum, May 16-19, 1980.
36. "Emission Characterization of an Alcohol/Diesel-Pilot
Fueled Compression-Ignition Engine and Its Heavy-Duty Diesel
Counterpart," Terry L. Ullman and Charles T. Hare, Southwest
Research Institute, EPA-460/3-81-023, August 1981.
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Table 1
Combustion Properties of Different Fuels [1,2,3,4]
Property
Heating Value
Heat of
Vaporization
Vapor Pressure
Boiling Point
Flash Point
Stoichiometric
A/F Ratio
Octane Number
Cetane Number
Flame Speed
Units
Btu/gallon
Btu/lb.
Btu/gallon
psi at 38°C
°C
°C
Ib. air/
lb. fuel
RON
MON
—
ft ./sec.
Methanol
57,000
8,600
3,320
5
65
11
6.4
106-110
90-92
3
2.5
Gasoline
114,000
18,000
940
6-15
30-225
-45
14.5
91-100
82-90
0-10
1.9
Diesel
125,000
18,400
880
—
180-330
75
14.6
30
—
50
—
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