The bioconversion of biomass to mixed alcohol fuels can be accomplished using the MixAlco process. Through bioconversion of biomass to a mixed alcohol fuel, more energy from the biomass will end up as liquid fuels than in converting biomass to ethanol by yeast fermentation.
The process uses a mixed culture of naturally occurring microorganisms found in natural habitats such as the rumen of cattle, termite guts, and marine and terrestrial swamps to anaerobically digest biomass into a mixture of carboxylic acids produced during the acidogenic and acetogenic stages of anaerobic digestion, however with the inhibition of the methanogenic final stage. The more popular methods for production of ethanol and cellulosic ethanol
use enzymes that must be isolated first to be added to the biomass and
thus convert the starch or cellulose into simple sugars, followed then
by yeast fermentation into ethanol. This process does not need the
addition of such enzymes as these microorganisms make their own.
As the microorganisms anaerobically digest the biomass and convert it into a mixture of carboxylic acids, the pH must be controlled. This is done by the addition of a buffering agent (e.g., ammonium bicarbonate, calcium carbonate), thus yielding a mixture of carboxylate salts. Methanogenesis, being the natural final stage of anaerobic digestion, is inhibited by the presence of the ammonium ions or by the addition of an inhibitor (e.g., iodoform).
The resulting fermentation broth contains the produced carboxylate
salts that must be dewatered. This is achieved efficiently by vapor-compression evaporation.
Further chemical refining of the dewatered fermentation broth may then
take place depending on the final chemical or biofuel product desired.
The condensed distilled water from the vapor-compression
evaporation system is recycled back to the fermentation. On the other
hand, if raw sewage or other waste water with high BOD
in need of treatment is used as the water for the fermentation, the
condensed distilled water from the evaporation can be recycled back to
the city or to the original source of the high-BOD waste water. Thus,
this process can also serve as a water treatment facility, while producing valuable chemicals or biofuels.
Because the system uses a mixed culture of microorganisms,
besides not needing any enzyme addition, the fermentation requires no
sterility or aseptic conditions, making this front step in the process
more economical than in more popular methods for the production of
cellulosic ethanol. These savings in the front end of the process, where
volumes are large, allows flexibility for further chemical
transformations after dewatering, where volumes are small.
Carboxylic acids
Carboxylic acids
can be regenerated from the carboxylate salts using a process known as
"acid springing". This process makes use of a high-molecular-weight tertiary amine (e.g., trioctylamine), which is switched with the cation
(e.g., ammonium or calcium). The resulting amine carboxylate can then
be thermally decomposed into the amine itself, which is recycled, and
the corresponding carboxylic acid. In this way, theoretically, no chemicals are consumed or wastes produced during this step.
Ketones
There are two methods for making ketones. The first one consists on
thermally converting calcium carboxylate salts into the corresponding
ketones. This was a common method for making acetone from calcium acetate during World War I. The other method for making ketones consists on converting the vaporized carboxylic acids on a catalytic bed of zirconium oxide.
Alcohols
Primary alcohols
The undigested residue from the fermentation may be used in gasification to make hydrogen (H2). This H2 can then be used to hydrogenolyze the esters over a catalyst (e.g., copper chromite), which are produced by esterifying either the ammonium carboxylate salts (e.g., ammonium acetate,
propionate, butyrate) or the carboxylic acids (e.g., acetic, propionic,
butyric acid) with a high-molecular-weight alcohol (e.g., hexanol, heptanol). From the hydrogenolysis, the final products are the high-molecular-weight alcohol, which is recycled back to the esterification, and the corresponding primary alcohols (e.g., ethanol, propanol, butanol).
Secondary alcohols
The secondary alcohols (e.g., isopropanol, 2-butanol, 3-pentanol) are obtained by hydrogenating over a catalyst (e.g., Raney nickel) the corresponding ketones (e.g., acetone, methyl ethyl ketone, diethyl ketone).
Drop-in biofuels
The primary or secondary alcohols obtained as described above may undergo conversion to drop-in biofuels, fuels which are compatible with current fossil fuel infrastructure such as biogasoline, green diesel
and bio-jet fuel. Such is done by subjecting the alcohols to
dehydration followed by oligomerization using zeolite catalysts in a
manner similar to the methanex process, which used to produce gasoline from methanol in New Zealand.
Acetic acid versus ethanol
Cellulosic-ethanol manufacturing plants are bound to be net exporters of electricity because a large portion of the lignocellulosic biomass, namely lignin,
remains undigested and it must be burned, thus producing electricity
for the plant and excess electricity for the grid. As the market grows
and this technology becomes more widespread, coupling the liquid fuel
and the electricity markets will become more and more difficult.
Acetic acid, unlike ethanol, is biologically produced from simple sugars without the production of carbon dioxide:
C6H12O6 → 2 CH3CH2OH + 2 CO2 (Biological production of ethanol)
C6H12O6 → 3 CH3COOH (Biological production of acetic acid)
Because of this, on a mass basis, the yields will be higher than in
ethanol fermentation. If then, the undigested residue (mostly lignin) is
used to produce hydrogen by gasification, it is ensured that more
energy from the biomass will end up as liquid fuels rather than excess
heat/electricity.
A more comprehensive description of the economics of each of the fuels is given on the pages alcohol fuel and ethanol fuel, more information about the economics of various systems can be found on the central page biofuel.
Stage of development
The
system has been in development since 1991, moving from the laboratory
scale (10 g/day) to the pilot scale (200 lb/day) in 2001. A small
demonstration-scale plant (5 ton/day) has been constructed and is under
operation and a 220 ton/day demonstration plant is expected in 2012.
n-Butanol, a C-4 hydrocarbon is a promising bio-derived fuel, which shares many properties with gasoline.
Butanol may be used as a fuel in an internal combustion engine. It is more similar to gasoline than it is to ethanol. A C4-hydrocarbon, butanol is a drop-in fuel and thus works in vehicles designed for use with gasoline without modification.
It can be produced from biomass (as "biobutanol") as well as fossil fuels (as "petrobutanol"). Both biobutanol and petrobutanol have the same chemical properties. Butanol from biomass is called biobutanol.
Although intriguing in many ways, butanol fuel is rarely economically competitive.
Genetically modified bacteria
This method of production offers a way to produce liquid fuels from sustainable sources.
Fermentation
however remains inefficient. Yields are low and separation is very
expensive. Obtaining higher yields of butanol involves manipulation of
the metabolic networks using metabolic engineering and genetic engineering.
Escherichia coli
Escherichia coli, or E. coli, is a Gram-negative, rod-shapedbacteria. E. coli is the microorganism most likely to move on to commercial production of isobutanol. In its engineered form E. coli produces the highest yields of isobutanol of any microorganism. Methods such as elementary mode analysis have been used to improve the metabolic efficiency of E. coli so that larger quantities of isobutanol may be produced. E. coli is an ideal isobutanol bio-synthesizer for several reasons:
E. coli is an organism for which several tools of genetic
manipulation exist, and it is an organism for which an extensive body
of scientific literature exists. This wealth of knowledge allows E. coli to be easily modified by scientists.
E. coli has the capacity to use lignocellulose (waste plant matter left over from agriculture) in the synthesis of isobutanol. The use of lignocellulose prevents E. coli
from using plant matter meant for human consumption, and prevents any
food-fuel price relationship which would occur from the biosynthesis of
isobutanol by E. coli.
Genetic modification has been used to broaden the scope of lignocellulose which can be used by E. coli. This has made E. coli a useful and diverse isobutanol bio-synthesizer.
The primary drawback of E. coli is that it is susceptible to bacteriophages when being grown. This susceptibility could potentially shut down entire bioreactors. Furthermore, the native reaction pathway for isobutanol in E. coli functions optimally at a limited concentration of isobutanol in the cell. To minimize the sensitivity of E. coli in high concentrations, mutants of the enzymes involved in synthesis can be generated by random mutagenesis. By chance, some mutants may prove to be more tolerant of isobutanol which will enhance the overall yield of the synthesis.
A strain of Clostridium can convert nearly any form of cellulose into butanol even in the presence of oxygen.
A strain of Clostridium cellulolyticum, a native cellulose-degrading microbe, affords isobutanol directly from cellulose.
A combination of succinate and ethanol can be fermented to produce butyrate (a precursor to butanol fuel) by utilizing the metabolic pathways present in Clostridium kluyveri. Succinate is an intermediate of the TCA cycle, which metabolizes glucose. Anaerobic bacteria such as Clostridium acetobutylicum and Clostridium saccharobutylicum also contain these pathways. Succinate is first activated and then reduced by a two-step reaction to give 4-hydroxybutyrate, which is then metabolized further to crotonyl-coenzyme A (CoA) . Crotonyl-CoA is then converted to butyrate. The genes corresponding to these butanol production pathways from Clostridium were cloned to E. coli.
Cyanobacteria
Cyanobacteria are a phylum of photosynthetic bacteria.
Cyanobacteria are suited for isobutanol biosynthesis when genetically
engineered to produce isobutanol and its corresponding aldehydes. Isobutanol producing species of cyanobacteria offer several advantages as biofuel synthesizers:
Cyanobacteria grow faster than plants and also absorb light more efficiently than plants. This means they can be replenished at a faster rate than the plant matter used for other biofuel biosynthesizers.
The supplements necessary for the growth of Cyanobacteria are CO2, H2O, and light. This presents two advantages:
Because CO2 is derived from the atmosphere,
Cyanobacteria do not need plant matter to synthesize isobutanol (in
other organisms which synthesize isobutanol, plant matter is the source
of the carbon necessary to synthetically assemble isobutanol).
Since plant matter is not used by this method of isobutanol production,
the necessity to source plant matter from food sources and create a
food-fuel price relationship is avoided.
Because CO2 is absorbed from the atmosphere by Cyanobacteria, the possibility of bioremediation (in the form of Cyanobacteria removing excess CO2 from the atmosphere) exists.
The primary drawbacks of cyanobacteria are:
Cyanobacteria are sensitive to environmental conditions when
being grown. Cyanobacteria suffer greatly from light of inappropriate
wavelength and intensity, CO2 of inappropriate concentration, or H2O of inappropriate salinity
though a wealth of cyanobacteria are able to grow in brackish and
marine waters. These factors are generally hard to control, and present a
major obstacle in cyanbacterial production of isobutanol.
Cyanobacteria bioreactors
require high energy to operate. Cultures require constant mixing, and
the harvesting of biosynthetic products is energy intensive. This
reduces the efficiency of isobutanol production via Cyanobacteria.
Blue-green algae
can be re-engineered to increase in butanol production, showing the
importance of ATP and cofactor driving forces as a design principle in
pathway engineering. Many organisms have the capacity to produce butanol
utilizing an acetyl-CoA
dependent pathway. The main problem with this pathway is the first
reaction involving the condensation of two acetyl-CoA molecules to acetoacetyl-CoA. This reaction is thermodynamically unfavorable due to the positive Gibbs free energy associated with it (dG = 6.8 kcal/mol).
Bacillus subtilis
Bacillus subtilis is a gram-positive rod-shaped bacteria. Bacillus subtilis offers many of the same advantages and disadvantages of E. coli, but it is less prominently used and does not produce isobutanol in quantities as large as E. coli. Similar to E. coli, Bacillus subtilis is capable of producing isobutanol from lignocellulose, and is easily manipulated by common genetic techniques. Elementary mode analysis has also been used to improve the isobutanol-synthesis metabolic pathway used by Bacillus subtilis, leading to higher yields of isobutanol being produced.
Saccharomyces cerevisiae
Saccharomyces cerevisiae, or S. cerevisiae, is a species of yeast. S. cerevisiae naturally produces isobutanol in small quantities via its valine biosynthetic pathway. S. cerevisiae is an ideal candidate for isobutanol biofuel production for several reasons:
S. cerevisiae can be grown at low pH levels, helping prevent contamination during growth in industrial bioreactors.
S. cerevisiae cannot be affected by bacteriophages because it is a eukaryote.
Extensive scientific knowledge about S. cerevisiae and its biology already exists.
Overexpression of the enzymes in the valine biosynthetic pathway of S. cerevisiae has been used to improve isobutanol yields. S. cerevisiae, however, has proved difficult to work with because of its inherent biology:
As a eukaryote, S. cerevisiaeis genetically more complex than E. coli or B. subtilis, and is harder to genetically manipulate as a result.
S. cerevisiae has the natural ability to produce ethanol. This natural ability can "overpower" and consequently inhibit isobutanol production by S. cerevisiae.
S. cerevisiae cannot use five carbon sugars to produce isobutanol. The inability to use five-carbon sugars restricts S. cerevisiae from using lignocellulose, and means S. cerevisiae
must use plant matter intended for human consumption to produce
isobutanol. This results in an unfavorable food/fuel price relationship
when isobutanol is produced by S. cerevisiae.
An electric current is run through the anodes, and through an electrochemical process H2O and CO2 are combined to synthesize formic acid.
A culture of Ralstonia eutropha (composed of a strain tolerant to electricity) is kept within the H2O and CO2 mixture.
The culture of Ralstonia eutropha then converts formic acid from the mixture into isobutanol.
The biosynthesized isobutanol is then separated from the mixture, and can be used as a biofuel.
Feedstocks
High
cost of raw material is considered as one of the main obstacles to
commercial production of butanols. Using inexpensive and abundant
feedstocks, e.g., corn stover, can enhance the process economic
viability.
Metabolic engineering can be used to allow an organism to use a cheaper substrate such as glycerol instead of glucose. Because fermentation processes require glucose derived from foods, butanol production can negatively impact food supply. Glycerol is a good alternative source for butanol production. While glucose sources are valuable and limited, glycerol is abundant and has a low market price because it is a waste product of biodiesel production. Butanol production from glycerol is economically viable using metabolic pathways that exist in Clostridium pasteurianum bacterium.
Improving efficiency
A process called cloud point separation could allow the recovery of butanol with high efficiency.
Producers and distribution
DuPont and BP plan to make biobutanol the first product of their joint effort to develop, produce, and market next-generation biofuels. In Europe the Swiss company Butalco
is developing genetically modified yeasts for the production of
biobutanol from cellulosic materials. Gourmet Butanol, a United
States-based company, is developing a process that utilizes fungi to
convert organic waste into biobutanol.
Properties of common fuels
Isobutanol
Isobutanol is a second-generation biofuel with several qualities that resolve issues presented by ethanol.
Isobutanol's properties make it an attractive biofuel:
relatively high energy density, 98% of that of gasoline.
does not readily absorb water from air, preventing the corrosion of engines and pipelines.
can be mixed at any proportion with gasoline, meaning the fuel can "drop into" the existing petroleum infrastructure as a replacement fuel or major additive.
can be produced from plant matter not connected to food supplies, preventing a fuel-price/food-price relationship.
n-Butanol
Butanol
better tolerates water contamination and is less corrosive than ethanol
and more suitable for distribution through existing pipelines for gasoline. In blends with diesel or gasoline, butanol is less likely to separate from this fuel than ethanol if the fuel is contaminated with water. There is also a vapor pressure
co-blend synergy with butanol and gasoline containing ethanol, which
facilitates ethanol blending. This facilitates storage and distribution
of blended fuels.
The octane rating of n-butanol is similar to that of gasoline but lower than that of ethanol and methanol. n-Butanol has a RON (Research Octane number) of 96 and a MON (Motor octane number)
of 78 (with a resulting "(R+M)/2 pump octane number" of 87, as used in
North America) while t-butanol has octane ratings of 105 RON and 89 MON. t-Butanol
is used as an additive in gasoline but cannot be used as a fuel in its
pure form because its relatively high melting point of 25.5 °C (79 °F)
causes it to gel and solidify near room temperature. On the other hand, isobutanol
has a lower melting point than n-butanol and favorable RON of 113 and
MON of 94, and is thus much better suited to high fraction gasoline
blends, blends with n-butanol, or as a standalone fuel.
A fuel with a higher octane rating is less prone to knocking
(extremely rapid and spontaneous combustion by compression) and the
control system of any modern car engine can take advantage of this by
adjusting the ignition timing. This will improve energy efficiency,
leading to a better fuel economy than the comparisons of energy content
different fuels indicate. By increasing the compression ratio, further
gains in fuel economy, power and torque can be achieved. Conversely, a
fuel with lower octane rating is more prone to knocking and will lower
efficiency. Knocking can also cause engine damage. Engines designed to
run on 87 octane will not have any additional power/fuel economy from
being operated with higher octane fuel.
Butanol characteristics: air-fuel ratio, specific energy, viscosity, specific heat
Alcohol
fuels, including butanol and ethanol, are partially oxidized and
therefore need to run at richer mixtures than gasoline. Standard
gasoline engines in cars can adjust the air-fuel ratio to accommodate
variations in the fuel, but only within certain limits depending on
model. If the limit is exceeded by running the engine on pure ethanol or
a gasoline blend with a high percentage of ethanol, the engine will run
lean, something which can critically damage components. Compared to
ethanol, butanol can be mixed in higher ratios with gasoline for use in
existing cars without the need for retrofit as the air-fuel ratio and
energy content are closer to that of gasoline.
Alcohol fuels have less energy per unit weight and unit volume
than gasoline. To make it possible to compare the net energy released
per cycle a measure called the fuels specific energy is sometimes used.
It is defined as the energy released per air fuel ratio. The net energy
released per cycle is higher for butanol than ethanol or methanol and
about 10% higher than for gasoline.
Substance
Kinematic viscosity at 20 °C
Butanol
3.64 cSt
Diesel
>3 cSt
Ethanol
1.52 cSt
Water
1.0 cSt
Methanol
0.64 cSt
Gasoline
0.4–0.8 cSt
The viscosity of alcohols increase with longer carbon chains. For
this reason, butanol is used as an alternative to shorter alcohols when a
more viscous solvent is desired. The kinematic viscosity of butanol is
several times higher than that of gasoline and about as viscous as high
quality diesel fuel.
The fuel in an engine has to be vaporized before it will burn.
Insufficient vaporization is a known problem with alcohol fuels during
cold starts in cold weather. As the heat of vaporization of butanol is
less than half of that of ethanol, an engine running on butanol should
be easier to start in cold weather than one running on ethanol or
methanol.
Butanol fuel mixtures
Standards
for the blending of ethanol and methanol in gasoline exist in many
countries, including the EU, the US, and Brazil. Approximate equivalent
butanol blends can be calculated from the relations between the stoichiometric fuel-air ratio of butanol, ethanol and gasoline. Common ethanol fuel mixtures
for fuel sold as gasoline currently range from 5% to 10%. It is
estimated that around 9.5 gigaliter (Gl) of gasoline can be saved and
about 64.6 Gl of butanol-gasoline blend 16% (Bu16) can potentially be
produced from corn residues in the US, which is equivalent to 11.8% of
total domestic gasoline consumption.
Consumer acceptance may be limited due to the potentially offensive banana-like smell of n-butanol.
Plans are underway to market a fuel that is 85% Ethanol and 15% Butanol
(E85B), so existing E85 internal combustion engines can run on a 100%
renewable fuel that could be made without using any fossil fuels.
Because its longer hydrocarbon chain causes it to be fairly non-polar,
it is more similar to gasoline than it is to ethanol. Butanol has been
demonstrated to work in vehicles designed for use with gasoline without
modification.
Butanol in vehicles
Currently
no production vehicle is known to be approved by the manufacturer for
use with 100% butanol. As of early 2009, only a few vehicles are
approved for even using E85 fuel (i.e. 85% ethanol + 15% gasoline) in
the USA. However, in Brazil all vehicle manufacturers (Fiat, Ford, VW,
GM, Toyota, Honda, Peugeot, Citroen and others) produce "flex-fuel" vehicles
that can run on 100% Gasoline and or any mix of ethanol and gasoline up
to 85% ethanol (E85). These flex fuel cars represent 90% of the sales
of personal vehicles in Brazil, in 2009. BP and Dupont, engaged in a
joint venture to produce and promote butanol fuel, claim that "biobutanol can be blended up to 10%v/v in European gasoline and 11.5%v/v in US gasoline". In the 2009 Petit Le Mans race, the No. 16 Lola B09/86 - Mazda MZR-R of Dyson Racing ran on a mixture of biobutanol and ethanol developed by team technology partner BP.
An octane rating, or octane number, is a standard measure of the performance of an engine or aviation fuel. The higher the octane number, the more compression
the fuel can withstand before detonating (igniting). In broad terms,
fuels with a higher octane rating are used in high-performance gasoline engines that require higher compression ratios. In contrast, fuels with lower octane numbers (but higher cetane numbers) are ideal for diesel engines,
because diesel engines (also referred to as compression-ignition
engines) do not compress the fuel, but rather compress only air and then
inject fuel into the air which was heated by compression. Gasoline
engines rely on ignition of air and fuel compressed together as a mixture, which is ignited at the end of the compression stroke using spark plugs. Therefore, high compressibility of the fuel matters mainly for gasoline engines. Use of gasoline with lower octane numbers may lead to the problem of engine knocking.
Principles
The problem: pre-ignition and knocking
In a normal Otto cycle
spark-ignition engine, the air-fuel mixture is heated as a result of
being compressed and is then triggered by the spark plug to burn
rapidly. During this combustion process, if the unburnt portion of the
fuel in the combustion chamber is heated (or compressed) too much,
pockets of unburnt fuel may self-ignite (detonate) before the main flame
front reaches them. Shockwaves produced by detonation can cause much
higher pressures than engine components are designed for, and can cause a
"knocking" or "pinging" sound. Knocking can cause major engine damage
if severe.
The most typically used engine management systems found in automobiles today have a knock sensor that monitors if knock is being produced by the fuel being used. In modern computer-controlled engines, the ignition timing will be automatically altered by the engine management system to reduce the knock to an acceptable level.
Octanes
are a family of hydrocarbons that are typical components of gasoline.
They are colorless liquids that boil around 125 °C (260 °F). One member
of the octane family, isooctane, is used as a reference standard to
benchmark the tendency of gasoline or LPG fuels to resist self-ignition.
The octane rating of gasoline is measured in a test engine and is defined by comparison with the mixture of 2,2,4-trimethylpentane (iso-octane) and heptane
that would have the same anti-knocking capacity as the fuel under test:
the percentage, by volume, of 2,2,4-trimethylpentane in that mixture is
the octane number of the fuel. For example, gasoline with the same
knocking characteristics as a mixture of 90% iso-octane and 10% heptane
would have an octane rating of 90.
A rating of 90 does not mean that the gasoline contains just iso-octane
and heptane in these proportions, but that it has the same detonation
resistance properties (generally, gasoline sold for common use never
consists solely of iso-octane and heptane; it is a mixture of many
hydrocarbons and often other additives). Because some fuels are more
knock-resistant than pure iso-octane, the definition has been extended
to allow for octane numbers greater than 100.
Octane ratings are not indicators of the energy content of fuels. (See Effects below and Heat of combustion).
They are only a measure of the fuel's tendency to burn in a controlled
manner, rather than exploding in an uncontrolled manner.
Where the octane number is raised by blending in ethanol, energy
content per volume is reduced. Ethanol energy density can be compared
with gasoline in heat-of-combustion tables.
It is possible for a fuel to have a Research Octane Number (RON)
more than 100, because iso-octane is not the most knock-resistant
substance available. Racing fuels, avgas, LPG and alcohol fuels such as methanol may have octane ratings of 110 or significantly higher. Typical "octane booster" gasoline additives include MTBE, ETBE, isooctane and toluene. Lead in the form of tetraethyllead
was once a common additive, but its use for fuels for road vehicles has
been progressively phased-out worldwide, beginning in the 1970s.
Measurement methods
A US gas station pump offering five different (R+M)/2 octane ratings
Research Octane Number (RON)
The most common type of octane rating worldwide is the Research Octane Number (RON). RON is determined by running the fuel in a test engine with a variable compression ratio
under controlled conditions, and comparing the results with those for
mixtures of iso-octane and n-heptane. The Compression ratio is varied
during the test in order to challenge the fuel's antiknocking tendency
as an increase in the compression ratio will increase the chances of
knocking.
Motor Octane Number (MON)
Another type of octane rating, called Motor Octane Number (MON), is determined at 900 rpm engine speed instead of the 600 rpm for RON.
MON testing uses a similar test engine to that used in RON testing,
but with a preheated fuel mixture, higher engine speed, and variable ignition timing
to further stress the fuel's knock resistance. Depending on the
composition of the fuel, the MON of a modern pump gasoline will be about
8 to 12 octane lower than the RON, but there is no direct link between
RON and MON. Pump gasoline specifications typically require both a
minimum RON and a minimum MON.
Anti-Knock Index (AKI) or (R+M)/2
In
most countries in Europe (also in Australia, Pakistan and New Zealand)
the "headline" octane rating shown on the pump is the RON, but in
Canada, the United States, Brazil, and some other countries, the
headline number is the simple mean or average of the RON and the MON,
called the Anti-Knock Index (AKI), and often written on pumps as (R+M)/2.
Difference between RON, MON, and AKI
Because
of the 8 to 12 octane number difference between RON and MON noted
above, the AKI shown in Canada and the United States is 4 to 6 octane
numbers lower than elsewhere in the world for the same fuel. This
difference between RON and MON is known as the fuel's Sensitivity, and is not typically published for those countries that use the Anti-Knock Index labelling system.
See the table in the following section for a comparison.
Observed Road Octane Number (RdON)
Another type of octane rating, called Observed Road Octane Number (RdON),
is derived from testing gasolines in real world multi-cylinder engines,
normally at wide open throttle. It was developed in the 1920s and is
still reliable today. The original testing was done in cars on the road
but as technology developed the testing was moved to chassis
dynamometers with environmental controls to improve consistency.
Octane Index
The
evaluation of the octane number by the two laboratory methods requires a
standard engine, and the test procedure can be both expensive and
time-consuming. The standard engine required for the test may not
always be available, especially in out-of-the-way places or in small or
mobile laboratories. These and other considerations led to the search
for a rapid method for the evaluation of the anti-knock quality of
gasoline. Such methods include FTIR, near infrared on-line analyzers and
others. Deriving an equation that can be used for calculating the
octane quality would also serve the same purpose with added advantages.
The term Octane Index is often used to refer to the calculated octane
quality in contradistinction to the (measured) research or motor octane
numbers. The octane index can be of great service in the blending of
gasoline. Motor gasoline, as marketed, is usually a blend of several
types of refinery grades that are derived from different processes such
as straight-run gasoline, reformate, cracked gasoline etc. These
different grades are considered as one group when blending to meet final
product specifications. Most refiners produce and market more than one
grade of motor gasoline, differing principally in their anti-knock
quality. The ability to predict the octane quality of the blends prior
to blending is essential, something for which the calculated octane
index is specially suited.
Aviation gasoline octane ratings
Aviation gasolines
used in piston aircraft engines common in general aviation have a
slightly different method of measuring the octane of the fuel. Similar
to an AKI, it has two different ratings, although it is referred to only
by the lower of the two. One is referred to as the "aviation lean"
rating and is the same as the MON of the fuel up to 100.
The second is the "aviation rich" rating and corresponds to the octane
rating of a test engine under forced induction operation common in
high-performance and military piston aircraft. This utilizes a
supercharger, and uses a significantly richer fuel/air ratio for
improved detonation resistance.
The most commonly used current fuel, 100LL, has an aviation lean rating of 100 octane, and an aviation rich rating of 130.
Examples
The RON/MON values of n-heptane
and iso-octane are exactly 0 and 100, respectively, by the definition
of octane rating. The following table lists octane ratings for various
other fuels.
"Shell V-Power 98", "Caltex Platinum 98 with Techron", "Esso Mobil Synergy 8000" and "SPC LEVO 98" in Singapore, "BP Ultimate 98/Mobil Synergy 8000" in New Zealand, "SP98" in France, "Super 98" in Belgium, Great Britain, Slovenia and Spain
Higher octane ratings correlate to higher activation energies:
the amount of applied energy required to initiate combustion. Since
higher octane fuels have higher activation energy requirements, it is
less likely that a given compression will cause uncontrolled ignition,
otherwise known as autoignition or detonation.
Because octane is a measured and/or calculated rating of the
fuel's ability to resist autoignition, the higher the octane of the
fuel, the harder that fuel is to ignite and the more heat is required to
ignite it. The result is that a hotter ignition spark is required for
ignition. Creating a hotter spark requires more energy from the ignition
system, which in turn increases the parasitic electrical load on the
engine. The spark also must begin earlier in order to generate
sufficient heat at the proper time for precise ignition. As octane,
ignition spark energy, and the need for precise timing increase, the
engine becomes more difficult to "tune" and keep "in tune". The
resulting sub-optimal spark energy and timing can cause major engine
problems, from a simple "miss" to uncontrolled detonation and
catastrophic engine failure.
The other rarely-discussed reality with high-octane fuels associated with "high performance" is that as octane increases, the specific gravity and energy content of the fuel per unit of weight are reduced. The net result is that to make a given amount of power, more high-octane fuel must be burned in the engine. Lighter and "thinner" fuel also has a lower specific heat,
so the practice of running an engine "rich" to use excess fuel to aid
in cooling requires richer and richer mixtures as octane increases.
Higher-octane, lower-energy-dense "thinner" fuels often contain alcohol compounds incompatible with the stock fuel system components, which also makes them hygroscopic.
They also evaporate away much more easily than heavier, lower-octane
fuel which leads to more accumulated contaminants in the fuel system.
Its typically the hydrochloric acids that form due to that water
and the compounds in the fuel that have the most detrimental effects on
the engine fuel system components, as such acids corrode many metals
used in gasoline fuel systems.
During the compression stroke of an internal combustion engine,
the temperature of the air-fuel mix rises as it is compressed, in
accordance with the ideal gas law.
Higher compression ratios necessarily add parasitic load to the engine,
and are only necessary if the engine is being specifically designed to
run on high-octane fuel. Aircraft engines run at relatively low speeds
and are "undersquare".
They run best on lower-octane, slower-burning fuels that require less
heat and a lower compression ratio for optimum vaporization and uniform
fuel-air mixing, with the ignition spark coming as late as possible in
order to extend the production of cylinder pressure and torque as far
down the power stroke as possible. The main reason for using high-octane
fuel in air-cooled engines is that it is more easily vaporized in a
cold carburetor and engine and absorbs less intake air heat which
greatly reduces the tendency for carburetor icing to occur.
With their reduced densities and weight per volume of fuel, the
other obvious benefit is that an aircraft with any given volume of fuel
in the tanks is automatically lighter. And since many airplanes are
flown only occasionally and may sit unused for weeks or months, the
lighter fuels tend to evaporate away and leave behind fewer deposits
such as "varnish". Aircraft also typically have dual "redundant"
ignition systems which are nearly impossible to tune and time to produce
identical ignition timing so using a lighter fuel that's less prone to
autoignition is a wise "insurance policy". For the same reasons, those
lighter fuels which are better solvents are much less likely to cause
any "varnish" or other fouling on the "backup" spark plugs.
Because of the high cost of unleaded, high-octane avgas,
and possible increased range before refueling, some general aviation
pilots attempt to save money by tuning their fuel-air mixtures and
ignition timing to run "lean of peak". Additionally, the decreased air
density at higher altitudes (such as Colorado) and temperatures (as in
summer) requires leaning (reduction in amount of fuel per volume or mass
of air) for the most power (crucial for takeoff). In almost all general
aviation piston engines, the fuel mixture is directly controlled by the
pilot, via a knob and cable or lever similar to (and next to) the throttle control. Leaning must be done carefully, as some combinations of fuel mixture and throttle position (that produce the highest EGT)
can cause detonation and/or pre-ignition, in the worst case destroying
the engine within seconds. Pilots are taught in primary training to
avoid settings that produce the highest exhaust gas temperatures, and
run the engine either "rich of peak" (more fuel than can be burned with
the available air) or "lean of peak" (less fuel, leaving some oxygen in
the exhaust) as either will keep the fuel-air mixture from detonating
prematurely.
Regional variations
The selection of octane ratings available at the pump can vary greatly from region to region.
Australia: "regular" unleaded
fuel is 91 RON, "premium" unleaded with 95 RON is widely available, and
98 RON fuel is also reasonably common. Shell used to sell 100 RON fuel
(5% ethanol content) from a small number of service stations, most of
which are located in major cities (stopped in August 2008). United
Petroleum used to sell 100 RON unleaded fuel (10% ethanol content) at a
small number of its service stations (originally only two, but then
expanded to 67 outlets nationwide) (stopped in September 2014).
All fuel in Australia is unleaded except for some aviation fuels. E85
unleaded fuel is also available at several United service stations
across the country. Recently E10 fuel has become quite common, and is available at almost every major fuel station. The Australian government makes stations advertise E10 as 94 RON.
Bahrain: 91 and 95 (RON), standard in all gasoline stations in the
country and advertised as (Jayyid) for Regular or 91 and (Mumtaz) for
Premium or 95 and 98 (RON) as super.
Bangladesh: Two types of fuel are available at petrol stations in
Bangladesh. Motor Gasoline Regular (marketed as "Petrol") which has RON
80 rating, and Motor Gasoline Premium (marketed as "Octane") which has
RON 95 rating.
Petrol stations in Bangladesh are privatised, but the prices are
regulated by the authorities and have a fixed price at BDT 86.00 (USD
1.04) and BDT 89.00 (USD 1.07) (as of 1 March 2018) per litre
respectively.
Brazil: As defined by federal law, the AKI standard is used and all
types of gasoline sold in all gas stations throughout the country are
unleaded (the latter since 1991). By default, it was defined by the
federal government that the regular (and the lowest) octane standard in
Brazil is 87 AKI, known in Portuguese as Gasolina Comum (English: "Common Gasoline") - Petrobras stations brand it as Gasolina Regular (English: "Regular Gasoline").
This type of gasoline can be found in most Brazilian petrol stations
and does not have any additives, except the inclusion of 25% of ethanol
(as required by the Brazilian National Agency of Petroleum, Natural Gas and Biofuels - Portuguese: Agência Nacional do Petróleo, Gás Natural e Biocombustíveis or simply ANP - since 2011).
Along with the "Common" gasoline, there is a second type of gasoline
that can also be found in most stations in Brazil. This gasoline is also
mixed with 25% of ethanol (to comply with the ANP regulation, that
prohibits the sale of the 100% "pure gasoline" compound in all Brazilian
stations),
but a few detergent and dispersant additives are also included in the
compound. This type of gasoline is known in Portuguese as Gasolina Aditivada (English: "Additived Gasoline") - Petrobras stations brand it as "Petrobras Grid";
nevertheless, the octane rating is also 87 AKI (these additives are
used to improve the performance and efficiency of the engine, but they
are not indicative of a higher octane rating). However, higher octane
levels of gasoline are found in many stations (all stations in Brazil,
regardless of the octane rating, have to conform the ANP requirement of
25% of ethanol mixed with the gasoline, and both "Common" and "Additived" gasolines can also be found in most of these stations), such as the "Premium Gasoline" (known in Portuguese as Gasolina Premium - 91 AKI), the "OctaPro" (96 AKI), sold at Ipiranga stations, and the "Petrobras Podium" (97 AKI), sold at Petrobras stations.
China: 92 and 95 (RON) (previously 93 and 97)
are commonly offered. In limited areas higher rating such as 98 RON is
available. In some rural areas it can be difficult to find fuel with
over 92 RON.
Chile: 93, 95 and 97 RON are standard at almost all gas stations thorough Chile. The three types are unleaded.
Colombia: "Ecopetrol", Colombia's monopoly of refining and
distribution of gasoline establishes a minimum AKI of 81 octanes for
"Corriente" gasoline and minimum AKI of 87 octanes for "Extra" gasoline. (91.5 RON corriente, and 91 RON for extra)
Costa Rica: RECOPE, Costa Rica's distribution monopoly, establishes
the following ratings: Plus 91 (at least 91 RON) and Super (at least 95
RON).
Croatia: All fuel stations offer unleaded "Eurosuper BS"
(abbreviation "BS" meaning "no sulfur content") 95 RON fuel, many also
offer "Eurosuper Plus BS" 98 RON. Some companies offer 100 RON fuel instead of 98.
Cyprus: All fuel stations offer unleaded 95 and 98 RON and a few offer 100 RON as well.
Denmark: 95 RON is a common choice, with 92 and 95 being widely
available. However several fuel stations are phasing out 92 RON. By law,
it is decided that all gasoline companies from July 2010 should use a
mix containing 5% bioethanol in the gasoline.
Ecuador: "Extra" with 87 and "Super" with 92 (RON) are available in
all fuel stations. "Extra" is the most commonly used. All fuels are
unleaded.
Egypt: Egyptian fuel stations had 90 RON until July 2014 when the
government found no remaining use for it, leaving only 92 RON and 95
RON. 80 RON is found in a very limited amount of fuel stations as they
are used only for extremely old cars that cannot cope with high octane
fuel. 95 RON was used limitedly due to its high price (more than twice
the price of 92 RON). But after the increasing the prices again in 2018, 95 RON price became only 15% higher than 92 RON, so it started to gain popularity.
Estonia: 95 RON and 98 RON are widely available.
Finland: 95 and 98 (RON), advertised as such, at almost all gas
stations. Most cars run on 95, but 98 is available for vehicles that
need higher octane fuel, or older models containing parts easily damaged
by high ethanol content. Shell offers V-Power, advertised as "over 99
octane", instead of 98. In the beginning of 2011 95 RON was replaced by
95E10 containing 10% ethanol, and 98 RON by 98E5, containing 5% ethanol.
ST1 also offers RE85 on some stations, which is 85% ethanol made from biodegradable waste (from which the advertised name "ReFuel" comes). RE85 is only suitable for flexifuel cars that can run on high-percentage ethanol.
Germany: "Super E10" 95 RON and "Super Plus E5" 98 RON are available practically everywhere. Big suppliers such as Shell or Aral offer 100 RON gasoline (Shell V-Power,
Aral Ultimate) at almost every fuel station. "Normal" 91 RON is only
rarely offered because lower production amounts make it more expensive
than "Super" 95 RON. Due to a new European Union law, gas stations are
being required to offer a minimum rate of the new mixture of "Super" 95
RON with up to 10% Ethanol branded as "Super E10". Producers are discontinuing "Super E5" 95 RON with <5 98="" are="" automotive="" cars="" e10="" ethanol="" fuel="" gasoline="" instead.="" must="" ron="" so="" span="" that="" to="" unable="" use="">
Greece (Hellas): 95 RON (standard unleaded), 97+ & 100 RON
unleaded offered by some companies (e.g. EKO, Shell, BP). Also available
Super LRP 96 RON for older (non-catalytic) vehicles.
Hong Kong: only 98 RON is available in the market. There have been
calls to re-introduce 95 RON, but the calls have been rejected by all
automotive fuel station chains, citing that 95 RON was phased out
because of market forces.
India: India's ordinary and premium petrol options are of 91 RON.
The premium petrols are generally ordinary fuels with additives, that do
not really change the octane value. Two variants, "Speed 93" and "Speed
97", were launched, with RON values of 93 and 97. Recently, Hindustan
Petroleum launched poWer 99 with an RON value of 99 which is currently
available only in Bangalore, Pune and now in Mumbai but expected to roll
out in other major cities soon.
India's economy-class vehicles usually have compression ratios under
10:1, thus enabling them to use lower-octane petrol without engine
knocking.
Indonesia: Indonesia's "Premium" gasoline rated at 88 RON. Other
options are "Pertalite", rated at 90 RON, "Pertamax", rated at 92 RON
and the "Pertamax Plus" rated at 95 RON, and "Pertamax Racing", a 100
RON fuel sold in few stations. Starting from August 2016 Pertamina has
started selling a new fuel variant rated at 98 RON marketed by the name
of Pertamax Turbo, serving as a replacement for Pertamax Plus. Total and
Shell stations only sell RON 92 and 95 gasoline. However, in early
2018, Shell launched a new variant "Regular", rated at 90 RON and
currently sold at certain locations. Petronas has decided to shut down
its retail business in Indonesia in 2012, after years of sluggish sales.
Iran: 92 RON (marketed as regular) and 95 RON (marketed as Super) are widely available in gas stations.
Ireland: 95 RON "unleaded" is the only gasoline type available
through stations, although E5 (99 RON) is becoming more commonplace.
Italy: 95 RON is the only compulsory gasoline offered (verde,
"green"), only a few fuel stations (Agip, IP, IES, OMV) offer 98 RON as
the premium type, many Shell and Tamoil stations close to the cities
offer also V-Power Gasoline rated at 100 RON. Recently Agip introduced
"Blu Super+", a 100 RON gasoline.
Israel: 95 RON & 98 RON are normally available at most
automotive fuel stations. 96 RON is also available at a large number of
gas stations but 95 RON is more preferred because it's cheaper and
performance differences aren't very wide and noticeable. "Regular" fuel
is 95 RON. All variants are unleaded.
Japan: Since 1986, "regular" is >=89 RON, and "high octane" is
>=96 RON, lead free. Those values are defined in standard JIS K 2202.
Sometimes "high octane" is sold under different names, such as "F-1".
Latvia: 95 RON and 98 RON widely available.
Lebanon: 95 RON and 98 RON are widely available.
Lithuania: 95 RON and 98 RON widely available. In some gas stations
E85 (bioethanol) gasoline, 98E15 (15% of ethanol), 98E25 (25% of
ethanol) are available.
Malaysia: 95 RON, 97 RON and 100 RON. "Regular" unleaded fuel is
95 RON; "Premium" fuel is rated at 97 RON (Shell's V-Power Racing is
rated 100 RON). Petron sells 100 RON in selected outlets.
Mexico: The standard octane index is 87 AKI for "regular" fuel and
92 AKI for "high octane" fuel. From 1938 to 2018, the Mexican government
held a monopoly in the distribution of fuel, and its brands for
unleaded fuel were "Pemex Magna" and "Pemex Premium". Mexican
regulations do not enforce any particular labels to identify different
grades of fuel,
but the established convention is to label "regular" fuel with green,
"high octane" fuel with red, and diesel with black. Shell sells its
"V-Power" high octane fuel labeled yellow.
Mongolia: 92 RON and 95 RON (advertised as A92 and A95 respectively)
are available at nearly all stations while slightly fewer stations
offer 80 RON (advertised as A80). 98 RON (advertised as A98) is
available in select few stations.
Montenegro: 95 RON is sold as a "regular" fuel. As a "premium" fuel, 98 RON is sold. Both variants are unleaded.
Myanmar: Most petrol stations carry 92 RON as standard especially in
rural areas. Most larger cities and highway stations have introduced 95
RON in the past few years. The highest grade available is 97 RON which
is only sold by a few stations in Yangon and Nay Pyi Taw (e.g., PTT,
MMTM, Petrotrans).
Netherlands: 95 RON "Euro" is sold at every station, whereas 98 RON
"Super Plus" is being phased out in favor of "premium" fuels, which are
all 95 RON fuels with extra additives. Shell V-Power is a 97 RON
(labelled as 95 due to the legalities of only using 95 or 98 labelling),
some independent tests have shown that one year after introduction it was downgraded to 95 RON, whereas in neighboring Germany Shell V-Power consists of the regular 100 RON fuel.
New Zealand: 91 RON "Regular" and 95 RON "Premium" are both widely
available. 98 RON is available instead of 95 RON at some (BP, Mobil,
Gull) service stations in larger urban areas. 100 RON is available at
selected NPD service stations in the South Island.
Norway: 95 RON are widely available, but 98 RON is also available at Shell; it is 10-20% more expensive as 95 RON fuel. Statoil has discontinued production and sale due to low demand.
Pakistan: 3 types of fuel available. 92, HOBC 95 & HOBC 97 RON.
Super marketed as 92 RON, 95 RON marketed by Shell as V-Power and 97 RON
by Total Parco Pakistan & Pakistan State Oil (PSO). Due to
proximity to Iran, low quality of fuel is often mixed by pump owners
with Super & HOBC products in southern regions of Pakistan. It is
openly available throughout the province of Balochistan as it is 30-40%
cheaper than govt. issued pricing for Super. HOBC pricing was
deregulated in October, 2016.
Philippines: A brand of Petron, Petron Blaze is rated at 100 RON (the only brand of gasoline in the Philippines without an ethanol
blend). Other "super premium" brands like Petron XCS, Caltex Gold,
Shell V-Power are rated at 95-97 RON, while Petron Xtra Unleaded, Caltex
Silver, and Shell Super Unleaded are rated at 93 RON.
Poland: Eurosuper 95 (RON 95) is sold in every gas station. Super
Plus 98 (RON 98) is available in most stations, sometimes under brand
(Orlen - Verva, BP - Ultimate, Shell - V-Power) and usually containing
additives. Shell offers V-Power Racing fuel which is rated RON 100.
Portugal: 95 RON "Euro" is sold in every station and 98 RON "Super" being offered in almost every station.
Russia and CIS
countries: 92 RON is the minimum available, the standard is 95 RON is
sold in every gas station. 98 RON is available in most stations. As a
"premium" fuel, 100 RON is sold, Gazpromneft and Lukoil both variants
are unleaded.
Saudi Arabia: Two types of fuel are available at all petrol stations
in Saudi Arabia. "Premium 91" (RON 91) where the pumps and liquid (look
fuel dyes)
are coloured green, and "Super Premium 95" (RON 95) where the pumps and
liquid are coloured red. While petrol stations in Saudi Arabia are
privatised, the prices are regulated by the authorities and have a fixed
at SR
1.44 (USD 0.38) and SR 2.10 (USD 0.56) (as of 14 April 2019) per litre
respectively; and is currently being increased at an quarterly rate to
bring it up to the worldwide average by 2020. Prior to 2006, only Super
Premium RON 95 was available and the pumps weren't coloured in any
specific order. The public didn't know what Octane rating was, therefore
big educating campaigns were spread, telling the people to use the "red
petrol" only for high end cars, and save money on using the "green
petrol" for regular cars and trucks.
Singapore: All four providers, Caltex, ExxonMobil, SPC and Shell have 3 grades of gasoline. Typically, these are 92, 95, and 98 RON. However, since 2009, Shell has removed 92 RON.
South Africa: "regular" unleaded fuel is 95 RON in coastal areas.
Inland (higher elevation) "regular" unleaded fuel is 93 RON; once again
most fuel stations optionally offer 95 RON.
South Korea: "regular" unleaded fuel is 91~94 RON, "premium" is 95+
RON nationally. However, not all gas stations carry "premium."
Spain: 95 RON "Euro" is sold in every station with 98 RON "Super"
being offered in most stations. Many stations around cities and highways
offer other high-octane "premium" brands.
Sri Lanka: In Ceypetco filling stations, 92 RON is the regular automotive fuel and 95 RON is called 'Super Petrol',
which comes at a premium price. In LIOC filling stations, 90 RON
remains as regular automotive fuel and 92 RON is available as 'Premium
Petrol'. The cost of premium gasoline is lower than the cost of super
gasoline. (Sri Lanka switched their regular gasoline from 90 RON to 92
RON on January 1, 2014)
Sweden: 95 RON, 98 RON and E85 are widely available.
Taiwan: 92 RON, 95 RON and 98 RON are widely available at gas stations in Taiwan.
Thailand: 91 RON and 95 RON are widely available. 91 RON automotive
fuel withdrawn on January 1, 2013 to increase uptake of gasohol fuels.
Trinidad and Tobago: 92 RON (Super) and 95 RON (Premium) are widely available.
Turkey: 95 RON and 95+ RON widely available in gas stations. 91 RON
(Regular) has been dropped in 2006. 98 and 100 RON (Shell V-Power
Racing) has been dropped in late 2009. The Gas which has been advertised
97 RON has been dropped in 2014 and renamed 95+.
Ukraine: 80 RON gasoline is available, the standard gasoline is 92
RON, but 95 RON gasoline is also widely available and popular.
United Kingdom: 'regular' gasoline has an octane rating of 95 RON, with 97 RON fuel being widely available as the Super Unleaded. Tesco and Shell both offer 99 RON fuel. In April 2006, BP started a public trial of the super-high octanegasolineBP Ultimate Unleaded 102, which as the name suggests, has an octane rating of 102 RON.
Although BP Ultimate Unleaded (with an octane rating of 97 RON) and BP
Ultimate Diesel are both widely available throughout the UK, BP Ultimate
Unleaded 102 was available throughout the UK in only 10 filling
stations, and was priced at about two and half times more than their 97
RON fuel. In March 2010, BP stopped sales of Ultimate Unleaded 102,
citing the closure of their specialty fuels manufacturing facility. Shell V-Power is also available, but in a 99 RON octane rating, and Tesco fuel stations also supply the Greenergy produced 99 RON "Momentum99".
United States: in the US octane rating is displayed in AKI. In most
areas, the standard grades are 87, 89-90 and 91-94 AKI. In the Rocky
Mountain (high elevation) states, 85 AKI (90 RON) is the minimum octane,
and 91 AKI (95 RON) is the maximum octane available in fuel. The reason for this is that in higher-elevation areas, a typical naturally aspirated engine
draws in less air mass per cycle because of the reduced density of the
atmosphere. This directly translates to less fuel and reduced absolute
compression in the cylinder, therefore deterring knock. It is safe to
fill a carbureted car that normally takes 87 AKI fuel at sea level with
85 AKI fuel in the mountains, but at sea level the fuel may cause damage
to the engine. However, since virtually all cars produced since the
1990s have fuel injection, 85 AKI fuel is not recommended for modern automobiles and may cause damage to the engine and decreased performance.
Another disadvantage to this strategy is that most turbocharged
vehicles are unable to produce full power, even when using the "premium"
91 AKI fuel. In some east coast states, up to 94 AKI (98 RON) is
available. As of January 2011, over 40 states and a total of over 2500 stations offer ethanol-based E-85 fuel with 94-96 AKI. Often, filling stations near US racing tracks will offer higher octane levels such as 100 AKI .
Venezuela: 91 RON and 95 RON gasoline is available nationwide, in
all PDV gas stations. 95 RON gasoline is the most widely used in the
country, although most cars in Venezuela would work with 91 RON
gasoline. This is because gasoline prices are heavily subsidized by the
government (0.$083 per gallon 95 RON, vs 0.$061 per gallon 91 RON). All
gasoline in Venezuela is unleaded.
Vietnam: 92 is in every gas station and 95 is in the urban area.
They start selling A92-E5 gasoline (A92 with 5 percent of Ethanol) at
2017. On January 1, 2018, Vietnamese gorvernment forced every gas
station stop selling 92 and sell 95 + A92-E5 instead.
Zimbabwe: 93 octane available with no other grades of fuels
available, E10 which is an ethanol blend of fuel at 10% ethanol is
available the octane rating however is still to be tested and confirmed
but it is assumed that its around 95 Octane. E85 available from 3
outlets with an octane rating AKI index of between 102-105 depending on
the base gasoline the ethanol is blended with.
