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Fuels With High Octane Number

Updated on October 22, 2011

The quality of a fuel is measured with its 'octane number'. A good quality fuel has a good octane number.

Octane number measures whether petrol is likely to cause knock in an engine. Knocking is caused by self-ignition in the engine's cylinders, which happens when the petrol/air-vapour mixture in the cylinder ignites before the plug sparks. This premature ignition pushes against the crankshaft instead of being with it, and produces a knocking or pinging sound. Knocking causes the engine to overheat and lose power, and it can damage the engine in the long run.

Octane number is measured as Research Octane Number (RON) and Motor Octane Number (MON). The RON correlates best with low speed and mild-knocking conditions. Every engine is designed in order to operate the best performance using a certain octane rating. For example, many Japanese cars are designed to run on 90 RON. However, the new engines developed to achieve greater fuel economy which requires higher-octane petrol but European studies suggest 95 RON petrol for high efficiency in engines. This measure provides a balance between fuel consumption by improving fuel performance and minimises the extra cost associated with production of high octane petrol. The octane requirement of vehicles also increases with age. Thus, using a fuel of octane which is higher than the required, does not improve the engine performance, but only costs more.

In addition, there are many possibilities for refineries to increase the octane number of the petrol pool. The refinery processes are employed for converting low octane components into higher octane ones by chemical reaction. To assist the production of greater quantities of premium (high octane) petrol the enhancers are used. There have also been noticed that the use of chemical additives and products to boost octane in petrol presents a number of issues, in particular potential impacts on public health and environment.

Tetra ethyl lead

The leaded gasoline was introduced in the market by Charles F. Kettering in 1923-24. The discovery of the anti-knock effect of tetraethyl lead in gasoline is ranked among the most celebrated achievements of automotive engineering in the 20th century. The introduction of lead provided an approach for development of engines with the higher compression ratios and better mileage. The leaded gasoline allowed increase in engine power and efficiency by raising fuel anti-knock quality. The first product marketed in 1923 was concentrated "Ethyl fluid" blended by pouring the concentrate by hand into the glass container at the service station pump. The lead based additives quickly became the universal octane enhancer. However, during the 1970s the research identified motor vehicles as a major source of urban air pollution.

The prime technology to reduce emissions from motor vehicles was the introduction of catalytic converters. Because the catalysts were irrevocably damaged by lead developed countries especially US introduced unleaded petrol. It was also recognised that lead poses a significant health risk. The lead emissions from motor vehicles contribute significant quantities of airborne lead in the ambient air near highways. These issues resulted in international movement to be away from leaded petrol.


It is a clean burning fuel and used as a high octane fuel in its own right. Its use is permitted under the US EPA rules for the production of reformulated gasoline (RFG). The main driver for the use of methanol is that it is made from natural gas and is easily transported as a liquid. Due to its high vapour pressure, it evaporates quickly from spills.

Vehicles fuelled by methanol are specifically made for this purpose as the use of methanol in general vehicle fleet damage to vehicles because this also acts as a solvent and corrodes metals high in the electrochemical series like zinc, aluminium and titanium. Any component containing these elements is attacked by methanol. Due to these concerns, experts recommend not to use methanol as alternative fuel in general vehicle fleet.

Methyl tertiary-butyl ether

It is the principle oxygenate and octane enhancer used by refineries worldwide due to its compatible blending properties and lower cost. It is oxygen-bearing additive used to reduce engine knocking and assist gasoline burn more cleanly. The world production capacity of MTBE is 21 Mt per annum, with a further seven Mt per annum of capacity in construction or in planning. It is widely used in Europe, US and the Far East.

The US Clean Air Act Amendments introduced in 1990, to attempt to reduce air pollution from the transport fleet by mandating the specifications of gasoline called ‘reformulated gasoline' (RFG). Among other things, this act managed the oxygen content of gasoline at two per cent in areas with severe air pollution. The MTBE addition to gasoline at approximately 10-15 per cent was able to assist in meeting this specification. This resulted in an enormous increase in demand for the product.

After the introduction of RFG, MTBE was started to be detected in ground water in several US states. The primary source of contamination was leaks or drainage from underground gasoline storage tanks and the pipes. Surface water was also contaminated through older recreational watercraft operating on lakes and waterways. However, majority of MTBE water contamination in the US was detected below the levels for the public health concern. The MTBE is detected by taste and odour at extremely low levels, at about less than 20 parts per billion (ppb).

Hence, the US EPA appointed the Blue Ribbon Panel in November 1998 to investigate air and water quality issues related to the use of MTBE. The final report was issued in September 1999, with the following pertinent recommendations:

1. MTBE should be substantially fazed out of gasoline in the US.

2. In order to facilitate the fazed out, the two per cent limit on oxygenate level in RFG should be waived.

MTBE was declared as "an environmental risk to California" in March 1999 on the basis of assessment performed by University of California. This activity is continued in the US with the US Executive promoting bills in Congress that would lead to MTBE fazed out nationally.


It has a long history of use as a petrol extender, octane enhancer and as alternative fuel. The normal practice in US is the use of about 10 per cent ethanol as an extender to the petrol (E10 blends). The momentum for using ethanol has been helped by the fact that it is produced from a wide variety of agricultural sources. It can be considered a renewable fuel when produced from these sources and there is a potential for greenhouse gas emissions abatement.

With the likely faze out of MTBE in the US, ethanol usage in petrol there is likely to become more widespread. There is also growing support for the use of ethanol in petrol from the sugar industry. The ethanol produced from biomass currently has an excise free status in Australia (equivalent to a tax benefit of about 38 cents/litre). Without this status, ethanol would probably be uncompetitive against low cost crude oil products and other chemical octane enhancers.

By the means of expected increase in ethanol use in the US, due to the anticipated MTBE faze out, there has been concern expressed about water supplies being contaminated by ethanol from petrol as it is also completely miscible with water. However, similar conclusions are likely to be expressed in relation to all octane enhancing products if they were widely used. The US study reports at 10 per cent ethanol by volume added to conventional gasoline results in statistically significant decreases in emissions of CO (13 per cent), Volatile Organic Compounds (six per cent) and benzene (11 per cent), and increases in NOX (five per cent) and acetaldehyde (159 per cent) as well as increases in evaporative emissions.

There are some concerns about ethanol's tendency to evaporate more readily than other fuel components. Ethanol is known to have developmental and neurotoxin effects, but the risk at the levels anticipated in the environment from its use as a fuel additive is unclear.

The use of ethanol at higher concentrations (>20 per cent) had detrimental effects on paints and finishes of some vehicles. The addition of ethanol to petrol blends must be carefully managed so that Vapour Pressure limits must not exceed. The refiners have outlined their concerns that ethanol may be inadequate for lifting Motor Octane Number (MON) while still maintaining final petrol specification. MMT (Methylcyclopentadienyl manganese tricarbonyl):

It is in widespread use overseas in both unleaded and lead replacement petrol, it is also permitted in Canada and the US, Europe, Asia, and Central and South America. MMT is the lowest cost alternative additive to the refiner; however, MMT use reduces vehicle mileage by two per cent. In addition, MMT use may raise the cost of vehicle maintenance. Manganese compounds are also known to be neurotoxins, though, the impact of low- level long-term exposure by inhalation is yet not known. The emissions of ultra-fine particulate manganese oxides also represent a health issue.

MMT has been used in Canadian petrol since 1976. In Canada, trade in MMT was restricted under the Manganese-based Fuel Additives Act- June 1997, which was based on representations by the Canadian automobile industry. The automobile industry maintained that MMT adversely affected automobile on-board diagnostic systems (OBDs). A malfunctioning OBD could fail to detect that a car is emitting higher levels of pollutants into the air. Bane was lifted in July 1998 after the report from independent panel.

In 1977, the MMT was prohibited in USA from being used in unleaded petrol. The Ethyl Corporation applied to the US EPA in 1977, 1981 and 1992 for MMT to be allowed to use in unleaded gasoline. These requests were all denied on the basis that MMT increased hydrocarbon emissions and blocked catalytic converters. However, later in November 1993, US EPA on the basis of extensive data submitted by Ethyl Corporation concluded that MMT did not contribute significantly to increases in hydrocarbon emissions or failure of catalysts.

In July 1994, the US EPA announced that it would deny Ethyl Corporation's waiver application on the grounds that there remained unresolved concerns regarding the health impact of manganese emissions produced by MMT in petrol. The literature review and analysis reports suggest that MMT oxidises were very quick in ambient air to manganese oxides. It is reported that MMT undergoes rapid photolysis in sunlight, with a half life of less than two minutes. The US EPA is also investigating to determine whether or not manganese can have any cumulative effect similar to that of lead by building up in the bloodstream.

The principle objective for the use of octane enhancers in petrol in is to ensure that they don't have adverse impacts on public health or even the environment, and that their use doesn't impede the adoption of emerging vehicle engine and emission control technologies. An assessment of the additives and products that are used to increase octane in petrol is necessary before they are adopted. The provision of fuel that facilitate the adoption of emerging vehicle engine and emission control technologies is a key strategy in managing air pollution and greenhouse gas emissions.


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    • profile image

      Labanu 8 years ago

      Thank u for your article. It's so helping me to make my task

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      sam Woodcock 8 years ago

      Thank you, very informative. I suspected that octane enhancers with mmt, after going through an engine would not be so bad for the environment if they improve engine performance and mileage and they have a rapid atmospheric photochemical degradation, is this the case?

    • profile image

      Revo Remapping 5 years ago

      Only just come across this article.

      Very interesting points which I have never considered before. Thank you for this. I have learn't a lot of things I can now implement.

    • profile image

      Lina 5 years ago

      thank you for these amazing data, and please help!

      I know based on my researches that the best octane Boosters are MTBE, MMT and Naphtha, either alone or mixed with alcohol, but what is the best octane booster? MTBE, MMT or Naphtha? If for sure used in the best way, which means for example MTBE with 10% ethanol, and MMT with the safest manganese level and Naphtha with 10% Ethanol, or each of those three with 1%Toluene?

    • profile image

      bestco 5 years ago

      i found this article extremely useful,am glad i came across it

    • profile image 5 years ago

      Mr. Hassam, your article above has many errors and you seem to get the whole concept wrong. For example: 1) "A good quality fuel has a good octane number.". Octane is NOT a measure of fuel quality but the "resistance" to premature combustion.

      Further on, there are more errors might be due to your poor command of English. Too many to mention. Please read from the following website for accurate description on this subject. Thank you.

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      M.Patel 5 years ago

      I want to make Ethanol fuel in Indian but could not the find the proper receipt.Could anyone tell me how to make ethanol from sugarcane.what would the the still temperature,how to remove water from the ethanol etc.How much yeast is required in 5L sugarcane juice etc.



    • profile image

      Iloh Wisdom Chiedu 5 years ago

      My thanks goes to the writer of this article.I must say it has realy helped me a lot.Once again THANK YOU.

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      Prasad patil 5 years ago

      But cetane noa can be increased by addition tTEL TML

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      solomon 5 years ago

      i want to present a research proposal on gasoline with ethanol blend(e-10)automobiles occurring major problems around the engine. in Ethiopia(addis ababa). would you help me how to prepare and to write the proposal please?

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