Gasoline Blends

[mts]

GASOLINE BLENDS

 

 

The disruption of oil supplies from the Middle East in the 70's spurred an effort to try to curb the U.S. dependence on foreign petroleum sources. Interest in alternative fuels was also created by the reduction or elimination of lead anti-knock additives in gasoline. The lead was removed because of its incompatibility with the catalytic converter, now standard on almost every car and light truck.

 

Ethanol

Ethanol has attracted the most attention as a blend. It can be fermented from a variety of bases, including grain and sugar cane, much the same way wine is produced from grapes. The U.S. Environmental Protection Agency (EPA) allows a 10% ethanol mixture with gasoline and it is being sold as "super unleaded" or "premium unleaded" gasoline, gasohol, or with no specific identification.

 

Methanol

Methanol comes from natural gas, but the technology can produce it from coal, wood and a variety of other materials. Like ethanol, methanol raises the octane of gasoline and reduces engine "knock" or "ping", without affecting the efficiency of the catalytic converter. A 5% blend of methanol may raise the octane rating at the pump by 1–1.5 numbers.

 

Methanol also reduces carbon monoxide exhaust emissions, but the trade-off can be high:

• Methanol has an adverse effect on fuel economy, especially in late model vehicles. A 5% blend of methanol with gasoline has an energy content 2.5% less than gasoline.
• Evaporative emissions rise substantially when methanol is blended with gasoline. In addition, methanol may increase the oxides of nitrogen emissions and affect the capacity of the charcoal in the evaporative emissions canister.
• Methanol causes both hot and cold weather driveabiity problems. Methanol can change the stoichiometric (chemically correct) air/fuel ratio in the fuel delivery system. The higher volatility of the fuel increases the chance of vapor lock in carbureted vehicles and the increased heat of vaporization of methanol increases cold start and stalling problems in winter.
• Methanol, when water is present even in trace (minute) amounts will separate gasoline into 2 layers — gasoline rich on top and *This reference banned by MW* and water on the bottom. The net effect is unsatisfactory vehicle operation. Since the engine draws fuel from the bottom of the tank, it will not run properly, even at idle. Some refiners add heavier *This reference banned by MW*, known as "cosolvents", to counter the separation, but they are not 100% effective.
• Methanol has an effect on the parts of the fuel system and is measured more in time than in mileage. Rubber, plastic and metal fuel system components in most motor vehicles were designed for use with gasoline and are subject to attack by methanol blended fuels. Water tends to cling to methanol, and any water in the fuel tank will be carried through the entire fuel system. Metal components (excluding brass) are subject to water corrosion. Plastic and rubber compounds tend to swell, lose strength and stretch when subjected to high concentrations of methanol.

Several fuel suppliers are successfully marketing blends of methanol and cosolvents with gasoline, but the long-term effects on engines and fuel systems are not known and vehicle manufacturers will not give unqualified sanction to the use of methanol blended fuels. Check your owner's manual to be sure.

 

Reformulated Gasoline

The Environmental Protection Agency (EPA), through the Clean Air Act, has mandated the use of reformulated gasoline in certain areas of the country from January 1, 1995.

 

Reformulated (RFP), is gasoline that the composition has been changed to reduce vehicle emissions. Reformulated gasoline has lower levels of volatile compounds and benzene. RFP also contains an oxygenate such as ether or ethanol.

 

Any oxygenated fuel will reduce fuel economy, this is true simply because it has less combustible material per gallon. But, because of the reduction of volatile compounds, vehicles which are in poor mechanical condition may alos experience an increased hesitation after start-up. Reformulated gasoline differs from oxygenated fuel in that it is intended for year round use with reduced emissions, whereas oxygenated fuels are designed to reduce carbon monoxide levels during the winter season.

[Seldomseen]

I just use the highest grade premium I can find...which is usually 91 up to 93.

[ing-schu@online.no]

Good info, but there is very significant information missing. The contence of a*l*c*o*hol*s in mixed a*l*c*o*hol*/gas fuels does not mix (emulgate) with the engine oil , which means it will cause trouble unless oil is changed at least twice as often. But I guess it could prevent the manufacturers from prescribing moneysaving (for them), lifeshortening (for the engine) longlife oils and extended oilchange intervals, always something.

[Seldomseen]

That nasty engine pinging, and knocking ain't nothing nice when a mofo decides to use regular unleaded on a car that requires premium grade fuel.