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Alcohol Blended Fuel

Blended fuel usually refers to a mixture composed of automotive gasoline and another liquid, other than a minimal amount of a product such as carburetor detergent or oxidation inhibitor that can be used as a fuel in a motor vehicle.

Alcohol refers to ethyl alcohol (ethanol, C₂H₅OH), which has a high octane number, RON being 110, and MON 90 and a good antiknock performance. If alcohol contains a certain amount of water, it is favorable to improve its antiknock performance; hence, the enhancement of the compression ratio of the engine occurs when the blended fuel is burned. Meanwhile, an alcohol blend requires no or reduced additive of antiknock substance, which may reduce air pollution caused by lead (Pb). But the effect on increasing of the octane number of blended fuel is not the same when gasoline is mixed with different kinds of alcohol.

The data (Table A-9) show that the change in octane number of blended fuel is in nonlinear correlation with the proportion of alcohol added. A 5 to 20% alcohol blend has a higher mixed octane number. This means that the effect on raising the octane number of blend fuel is more notable. In addition, the lower the octane number of base gasoline is, the more notable the effect on raising the octane number of blended fuel will be.

Table A-9 Octane number (motor method).

Ethanol, % v/v	Octane number
0	72.5
5	74.8
10	76.6
15	78.5
20	80.3
25	81.4
100	90.0

Selecting a 15 to 20% blend of alcohol has the advantage of the high antiknock performance of the alcohol. However, if low octane gasoline is used as the base for the blend, without adding any antiknock fluid, not only can the pollution be reduced but the cost of fuel is decreased, thus making the use of mixed fuel on gasoline engine more adaptable.