Ethanol

6-02 Analyze the usage of ethanol in automotive applications.

Ethanol is heavier than air and is hygroscopic, which means it readily absorbs water vapor from the atmosphere. Ethanol is a high-octane fuel (around 100 RON/MON/2 octane), depending on various factors. It is a renewable fuel intended for SI engines. It is used in FFVs in the United States in a blend of up to 85% ethanol to 15% gasoline, called E85 (FIGURE 6-8). Some countries use 100% ethanol instead of gasoline, which would be E100. Ethanol is primarily used to reduce the negative emission effects of gasoline and as a gasoline oxygenate to replace harmful methyl tertiary-butyl ether. This mixture may be harmful to gasoline/petrol-fueled vehicles without the proper FFV seals and elastomers. Equipping an OEM vehicle for FFV use is inexpensive, and more and more OEMs are doing so in the interest of making their vehicle offerings “green.” Vehicle computers calculate the percentage of ethanol blend by a variety of methods and alter injection quantity and spark timing to achieve the desired stoichiometric ratio of fuel and air and the resulting low emissions possible with ethanol.

FIGURE 6-8 Using a plant-based material to distill fuel is an option when looking to find a way to power combustion engines.

Ethanol separates and evaporates quickly from water, which makes it less polluting to streams and waterways in the event of a spill. Compared to gasoline, ethanol burns particulate-free and releases fewer toxic emissions than gasoline/petrol. Its luminosity (visibility when it burns) is hard to detect in sunlight, thus making it somewhat dangerous in the event of a vehicle fire. It does release carbon dioxide during the combustion process, but again, less than the equivalent amount of gasoline/petrol. A downside to the use of ethanol is the reduced heat capacity which increases the amount of ethanol that must be used to maintain the power that petroleum produces. Ethanol holds great promise for reducing petroleum usage and providing greater engine power when engines are optimized (through valve timing or stroke variation) for use of higher octane ethanol, as compared to gasoline. When used in plug-in hybrid FFVs, such vehicles are said to achieve a gasoline-per-gallon equivalent as high as 500 mpg.

What Is Ethanol Made Of?

First-generation biofuels like ethanol are usually derived from an organic process—for example, the fermentation of sugars that come from plants such as corn, cane sugar, sugar beet, or grains. Second-generation bio-ethanol is derived from a variety of cellulose-based plants such as switchgrass. Third-generation biofuels like ethanol are algae based—that is, produced by/from algae. Algae-based ethanol production is the most promising in terms of yield per acre/hectare. Bio-ethanol is a renewable resource and is also known as grain alcohol.

What Kind of Octane Levels Are Used?

The ethanol that is used in today’s vehicles is mixed with gasoline so that it can operate in fuel systems that are designed for vehicles currently in production. The benefits of ethanol are that it is cleaner burning, helps ease the petroleum requirements of the internal combustion engine, and keeps the engine cleaner (FIGURE 6-9). An added benefit of using alcohol in an internal combustion engine is that it allows for higher compression ratio because it resists detonation much better than conventional gasoline. Since it resists detonation, the ignition timing can be increased as well as the camshaft events. All of this translates into better power, but the original equipment manufacturers are not utilizing it to the fullest potential. When doing an octane calculation there is a particular formula to account for the ethanol content in the gasoline, which usually produces an octane rating of 94-96 on E85 standard ethanol fuel.

FIGURE 6-9 When compared to gasoline, ethanol has a higher octane number that helps it to resist detonation and pre-ignition. Because of this the fuel requirements and ignition requirements are slightly different than gasoline.

Where Is Ethanol Used around the World?

Ethanol is used in many countries and utilized because of the flexibility of production methods. The ability of ethanol to be made from many different base stocks makes it a very versatile fuel which also is very renewable. The renewability of ethanol is part of its appeal, and users feel they are being good for the environment. South America’s economies have been using a form or ethanol for years as they distill it from sugar cane that is easily grown in the region (FIGURE 6-10). The infrastructure is built up enough to support the industry to a point that vehicles made for South America are built only for South American fuel. North America is a late adopter of ethanol usage as the governmental incentives to kick start the industry are needed to create infrastructure to sustain the ethanol movement. As the demand for ethanol rises the cost of the food stocks used to create the fuel will cause grain prices to rise to a point where it won’t be economically feasible to buy grain to feed the families of the world.

FIGURE 6-10 Ethanol can be made out of various plant sources that are distilled into an alcohol, which usually involves heat and pressure.