Alternative Fuels

The Use of Fossil Fuels

Internal combustion engines get their name from their combustion of fossil fuels, specifically gasoline. Used efficiently, the process converts gas into mechanical energy, powering the vehicle. Unfortunately, the process also sends a substantial volume of polluting by-products out into the air through an exhaust pipe. In addition to carbon dioxide (CO2) and water vapor, the by-products include carbon monoxide, benzene, and nitrogen oxide (NOx). Sulfur dioxide (SO2) may also be emitted due to gasoline impurities. These by-products adversely affect air quality by increasing smog, which particularly correlates to SO2. Greenhouse gases like CO2 also contribute to global warming. Nitrogen oxide is a factor in acid rain.

Because of these negative effects from using gasoline to power internal combustion engines, many people want to use alternative fuels for their cars and trucks instead. Their hope is that these will pollute less, helping protect the environment. There are many different kinds of alternative fuels that can be used to power automobiles.

Biodiesel

Some vehicles have compression ignition engines, also called diesel engines, which do not require a spark for ignition. They have a high rate of thermal efficiency compared to nondiesel internal combustion engines (ICEs). Because of that, they maximize the amount of mechanical energy that can be derived [Page 151]from a given amount of fuel. Typically, the rate of conversion is 45 percent. That contrasts to regular ICEs using gasoline, which only have a 30 percent conversion rate. Additionally, diesel engines using fossil fuels have only minimal CO2 output in exhaust but do produce substantial amounts of nitrogen oxides when using fuel distilled from petroleum. That problem can be moderated by incorporating an alternative fuel called biodiesel.

Biodiesel is based on a lipid such as vegetable oil or tallow. Fatty acid esters are produced when the base substance is reacted with an alcohol, producing the mono-alkyl ester used for fuel. In standard diesel engines, biodiesel is not used exclusively. Instead, it is combined with petroleum-derived fuels in various percentages. For example, if the fuel used is 20 percent biodiesel and 80 percent sourced from petroleum, it would be labeled B20 (meaning biodiesel 20 percent). Using B100 (100 percent biodiesel with no petroleum-based constituents) can necessitate modifications to the diesel engine being used for the process to operate at peak efficiency.

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