Nitrogen accounts for approximately...
Nitrogen accounts for approximately 79 percent of the atmosphere. For the most part, nitrogen passes through without reacting, other than small amounts that form NOx emissions. For the sake of simplicity, we do not consider this here.
Although the study of combustion and reaction kinetics is extremely complex (requiring a book unto itself), a few interesting tidbits can be derived from looking at these stoichiometric equations.
First, both methanol and ethanol contain an oxygen atom. Since one of the critical energy-releasing reactions (exothermic reaction) in hydrocarbon combustion is the carbon monoxide oxidation process, the reduced C/H (carbon/hydrogen) ratio in ethanol and methanol results in less energy per molecule relative to the gasoline counterpart.
Second, the ratio of water formed, relative to the number of C/H bonds, is less favorable for the alcohols. Since water exists in the exhaust as a vapor, the heat of condensation can't be extracted as the piston expands and is wasted (this is the difference between lower and higher heating values). Simply, 100 percent combustion of ethanol can't make up the energy deficit relative to a higher saturated carbon-based petroleum-fuel counterpart, so a larger volume of fuel needs to be consumed to get the same amount of work out of an engine. This needs to be taken into consideration for fuel cell sizing, as well as cost, which will be considered here.
The current cost of E85 on a gallon-equivalent basis is lower than gasoline. However, comparing ethanol on a gasoline-equivalent energy basis (how much energy one can extract from a fixed quantity), the costs are slightly higher, as illustrated in Table 1 on the previous page. (Note: The cost comparison against gasoline in this table is relative to pump gas, and not 100-octane race fuel, which is vastly more expensive.)
Is it really green? Another issue associated with ethanol use is the perception that the fuel displaces food stocks and uses large amounts of fertile land and water sources to grow. This issue depends on the source of the feedstock. A study conducted by the U.S. Department of Energy found that more than 1 billion dry tons of naturally occurring biomass (dead leaves, grass clippings, farm plant waste, and so on) could be sustainably harvested from fields and forests and would sufficiently displace 30 percent of the nation's annual petroleum needs for transportation fuels. Using this source for fuel, such volumes would sufficiently cover all of racing and simultaneously avoid issues associated with food or water for fuel debates.
The final issue discussed here concerning alcohol fuels is corrosiveness to certain non-synthetic and natural rubber materials, as well as non-treated aluminum. For ethanol, the corrosion can come from reactions with the rubber-based material, ethanol's hydrophilic nature with water (and if water is present in the fuel, it can rust certain components), or sometimes galvanic reactions.
However, synthetic materials are now used to replace rubber components that are reactive with ethanol, and fuel system parts can either be substituted with materials less prone to corrosion or coated (i.e., anodized), which eliminate the issue. Ethanol is, however, less corrosive than its cousin methanol.
For methanol, the following reaction occurs in the presence of aluminum:
6 CH3OH + Al2O3 => 2 Al(OCH3)3 + 3 H2O
This reaction represents methanol's corrosive nature with aluminum oxide; the surface coatings normally used in racing to protect the aluminum from direct contact with the fuel, keep it from oxidizing and corroding. In addition, there are safety issues with methanol that need to be addressed.
First, it is nearly colorless when combusting. This greatly reduces the realization of fires, which can cause obvious safety issues. Also, methanol exhibits much higher levels of toxicity in humans. Methanol is toxic to humans in low concentrations and is readily absorbed through the skin, so extra care needs to be taken in handling.