Determining energy content in fuels

Question

How does the presence of oxygen in the structure of a fuel affect its heat content? Give an explanation for the difference?

pls. help me.... :(

Answer 1

Oxygen in the fuel reduces it's energy content; that's why ethanol blended gasolines result in lower mileage than pure gasoline.  The energy content of a fuel results from the combustion of hydrocarbons.  If a fuel has a high oxygen content, then a portion of those hydrocarbon bods have already been replaced with carbon - oxygen bonds, which do not contribute any energy to the process.  The result is lower per unit mass energy content of the fuel.

Oxygenated fuels were originally introduced to reduce certain emissions (carbon monoxide) however were eventually found to increase levels of other, equally harmful emissions.  In the case of MTBE, it was also found to increase ground water contamination due to it's high water solubility relative to unblended gasoline.

One commonly known exception to this rule is the use of nitromethane in dragsters.  In this case, the oxygen in the molecule is available to support the combustion process as it is connected nitrogen, not carbon, in the fuel.

Answer 2

Oxygen is both necessary and a catalyst in the combustion process. Unless you are dealing with fuels that do not require oxygen to burn, the presence of oxygen will cause the combustion.

Combustion occurs when energy trapped inside a gas, molecule, liquid or solid is released through a chemical reaction. Thus, when oxygen is present it hastens the combustion process and releases the energy. The more oxygen, the more likely and the quicker the reaction, hence the more efficient the release of energy.

It is part of the laws of thermodynamics.