How can you not have free carbon if there isn't enough oxygen for it to bind to?
Measuring Stoichiometric Combustion Processes
In any combustion process, an amount of oxygen reacts with an amount of fuel. If the amount of oxygen exactly matches the amount of fuel,
combustion is complete. This is called
stoichiometric combustion.
When there is a
shortage of oxygen, combustion is incomplete and a mixture remains that still contains fuel. That is combustible. With this incomplete combustion of hydrocarbons, not only carbon dioxide but also toxic carbon monoxide remains. A shortage of oxygen is therefore
inefficient and dangerous.
An
excess of oxygen results in soot formation, which causes
problems with emission requirements. A second disadvantage of too much oxygen is that the air is heated. This is at the cost of process energy and therefore
less efficient. Controlling the combustion process to keep the chemical reaction stoichiometric is therefore very important.
