Equations of this type are called net ionic equations . When a hydrocarbon is burned with sufficient oxygen supply, the products are always carbon dioxide and water vapor. If the supply of oxygen is low or restricted, then carbon monoxide will be produced. This is why it is so dangerous to have an automobile engine running inside a closed garage or to use a charcoal grill indoors. Complete combustion means the higher oxidation number is attained.
Incomplete combustion means the lower oxidation number is attained.