### ZIMSEC O Level Combined Science Notes: Fuel efficiency

• Fuel efficiency measures the amount of energy that can be obtained from a given quantity of fuel
• It is often useful to know which fuel gives the most energy(heat) per given unit
• In a laboratory fuel efficiency can be determined by measuring the temperature rise of water when it is heated using a known mass of fuel
• Usually when a fuel burns in a plentiful oxygen supply
• It produces carbon dioxide and water
• This is known as complete combustion
• When a fuel is burnt in an insufficient oxygen supply environment
• The word equation for complete combustion is:
• $\text{octane (fuel)+oxygen} \rightarrow \text{carbon dioxide + water}$
• There is incomplete combustion
• Carbon monoxide and soot(which is unburned carbon) are produced
• The word equation for incomplete combustion is:
• $\text{octane (fuel)+oxygen} \rightarrow \text{carbon monoxide + carbon+water}$
• Carbon monoxide is a poisonous gas
• It is thus not recommended to make a fire in a room that is not well ventilated
• Soot is often observed in the exhaust pipes of motor vehicles
• It is also observed as the dark colored part of smoke that comes out of motor vehicle exhausts ans well as factory chimneys
• When the carbon in fuels in completely oxidized to carbon dioxide
• That is when there is complete combustion
• More energy is released than when only
• Carbon dioxide is partly oxidized to carbon monoxide
• That is when combustion is incomplete
• Complete combustion results in more fuel efficiency than incomplete combustion

To access more topics go to the Combined Science Notes page.