Fuels and combustion & emissions
The calorific value of a fuel is the amount of energy that is released by the combustion of 1 kg of the fuel. When considering products of combustion it is useful to take account of some simple chemistry relating to the combustion equations for carbon and hydrogen. An adequate supply of oxygen is required to ensure complete combustion and this is obtained from atmospheric air. Combustion in spark ignition engines such as the petrol engine is initiated by the spark at the sparking plug and the burning process is aided by factors such as combustion chamber design, temperature in the cylinder, and mixture strength. Petrol engine combustion chambers are designed so that the combustion that is initiated by the spark at the sparking plug is able to spread uniformly throughout the combustion chamber. Exhaust emissions and engine performance are affected by conditions in the combustion chamber; two effects that are associated with combustion in petrol engines are detonation and pre-ignition.