But American researchers have found a way to make an engine behave as if it's warmed up all along, reducing pollution from the moment you turn the ignition key. To keep a proportion of the car's most volatile fuel to one side and use it for the engine's starting phase.
Car engines can only burn petrol once it has been vaporised.
But much of the fuel drawn into a cold engine remains as a liquid and is emitted from the exhaust without being burnt. This unburnt fuel reacts with nitrogen oxides to create ozone, one of the major components of smog. To counter this, the researchers have developed a distillation device that uses heat from the car's engine to separate out the 5 per cent of the fuel made of the smallest, most easily vaporised hydrocarbon molecules. This is stored in a separate reservoir to be used when the engine is started. Since most of this fuel is vaporised even in a cold engine, it slashes the amount of unburnt hydrocarbons emitted by more than 50 per cent in the start-up phase.