Winter & Summer Petrol
Petrol has to be blended to get the right properties, one important property is its volatility. Petrol is mixed with air in the car engine. When the weather is cold, petrol is difficult to vaporise, so the car is difficult to start. Petrol companies make four different blends for different times of the year. In the winter there are more volatile components, i.e. smaller hydrocarbon molecules. In the summer the blend has fewer more volatile components.