Petrol is a mixture of:
Alkanes (Aliphatic/saturated) which are often in the three forms of
Straight chains (Typical hydrocarbons such as Ethane)
Branched chains (Hydrocarbons with extra bonds such as 2-Methyl butane)
Cyclic chains (Hydrocarbons in a circular structure such as Cyclohexane).
A few Alkenes such as the aromatic Benzene C6H6
(Aromatic Hydrocarbons: Hydrocarbons characterized by general alternating double and single bonds between carbons)
Which is increasing in amounts as a component in fuel over the years.
e.g. Ethanol and Ethers
(Ethers are 2 alkenes connected by an Oxygen [such as Ethoxyethane])
Petrol is/needs to be a blend of volatilities, and to burn well, i.e. not produce a lot of carbon monoxide.
Alcohols and ethers are known as oxygenates as they contain Oxygen.
Ethanol can be produced from fermentation, so it’s a biofuel.
Cons: Ethanol and ethers produce less energy per unit. (Low energy density) and that Ethanol is hydroscopic (Absorbs water) which may cause rust in vital components i.e. engine.