Tag: petrol

The Chemistry of Leaded Petrol, Unleaded Petrol & Diesel

The Chemistry of Petrol & The Tetraethyl Lead Story

Infographic on the chemistry of petrol and diesel. Both petrol and diesel are obtained from fractional distillation of crude oil. Diesel is removed at a higher boiling point and contains a larger quantity of energy per litre. In engines, air and fuel are injected, the fuel is compressed, then combustion of the fuel takes place, with waste gases ejected through the exhaust. Knocking can occur when combustion doesn't occur in sync with the engine cycle, with octane ratings gauging how well fuel avoids this problem. Higher octane ratings indicate less knocking. Compounds added to petrol can boost its octane rating: tetraethyl lead was used as an anti-knocking agent in leaded petrol which has now been phased out. Alternative anti-knocking agents are now used.
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Tomorrow (18th May) marks the date of birth of Thomas Midgley, who made significant contributions to something many of us make use of on a regular basis: petrol. Midgley was the research assistant to Charles Kettering, and the duo were responsible for the addition of the compound tetraethyl lead to petrol. This innovation would have a lasting legacy – although perhaps not in the manner that they may have originally envisioned.

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