Motoring Weekly

The two main fuels that impact motorists are Petrol and Diesel. LPG is another by product of the refining process that can be used but won’t be discussed here.

One process used at an oil refinery is called fractional distillation and uses heat to split the oil into different components. Petrol is split at around 150°C and Diesel is split at around 300°C. This is a very simplified description as there are many processes undertaken to clean and refine the end products.

Petrol, used as a fuel for the internal combustion engine, is created by adding benzene and other oil based refined chemicals. This mixture improves the Octane Number but also makes it more volatile than the original distilled liquid.

Diesel, from crude oil, is about 75% saturated hydrocarbons (i.e. paraffin) and 25% aromatic hydrocarbons (naphthalene and alkylbenzene). Diesel can also be developed using other oils such as vegetable oil and many new biodiesels are currently being developed.

Each fuel uses a different type of engine. Petrol engines use a mix of air and fuel that is ignited by a spark. There are typically 3 types:

The 2-Stroke – two strokes to suck in fuel, compress, ignite and exhaust the gases. The 2-stroke was developed by Dugald Clark around 1880.

The 4-Stroke – four strokes to provide a better-balanced engine, known as the Otto Cycle. It was developed by a number of different people in the 1860s but named after Nicolaus Otto. It uses 1 stroke for each function: suck, compress, ignite & exhaust.

Finally there is the Wankel engine – a rotary style engine developed by Felix Wankel in the 1950s and today is most commonly used by Mazda in the RX series.