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Automotive petrol

Like most motor fuels, automotive petrol consists mainly of carbon and hydrogen. If burned with oxygen, it releases thermal energy which is subsequently transformed into mechanical energy, with varying levels of efficiency. Liquid fuels are advantageous particularly because they burn quickly, are relatively easy to store, and their operation is safe.

Automotive petrol is typically defined as a mixture mainly of petroleum hydrocarbons with 3 to 12 carbon atoms in their molecules and a boiling point within the range of roughly 30 to 210°C. However, these properties are not sufficient to enable the use of this mixture as a fuel in spark-ignition engines. The fuel must comply with a number of other qualitative parameters as well.

Petrol began to be used as a motor fuel in the late 19th century. It was obtained via a simple process of distilling petroleum, and its properties were determined by the random composition of hydrocarbons according to the place of origin of the processed petroleum. With the gradual evolution and improvement of the petrol engine, engineers realised that different types of petrol had different impacts on engine performance, particularly as regards the manner in which the compressed mixture of petrol vapour and air burned in the cylinders, something expressed in a more or less pronounced tendency to detonate prematurely – to cause the so-called “knocking” of the engine.

To measure this phenomenon, the octane number was introduced. And it was precisely the increase in the octane number that turned out to be the most important prerequisite to achieving higher performance in the spark-ignition combustion engine. There are basically two possible ways of accomplishing this: changing the composition of the automotive petrol or using suitable additives. In fact, the progress made in improving the quality of automotive petrol made use of different variations and combinations of these options, boosted by the ever stricter requirements for reducing emissions and protecting the environment. In connection with improved combustion engine design and increased compression ratios, the requirements for antiknock properties, i.e. octane numbers, gradually increased and settled at the present level in the mid-1970s.

The 1980s can be described as a period of the radical reduction of the content of lead, which was the basis for the most commonly used antiknock additive in automotive petrol. Lead content was gradually decreased in the Czech Republic from the original levels of almost 1 gram of lead per litre down to 0.15 g Pb/l in 1987 – a rate comparable to the most developed European countries, with perhaps only Germany and the Scandinavian nations ahead of us. Thanks to progress made in the refinery industry, the required octane numbers could be reached without the use of antiknock additives, particularly lead-based compounds.

In 1985 the Czech Republic began producing BA-91 unleaded petrol – at first mainly for export. In the late 1980s we switched from unleaded petrol of octane number 91 to the so-called Eurosuper of octane number 95. The share of unleaded petrol in the Czech Republic quickly grew, particularly in connection with the introduction of catalytic converters, upon which lead acts as a catalytic poison. Since 1 January 2001 the use of leaded automotive petrol is completely prohibited on the territory of the Czech Republic, the same as in the other EU countries. Currently, by far the most widespread type of automotive petrol in the country is Natural 95 Super – its consumption represents about 4/5 of the total consumption of automotive petrol on the Czech market.

Today, the quality of automotive petrol is most influenced by the increasing requirements for environmental protection. This is reflected particularly in the reduction of aromatic hydrocarbons, especially benzene, reduced sulphur content and a decrease in the overall volatility of automotive petrol.

Produced motor petrol must at the present time comply with requirements, concerning maximum content of aromatic hydrocarbons in level of 35% V/V, benzene content must not exceed 1% V/V and sulphur content must be under 50, in respect 10 mg/kg.