Every car user knows that diesel is different from petrol. However, not all drivers know why these fuels cannot be used interchangeably and why ON is cheaper. Myths and facts about the use and properties of both fuels.
Diesel and petrol are fuels most often derived from crude oil. They are hydrocarbons - compounds of carbon and hydrogen. It is also possible to obtain a substitute for petrol and diesel, e.g. by production from coal and vegetable oils.
However, from the point of view of the car engine, they differ strongly, particularly in their chemical composition and physical and chemical parameters. Such as calorific value, flash point, viscosity, etc.
Petrol without secrets
Petrol is a liquid fuel, a mixture of hydrocarbons with a boiling point in the range 40-200oC and a density of ~0.7 kg/dm3. One of its main characteristics when used in spark-ignition (petrol) engines is its resistance to knocking - a very dangerous phenomenon for the engine.
Petrol is defined by a parameter called the octane number (LO). It is obtained, using a test method, by comparison with a standard on special reference engines. A mixture of two hydrocarbons is used as a reference: iso-octane (LO=100) and heptane (LO=0). Their ratio determines the octane number, e.g. 95% isooctane and 5% heptane is the octane number of a fuel with LO=95.
However, pure petrol cannot achieve an octane number above 90, additives are needed to achieve this. In the past, this was mainly lead tetraethyl, but it had to be phased out due to the use of three-way catalytic converters and, most generally, environmental issues.
Today, iron carbonyl or methanol is used. However, contrary to popular opinion, a higher octane number does not ensure better engine performance. It does, however, ensure that the engine is resistant to knocking combustion and must be used in some designs. Burning higher octane fuel in an engine that does not need it is unnecessary and does not affect the performance of the unit.
