A fuel is a mixture of different hydrocarbons (including octane and heptane) that are present in different dosages. The ratio expressed in % between the content of octane and heptane is called the octane number.
According to the European directive, gasoline SP98 has an octane number of 98 and is composed of 98% octane and 2% heptane; gasoline SP95 has an octane number of 95 and is composed of 95% octane and 5% heptane.
And as for the engine?The ratio of octane to heptane has an impact on the engine's auto-ignition mechanism. In practice, SP98 ignites at a higher temperature and pressure than SP95. This distinction is a result of how the different hydrocarbons respond to pressure. For example, octane will ignite less quickly than heptane. The lower the octane number, the greater the risk of spontaneous combustion at the time of compression in the engine cylinders.
Which petrol for which car?Initially, it is recommended to use the fuel recommended by your car manufacturer.
Anyone who thinks that a higher octane number leads to better performance is wrong.If your engine is equipped to run on SP95 gasoline, like most regular cars, there's no point in filling up SP98. Certainly not in our Jazz with an ICE that runs with Atkinson cycle... You will pay more without getting more in return.
The proper functioning of your car depends on the compression level of your engine. This has an impact when the contact of the petrol with the air produces a spark. This explosion takes place at the right time with the right fuel, sensor checked.
And now that "damned" E10.
What is E10 petrol and bioethanol?
E10 fuel consists of a minimum of 90% petrol and a maximum of 10% bioethanol (so it can also be 94.5% petrol and 5.5% ethanol...). If the percentage of ethanol is below 5%, the gasoline is sold under the name E5. Ethanol, another word for alcohol, is often added to gasoline to reduce reliance on fossil fuels. Because the production and composition of E10 petrol is less bad for the environment, it is referred to as a sustainable petrol.
In principle, with a full tank of E10 fuel you will get a little less far than with a tank of regular E5 petrol. This is because E10 has a slightly lower energy density. A petrol engine consumes a maximum of about two percent more when E10 is refueled.
Two percent... Here in Poland we don't have E10 (yet), so we use E5. Our Jazz has so far a measured average consumption of 4.55 l/100 km = 63.5 mpg. So theoretically, consumption on E10 would have been 63.5 - 2% = 62.2 mpg.
Overtaking two, three, maybe four times quickly, a hundred miles more highway, more often headwind, less tailwind, etcetera etcetera probably gives more difference in consumption...
Oh... and maybe the air will also stay about 2% cleaner with E10...