The octane number written on the gas pump is Anti-Knock Index (AKI). It’s an average of two octane ratings using the same test equipment but using different operating conditions. The methods produce a Research Octane number (RON) and a Motor Octane Number (MON). Both were once considered important and that’s why AKI is an average of the two. With modern engines and fuels systems, recent studies have shown that RON is more important than MON. So in these cars, the higher the RON the better these cars perform. For an AKI rating of 91 the lower the MON the higher the RON. This difference is called sensitivity. All gasoline components have different sensitivity. Most hydrocarbon components have low sensitivity. Ethanol has high sensitivity and so, modern performance cars benefit from gasolines with ethanol. Why does ethanol have higher sensitivity? One reason is related to the cooler combustion that results from ethanol combustion. Higher knock tendency is directly related to higher combustion temperature.
Here is a comparison of two fuels with different octane with and without ethanol.
91 Grade - no ethanol
RON 97.2
MON 85.6
Ultra 94 - with ethanol
RON 101.5
MON 88
Notice the difference in RON number from 91 grade without ethanol (97.2) and the RON of Ultra 94 (101.5). The difference is 4.3 numbers. That is significantly more than the 3 numbers difference between 94 and 91 AKI labelled on the pump. That is why gasoline with ethanol can be the best performance fuel for today's cars.
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Trois-Rivieres compte maintenant 6 station services avec 94 !
rive sud
-autoroute55 sortie st-angele
rive nord
-autoroute55 sortie des chenaux (2 stations a moins de 1 km)
-autoroute40 sortie 198 des recollets
-autoroute40 sortie centre-ville
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