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An octane rating, or octane number, is a standard measure of a fuel's ability to withstand compression in an internal combustion engine without causing engine knocking.The higher the octane number, the more compression the fuel can withstand before detonating.
The compression ratio may be higher in engines running exclusively on liquefied petroleum gas (LPG or "propane autogas") or compressed natural gas, due to the higher octane rating of these fuels. Kerosene engines typically use a compression ratio of 6.5 or lower.
High percentage ethanol mixtures are used in some racing engine applications as the very high octane rating of ethanol is compatible with very high compression ratios. Ethanol fuel mixtures have "E" numbers which describe the percentage of ethanol fuel in the mixture by volume, for example, E85 is 85% anhydrous ethanol and 15% gasoline. Low ...
The greater the expansion ratio, the more efficient the engine, in principle, and higher compression / expansion -ratio conventional engines in principle need gasoline with higher octane value, though this simplistic analysis is complicated by the difference between actual and geometric compression ratios. High octane value inhibits the fuel's ...
Octane rating became important as the military sought higher output for aircraft engines in the late 1920s and the 1940s. A higher octane rating allows a higher compression ratio or supercharger boost, and thus higher temperatures and pressures, which translate to
According to the manufacturer, this is due to the cooling properties of ethanol. E85 has an octane rating higher than that of regular gasoline's typical rating of 87, or premium gasoline's 91-93. This allows it to be used in higher-compression engines, which tend to produce more power per unit of displacement than their gasoline counterparts.
In spark ignition engines, both alcohols can run at much higher exhaust gas recirculation rates and with higher compression ratios. Both alcohols have a high octane rating, with ethanol at 109 RON (Research Octane Number), 90 MON (Motor Octane Number), (which equates to 99.5 AKI) and methanol at 109 RON, 89 MON (which equates to 99 AKI). [2]
the use of a fuel with high octane rating, which increases the combustion temperature of the fuel and reduces the proclivity to detonate; enriching the air–fuel ratio which alters the chemical reactions during combustion, reduces the combustion temperature and increases the margin to detonation; reducing peak cylinder pressure