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The most common type of octane rating worldwide is the Research Octane Number (RON). RON is determined by running the fuel in a test engine at 600 rpm with a variable compression ratio under controlled conditions, and comparing the results with those for mixtures of iso-octane and n-heptane. [8]
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 ...
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 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 ...
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. The first production car running entirely on ethanol was the Fiat 147, introduced in 1978 in Brazil by Fiat. Ethanol is commonly made from biomass such as corn or sugarcane.
This engine had an advertised compression ratio of 10.5-to-1 and the 1958 AMA Specifications stated that the octane requirement was 96–100 RON. [61] At 243 kilograms (535 lb) (1959 with aluminum intake), it took 0.86 kilograms (1.9 lb) of engine weight to make 0.75 kilowatts (1 hp).
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.