Um, just to clarify your clarification, Camrycev...Octane purely refers to knock-resistance and is comparing the fuel blend in question to a mixture of Octane and Heptane. There is not necessarily any octane or heptane in the fuel you're pumping, but in terms of knock (eg premature self-ignition) it will perform the same. Or rather, by averaging the results of two different measurement methods (Motor and Research (testing at I believe 500 and 700 rpm respectively...if anyone really cares I can check my ICE textbook when I get home) (hence the (M+R)/2 indicated on the pump next to the Octane rating)), the results are the same as the above-described mixture of Iso-octane and n-Heptane.
And octane doesnt specifically affect the BTU/lb of the fuel, but a higher octane enables a higher compression ratio which increases the thermodynamic efficiency of the combustion process allowing the engine to extract a higher percentage of the energy contained within the gasoline.
All gasoline basically has the same energy content (LHV, Lower heating value, again, I can look up values out of my text when I get home if people care).
Yes I'm an engineer, yes I've taken an internal combustion engines course and yes I've helped build race cars
PS And the reason ethanol has a higher octane rating is because alcohols are generally more resistant to self-ignition, but the oxygen contained within the ethanol (C2H5OH) when compared to the pure hydrocarbons (CnHm) basically absorbs or rather just 'holds onto' more of the energy innately contained within the chemical bonds in the fuel.
And octane doesnt specifically affect the BTU/lb of the fuel, but a higher octane enables a higher compression ratio which increases the thermodynamic efficiency of the combustion process allowing the engine to extract a higher percentage of the energy contained within the gasoline.
All gasoline basically has the same energy content (LHV, Lower heating value, again, I can look up values out of my text when I get home if people care).
Yes I'm an engineer, yes I've taken an internal combustion engines course and yes I've helped build race cars
PS And the reason ethanol has a higher octane rating is because alcohols are generally more resistant to self-ignition, but the oxygen contained within the ethanol (C2H5OH) when compared to the pure hydrocarbons (CnHm) basically absorbs or rather just 'holds onto' more of the energy innately contained within the chemical bonds in the fuel.
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