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The octane rating of gasoline is measured in a test engine and is defined by comparison with the mixture of 2,2,4-trimethylpentane (iso-octane) and normal heptane that would have the same anti-knocking capability as the fuel under test. The percentage, by volume, of 2,2,4-trimethylpentane in that mixture is the octane number of the fuel.
For example, if the static compression ratio is 10:1, and the dynamic compression ratio is 7.5:1, a useful value for cylinder pressure would be 7.5 1.3 × atmospheric pressure, or 13.7 bar (relative to atmospheric pressure). The two corrections for dynamic compression ratio affect cylinder pressure in opposite directions, but not in equal strength.
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 ...
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 ...
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
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 ...
However, since ethanol has a higher octane rating, the engine can be made more efficient by raising its compression ratio. [ 33 ] [ 34 ] For E10 (10% ethanol and 90% gasoline), the increase in fuel consumption in unmodified vehicles is small (up to 2.8%) when compared to conventional gasoline, [ 35 ] and even smaller (1–2%) when compared to ...
The flame speeds are not the actual engine flame speeds, A 12:1 compression ratio gasoline engine at 1500 rpm would have a flame speed of about 16.5 m/s, and a similar hydrogen engine yields 48.3 m/s, but such engine flame speeds are also very dependent on stoichiometry [5]