Octane Calculator
This calculatordetermines the minimum octanerating, also know as the knock index, by the formula (R+M)/2. Octanerating number is defined as a value used to indicate the resistance of a motor fuel to knock. Octanenumbers are based on a scale on which isooctane is 100 (minimal knock) and heptane is 0 (bad knock). A gasoline with an octane number of 92 has the same knock as a mixture of 92% isooctane and 8% heptane. To calculate simply enter the Research octaneNumber (RON) and the Motor octaneNumber (MON) ; click on Calculate and the minimum octanenumber, what you see at the pump, is returned. We have inserted potential defaults that are correct for the most popular octanerating of 87. You may however, change the values appropriately. This method of calculation is good for all internal combustion engines, including automotive or general aviation. Consult the appropriate engine manual or vehicle owner's manual for the suggested minimum octanerating. You may wish to experiment to see if you can use a grade lower fuel without creating engine ping, in order to be optimally cost efficient.
In internal combustion engines, the compressed gasoline-air mixtures have a tendency to ignite prematurely rather than burning smoothly. This creates engine knock, a characteristic rattling or pinging sound in one or more cylinders. The octanenumber of gasoline is a measure of its resistance to knock. The octanenumber is determined by comparing the characteristics of a gasoline to isooctane (2,2,4-trimethylpentane) and heptane. Isooctane is assigned an octanenumber of 100. It is a highly branched compound that burns smoothly, with little knock. On the other hand, heptane is given an octanerating of zero. It is an unbranched compound and knocks badly.
Straight-run gasoline has an octanenumber of about 70. In other words, straight-run gasoline has the same knocking properties as a mixture of 70% isooctane and 30% heptane. Cracking, isomerization, and other processes can be used to increase the octanerating of gasoline to about 90. Anti-knock agents may be added to further increase the octanerating. Tetraethyl lead, Pb(C 2 H 5 ) 4 , was one such agent, which was added to gas at the rate of up to 2.4 grams per gallon of gasoline. The switch to unleaded gasoline has required the addition of more expensive compounds, such as aromatics and highly branched alkanes, to maintain high octanenumbers.
Gasoline pumps typically post octanenumbers as an average of two different values. Often you may see the octanerating quoted as (R+M)/2. One value is the research octanenumber (RON), which is determined with a test engine running at a low speed of 600 rpm. The other value is the motor octanenumber (MON), which is determined with a test engine running at a higher speed of 900 rpm. If, for example, a gasoline has an RON of 98 and a MON of 90, then the posted octanenumber would be the average of the two values or 94.
High octanegasoline does not out perform regular octanegasoline in preventing engine deposits from forming, in removing them, or in cleaning the engine. You should select the lowest octanegrade at which the car's engine runs without knocking. Occasional light knocking or pinging won't harm the engine, and doesn't indicate a need for higher octane. A heavy or persistent knock may result in engine damage.
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