What is an Octane Rating?

Have you ever wonder what does gasoline Octane Rating means? That numbers shown in the gas pumps? Every time we go to a gas pump to fill our car's tank, we all the time have the selection of what octane rating we wish to put in. We can also see a emblem on the gas pump with the distinct ratings ready in that middle point and if living on the Usa, will also see the rating calculation formula used.

In Usa, those ratings vary among 87, 89, 91 or 93 octane. Gas with higher numbers than those, is called "Racing Gas" and (1) it is not generally seen on acceptable gas stations and (2) price is considerably higher than acceptable octane rating gas. But, what about it???

Octane rating is a number to define the asset of gasoline to resist detonation by high pressure and high climatic characteristic conditions, in a exact range. It does Not mean that 93 octane gas is way more excellent than 87 octane, like Dynamite is way more excellent than gun powder. Resistance to detonation means; how hard can we push or compress that gasoline in our engines (taking in inventory temperature) before it detonates without the spark plug firing. When that later unwanted health occurs, it is called pre-ignition, knocking, pinging or plainly detonation. Remember that it is a internal combustion motor or "Explosion engine". Detonations are way more powerful, faster and destructive than explosions. Detonations provides no usable power to the engine.

The higher the octane rating, the more it will resist the above situation from happening. Racing and muscle cars, often yield a lot of compression and elevated temperatures inside their engines and that is why it is normal to use very high octane rating gas on such vehicles.

Detonations

It is not suitable at all that gasoline fire before it is meant to as it will cause a lot of issue to the engine, affecting its execution and endangering it to get broken. Just dream the gas, detonating at the compression stoke, several degrees before the "Top Dead Center" or Tdc. That will be an unwanted situation where the piston pushes upward while the detonation pushes downward at the same time, in the same stroke. Very bad! It produces zero power as the detonation won't follow pushing the piston down because of the fact that it is still settled before top dead center and there will be authentically no down movement until that point is passed. Also, detonations occur in microseconds, which wouldn't be of any mechanical advantage. It will be more like hammering the piston instead of pushing it down.

When detonations occur, power is lost by two conditions, first, the inescapable one; a detonation is too fast and all the time occur against motor timing and secondly, if the knock sensor "notices" the detonation, there will be a response from the car computer (ecu), which will slow down ignition timing several degrees until no more detonations are detected. That is a response programmed in the ecu's software to protect the motor in case of detonations. The down side is that it will make the car to stall.

Summarizing

Octane is not a direct part of gasoline power. All gasoline will have similar combustion reactions (explosive power) depending on its refining quality and cleanliness, regardless of what octane it is rated (87, 89, 91, 93, 104, etc.). The discrepancy will be that lower rating gas (87 and 89 octane) will go to combustion before higher rating gas (91, 93 and higher octane) under the same temperature, pressure and volumetric conditions, without spark.

Octane Rating Calculation Methods

There are discrete calculation methods, Ron, Mon, and Pon or Aki.

Ron: (Research Octane Number). Most coarse fuel used in Europe, Australia and some other Countries. It is determined with measurements of fuel behavior in a variable compression engine. Results are compared with other iso-octane fuels, wish means, compared with other fuel types with equal number of similar octane molecules present, but not the of the same organic compound.

Mon: (Motor Octane Number). determined also with a variable compression engine, but with the fuel already preheated, variable ignition timing and higher Rpms than the Ron method. This formula is more spoton on determining fuel behavior on an loaded engine.

Pon or Aki: (Pump Octane Rating or Anti-Knock Index): This is the formula used in Usa and Canada, expressed as [R+M]/2, wish means Ron number plus Mon number, divided by 2. In other words, it is the average between both methods above.

Equivalency

So, due to the fact that Ron is all the time from 4 to 5 points higher of its equivalent to Pon or Aki, the number conversion between Usa and Europe octane ratings will approximately be as follows: