Fuel

Octane - MON, RON, and PON

Three different systems of octane ratings exist. RON (Research Octane Number, ASTM D2699 ), MON (Motor Octane Number, ASTM D2700), and PON (Pump Octane Number, sometimes refered to as RdON, Road Octane Number or AKI, Anti Knock Index). RON and MON are octane ratings that correspond to a similar test motor under certian different conditions and a benchmarked Highest Usable Compression Ratio (HUCR). PON is approximately an average of these two numbers and is what we see labled on the pumps and in most of our owners manuals. A nifty conversion calculator is available HERE.

OUTSIDE THE US AND CANADA, GASOLINE TENDS TO BE LABLED BY THE RON NUMBER, NOT THE PON NUMBER!!

Customary Octane Required by bikes

If your engine is basically stock, run gasoline with an octane that is ONR (octane number requirement) recommended from the factory. A higher octane will do nothing for your bike but cost more money. Higher octanes are to prevent pre-detonation and knocking in higher compression engines. That is all. IN GENERAL, no more power, no more performance. My Honda F4i is specified to take 86 PON (Pump Octane Number) or higher octane. I've been running 87 PON for some time with no knocking or pinging problems whatsoever. Honda allows for the use of fuel that contains less than 10% Ethanol, or 15% MTBE, or 5% Methanol. Other motor manufacturers may have different tolerances.

Energy Content

For performance oriented riders, of the greatest concern is the engergy content in the gasoline rather than octane rating. This heating value is truely the measure of what you will get from the gasoline. Energy content can be expressed either gravimetrically (energy per unit weight of fuel) or volumetrically (energy per unit volume of fuel). The International Metric (SI) units are megajoules per kilogram (MJ/kg) and megajoules per liter (MJ/L). In the United States, the gravimetric unit is British thermal units per pound (Btu/lb), and the volumetric unit is British thermal units per gallon (Btu/gal).

Non oxygenated gasoline (all grades) would have a net heat content of 114,900 Btu/gal. Oxygenating this gasoline with 10 volume percent ethanol or 15% volume percent MTBE would lower it's heat content 3% to 111,400 Btu/gal. Traditionally, premium grade gasoline has had a slightly higher heating value than regular. The difference-less than 1%. The differences likely to be less or non existent between grades of reformulated gasoline. There can be differences in heating values among batches of gasoline from the same refinery or among brands of gasoline from different refiners because of compositional differences. The differences are small and there is no practical way for the consumer to identify the gasoline with a higher heating value. ---CHEVRON

Additives

Remember that the presence and amount of oxigenates in the gas (Ethanol, or MTBE, or Methanol) will effect the necessary jetting (or mapping) and the specific heat content that the fuel contains. This usually results in slight changes in the power curve.

Racing Fuel

The added expense and bother of running a racing fuel is that a racing fuel will have far more energy content than a pump grade alternative. While racing fuels are supplied in some of the highest octanes on the market, that has a lot more to do with the spcial engines and compression ratios running in them.

• VP Racing Fuels uses the MON system of rating octaine. The MON test is performed at a higher temperature and a higher RPM than the RON, so it is probably the best measure to use for higher performance applications. VP explains it's use of MON ratings HERE.
• Sunoco another supplier of racing gas uses the PON numbers. You really have to keep your eyes open when working with gas.

Testing

Automotive gasoline is generally tested acording to ASTM D4814-04a Standard Specification for Automotive Spark-Ignition Engine Fuel

See Also

• Chevron's Motor Gasolines Technical Review Manual Chapter 1
• American Petrolium Institute
• Exxon/Mobil also has some usefull information.
• A great site that describes the various octane systems is HERE.
• The World Wide Fuel Charter attempts to standardize fuel around the globe.

If you like to think about fuel, you need to go to THIS site. It get's pretty heavy into the subject. THIS article by Robin Tuluie is farely quick and to the point and is followed up by THIS article on the detonation process and THIS article on octane testing. Also THIS is another good gasoline article.