Reply to "Toluene as an Octane Enhancement"

Toluene has a RON octane rating of 121 and a MON rating of 107, leading to a (R+M)/2 rating of 114. (R+M)/2 are how ordinary fuels are rated in the US. Toluene has a sensitivity rating of 14 (RON: 121-107 MON). This compares favorably with alcohols, which have sensitivities in the 20 to 30 range. The more sensitive a fuel is the more its performance degrades under load. Toluene's low sensitivity means that it is an excellent fuel for a heavily loaded engine.



Toluene is denser than ordinary gasoline and contains more energy per unit volume. Thus combustion of toluene leads to more energy being liberated and thus more power generated. This is in contrast to oxygenated octane boosters like ethanol or Methyl Tertiary Butyl Ether (MTBE), which contain less energy per unit volume compared to gasoline. The higher heating value of toluene also means that the exhaust gases contain more kinetic energy, which in turn means that there is more energy to drive turbocharger vanes.



Toluene is such an effective anti knock fuel that it takes a smaller quantity to achieve the same octane boost compared to 100 octane racing gas.



Toluene is such an effective anti knock fuel it also means that it is more difficult to ignite at low temperatures. The Formula 1 cars that ran on 84 per cent toluene needed to have hot radiator air diverted to heat its fuel tank to 70oC to assist its vaporization. Thus too strong a concentration of toluene will lead to poor cold start and running characteristics. It’s recommended that the concentration of toluene used not to exceed 30 per cent or what the engine is capable of utilizing.