An anecdote from the fuel business; in the past two years there has been much discussion of "high-energy" fuels. As distinct from high-specific-gravity fuels, whose purpose is to extend the range of a race vehicle with regulated tank volume, such high-energy fuels would actually increase the power given by the engine. The conventional approach has been to add alcohol, which works by refrigerating the charge, thereby increasing its density, or to add nitro compounds, which work by releasing oxygen that can in turn combine with more than the normal amount of fuel.
Both alcohol and nitro compounds are illegal for gasoline classes, being readily detected by the dielectric meter owing to their high molecular polarity.
The usual petroleum hydrocarbons all give closely equal energy when compared on a per-cubic-foot-of-mixture basis, except for certain compounds such as acetylenes, butadienes, and so forth. Normall, energy yield is computed on the basis of so much for each hydrogen, so much for each carbon, but it may be that the energy holding the original compound together is important as well. Petroleum is highly stable -- otherwise it could not have remained what it is for a quarter- to a half-billion years of underground storage (try that with cabbage). That stability takes energy to overcome -- energy that will be subtracted from the bang that the stuff gives in the engine cylinder. Unstable double and triple-bond compounds may achieve their gains in this way. Any comments from you chemists? Yes, laugh and point if you must -- I just want to know what's going on here.
At any rate, one blender adds enough of this hypothetical high-energy component so that the rider of the bike even notices the improved acceleration. Trouble is, the stuff degrades octane number so that the bike won't top-end now. Therefore the blender adds some tetraethyl lead (TEL), expecting to get a couple of points of octane number gain. Instead, he gets flat performance. Ditto when he tries manganese -- acceleration is killed, advantage gone. Is this why people are adding MTBE to race gas in such quantities? At Eastern Creek in Australia, the place reeked of it. MTBE has a bare octane rating of 115.
An examination of the literature shows that TEL is actually slightly pro-knock when used with unsaturated cyclic hydrocarbons -- but is knock the problem?
In action, TEL breaks down to form lead oxide in small, 100 Angstrom crystalline particles, and these heavy guys seem to catalyse destruction of the potent OH radicals and maybe peroxides that are the precursors of DETONATION. In doing so they also hold up the combustion process somewhat. Could it be that with the high-energy component(s), whatever it(they) may be, the TEL holds things up enough to smear the pressure rise out flat?
I'm studying but getting nowhere. I think tomorrow I'll have to start calling up people until I can get a handle on this.