Antiknock dopes effect

Thus, a,a- and /J,/9-dinaphthylamines, and hydroquinone markedly check autoxidation of paraffins at 160° C. but lead tetraethyl and other antiknocks have but little effect.89 Layng and Youker found that in comparison with lead tetraethyl in the gas phase, diphenylamine had a hundred times the effectiveness as an oxidation inhibitor as it possessed as an antiknock dope. Some distinction evidently must be made between inhibitors which act at low or moderate temperatures and antiknock dopes which alter combustion phenomena but do not affect low temperature oxidation. Moureu, Dufraisse and Cliaux explain the ineffectiveness of lead tetraethyl at low temperatures as due to extreme ease of oxidation but this has not been demonstrated. On the contrary it has been shown that the effective antiknock dopes are not readily oxidized by air.01... 

The theories that have been advanced to the effect that the decomposition products of the antiknock dopes and not the compounds themselves are the effective centers of the action has been tested by the use of metallic colloids, prepared in various ways, in the fuels by which engines were operated. The work on colloidal metal sols has been based on the theory that knocking is due to the spontaneous ignition of the unburned charge in an engine cylinder. By acting as catalysts for combustion these substances insure a slow, homogeneous combustion rather than a detonation. 

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