Antiknock dopes

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... 

As much controversy has existed regarding the cause of the actual knock in an engine as exists in regard to the mechanism of the combustion and action of antiknock dopes during engine operation, and a number of theories lias been proposed, the very diversity of which indicates their Inadequacy. Just as in the case of oxidation mechanism studies, a large numlier of experiments have been performed at other than conditions... 

Radiation and ionization. The work with bombs and engines has indicated that small amounts of antiknock dopes eliminated the shock wave in combustions of explosive mixtures and induce a continuous combustion in the wake of the flame front. It has also shown that during knocking combustion a partial burning outruns the remainder and causes a violent liberation of energy during some portion of the cycle. ... 

Table XXVI.—Comparison of Efficiency of Antiknock Dopes.

The relative efficiency of a number of antiknock dopes in suppressing knocking of a kerosene is shown by Table XXVII. 

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. 

By comparison with Weerman s results Egerton and Gates obtained even higher rises in iguition temperature relative to the amount of antiknock dope used.43 Some of their results with both metallic and non-metallic dopes are shown in Table XXXII. A modified Moore apparatus was used. 

Table XXXII.—-Rise of Ignition Temperature of Gasoline by Antiknock Dopes.

A somewhat similar theory10 postulates the formation of colloidal lead by the decomposition of lead tetraethyl, which deposits on sharp points, edges, and projections in the cylinder which would otherwise aid reaction to an extent that a detonation wave would result. The theory fails to explain the action of organic amines, of di- and tetravalent. selenium, of the colloidal metal sols, and fails to account for the immediate recurrence of knocking when the antiknock dope is discontinued in the gasoline feed. However, tubes coated with lead oxide have been found to reduce the oxidation of hexane more than lead tetraethyl vapors.1158 On the basis of this finding the hypothesis was advanced that oxidation occurs to some extent prior to compression and at the first contact of the gaseous mixture with the hot walls, aud that in the presence of the lead... 

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