The combined effect of sulphur and nitrogen compounds on alkane combustion

Abstract

Studies of the effects of dipropyl disulphide and some organic nitrogen compounds on the combustion behaviour of 2,2,4-trimethylpentane and heptane have shown that relatively small quantities of certain aromatic amines can counteract the proknock and lead-antagonistic effects of the sulphur. A good correlation was found between changes in the induction period preceding the first cool flame, as measured in the laboratory, and changes in the Research Octane Number, as determined in an engine. Measurements of the induction period could thus be used as a quick way of assessing the proknock or antiknock effect of the additives. In the laboratory, the promoting effect of dipropyl disulphide was more than counterbalanced by less than half the equivalent molar amount of some of the amines. Similar synergistic effects were observed in the engine experiments, where certain amines were especially effective in removing lead-sulphur antagonism. The ability of the amines to combat the promoting action of the sulphur compound is explained in terms of changes both in the chain-propagation steps involved and in the stability of the intermediate free radicals. The amines appear, however, also to influence various heterogeneous processes.