The behaviour of additives in explosions and the mechanism of antiknock. I

Abstract

The behaviour of TeMe2, I2, SiMe4, SnEt4, methylcyclopentadienyl manganese tricarbonyl (AK-33X), Fe(CO)5, ferrocene, Hg vapour and Hg (iso-propyl)2was observed during explosions of amyl nitrite (sensitizer),n-heptane and oxygen. After flash initiation, the reactions were followed by kinetic absorption and emission spectroscopy. The effect of these substances with respect to antiknock action, smoke formation, effect on induction period (preflame reaction) and the emission of light, has been recorded. With the tin and transition metal additives, smokes formed during the induction periods, characterized by a continuous scattering over the entire continuum. A K -33X increased or decreased the induction periods, according to the conditions. TeMe2 and I 2 increased the induction periods by homogeneous reactions. None of the other compounds changed the duration of the induction periods, including the iron compounds which are known to be antiknocks. With the iron and tin compounds included in the charges, smokes formed early in the induction periods and it was therefore concluded that the colloidal solids formed during the combustion of these compounds do not delay auto-ignition by preflame end gas reactions. It follows that there are two mechanisms of antiknock. It is suggested that the occurrence of heterogeneous inhibition is contrary to experience: (a) because there is insufficient surface exposed, (b) because the efficiency of reaction of chain centres at surfaces is low, (c) because the other antiknocks, TeMe2I2and PbEt4act homogeneously. It is proposed that the second mechanism of antiknock, into which category the iron and manganese compounds fall, is a result of the reaction of the additive on the burnt or burning gases, rather than on the unburned gases. An intense emission of infra-red and visible light from explosions containing iron and manganese may be related to their mechanism as antiknocks; it is suggested that the increase in radiative cooling, caused by excitation and fluorescence of gaseous metal oxides and/or specific deactivation of propagating centres by metal or metal oxide species, plays an important role in this effect. The manganese compound also exhibits antiknock properties of the first type.