Gaseous Explosions

Abstract

FIE knocking tendency of a motor fuel is ap-T parently dependent, in large measure, upon its autoignition tcmperatnre (32, 20) and the rate of rise of pressure accompanying the normal combustion of the explosive mixture (6). For this reason it seems that important information concerning the action of tetraethyl lead in suppressing engine knock may be obtained by investigating its effect, in various concentrations, on the ignition temperatures and on the rates of rise of pressure of different explosive mixtures. The subject of the ignition temperatures of fuels has for some time received a great deal of attention, and con-Explosive mixtures of different types of hydrocarbons were prepared containing varying amounts of tetraethyl lead. The rate of rise of pressure following ignition was determined from pressure-time curves.The effect of tetraethyl lead was found to be essentially independent of the chemical structure of the fuel, but governed by the type or rate of combustion of the explosive mixture. As the rate of reaction (or rise in pressure) increases, the retarding action of tetraethyl lead disappears and is replaced by an accelerating action on the combustion. A similar effect was observed upon adding increasing amounts of tetraethyl lead to the mixture. Small amounts of tetraethyl lead tend to retard slow combustion, but larger concentrations of tetraethyl lead showed no retarding action and in many cases a positive accelerating effect.These actions may be explained on the assumption that the decomposition products of tetraethyl lead are the active agents, and by considering the relative rates of decomposition of tetraethyl lead and of reaction of the explosive mixture.p e r a t u r e s , determined by Moore's method, of a large n u m b e r of substances and mixtures, and indicated that the effect of tetraethyl lead in increasing proportions differed with different fuels. The ignition temperature of n-heptane (451 " C.) nas r a y idly increased by the addition of tetraethyl lead, apparently reaching a maximum of about 545" C. by the addition of 8 cc. of tetraethyl lead per gallon. The addition of 62 cc. per gallon also gave 545" C. The ignition temperature of benzene, on the other hand, was found to decrease from about 650" C. to 630" C. as the tetraethyl lead was increased from zero to 5 cc. per gallon. Further additions UD siderable data on the effect of tetraethyl lead on ignition temperature are available.Dixon and Coward (12) studied igniting temperatures of gases in 1909. Probably the earliest determinations on combustible liquids were made by Holm (2.4) using a heated porcelain plate upon which he dropped the fuels. Seeking to explain the knocking characteristics of fuels on the basis of their ignition temperatures, Moore (32) developed an improved modification of Holm's method which has been widely adopted by later investigators.The fact that these investigations showed that non-knocking fuels possessed high ignition temperatures led to numerous investigations of the effect of knock suppressors, suc...