Knocking in internal combustion engines

Antidetonanti, in Ital and Antidetonants, in Fr). Substances such as lead tetraethyl Pb(C2Hs )4 tin tetraethyl Sn(CjHs)4, ferro-earbonyl Fe(CO)5, nickel carbonyl Ni(C0)4, aniline, etc possess the property of preventing knock in internal combustion engines and for this reason are also called "antiknock substances. For their description see Refs 3,5,7 8... 

The first attempts to understand quantitatively the high-temperature chemical processes were related to combustion. They took place in the first part of the last century, partly with the development of thermal theories and theories for chain reactions and partly with work on high-temperature oxidation of hydrocarbons (to understand flame propagation) and low-temperature oxidation (to understand autoignition and knock in internal combustion engines). 

Edgar, G. Theory of Knock in Internal Combustion Engines. In The Science of Petroleum, Vol. IV, p. 2927 Dunstan, A. E., Ed. London Oxford University Press 1938. 

The chain reaction sustains itself until it is terminated by direct combination of H and Cl, probably at the walls of the containing vessel. Such a reaction therefore tends to propagate itself without further encouragement until the reactants are exhausted. There are many examples of chain reactions in organic chemistry, where the active intermediate is often a free radical such as CH 3. Sometimes these are undesirable e.g. in the premature oxidation of hydrocarbons under pressure, which causes knocking in internal combustion engines) and it is necessary to inhibit them by suitable additives which operate by terminating the chains. 

The Cause and Suppression of Knocking in Internal Combustion Engines... 

In the attempts that have been made to explain the action of certain compounds in suppressing the knock in internal combustion engines, it was early recognized that an understanding of the mechanism by which combustion occurred was essential to a successful solution of the problem. Consequently considerable experimental work and much speculation has been expended in the formulation of combustion mechanisms. A number of the earlier proposed theories have been largely discredited and more suitable ones substituted. 

The cool flames associated with the low-temperature oxidation of hydrocarbon have great relevance, being the fundamental cause of knock in internal combustion engines. Their mechanistic origin arises through a thermokinetic feedback [2]. The crucial feature is the reaction through which O2 reacts by addition to an alkyl... 

Lenin prize. The B-Z reaction, as it is now known, has been studied intensivety and many other cases of oscillations in homogeneous chemical systems have been identified. Figure 8.3 shows an example from the combustion of hydrogen. Similar fluctuations during the oxidation of hydrocarbon fuels are responsible for knock in internal combustion engines. 

The highly branched compound 2,2,4-trimethylpentane (called isooctane in the petroleum industry) burns very smoothly (without knocking) in internal combustion engines and is used as one of the standards by which the octane rating of gasolines is established. 

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