The effect of aromatic compounds on the vapour-phase oxidation of fuels. Part I.—the effect on the vapour-phase oxidation of ethers

Chamberlain, G. H. N.; Walsh, A. D.

doi:10.1039/tf9494501032

Cited by 10 publications

(7 citation statements)

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“…Acetaldehyde, another product, has little or no influence on the induction period at 153 °C, but it increases the rate of the second part of the reaction (table 3). The failure of acetaldehyde to markedly change the kinetics of the reaction is in agree ment with earlier results (Chamberlain & Walsh 1949 a).…”

Section: Influence Of Added Productssupporting

confidence: 92%

“…Such an attack on the ether molecule has already been predicted (Townend & Chamberlain 1937;Chamberlain & Walsh 1949 a). Reaction between ether and oxygen can be inhibited readily by small additions of a negative catalyst (Chamberlain & Walsh 1949a, b, 1952Lemay & Ouellet 1957;Waddington 1959), and thus t bimolecular reaction is probably infrequent. Hence, the formation of ether radicals may also be effected by the attack on ether molecules by oxygenated radicals (Lemay & Ouellet 1955).…”

Section: Discussionmentioning

confidence: 73%

“…Although considerable attention has been paid to the oxidation of paraffin hydrocarbons and many of their derivatives, ethers have been comparatively neg lected. Several studies have been made on the cool and hot flames of ether + oxygen mixtures and of the limits of imflammability (Townend & Chamberlain 1937;Ermakova 1940;Chamberlain & Walsh 1949;Ouellet, Leger & Ouellet 1950;Ouellet & Ouellet 1951;Leger & Ouellet 1953), and the relative oxidation rates of the lower aliphatic ethers have been determined (Eastwood & Hinshelwood 1952). A number of compounds retard the oxidation of ethers; these include lead tetraethyl (Chamberlain & Walsh 1952), nitric oxide and formaldehyde (Lemay & Ouellet 1957), aromatic amines Walsh 1949 andaliphatic amines (Waddington 1959).…”

Section: Introductionmentioning

confidence: 99%

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The gaseous oxidation of diethyl ether

1959

Proc. R. Soc. Lond. A

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A detailed study has been made of the gaseous oxidation of diethyl ether in the low-temperature region. The reaction has many characteristics of hydrocarbon oxidation, although there is one essential difference: excess oxygen tends to retard the rate of ether combustion. The principal products during the induction period are acetaldehyde, peracetic acid and ethanol. In the later stages of reaction, acetaldehyde and peracetic acid are consumed; ethanol and acetic acid being the principal end-products. It is assumed that an ‘ether radical’, CH 3 CHOCH 2 CH 3 , formed by the initiation process, decomposes to yield acetaldehyde and an ethyl radical. Subsequently, there are two concurrent reactions. First, the ethy radicals are oxidized throughout the course of the reaction, ethanol being the principal product of this process. Secondly, acetaldehyde is oxidized to peracetic acid, the peracetic acid decomposing in the later stages of reaction to form copious amounts of acetic acid. It is thought that the peracetic acid is the compound that is primarily responsible for chain-branching.

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Section: Influence Of Added Productssupporting

confidence: 92%

Section: Discussionmentioning

confidence: 73%

Section: Introductionmentioning

confidence: 99%

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The gaseous oxidation of diethyl ether

1959

Proc. R. Soc. Lond. A

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“…aromatic compounds with unsaturated side chains such as styrene, some conjugated diolefins) are just the fuels which one would expect (because of self-inhibition ; see ref. (15)) to oxidize by many very short chains and so to be relatively little affected by an inhibitor destroying chain carriers, leaving the (normally masked) small promoting effect a clear field in which to reveal itself. It has in fact long been practically certain that inhibition by lead tetraethyl is primarily due to the metallic part of the molecule since very early experiments showed that (a) the vapour from a lead arc drawn into the air intake of an engine,lG (6) colloidal solutions of lead in petrol,l7 could exert a strong anti-knock effect.…”

Section: Earlier Theories Of Action-(i)mentioning

confidence: 99%

The mode of action of lead tetraethyl as an inhibitor of combustion processes

Chamberlain¹,

Hoare²,

Walsh³

1953

Discuss. Faraday Soc.

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Older theories of action of lead tetraethyl are briefly discussed. New experiments are summarized, showing (i) lead tetraethyl, on oxidation, first forms PbO as a colloidal fog, (ii) lead tetraethyl almost certainly inhibits by virtue of forming PbO, (iii) PbO is an inhibitor because it causes a surface destruction of chains. A simple way is described of coating a quartz reaction vessel with a thin film of PbO. Such a vessel is then used for the study of the effect of PbO on particular combustion reactions. This procedure obviates the uncertainty and difficulty in kinetic studies of the essential inhibiting action of lead tetraethyl, of starting with the alkyl itself. In a PbOcoated vessel " degenerate branching" in methane oxidation near 500°C may be eliminated. An implication is that the secondary chains which are responsible for the degenerate branching probably do not involve the formation of H atoms, 0 atoms or OH radicals. The reason is that, under the conditions used, the rates of reaction of these atoms or radicals with methane are not slow compared to their rates of diffusion to, and reaction with, a PbO surface ; and therefore that a PbO surface could not cut out degenerate branching if these atoms or radicals were formed in the secondary chains. Another implication is that inhibition by PbO in the methane + oxygen system is most probably due to a particular destruction of HO;! radicals. Only these (or possibly HC03), radicals appear sufficiently unreactive in the gas phase to be supposed capable of diffuslng, under the experimental conditions used, to a PbO surface and there being predominantly destroyed. These conclusions are bound up with further implications concerning the relative rates of certain free radical reactions. Inhibition by PbO of hydrocarbon oxidation generally appears to be limited to those conditions where the secondary oxidation of aldehydes is important; and is probably due to the same action as is involved in methane oxidation. PbO also inhibits the hydrogen -toxygen and carbon monoxide -1-oxygen reactions in such a way as to show that its ability to destroy chain carriers is not limited to HO2 radicals. It so happens, however, that in the conditions used for many oxidation systems only comparatively inert radicals, such as HO2, have much chance of reaching the surface and there being destroyed.

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“…Hand in hand with the engine experiments, extensive work has been proceeding on combustion in a glass apparatus (Chamberlain & Walsh 1949Malherbe & Walsh 1950). The engine and non-engine investigations are complementary, and each has helped the understanding of the other.…”

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confidence: 99%

A study of the reactions that lead to 'knock' in the spark-ignite engine

Downs¹,

Walsh²,

Wheeler³

1951

Phil. Trans. R. Soc. Lond. A

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Previous work has demonstrated that knock in the spark-ignition engine is a phenomenon confined to the last part of the charge to burn, and that it is the chemical reactions in this ‘ end-gas ’ which determine whether or not knock will occur. The purpose of this paper is to try to elucidate the nature of these reactions and to discover some of the critical chemical factors controlling the occur- rence of knock. This has been done in three main ways: ( a ) the sequence of chemical reactions occurring in the ‘end-gas’ prior to knock has been followed by means of a specially designed electromagnetic gas-sampling valve which can abstract samples of this gas at various stages in the combustion cycle, ( b ) the effect of the addition of various substances to the cylinder charge on the knock-limited compression ratio of the engine has been determined and ( c ) a study has been made in a motored engine of the limits of cool and hot flame formation. Ricardo E. 6 variable-compression engines were used for all these investigations. Preliminary tests with small quantities of additives, such as azomethane, alkyl nitrites and nitrates, carbon tetrachloride and chloropicrin, demonstrated that substances which would be expected to give rise to free radicals in the engine cylinder are strong pro-knocks. This and the anti-knock action of minute quantities of additives such as lead tetraethyl show the chain nature of the reactions leading to knock. Experiments are described to demonstrate that these reactions are substantially independent of the nature of the cylinder walls. Qualitative sampling tests indicated that knock depends not so much on the formation of some new substance which was not present under non-knocking conditions but rather on the attainment of a critical rate of formation of products present under both conditions. Further experiments with additives in which various intermediate products of reaction, such as aldehydes, nitrogen peroxide and organic peroxides, were tested, showed that with normal fuels the organic peroxides were the only products which were strongly pro-knock and formaldehyde the only product which had an anti-knock effect. This led to the subsequent sampling investigation being concentrated largely on the estimation of these two products in the ‘end-gases’. A method for analyzing for organic peroxides in small concentration and in the presence of other reaction products, such as nitrogen peroxide, was developed. Use of this method with a higher paraffinic fuel showed that peroxide formation was two-stage in nature. The first stage culminated in the formation of a point of inflexion or small peak in the curve of peroxide concentration about 1 ° after top dead centre. In the second stage the curve normally rose again to a higher peak at about 7° 1. Lead tetraethyl had a much greater depressing effect on the peak at 7° L compared with that at 1° 1. The mixture strength giving maximum knock was the same as that giving maximum peroxide concentration. Analyses were also made for aldehydes, shown to be mainly formaldehyde. The main growth of the formaldehyde formation took place in the second of the two stages of peroxide formation. A much smaller quantity of peroxide appeared to be formed when methane was the fuel, and this was eliminated when lead tetraethyl was added to suppress the knock. Benzene formed no peroxides, and none was detected with the alkyl benzenes up to cumene. This difference between benzene and methane on the one hand and the higher paraffinic fuels on the other in regard to peroxide formation was paralleled by the different effect of additives on the two classes of fuel. Formaldehyde was an anti-knock in the latter class and a pro-knock in the former class; acetaldehyde and benzaldehyde were ineffective in the latter but strongly pro-knock in the former; nitrogen peroxide has only a slight pro-knock effect in the latter but was strongly pro knock in the former. Experiments with the higher paraffinic fuels on a motored engine showed that if conditions of temperature and pressure were such as to simulate those obtaining in the ‘end-gas’ prior to knock, cool flames were formed at a time in the cycle approximately corresponding to the point of inflexion of the peroxide sampling curves. No cool flames were detected with benzene or methane. Bright blue flames were observed near the ignition point over certain ranges of mixture strength with benzene and methane as well as with the higher paraffins. Non-engine work has shown the existence of two main types of combustion, namely, so-called ‘low’- and ‘ high ’-temperature types. Of these the first is associated with peroxide and cool-flame formation, ignition taking place by a two-stage process, whereas ignition of the second type is a single-stage process and not usually associated with cool flames or peroxide formation. From the evidence of (1) the peroxide analyses, (2) the experiments with additives and (3) the experiments with a motored engine, it is clear that normal fuels knock by the ‘low’-temperature process but that benzene and methane knock by the ‘ high’-temperature process. Experiments in which formaldehyde was used as a fuel and the effect of various additives on its knock limit determined, showed that its oxidation is best classified as of the ‘ high ’-temperature type and yielded further understanding of the nature of the reactions leading to knock. The effect of hydrogen as an additive with other fuels and the effect of various additives on its own highest useful compression ratio was determined. No peroxides were detected in engine samples when hydrogen was used as the fuel.

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The effect of aromatic compounds on the vapour-phase oxidation of fuels. Part I.—the effect on the vapour-phase oxidation of ethers

Cited by 10 publications

References 0 publications

The gaseous oxidation of diethyl ether

The gaseous oxidation of diethyl ether

The mode of action of lead tetraethyl as an inhibitor of combustion processes

A study of the reactions that lead to 'knock' in the spark-ignite engine

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