Oscillatory ignitions and cool flames in the oxidation of butane in a jet-stirred reactor

1991 ◽  
Vol 337 (1646) ◽  
pp. 211-221 ◽  
Keyword(s):  
High Temperature ◽  
Stationary State ◽  
Initial Pressure ◽  
Probe Laser ◽  
Cool Flame ◽  
Cool Flames ◽  
Stirred Reactor ◽  
Ignition Region ◽  
Flame Region ◽  
Temperature And Pressure

The oxidation of butane ([C 4 H 10 ] : [ O 2 ] = 1.13:1.00) has been studied over the temperature and pressure ranges 371 ⩽ T/ K ⩽ 675, 226 ⩽ P /Torr ⩽ 489 in a jet stirred reactor with a residence time of 9.4 s (1 Torr ≈ 133.3 Pa), The gas temperature and pressure were probed and phase diagrams constructed delineating regions of oscillatory ignitions and cool flames, and high- and low -temperature stationary states. On heating at an initial pressure of 400 Torr from 570 K sharp transitions were observed, first to an oscillatory ignition and then to an oscillatory cool flame region, followed by a smooth transition to a high-temperature stationary state via a supercritical Hopf bifurcation. On cooling from this high - temperature stationary state, oscillatory cool flames were observed with a sharp extinction at 542 K, without any entry to the oscillatory ignition region. The latter could be entered, however, by suddenly cooling the system from the oscillatory cool flame region by temporarily substituting nitrogen for oxygen in the gas streams. Complex waveforms, consisting of bursts of oscillatory cool flames interspersed with periods of monotonic cooling, were also observed at lower pressures. A Nd : YAG pumped dye laser was used to probe laser induced fluorescence from form aldehyde in the oscillatory ignition region. Variations in the internal surface of the reactor demonstrated the significance of surface reactions. An outline mechanism, based on detailed numerical simulations, is presented to account for the shape of the ignition profiles and the transition from multiple ignitions to oscillatory cool flames.

The oxidation of hexane in the cool-flame region

1952 ◽  
Vol 212 (1110) ◽  
pp. 311-330 ◽  
Keyword(s):  
Atmospheric Pressure ◽  
Chemical Nature ◽  
Complex Mixture ◽  
Cyclic Ethers ◽  
Reaction Products ◽  
Cool Flame ◽  
Oxidation Of Methane ◽  
Cool Flames ◽  
Flame Region ◽  
Considerable Support

The chemical nature of the cool flame of hexane at 300°C, maintained stationary in a flow system at atmospheric pressure, has been investigated. The relative intensities of cool flames obtained from mixtures of differing composition have been measured, using a photomultiplier cell, and correlated with analyses made of the complex mixture of reaction products. The stationary two-stage flames which may be obtained at either higher oxygen concentrations or higher pressures than the cool flame are also described, and investigated similarly. The results are examined in the light of a theory of combustion of the higher hydrocarbons via aldehydes and hydroxyl radicals, which is an extension of a mechanism derived for the oxidation of methane. This receives considerable support, particularly from the identification of the complete homologous series of saturated aldehydes which can result from the hexane molecule. Associated with these reactions are others due to the greater stability of peroxide radicals at 300°C than at the higher temperatures of methane oxidation. Thus the building up of a partial pressure of hydroperoxide sufficient to ignite in the presence of oxygen may initiate the cool flame, and considerable amounts of cyclic ethers have been found which probably had a peroxidic precursor.

Alkylperoxy radical rearrangements during the gaseous oxidation of isobutene

1963 ◽  
Vol 273 (1354) ◽  
pp. 427-434 ◽  
Keyword(s):  
Methyl Ethyl Ketone ◽  
Peroxy Radical ◽  
Methyl Ethyl ◽  
Isotopic Tracer ◽  
Cool Flame ◽  
Cool Flames ◽  
Tracer Techniques ◽  
Slow Combustion ◽  
Flame Region ◽  
Subsequent Decomposition

Isotopic tracer techniques have been used to elucidate the mechanism of production of ketones in the gaseous oxidation of isobutane. Both acetone and methyl ethyl ketone are formed from this hydrocarbon, the former predominating in the products of slow combustion and the latter in the products of cool flames. Addition of [1,3- 14 C] acetone to reacting isobutane + oxygen mixtures has established that none of the methyl ethyl ketone formed in the cool-flame region and only 25% of that formed during slow combustion arises from further reactions of acetone. The formation of methyl ethyl ketone probably involves predominantly rearrangement and subsequent decomposition of the tert .-butyl peroxy radical and this indeed appears to be the almost exclusive fate of this radical under cool-flame conditions.

Spectra of cool flames and pre-ignition glows

1955 ◽  
Vol 233 (1193) ◽  
pp. 184-194 ◽  
Keyword(s):  
Formaldehyde Emission ◽  
Cool Flame ◽  
Cool Flames ◽  
Auto Ignition ◽  
Weak Limits ◽  
Flame Region ◽  
The Rich ◽  
Reaction Processes ◽  
Rich Mixtures ◽  
Simple Flow

Cool flames and pre-ignition glows of rich and weak mixtures of propane with air and oxygen have been studied in a simple flow system at atmospheric pressure. In the cool-flame region the spectrum shows the usual formaldehyde emission bands, but in the pre-ignition glow near the high-temperature ignition limit the spectrum is quite different, consisting mainly of hydrocarbon flame bands, due to HCO. With weak mixtures the HCO bands are accompanied by strong OH and some CH and CO-flame bands and the spectrum is rather similar to that of the hot flame. With rich mixtures, the HCO bands are accompanied by some CH and formaldehyde bands and weak OH but no C 2 , so that the spectrum is quite different from that of the rich hot flame, which is dominated by C 2 and CH emission and shows little HCO. The unusual observation of strong HCO with rich mixtures is discussed. It is suggested that the C 2 and CH emission occurs under conditions when free atoms and radicals diffuse back from the burnt mixture, while the HCO emission is associated with chain termination or thermal initiation processes. This supports the view that radical diffusion is important in flame propagation. No pre-ignition glow was observed with methane or formaldehyde. The pre-ignition glow of CO occurs readily at both rich and weak limits at atmospheric and low pressure and shows CO-flame bands (attributed to CO 2 ). Addition of methane or formaldehyde to the CO modifies the ignition limits and reduces the glow region, but with a little methane added to rich CO + O 2 , clear spectra were obtained which showed the cool flame bands of formaldehyde superposed on the CO-flame bands. Addition of formaldehyde instead of methane did not produce the formaldehyde bands. The reaction processes are discussed, and it is suggested that during oxidation of CO, free O atoms or O 3 are produced which may react with methane to result in cool flame processes. The relation of these observations to previous work on the auto-ignition of methane is discussed.

Hydrocarbon cool flames and the influence of hydrogen bromide

1974 ◽  
Vol 338 (1614) ◽  
pp. 327-340 ◽  
Keyword(s):  
Induction Period ◽  
Initial Conditions ◽  
Hydrogen Bromide ◽  
Initial Pressure ◽  
Pressure Change ◽  
Two Stage ◽  
Cool Flame ◽  
The Third ◽  
Cool Flames ◽  
Stage Process

Small amounts of hydrogen bromide added to n -pentane + 1.33 O 2 mixtures lower both the limiting pressure for the onset of two-stage ignition and also, to a smaller extent, that for the appearance of cool flames. The induction period preceding the first cool flame, ז 1 , is shown to be related to the initial pressure, P 0 , by a relation of the form ז 1 = kP -n 0 + c , where k , n and c are constants for a given set of initial conditions. The results show that c ≠ 0 and that the addition of hydrogen bromide reduces both ז 1 and c . However, since ז 1 ≽ c and c is always finite, it is clear that, even at temperatures above the ignition profiles, ignition continues to take place as a two-stage process. Plots of lg ז 1 against reciprocal temper­ature are invariably characterized by a well-defined change in slope and the temperature at which this occurs decreases with increasing concentration of hydrogen bromide, eventually reaching a limiting value of ca . 270 °C. Above this temperature the slopes of the plots are more or less independent of hydrogen bromide and correspond to an overall activation energy of 82 kJ mol -1 . Below this temperature the apparent energy of activation decreases from 206 to 113 kJ mol -1 as the concentration of hydrogen bromide is increased. Similarly there is a limiting concentration of the additive above which the pressure change accompanying the first cool flame is not appreciably increased except at low temperatures. In systems which exhibit multiple cool flames, the second and fourth cool flames are generally too indistinct for their characteristics to be measured with any accuracy. However, the third cool flame appears as a well-defined but relatively weak pressure pulse. In striking contrast to the behaviour of the first cool flame, neither the third cool flame nor the induction period preceding it is appreciably affected by the presence of hydrogen bromide. It thus appears that, although the halogen compound is pre­sumably involved in the chemical reactions leading to the first cool flame, the third cool flame is propagated by intermediates whose mode of forma­tion is independent of the additive.

The cool-flame oxidation of 3-ethylpentane

1971 ◽  
Vol 325 (1563) ◽  
pp. 469-492 ◽  
Keyword(s):  
Carbon Number ◽  
Sole Source ◽  
Initial Reaction ◽  
Cool Flame ◽  
Cool Flames ◽  
Lower Molecular Mass ◽  
Flame Region ◽  
Group Migration ◽  
Flame Oxidation ◽  
Alkylperoxy Radicals

Detailed studies have been carried out of the combustion of 3-ethylpentane with special reference to the chemical changes taking place in the cool-flame region, where at least 74 individual products are formed. At ca . 300 °C, the first products to appear are 3-ethylpent-1-ene and 3-ethylpent-2-ene, C 7 O -heterocycles and alkenes of carbon number less than seven; the rates of consumption of 3-ethylpentane and of formation of all products increase dramatically just before propagation of the first cool-flame but do not vary appreciably when subsequent cool-flames pass. As the temperature is raised to ca . 400 °C, the quantities of 3-ethylpentane consumed and of lower molecular mass products formed increase markedly while the amounts of most C 7 products decrease. Consideration of the analytical results indicates that alkylperoxy radical isomerization plays an important part in the primary chain-propagation cycle both in and out of the cool-flame region and at temperatures as high as 400 °C. It appears that the initial reaction of alkyl radicals with oxygen takes place, largely, if not exclusively, by direct addition to form alkylperoxy radicals. Different modes of isomerization of these radicals leads to the wide variety of products found and decomposition of the a-hydroperoxyalkyl radicals by direct loss of HO 2 is probably the sole source of the conjugate alkenes. The results also provide the first recorded evidence of ethyl group migration during alkylperoxy radical isomerization.

scholarly journals Fatigue simulation of a short fiber re-inforced oil-filter under high temperature and pressure load

2018 ◽  
Vol 213 ◽  
pp. 207-214 ◽  
Author(s):  
Michael Hack ◽  
Wolfgang Korte ◽  
Stefan Sträßer ◽  
Matthias Teschner
Keyword(s):  
High Temperature ◽  
Short Fiber ◽  
Pressure Load ◽  
High Temperature And Pressure ◽  
Temperature And Pressure

Creep Modeling of Welded Joints Using the Theta Projection Concept and Finite Element Analysis

1999 ◽  
Vol 122 (1) ◽  
pp. 22-26 ◽  
Author(s):  
M. Law ◽  
W. Payten ◽  
K. Snowden
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
High Temperature ◽  
Welded Joints ◽  
Creep Model ◽  
Projection Data ◽  
Predictive Capability ◽  
Element Analysis ◽  
High Temperature And Pressure ◽  
Temperature And Pressure

Modeling of welded joints under creep conditions with finite element analysis was undertaken using the theta projection method. The results were compared to modeling based on a simple Norton law. Theta projection data extends the accuracy and predictive capability of finite element modeling of critical structures operating at high temperature and pressure. In some cases analyzed, it was found that the results diverged from those gained using a Norton law creep model. [S0094-9930(00)00601-6]

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