Spontaneous ignition characteristics of gaseous hydrocarbon-air mixtures

Experiments are conducted to determine the spontaneous ignition delay times of gaseous propane, kerosine vapor, and n-heptane vapor in mixtures with air, and oxygen-enriched air, at atmospheric pressure. Over a range of equivalence ratios from 0.2 to 0.8 it is found that ignition delay times are sensibly independent of fuel concentration. However, the results indicate a strong dependence of delay times on oxygen concentration. The experimental data for kerosine and propane demonstrate very close agreement with the results obtained previously by Mullins and Lezberg respectively

The influence of turbulence on the structure and propagation of enclosed flames

Although it has long been established that burning rates can be appreciably increased by turbulence, the actual extent of this increase and the precise mechanism involved are still far from clear. The object of the present research was to examine the effects of turbulence on burning velocity and on the physical structure of the flame surface under flow conditions similar to those experienced in turbojet afterburner systems

Atomization of broad specification aircraft fuels

The atomization properties of liquid fuels for the potential use in aircraft gas turbine engines are discussed. The significance of these properties are addressed with respect to the ignition and subsequent combustion behavior of the fuel spray/air mixture. It is shown that the fuel properties which affect the atomization behavior (viscosity, surface tension, and density) are less favorable for the broad specification fuels as compared to with those for conventional fuels

Spontaneous Ignition Characteristics of Hydrocarbon Fuel-air Mixtures

Although the subject of spontaneous ignition of liquid fuels has received considerable attention in the past, the role of fuel evaporation in the overall spontaneous ignition process is still unclear. A main purpose of this research is to carry out measurements of ignition delay times, using fuels of current and anticipated future aeronautical interest, at test conditions that are representative of those encountered in modern gas turbine engines. Attention is focused on the fuel injection process, in particlar the measurement and control of man fuel drop size and fuel-air spatial distribution. The experiments are designed to provide accurate information on the role of fuel evaporation processes in determining the overall ignition delay time. The second objective is to examine in detail the theoretical aspects of spontaneous ignition in order to improve upon current knowledge and understanding of the basic processes involved, so that the results of the investigation can find general and widespead application

Repetition and difference: Lefebvre, Le Corbusier and modernity's (im)moral landscape: a commentary

This article engages with the relationship between social theory, architectural theory and material culture. The article is a reply to an article in a previous volume of the journal in question (Smith, M. (2001) ‘Repetition and difference: Lefebvre, Le Corbusier and modernity’s (im)moral landscape’, Ethics, Place and Environment, 4(1), 31-34) and, consequently, is also a direct engagement with another academic's scholarship. It represents a critique of their work as well as a recasting of their ideas, arguing that the matter in question went beyond interpretative issues to a direct critique of another author's scholarship on both Le Corbusier and Lefebvre. A reply to my article from the author of the original article was carried in a later issue of the journal (Smith, M. (2002) ‘Ethical Difference(s): a Response to Maycroft on Le Corbusier and Lefebvre’, Ethics, Place and Environment, 5(3), 260-269)

Changes in the subsurface stratification of the Sun with the 11-year activity cycle

We report on the changes of the Sun's subsurface stratification inferred from helioseismology data. Using SOHO/MDI (SOlar and Heliospheric Observatory/Michelson Doppler Imager) data for the last 9 years and, more precisely, the temporal variation of f-mode frequencies, we have computed the variation of the radius of subsurface layers of the Sun by applying helioseismic inversions. We have found a variability of the ``helioseismic'' radius in antiphase with the solar activity, with the strongest variations of the stratification being just below the surface around 0.995$R_{\odot}$. Besides, the radius of the deeper layers of the Sun, between 0.975$R_{\odot}$ and 0.99$R_{\odot}$ changes in phase with the 11-year cycle.Comment: 14 pages, 7 figures, accepted in ApJ

Spontaneous ignition delay characteristics of hydrocarbon fuel-air mixtures

The influence of pressure on the autoignition characteristics of homogeneous mixtures of hydrocarbon fuels in air is examined. Autoignition delay times are measured for propane, ethylene, methane, and acetylene in a continuous flow apparatus featuring a multi-point fuel injector. Results are presented for mixture temperatures from 670K to 1020K, pressures from 1 to 10 atmospheres, equivalence ratios from 0.2 to 0.7, and velocities from 5 to 30 m/s. Delay time is related to pressure, temperature, and fuel concentration by global reaction theory. The results show variations in global activation energy from 25 to 38 kcal/kg-mol, pressure exponents from 0.66 to 1.21, and fuel concentration exponents from 0.19 to 0.75 for the fuels studied. These results are generally in good agreement with previous studies carried out under similar conditions

An investigation of combustion instability in aircraft-engine reheat systems

The principal objective of this study was to examine experimentally the effects of upstream temperature, velocity, gutter blockage, tailpipe length, and main and pilot fuel flows, on the form of combustion instability encountered in aircraft reheat systems which is sometimes referred to as 'buzz'. Tests were carried out at atmospheric pressure for upstream temperatures of between 200 and 500°C, and upstream velocities ranging from 140 to 200 ft/sec. Three values of stabilizer blockage were employed, namely 25, 30 and 35%. The tailpipe length was varied between 9 and 45 inches. Auto-correlation techniques were used in the frequency analysis of the buzz waveforms. It was found that a certain minimum tailpipe length is necessary in order to produce buzz which is then strengthened as the tailpipe length is increased. Buzz also becomes more pronounced with an increase in gas velocity but stabilizer blockage appears to have no discernible effect … [cont.]

Anisotropy induced Feshbach resonances in a quantum dipolar gas of magnetic atoms

We explore the anisotropic nature of Feshbach resonances in the collision between ultracold magnetic submerged-shell dysprosium atoms, which can only occur due to couplings to rotating bound states. This is in contrast to well-studied alkali-metal atom collisions, where most Feshbach resonances are hyperfine induced and due to rotation-less bound states. Our novel first-principle coupled-channel calculation of the collisions between open-4f-shell spin-polarized bosonic dysprosium reveals a striking correlation between the anisotropy due to magnetic dipole-dipole and electrostatic interactions and the Feshbach spectrum as a function of an external magnetic field. Over a 20 mT magnetic field range we predict about a dozen Feshbach resonances and show that the resonance locations are exquisitely sensitive to the dysprosium isotope.Comment: 5 pages, 4 figure