9,162 research outputs found
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
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.]
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 improved reconstruction procedure for the correction of local magnification effects in three-dimensional atom-probe
A new 3DAP reconstruction procedure is proposed that accounts for the
evaporation field of a secondary phase. It applies the existing cluster
selection software to identify the atoms of the second phase and, subsequently,
an iterative algorithm to homogenise the volume laterally. This Procedure,
easily implementable on existing reconstruction software, has been applied
successfully on simulated and real 3DAP analyses
Управление направлениями повышения эффективности отрасли виноградарства
Целью статьи является изучение порядка управления затратами и прибылью с
целью повышения экономической эффективности производства винограда и определение важности отрасли
виноградарства
Zero kinetic energy-pulsed field ionization and resonance enhanced multiphoton ionization photoelectron spectroscopy: Ionization dynamics of Rydberg states in HBr
The results of rotationally resolved resonance enhanced multiphoton ionization photoelectron spectroscopy and zero kinetic energy‐pulsed field ionization studies on HBr via various rotational levels of the F^ 1Δ_2 and f^ 3Δ_2 Rydberg states are reported. These studies lead to an accurate determination of the lowest ionization threshold as 94 098.9±1 cm^(−1). Observed rotational and spin–orbit branching ratios are compared to the results of ab initio calculations. The differences between theory and experiment highlight the dominant role of rotational and spin–orbit interactions for the dynamic properties of the high‐n Rydberg states involved in the pulsed field ionization process
Laser-induced fluorescence studies of HfF+ produced by autoionization
Autoionization of Rydberg states of HfF, prepared using the optical-optical
double resonance (OODR) technique, holds promise to create HfF+ in a particular
Zeeman level of a rovibronic state for an electron electric dipole moment
(eEDM) search. We characterize a vibronic band of Rydberg HfF at 54 cm-1 above
the lowest ionization threshold and directly probe the state of the ions formed
from this vibronic band by performing laser-induced fluorescence (LIF) on the
ions. The Rydberg HfF molecules show a propensity to decay into only a few ion
rotational states of a given parity and are found to preserve their orientation
qualitatively upon autoionization. We show empirically that we can create 30%
of the total ion yield in a particular |J+,M+> state and present a simplified
model describing autoionization from a given Rydberg state that assumes no
angular dynamics.Comment: 8 pages, 5 figure
Hyperfine, rotational and Zeeman structure of the lowest vibrational levels of the Rb \tripletex state
We present the results of an experimental and theoretical study of the
electronically excited \tripletex state of Rb molecules. The
vibrational energies are measured for deeply bound states from the bottom up to
using laser spectroscopy of ultracold Rb Feshbach molecules. The
spectrum of each vibrational state is dominated by a 47\,GHz splitting into a
\cog and \clg component caused mainly by a strong second order spin-orbit
interaction. Our spectroscopy fully resolves the rotational, hyperfine, and
Zeeman structure of the spectrum. We are able to describe to first order this
structure using a simplified effective Hamiltonian.Comment: 10 pages, 7 figures, 2 table
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