1,611 research outputs found
An assessment of the use of antimisting fuel in turbofan engines
An evaluation was made on the effects of using antimisting kerosene (AMK) on the performance of the components from the fuel system and the combustor of current in service JT8D aircraft engines. The objectives were to identify if there were any problems associated with using antimisting kerosene and to determine the extent of shearing or degradation required to allow the engine components to achieve satisfactory operation. The program consisted of a literature survey and a test program which evaluated the antimisting kerosene fuel in laboratory and bench component testing, and assessed the performance of the combustor in a high pressure facility and in an altitude relight/cold ignition facility
NASA/Pratt and Whitney experimental clean combustor program: Engine test results
A two-stage vorbix (vortex burning and mixing) combustor and associated fuel system components were successfully tested in an experimental JT9D engine at steady-state and transient operating conditions, using ASTM Jet-A fuel. Full-scale JT9D experimental engine tests were conducted in a phase three aircraft experimental clean combustor program. The low-pollution combustor, fuel system, and fuel control concepts were derived from phase one and phase two programs in which several combustor concepts were evaluated, refined, and optimized in a component test rig. Significant pollution reductions were achieved with the combustor which meets the performance, operating, and installation requirements of the engine
Lean, premixed, prevaporized fuel combustor conceptual design study
Four combustor concepts, designed for the energy efficient engine, utilize variable geometry or other flow modulation techniques to control the equivalence ratio of the initial burning zone. Lean conditions are maintained at high power to control oxides of nitrogen while near stoichometric conditions are maintained at low power for low CO and THC emissions. Each concept was analyzed and ranked for its potential in meeting the goals of the program. Although the primary goal of the program is a low level of nitric oxide emissions at stratospheric cruise conditions, both the ground level EPA emission standards and combustor performance and operational requirements typical of advanced subsonic aircraft engines are retained as goals as well. Based on the analytical projections made, two of the concepts offer the potential of achieving the emission goals; however, the projected operational characteristics and reliability of any concept to perform satisfactorily over an entire aircraft flight envelope would require extensive experimental substantiation before engine adaptation can be considered
Evaluation of Federal Aviation Administration ion engine exhaust sampling rake
A FAA exhaust emissions rake was tested in the Experimental Clean Combustor Program, Phase 3 to permit comparison of the values of gaseous emissions and smoke measured by the FAA rake with those measured with the NASA Pratt and Whitney Aircraft (P and WA) rake used in the Phase 3 Experimental Clean Combustor Program and with station seven probes. The results showed that the levels of CO, THC, NOx and smoke measured by the FAA and NASA/P and WA rakes agree well at high power, but that CO emissions measured by the FAA rake were approximately 10 percent higher than those measured by the NASA/P and WA rake at low power
Lean, premixed, prevaporized combustor conceptual design study
The seven month study program has the objective to identify and evaluate promising lean, premixed, prevaporized combustor concepts utilizing variable geometry and/or other flow control techniques. The general approach taken to accomplish this objective is outlined and consists of combustor design, design analysis and design ranking. The schedule being taken to achieve this program is shown. Although the ultimate goal of this program is the significant reduction of cruise oxides of nitrogen, both the EPA emission standards and combustor performance levels outlined are retained as goals as well
Secure self-calibrating quantum random bit generator
Random bit generators (RBGs) are key components of a variety of information
processing applications ranging from simulations to cryptography. In
particular, cryptographic systems require "strong" RBGs that produce
high-entropy bit sequences, but traditional software pseudo-RBGs have very low
entropy content and therefore are relatively weak for cryptography. Hardware
RBGs yield entropy from chaotic or quantum physical systems and therefore are
expected to exhibit high entropy, but in current implementations their exact
entropy content is unknown. Here we report a quantum random bit generator
(QRBG) that harvests entropy by measuring single-photon and entangled
two-photon polarization states. We introduce and implement a quantum
tomographic method to measure a lower bound on the "min-entropy" of the system,
and we employ this value to distill a truly random bit sequence. This approach
is secure: even if an attacker takes control of the source of optical states, a
secure random sequence can be distilled.Comment: 5 pages, 2 figure
On the central helium-burning variable stars of the LeoI dwarf spheroidal galaxy
We present a study of short period, central helium-burning variable stars in
the Local Group dwarf spheroidal galaxy LeoI, including 106 RR Lyrae stars and
51 Cepheids. So far, this is the largest sample of Cepheids and the largest
Cepheids to RR Lyrae ratio found in such a kind of galaxy. The comparison with
other Local Group dwarf spheroidals, Carina and Fornax, shows that the period
distribution of RR Lyrae stars is quite similar, suggesting similar properties
of the parent populations, whereas the Cepheid period distribution in LeoI
peaks at longer periods (P \sim 1.26d instead of ~0.5d) and spans over a
broader range, from 0.5 to 1.78d.
Evolutionary and pulsation predictions indicate, assuming a mean metallicity
peaked within -1.5<= [Fe/H]<=-1.3, that the current sample of LeoI Cepheids
traces a unique mix of Anomalous Cepheids (blue extent of the red--clump,
partially electron degenerate central helium-burning stars) and short-period
classical Cepheids (blue-loop, quiescent central helium-burning stars). Current
evolutionary prescriptions also indicate that the transition mass between the
two different groups of stars is MHeF \sim 2.1 Mo, and it is constant for stars
metal-poorer than [Fe/H]\sim-0.7. Finally, we briefly outline the different
implications of the current findings on the star formation history of LeoI.Comment: 5 Pages, 4 Figures, ApJ letter, accepte
Biogas from source separated organic waste within a circular and life cycle perspective. A case study in Ontario, Canada
Abstract The appropriate transformation and valorisation of biogas offers environmental and economic opportunities in a future with restrictions upon fossil-based fuels and materials. The LCA method was used to quantify and compare the potential environmental impacts of an AD plant incorporating biogas co-generation and upgrading options, namely AD-CHP and AD-RNG. Using an average Anaerobic Digestion facility in Ontario, Canada, modelled after real facilities, as a case study, electricity and steel were identified as potential hotspot input materials carrying a disproportionate environmental burden for biogas production. With a system expansion approach, the biogas was subsequently utilized to produce (1) both heat and electricity using a Combined Heat and Power (CHP) system, or (2) upgraded to renewable natural gas (also called biomethane) through chemical amine scrubbing, respectively. In comparing the biogas co-generation and upgrading options, the AD-CHP alternative resulted in a lesser environmental load, two times lower when compared to the AD-RNG biomethane recovery option. Furthermore, the avoided burden of producing fossil-based electricity, natural gas, and chemical fertilizer was analyzed and compared against their renewable counterparts. Significant reductions in emissions and in the depletion of fossil fuels were achieved, thus confirming the positive efforts of diverting organic waste from landfills to reduce organic waste disposal impacts and improve the management of organic waste. The analysis has provided useful insights to bioenergy project developers, policy makers and the scientific community regarding the processing of source separated organic waste, biogas production, and its upgrading alternatives in a circular economy perspective
Astrometry with MCAO: HST-GeMS proper motions in the globular cluster NGC 6681
Aims: for the first time the astrometric capabilities of the Multi-Conjugate
Adaptive Optics (MCAO) facility GeMS with the GSAOI camera on Gemini-South are
tested to quantify the accuracy in determining stellar proper motions in the
Galactic globular cluster NGC 6681. Methods: proper motions from HST/ACS for a
sample of its stars are already available, and this allows us to construct a
distortion-free reference at the epoch of GeMS observations that is used to
measure and correct the temporally changing distortions for each GeMS exposure.
In this way, we are able to compare the corrected GeMS images with a
first-epoch of HST/ACS images to recover the relative proper motion of the
Sagittarius dwarf spheroidal galaxy with respect to NGC 6681. Results: we find
this to be (\mu_{\alpha}cos\delta, \mu_{\delta}) = (4.09,-3.41) mas/yr, which
matches previous HST/ACS measurements with a very good accuracy of 0.03 mas/yr
and with a comparable precision (r.m.s of 0.43 mas/yr). Conclusions: this study
successfully demonstrates that high-quality proper motions can be measured for
quite large fields of view (85 arcsec X 85 arcsec) with MCAO-assisted,
ground-based cameras and provides a first, successful test of the performances
of GeMS on multi-epoch data.Comment: 5 pages, 4 figures. Accepted for publication by A&A Letter
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