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24 results on '"Holley A.T."'

1. The neutron electric dipole moment experiment at the Spallation Neutron Source

Author

Leung K.K.H., Ahmed M., Alarcon R., Aleksandrova A., Baeßler S., Barrón-Palos L., Bartoszek L., Beck D.H., Behzadipour M., Bessuille J., Blatnik M.A., Broering M., Broussard L.J., Busch M., Carr R., Chu P.-H., Cianciolo V., Clayton S.M., Cooper M.D., Crawford C., Currie S.A., Daurer C., Dipert R., Dow K., Dutta D., Efremenko Y., Erickson C.B., Filippone B.W., Fomin N., Gao H., Golub R., Gould C.R., Greene G.L., Haase D.G., Hasell D., Hawari A.I., Hayden M.E., Holley A.T., Holt R.J., Huffman P.R., Ihloff E., Ito T.M., Kelsey J., Kim Y.J., Korobkina E., Korsch W., Lamoreaux S.K., Leggett E., Lipman A., Liu C.-Y., Long J., MacDonald S.W.T., Makela M., Matlashov A., Maxwell J., McCrea M., Mendenhall M., Meyer H.O., Milner R., Mueller P., Nouri N., O'Shaughnessy C.M., Osthelder C., Peng J.-C., Penttila S., Phan N.S., Plaster B., Ramsey J., Rao T., Redwine R.P., Reid A., Saftah A., Seidel G.M., Silvera I.F., Slutsky S., Smith E., Snow W.M., Sondheim W., Sosothikul S., Stanislaus T.D.S., Sun X., Swank C.M., Tang Z., Dinani R. Tavakoli, Tsentalovich E., Vidal C., Wei W., White C.R., Williamson S.E., Yang L., Yao W., and Young A.R.

Subjects
Physics, QC1-999
Abstract

Novel experimental techniques are required to make the next big leap in neutron electric dipole moment experimental sensitivity, both in terms of statistics and systematic error control. The nEDM experiment at the Spallation Neutron Source (nEDM@SNS) will implement the scheme of Golub & Lamoreaux [Phys. Rep., 237, 1 (1994)]. The unique properties of combining polarized ultracold neutrons, polarized 3He, and superfluid 4He will be exploited to provide a sensitivity to ∼ 10−28 e · cm. Our cryogenic apparatus will deploy two small (3 L) measurement cells with a high density of ultracold neutrons produced and spin analyzed in situ. The electric field strength, precession time, magnetic shielding, and detected UCN number will all be enhanced compared to previous room temperature Ramsey measurements. Our 3He co-magnetometer offers unique control of systematic effects, in particular the Bloch-Siegert induced false EDM. Furthermore, there will be two distinct measurement modes: free precession and dressed spin. This will provide an important self-check of our results. Following five years of “critical component demonstration,” our collaboration transitioned to a “large scale integration” phase in 2018. An overview of our measurement techniques, experimental design, and brief updates are described in these proceedings.

Published
2019
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2. Search for neutron dark decay: n → χ + e+e−

Author

Sun X., Adamek E., Allgeier B., Blatnik M., Bowles T.J., Broussard L.J., Brown M.A.-P., Carr R., Clayton S., Cude-Woods C., Currie S., Dees E.B., Ding X., Filippone B.W., García A., Geltenbort P., Hasan S., Hickerson K.P., Hoagland J., Hong R., Hogan G.E., Holley A.T., Ito T.M., Kneckt A., Liu C.-Y., Liu J., Makela M., Mammei R., Martin J.W., Melconian D., Mendenhall M.P., Moore S.D., Morris C.L., Nepal S., Nouri N., Pattie R.W., Galván A.P., Phillips II D.G., Picker R., Pitt M.L., Plaster B., Ramsey J.C., Rios R., Salvat D.J., Saunders A., Sondheim W., Sjue S., Slutsky S., Swank C., Swift G., Tatar E., Vogelaar R.B., VornDick B., Wanchun W., Wang Z., Wexler J., Womack T., Wrede C., Young A.R., and Zeck B.A.

Subjects
Physics, QC1-999
Abstract

In January, 2018, Fornal and Grinstein proposed that a previously unobserved neutron decay branch to a dark matter particle (χ) could account for the discrepancy in the neutron lifetime observed in two different types of experiments. One of the possible final states discussed includes a single χ along with an e+e− pair. We use data from the UCNA (Ultracold Neutron Asymmetry) experiment to set limits on this decay channel. Coincident electron-like events are detected with ∼ 4π acceptance using a pair of detectors that observe a volume of stored Ultracold Neutrons (UCNs). We use the timing information of coincidence events to select candidate dark sector particle decays by applying a timing calibration and selecting events within a physically-forbidden timing region for conventional n → p + e- + ν̅e decays. The summed kinetic energy (Ee+e−) from such events is reconstructed and used to set limits, as a function of the χ mass, on the branching fraction for this decay channel.

Published
2019
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3. Final results for the neutron β-asymmetry parameter A0 from the UCNA experiment

Author

Plaster B., Adamek E., Allgeier B., Anaya J., Back H.O., Bagdasarova Y., Berguno D.B., Blatnik M., Boissevain J.G., Bowles T.J., Broussard L.J., Brown M.A.-P., Carr R., Clark D.J., Clayton S., Cude-Woods C., Currie S., Dees E.B., Ding X., Du S., Filippone B.W., García A., Geltenbort P., Hasan S., Hawari A., Hickerson K.P., Hill R., Hino M., Hoagland J., Hoedl S.A., Hogan G.E., Hona B., Hong R., Holley A.T., Ito T.M., Kawai T., Kirch K., Kitagaki S., Knecht A., Lamoreaux S.K., Liu C.-Y., Liu J., Makela M., Mammei R.R., Martin J.W., Meier N., Melconian D., Mendenhall M.P., Moore S.D., Morris C.L., Mortensen R., Nepal S., Nouri N., Pattie R.W., Pérez Galván A., Phillips II D.G., Pichlmaier A., Picker R., Pitt M.L., Ramsey J.C., Rios R., Russell R., Sabourov K., Sallaska A.L., Salvat D.J., Saunders A., Schmid R., Seestrom S.J., Servicky C., Sharapov E.I., Sjue S.K.L., Slutsky S., Smith D., Sondheim W.E., Sun X., Swank C., Swift G., Tatar E., Teasdale W., Terai C., Tipton B., Utsuro M., Vogelaar R.B., VornDick B., Wang Z., Wehring B., Wexler J., Womack T., Wrede C., Xu Y.P., Yan H., Young A.R., Yuan J., and Zeck B.A.

Subjects
Physics, QC1-999
Abstract

The UCNA experiment was designed to measure the neutron β-asymmetry parameter A0 using polarized ultracold neutrons (UCN). UCN produced via downscattering in solid deuterium were polarized via transport through a 7 T magnetic field, and then directed to a 1 T solenoidal electron spectrometer, where the decay electrons were detected in electron detector packages located on the two ends of the spectrometer. A value for A0 was then extracted from the asymmetry in the numbers of counts in the two detector packages. We summarize all of the results from the UCNA experiment, obtained during run periods in 2007, 2008–2009, 2010, and 2011–2013, which ultimately culminated in a 0.67% precision result for A0.

Published
2019
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4. Status of the UCNτ experiment

Author

Pattie R.W., Callahan N.B., Cude-Woods C., Adamek E.R., Adams M., Barlow D., Blatnik M., D. Bowman, Broussard L.J., Clayton S., Currie S., Dees E.B., Ding X., Fellers D., Fox W., Fries E., Gonzalez F., Geltenbort P., Hickerson K.P., Hoffbauer M.A., Hoffman K., Holley A.T., Howard D., Ito T.M., Komives A., Liu C.Y., M. Makela, Medina J., Morley D., Morris C.L., O'Connor T., Penttilä S.I., Ramsey J.C., Roberts A., Salvat D., Saunders A., Seestrom S.J., Sharapov E.I., Sjue S.K.L., Snow W.M., Sprow A., Vanderwerp J., Vogelaar B., P.L. Walstrom, Wang Z., Weaver H., Wexler J., Womack T.L., Young A.R., and Zeck B.A.

Subjects
Physics, QC1-999
Abstract

The neutron is the simplest nuclear system that can be used to probe the structure of the weak interaction and search for physics beyond the standard model. Measurements of neutron lifetime and β-decay correlation coefficients with precisions of 0.02% and 0.1%, respectively, would allow for stringent constraints on new physics. The UCNτ experiment uses an asymmetric magneto-gravitational UCN trap with in situ counting of surviving neutrons to measure the neutron lifetime, τn = 877.7s (0.7s)stat (+0.4/−0.2s)sys. We discuss the recent result from UCNτ, the status of ongoing data collection and analysis, and the path toward a 0.25 s measurement of the neutron lifetime with UCNτ.

Published
2019
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5. Demonstration of sub-micron UCN position resolution using room-temperature CMOS sensor

Author

Lin, S., Baldwin, J.K., Blatnik, M., Clayton, S.M., Cude-Woods, C., Currie, S.A., Filippone, B., Fries, E.M., Geltenbort, P., Holley, A.T., Li, W., Liu, C.-Y., Makela, M., Morris, C.L., Musedinovic, R., O’Shaughnessy, C., Pattie, R.W., Jr., Salvat, D.J., Saunders, A., Sharapov, E.I., Singh, M., Sun, X., Tang, Z., Uhrich, W., Wei, W., Wolfe, B., Young, A.R., and Wang, Z.

Published
2023
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6. Projection imaging with ultracold neutrons

Author

Kuk, K., Cude-Woods, C., Chavez, C.R., Choi, J.H., Estrada, J., Hoffbauer, M., Holland, S.E., Makela, M., Morris, C.L., Ramberg, E., Adamek, E.R., Bailey, T., Blatnik, M., Broussard, L.J., Brown, M.A.-P., Callahan, N.B., Clayton, S.M., Currie, S., Filippone, B.W., Fries, E.M., Geltenbort, P., Gonzalez, F., Hassan, M.T., Hayen, L., Hickerson, K.P., Holley, A.T., Ito, T.M., Liu, C.-Y., Merkel, P., Musedinovic, R., O’Shaughnessy, C., Pattie, R.W., Jr., Plaster, B., Salvat, D.J., Saunders, A., Sharapov, E.I., Sun, X., Tang, Z., Wei, W., Wexler, J.W., Young, A.R., and Wang, Zhehui

Published
2021
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7. Detection system for neutron β decay correlations in the UCNB and Nab experiments

Author

Broussard, L.J., Zeck, B.A., Adamek, E.R., Baeßler, S., Birge, N., Blatnik, M., Bowman, J.D., Brandt, A.E., Brown, M., Burkhart, J., Callahan, N.B., Clayton, S.M., Crawford, C., Cude-Woods, C., Currie, S., Dees, E.B., Ding, X., Fomin, N., Frlez, E., Fry, J., Gray, F.E., Hasan, S., Hickerson, K.P., Hoagland, J., Holley, A.T., Ito, T.M., Klein, A., Li, H., Liu, C.-Y., Makela, M.F., McGaughey, P.L., Mirabal-Martinez, J., Morris, C.L., Ortiz, J.D., Pattie, R.W., Jr., Penttilä, S.I., Plaster, B., Počanić, D., Ramsey, J.C., Salas-Bacci, A., Salvat, D.J., Saunders, A., Seestrom, S.J., Sjue, S.K.L., Sprow, A.P., Tang, Z., Vogelaar, R.B., Vorndick, B., Wang, Z., Wei, W., Wexler, J., Wilburn, W.S., Womack, T.L., and Young, A.R.

Published
2017
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8. Position-sensitive detection of ultracold neutrons with an imaging camera and its implications to spectroscopy

Author

Wei, Wanchun, Broussard, L.J., Hoffbauer, M.A., Makela, M., Morris, C.L., Tang, Z., Adamek, E.R., Callahan, N.B., Clayton, S.M., Cude-Woods, C., Currie, S., Dees, E.B., Ding, X., Geltenbort, P., Hickerson, K.P., Holley, A.T., Ito, T.M., Leung, K.K., Liu, C.-Y., Morley, D.J., Ortiz, Jose D., Pattie, R.W., Jr., Ramsey, J.C., Saunders, A., Seestrom, S.J., Sharapov, E.I., Sjue, S.K., Wexler, J., Womack, T.L., Young, A.R., Zeck, B.A., and Wang, Zhehui

Published
2016
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9. A multilayer surface detector for ultracold neutrons

Author

Wang, Zhehui, Hoffbauer, M.A., Morris, C.L., Callahan, N.B., Adamek, E.R., Bacon, J.D., Blatnik, M., Brandt, A.E., Broussard, L.J., Clayton, S.M., Cude-Woods, C., Currie, S., Dees, E.B., Ding, X., Gao, J., Gray, F.E., Hickerson, K.P., Holley, A.T., Ito, T.M., Liu, C.-Y., Makela, M., Ramsey, J.C., Pattie, R.W., Jr., Salvat, D.J., Saunders, A., Schmidt, D.W., Schulze, R.K., Seestrom, S.J., Sharapov, E.I., Sprow, A., Tang, Z., Wei, W., Wexler, J., Womack, T.L., Young, A.R., and Zeck, B.A.

Published
2015
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11. Sealed drift tube cosmic ray veto counters

Author

Rios, R., Tatar, E., Bacon, J.D., Bowles, T.J., Hill, R., Green, J.A., Hogan, G.E., Ito, T.M., Makela, M., Morris, C.L., Mortenson, R., Pasukanics, F.E., Ramsey, J., Saunders, A., Seestrom, S.J., Sondheim, W.E., Teasdale, W., Saltus, M., Back, H.O., Cottrell, C.R., Holley, A.T., Pattie, R.W., Jr., Young, A.R., Broussard, L.J., Filippone, B.W., Hickerson, K.P., Liu, J., Mendenhall, M.P., Plaster, B., Mammei, R.R., Pitt, M.L., Vogelaar, R.B., and Martin, J.W.

Published
2011
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15. Multi-wire proportional chamber for ultra-cold neutron detection

Author

Morris, C.L., Bowles, T.J., Gonzales, J., Hill, R., Hogan, G., Makela, M., Mortenson, R., Ramsey, J., Saunders, A., Seestrom, S.J., Sondheim, W.E., Teasdale, W., Back, H.O., Pattie, R.W., Jr., Holley, A.T., Young, A.R., Broussard, L.J., Hickerson, K.P., Liu, J., Mendenhall, M.P., Plaster, B., Mammei, R.R., Pitt, M., Vogelaar, R.B., Rios, R., and Martin, J.

Published
2009
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19. Improved limits on Fierz Interference using asymmetry measurements from the UCNA experiment

Author

Sun, X., Adamek, E., Allgeier, B., Bagdasarova, Y., Berguno, D.B., Blatnik, M., Bowles, T.J., Broussard, L.J., Brown, M.A.-P., Carr, R., Clayton, S., Cude-Woods, C., Currie, S., Dees, E.B., Ding, X., Filippone, B.W., GarcÍa, A., Geltenbort, P., Hasan, S., Hickerson, K.P., Hoagland, J., Hong, R., Holley, A.T., Ito, T.M., Knecht, A., Liu, C.-Y., Liu, J., Makela, M., Mammei, R., Martin, J.W., Melconian, D., Mendenhall, M.P., Moore, S.D., Morris, C.L., Nepal, S., Nouri, N., Pattie, R.W., Pérez Galván, A., Phillips, D.G., Picker, R., Pitt, M.L., Plaster, B., Salvat, D.J., Saunders, A., Sharapov, E.I., Sjue, S., Slutsky, S., Sondheim, W., Swank, C., Tatar, E., Vogelaar, R.B., Vorndick, B., Wang, Z., Wei, W., Wexler, J.W., Womack, T., Wrede, C., Young, A.R., Zeck, B.A., Institut Laue-Langevin (ILL), ILL, and UCNA

Subjects
FOS: Physical sciences, High Energy Physics::Experiment, Nuclear Experiment (nucl-ex), [PHYS.NEXP]Physics [physics]/Nuclear Experiment [nucl-ex], Nuclear Experiment
Abstract

The Ultracold Neutron Asymmetry (UCNA) experiment was designed to measure the $\beta$-decay asymmetry parameter, $A_0$, for free neutron decay. In the experiment, polarized ultracold neutrons are transported into a decay trap, and their $\beta$-decay electrons are detected with $\approx 4\pi$ acceptance into two detector packages which provide position and energy reconstruction. The experiment also has sensitivity to $b_{n}$, the Fierz interference term in the neutron $\beta$-decay rate. In this work, we determine $b_{n}$ from the energy dependence of $A_0$ using the data taken during the UCNA 2011-2013 run. In addition, we present the same type of analysis using the earlier 2010 $A$ dataset. Motivated by improved statistics and comparable systematic errors compared to the 2010 data-taking run, we present a new $b_{n}$ measurement using the weighted average of our asymmetry dataset fits, to obtain $b_{n} = 0.066 \pm 0.041_{\text{stat}} \pm 0.024_{\text{syst}}$ which corresponds to a limit of $-0.012 < b_{n} < 0.144$ at the 90% confidence level., Comment: 6 pages, 3 figures. Submission to PRC

Published
2019

20. Search for neutron dark decay: n $\rightarrow \chi + e^+e^-$

Author

Sun, X., Adamek, E., Allgeier, B., Blatnik, M., Bowles, T.J., Broussard, L.J., Brown, M.A.P., Carr, R., Clayton, S., Cude-Woods, C., Currie, S., Dees, E.B., Ding, X., Filippone, B.W., GarcÍa, A., Geltenbort, P., Hasan, S., Hickerson, K.P., Hoagland, J., Hong, R., Hogan, G.E., Holley, A.T., Ito, T.M., Kneckt, A., Liu, C.Y., Liu, J., Makela, M., Mammei, R., Martin, J.W., Melconian, D., Mendenhall, M.P., Moore, S.D., Morris, C.L., Nepal, S., Nouri, N., Pattie, R.W., Galván, A.P., II, D.G.Phillips, Picker, R., Pitt, M.L., Plaster, B., Ramsey, J.C., Rios, R., Salvat, D.J., Saunders, A., Sondheim, W., Sjue, S., Slutsky, S., Swank, C., Swift, G., Tatar, E., Vogelaar, R.B., Vorndick, B., Wanchun, W., Wang, Z., Wexler, J., Womack, T., Wrede, C., Young, A.R., Zeck, B.A., Institut Laue-Langevin (ILL), and ILL

Subjects
energy: kinetic, branching ratio: upper limit, n: decay, n: branching ratio, talk: Grenoble 2018/05/24, calibration, dark matter, mass dependence, electron: pair production, [PHYS.HEXP]Physics [physics]/High Energy Physics - Experiment [hep-ex], High Energy Physics::Experiment, n: lifetime, acceptance, experimental results
Abstract

International audience; In January, 2018, Fornal and Grinstein proposed that a previously unobserved neutron decay branch to a dark matter particle (χ) could account for the discrepancy in the neutron lifetime observed in two different types of experiments. One of the possible final states discussed includes a single χ along with an e+e− pair. We use data from the UCNA (Ultracold Neutron Asymmetry) experiment to set limits on this decay channel. Coincident electron-like events are detected with ∼ 4π acceptance using a pair of detectors that observe a volume of stored Ultracold Neutrons (UCNs). We use the timing information of coincidence events to select candidate dark sector particle decays by applying a timing calibration and selecting events within a physically-forbidden timing region for conventional n → p + e- + ν̅e decays. The summed kinetic energy (Ee+e−) from such events is reconstructed and used to set limits, as a function of the χ mass, on the branching fraction for this decay channel.

Published
2018
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21. New result for the neutron $\beta$-asymmetry parameter $A_0$ from UCNA

Author

Brown, M.A.-P., Dees, E.B., Adamek, E., Allgeier, B., Blatnik, M., Bowles, T.J., Broussard, L.J., Carr, R., Clayton, S., Cude-Woods, C., Currie, S., Ding, X., Filippone, B.W., GarcÍa, A., Geltenbort, P., Hasan, S., Hickerson, K.P., Hoagland, J., Hong, R., Hogan, G.E., Holley, A.T., Ito, T.M., Knecht, A., Liu, C.-Y., Liu, J., Makela, M., Martin, J.W., Melconian, D., Mendenhall, M.P., Moore, S.D., Morris, C.L., Nepal, S., Nouri, N., Pattie, R.W., Pérez Galván, A., Phillips, D.G., Picker, R., Pitt, M.L., Plaster, B., Ramsey, J.C., Rios, R., Salvat, D.J., Saunders, A., Sondheim, W., Seestrom, S.J., Sjue, S., Slutsky, S., Sun, X., Swank, C., Swift, G., Tatar, E., Vogelaar, R.B., Vorndick, B., Wang, Z., Wexler, J., Womack, T., Wrede, C., Young, A.R., Zeck, B.A., Institut Laue-Langevin (ILL), ILL, UCNA, and Institut Laue-Langevin ( ILL )

Subjects
electron, axial-vector, [PHYS.NEXP]Physics [physics]/Nuclear Experiment [nucl-ex], weak coupling, Automatic Keywords, statistics, S017AV, correlation, High Energy Physics::Experiment, [ PHYS.NEXP ] Physics [physics]/Nuclear Experiment [nucl-ex], Nuclear Experiment, n: spin, S017BA, asymmetry, experimental results
Abstract

The neutron $\beta$-decay asymmetry parameter $A_0$ defines the correlation between the spin of the neutron and the momentum of the emitted electron, which determines $\lambda=\frac{g_{A}}{g_{V}}$, the ratio of the axial-vector to vector weak coupling constants. The UCNA Experiment, located at the Ultracold Neutron facility at the Los Alamos Neutron Science Center, is the first to measure such a correlation coefficient using ultracold neutrons (UCN). Following improvements to the systematic uncertainties and increased statistics, we report the new result $A_0 = -0.12054(44)_{\mathrm{stat}}(68)_{\mathrm{syst}}$ which yields $\lambda\equiv \frac{g_{A}}{g_{V}}=-1.2783(22)$. Combination with the previous UCNA result and accounting for correlated systematic uncertainties produces $A_0=-0.12015(34)_{\mathrm{stat}}(63)_{\mathrm{syst}}$ and $\lambda\equiv \frac{g_{A}}{g_{V}}=-1.2772(20)$., Comment: 9 pages, 7 figures, updated to as-published version

Published
2018
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22. First direct constraints on Fierz interference in free neutron $\beta$ decay

Author

Hickerson, K.P., Sun, X., Bagdasarova, Y., Bravo-Berguño, D., Broussard, L.J., Brown, P., Carr, R., Currie, S., Ding, X., Filippone, B.W., GarcÍa, A., Geltenbort, P., Hoagland, J., Holley, A.T., Hong, R., Ito, T.M., Knecht, A., Liu, C.-Y, Liu, J.L., Makela, M., Mammei, R.R., Martin, J.W., Melconian, D., Mendenhall, M.P., Moore, § S.D., Morris, C.L., Pattie, R.W., Pérez Galván, A., Picker, R., Pitt, M.L., Plaster, B., Ramsey, J.C., Rios, R., Saunders, A., Seestrom, S.J., Sharapov, E.I., Sondheim, W.E., Tatar, E., Vogelaar, R.B., Vorndick, B., Wrede, C., Young, A.R., Zeck, B.A., Institut Laue-Langevin (ILL), ILL, and Institut Laue-Langevin ( ILL )

Subjects
Particle physics, scale: TeV, Astrophysics::High Energy Astrophysical Phenomena, interference, n: decay, Weak interaction, [PHYS.NEXP]Physics [physics]/Nuclear Experiment [nucl-ex], Interference (wave propagation), 01 natural sciences, Standard Model, Nuclear physics, weak interaction, statistical analysis, 0103 physical sciences, Fierz-Pauli equation, Neutron, Tensor, [ PHYS.NEXP ] Physics [physics]/Nuclear Experiment [nucl-ex], 010306 general physics, Nuclear Experiment, Monte Carlo, Physics, Spectrometer, 010308 nuclear & particles physics, precision measurement, new physics, n: decay rate, Electroweak interaction, semileptonic decay, coupling: tensor, Beta decay, High Energy Physics::Experiment, spectrometer, experimental results
Abstract

Precision measurements of free neutron $\beta$-decay have been used to precisely constrain our understanding of the weak interaction. However the neutron Fierz interference term $b_n$, which is particularly sensitive to Beyond-Standard-Model tensor currents at the TeV scale, has thus far eluded measurement. Here we report the first direct constraints on this term, finding $b_n = 0.067 \pm 0.005_{\text{stat}} {}^{+0.090}_{- 0.061}{}_{\text{sys}}$, consistent with the Standard Model. The uncertainty is dominated by absolute energy reconstruction and the linearity of the beta spectrometer energy response.

Published
2017
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24. An assessment of the lean flammability limits of CH4/air and C3H8/air mixtures at engine-like conditions.

Author

Egolfopoulos, F.N., Holley, A.T., and Law, C.K.

Subjects
COMBUSTION, FLAMMABILITY, FACTOR analysis, THERMOCHEMISTRY
Abstract

Abstract: The lean flammability limits of CH4/air and C3H8/air mixtures were numerically determined for a wide range of pressures and unburned mixture temperatures in order to assess the near-limit flame behavior under conditions of relevance to internal combustion engines. The study included the simulation of freely propagating flames with the inclusion of detailed descriptions of chemical kinetics and molecular transport, radiative loss, and a one-point continuation method to solve around singular points as the flammability limit is approached. Results revealed that both pressure and unburned mixture temperature have significant effects on the lean flammability limit as well as the attendant limit flame temperature. Specifically, the lean limit was found to first increase and then decrease with pressure, while the limit temperature decreases with pressure in general, and can be reduced to values as low as 900K under engine-like conditions. Through sensitivity and species consumption path analyses it was further shown that the chain mechanisms that control the near-limit flame response critically depend on the thermodynamic state of the mixture. Thus, mechanisms that are identified as important at near-atmospheric conditions may not be relevant at higher pressures and unburned mixture temperatures. In particular, the response of near-limit flames was found to resemble the homogeneous explosion limits of hydrogen/oxygen mixtures in that while at low pressures the main branching and termination reactions are respectively H+O2 →OH+O and H+O2 +M→HO2 +M, at the elevated pressures relevant to internal combustion engines the system branching is controlled by the HO2–H2O2 kinetics. Potential avenues for extending the lean operation limits of internal combustion engines are suggested based on the understanding gained herein. [Copyright &y& Elsevier]

Published
2007
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