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0000-0003-0539-7951
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UNSW Sydney
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Publisher: Elsevier BV
Date: 06-2021
Publisher: Elsevier BV
Date: 2015
Publisher: Elsevier BV
Date: 06-2018
Publisher: Elsevier BV
Date: 2019
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 12-2011
Publisher: Elsevier BV
Date: 2009
Publisher: Elsevier BV
Date: 04-2016
Publisher: Elsevier BV
Date: 08-2019
Publisher: Elsevier BV
Date: 08-2012
Publisher: Elsevier BV
Date: 06-2016
Publisher: Elsevier BV
Date: 12-2008
Publisher: SAE International
Date: 05-04-2016
DOI: 10.4271/2016-01-0857
Publisher: SPIE
Date: 25-08-2015
DOI: 10.1117/12.2186477
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 03-2007
DOI: 10.1109/MCSE.2007.42
Publisher: Elsevier BV
Date: 07-2018
Publisher: Elsevier BV
Date: 03-2015
Publisher: Elsevier BV
Date: 2017
Publisher: IOP Publishing
Date: 09-2006
Publisher: SAE International
Date: 11-2014
DOI: 10.4271/2014-01-9079
Publisher: Elsevier BV
Date: 07-2018
Publisher: Elsevier BV
Date: 2017
Publisher: SAE International
Date: 06-09-2015
DOI: 10.4271/2015-24-2489
Publisher: American Society of Mechanical Engineers
Date: 06-05-2012
Abstract: Diesel knock is a phenomenon that generates undesirable noise and vibration that can be destructive to diesel engine structures and components for long-term operation. The diesel knock occurs when a large quantity of air-fuel is mixed prior to combustion when the ignition delay is long. This leads to a drastic pressure rise during the premixed phase of the combustion, which is followed by a pressure ringing. The main focus of this study is to examine effect of pilot injection on the pressure ringing and associated in-cylinder flame behaviour. In a single-cylinder small-bore optical engine, in-cylinder pressure measurement and high-speed imaging of the natural combustion luminosity have been performed. Results demonstrate that pilot injection helps reduce the in-cylinder pressure ringing by reducing the pressure rise rate of the main injection. Moreover, oscillation of the flames observed during the knocking events appears to diminish when the pilot injection is applied. How the pilot injection duration and timing affect the diesel knock behaviour is also discussed in detail.
Publisher: Elsevier BV
Date: 10-2022
Publisher: Elsevier BV
Date: 03-2010
Publisher: Elsevier BV
Date: 04-2013
Publisher: Elsevier BV
Date: 2019
Publisher: Elsevier BV
Date: 04-2017
Publisher: Elsevier BV
Date: 2015
Publisher: Elsevier BV
Date: 2023
Publisher: SAE International
Date: 30-08-2011
DOI: 10.4271/2011-01-1981
Publisher: Elsevier BV
Date: 2011
Publisher: Elsevier BV
Date: 09-2023
Publisher: Elsevier BV
Date: 2007
Publisher: Elsevier BV
Date: 2021
Publisher: Elsevier BV
Date: 09-2016
Publisher: Cambridge University Press (CUP)
Date: 04-07-2017
DOI: 10.1017/JFM.2017.282
Abstract: A three-dimensional direct numerical simulation is conducted for a temporally evolving planar jet of n -heptane at a pressure of 40 atmospheres and in a coflow of air at 1100 K. At these conditions, n -heptane exhibits a two-stage ignition due to low- and high-temperature chemistry, which is reproduced by the global chemical model used in this study. The results show that ignition occurs in several overlapping stages and multiple modes of combustion are present. Low-temperature chemistry precedes the formation of multiple spatially localised high-temperature chemistry autoignition events, referred to as ‘kernels’. These kernels form within the shear layer and core of the jet at compositions with short homogeneous ignition delay times and in locations experiencing low scalar dissipation rates. An analysis of the kernel histories shows that the ignition delay time is correlated with the mixing rate history and that the ignition kernels tend to form in vortically dominated regions of the domain, as corroborated by an analysis of the topology of the velocity gradient tensor. Once ignited, the kernels grow rapidly and establish edge flames where they envelop the stoichiometric isosurface. A combination of kernel formation (autoignition) and the growth of existing burning surface (via edge-flame propagation) contributes to the overall ignition process. An analysis of propagation speeds evaluated on the burning surface suggests that although the edge-flame speed is promoted by the autoignitive conditions due to an increase in the local laminar flame speed, edge-flame propagation of existing burning surfaces (triggered initially by isolated autoignition kernels) is the dominant ignition mode in the present configuration.
Publisher: Springer Berlin Heidelberg
Date: 14-09-2011
Publisher: Elsevier BV
Date: 04-2006
Publisher: Elsevier BV
Date: 04-2006
Publisher: Elsevier BV
Date: 09-2012
Publisher: Cambridge University Press (CUP)
Date: 12-07-2012
DOI: 10.1017/JFM.2012.264
Abstract: This paper presents an analysis of the energy transported by disturbances in gaseous combustion. It extends the previous work of Myers ( J. Fluid Mech. , vol. 226, 1991, 383–400) and so includes non-zero mean-flow quantities, large- litude disturbances, varying specific heats and chemical non-equilibrium. This extended form of Myers’ ‘disturbance energy’ then enables complete identification of the conditions under which the famous Rayleigh source term can be derived from the equations governing combusting gas motion. These are: small disturbances in an irrotational, homentropic, non-diffusive (in terms of species, momentum and energy) and stationary mean flow at chemical equilibrium. Under these assumptions, the Rayleigh source term becomes the sole source term in a conservation equation for the classical acoustic energy. It is also argued that the exact disturbance energy flux should become an acoustic energy flux in the far-field surrounding a (reacting or non-reacting) jet. In this case, the volume integral of the disturbance energy source terms are then directly related to the area-averaged far-field sound produced by the jet. This is demonstrated by closing the disturbance energy budget over a set of aeroacoustic, direct numerical simulations of a forced, low-Mach-number, laminar, premixed flame. These budgets show that several source terms are significant, including those involving the mean-flow and entropy fields. This demonstrates that the energetics of sound generation cannot be examined by considering the Rayleigh source term alone.
Publisher: Elsevier BV
Date: 2006
Publisher: Elsevier BV
Date: 2017
Publisher: Elsevier BV
Date: 08-2018
Publisher: Elsevier BV
Date: 2019
Publisher: Elsevier BV
Date: 2023
Publisher: Elsevier BV
Date: 03-2021
Publisher: Elsevier BV
Date: 12-2023
Publisher: The Optical Society
Date: 25-02-2013
DOI: 10.1364/AO.52.001413
Publisher: Elsevier BV
Date: 02-2012
Publisher: SAE International
Date: 28-03-2017
DOI: 10.4271/2017-01-0657
Publisher: Cambridge University Press (CUP)
Date: 07-08-2014
DOI: 10.1017/JFM.2014.392
Abstract: Kinetic energy and reactive scalar spectra in turbulent premixed flames are studied from compressible three-dimensional direct numerical simulations (DNS) of a temporally evolving rectangular slot-jet premixed flame, a statistically one-dimensional configuration. The flames correspond to a lean premixed hydrogen–air mixture at an equivalence ratio of 0.7, preheated to 700 K and at 1 atm, and three DNS are considered with a fixed jet Reynolds number of 10 000 and a jet Damköhler number varying between 0.13 and 0.54. For the study of spectra, motivated by the need to account for density change, which can be locally strong in premixed flames, a new density-weighted definition for two-point velocity/scalar correlations is proposed. The density-weighted two-point correlation tensor retains the essential properties of its constant-density (incompressible) counterpart and recovers the density-weighted Reynolds stress tensor in the limit of zero separation. The density weighting also allows the derivation of balance equations for velocity and scalar spectrum functions in the wavenumber space that illuminate physics unique to combusting flows. Pressure–dilatation correlation is a source of kinetic energy at high wavenumbers and, analogously, reaction rate–scalar fluctuation correlation is a high-wavenumber source of scalar energy. These results are verified by the spectra constructed from the DNS data. The kinetic energy spectra show a distinct inertial range with a $\\def \\xmlpi #1{}\\def \\mathsfbi #1{\\boldsymbol {\\mathsf {#1}}}\\let \\le =\\leqslant \\let \\leq =\\leqslant \\let \\ge =\\geqslant \\let \\geq =\\geqslant \\def \\Pr {\\mathit {Pr}}\\def \\Fr {\\mathit {Fr}}\\def \\Rey {\\mathit {Re}}-5/3$ scaling followed by a ‘diffusive–reactive’ range at higher wavenumbers. The exponential drop-off in this range shows a distinct inflection in the vicinity of the wavenumber corresponding to a laminar flame thickness, $\\delta _L$ , and this is attributed to the contribution from the pressure–dilatation term in the energy balance in wavenumber space. Likewise, a clear spike in spectra of major reactant species (hydrogen) arising from the reaction-rate term is observed at wavenumbers close to $\\delta _L$ . It appears that in the inertial range classical scaling laws for the spectra involving the Kolmogorov scale are applicable, but in the high-wavenumber range where chemical reactions have a strong signature the laminar flame thickness produces a better collapse. It is suggested that a full scaling should perhaps involve the Kolmogorov scale, laminar flame thickness, Damköhler number and Karlovitz number.
Publisher: Elsevier BV
Date: 02-2016
Publisher: Cambridge University Press (CUP)
Date: 19-08-2010
DOI: 10.1017/S0022112010001278
Abstract: A turbulent flame–wall interaction (FWI) configuration is studied using three-dimensional direct numerical simulation (DNS) and detailed chemical kinetics. The simulations are used to investigate the effects of the wall turbulent boundary layer (i) on the structure of a hydrogen–air premixed flame, (ii) on its near-wall propagation characteristics and (iii) on the spatial and temporal patterns of the convective wall heat flux. Results show that the local flame thickness and propagation speed vary between the core flow and the boundary layer, resulting in a regime change from flamelet near the channel centreline to a thickened flame at the wall. This finding has strong implications for the modelling of turbulent combustion using Reynolds-averaged Navier–Stokes or large-eddy simulation techniques. Moreover, the DNS results suggest that the near-wall coherent turbulent structures play an important role on the convective wall heat transfer by pushing the hot reactive zone towards the cold solid surface. At the wall, exothermic radical recombination reactions become important, and are responsible for approximately 70% of the overall heat release rate at the wall. Spectral analysis of the convective wall heat flux provides an unambiguous picture of its spatial and temporal patterns, previously unobserved, that is directly related to the spatial and temporal characteristic scalings of the coherent near-wall turbulent structures.
Publisher: Elsevier BV
Date: 2020
Publisher: OSA
Date: 2014
Publisher: Springer Science and Business Media LLC
Date: 16-03-2010
Publisher: Cambridge University Press (CUP)
Date: 23-02-2017
DOI: 10.1017/JFM.2017.53
Abstract: This article reports an analysis of the first detailed chemistry direct numerical simulation (DNS) of a high Karlovitz number laboratory premixed flame. The DNS results are first compared with those from laser-based diagnostics with good agreement. The subsequent analysis focuses on a detailed investigation of the flame area, its local thickness and their rates of change in isosurface following reference frames, quantities that are intimately connected. The net flame stretch is demonstrated to be a small residual of large competing terms: the positive tangential strain term and the negative curvature stretch term. The latter is found to be driven by flame speed–curvature correlations and dominated in net by low probability highly curved regions. Flame thickening is demonstrated to be substantial on average, while local regions of flame thinning are also observed. The rate of change of the flame thickness (as measured by the scalar gradient magnitude) is demonstrated, analogously to flame stretch, to be a competition between straining tending to increase gradients and flame speed variations in the normal direction tending to decrease them. The flame stretch and flame thickness analyses are connected by the observation that high positive tangential strain rate regions generally correspond with low curvature regions these regions tend to be positively stretched in net and are relatively thinner compared with other regions. High curvature magnitude regions (both positive and negative) generally correspond with lower tangential strain these regions are in net negatively stretched and thickened substantially.
Publisher: Elsevier BV
Date: 2017
Publisher: Elsevier BV
Date: 09-2015
Publisher: Springer Science and Business Media LLC
Date: 16-04-2013
Publisher: Elsevier BV
Date: 2017
Publisher: Elsevier BV
Date: 2017
Publisher: Cambridge University Press (CUP)
Date: 19-03-2018
DOI: 10.1017/JFM.2018.115
Abstract: This paper presents a numerical study of the sound generated by turbulent, premixed flames. Direct numerical simulations (DNS) of two round jet flames with equivalence ratios of 0.7 and 1.0 are first carried out. Single-step chemistry is employed to reduce the computational cost, and care is taken to resolve both the near and far fields and to avoid noise reflections at the outflow boundaries. Several significant features of these two flames are noted. These include the monopolar nature of the sound from both flames, the stoichiometric flame being significantly louder than the lean flame, the observed frequency of peak acoustic spectral litude being consistent with prior experimental studies and the importance of so-called ‘flame annihilation’ events as acoustic sources. A simple model that relates these observed annihilation events to the far-field sound is then proposed, demonstrating a surprisingly high degree of correlation with the far-field sound from the DNS. This model is consistent with earlier works that view a premixed turbulent flame as a distribution of acoustic sources, and provides a physical explanation for the well-known monopolar content of the sound radiated by premixed turbulent flames.
Publisher: IEEE
Date: 06-2015
Publisher: Elsevier BV
Date: 07-2013
Publisher: AIP Publishing
Date: 09-2016
DOI: 10.1063/1.4962501
Abstract: In the present work, direct numerical simulation (DNS) of a laboratory premixed turbulent jet flame was performed to study turbulence-flame interactions. The turbulent flame features moderate Reynolds number and high Karlovitz number (Ka). The orientations of the flame normal vector n, the vorticity vector ω and the principal strain rate eigenvectors ei are examined. The in-plane and out-of-plane angles are introduced to quantify the vector orientations, which also measure the flame geometry and the vortical structures. A general observation is that the distributions of these angles are more isotropic downstream as the flame and the flow become more developed. The out-of-plane angle of the flame normal vector, β, is a key parameter in developing the correction of 2D measurements to estimate the corresponding 3D quantities. The DNS results show that the correction factor is unity at the inlet and approaches its theoretical value of an isotropic distribution downstream. The alignment characteristics of n, ω and ei, which reflect the interactions of turbulence and flame, are also studied. Similar to a passive scalar gradient in non-reacting flows, the flame normal has a tendency to align with the most compressive strain rate, e3, in the flame, indicating that turbulence contributes to the production of scalar gradient. The vorticity dynamics are examined via the vortex stretching term, which was found to be the predominant source of vorticity generation balanced by dissipation, in the enstrophy transport equation. It is found that although the vorticity preferentially aligns with the intermediate strain rate, e2, the contribution of the most extensive strain rate, e1, to vortex stretching is comparable with that of the intermediate strain rate, e2. This is because the eigenvalue of the most extensive strain rate, λ1, is always large and positive. It is confirmed that the vorticity vector is preferentially positioned along the flame tangential plane, contributing to the dominance of cylindrical curvature of the flame front. Finally, the effect of heat release on the turbulence-flame interactions is examined. It is found that heat release has only limited impact on the statistics due to the minor role played by the strain rate induced by heat release rate in the current high Ka flame.
Publisher: Begell House
Date: 2011
Publisher: Elsevier BV
Date: 2021
Publisher: Elsevier BV
Date: 08-2014
Publisher: Elsevier BV
Date: 2019
Publisher: Elsevier BV
Date: 06-2017
Publisher: Cambridge University Press (CUP)
Date: 13-10-2022
DOI: 10.1017/JFM.2022.764
Abstract: Point-particle direct numerical simulations have been employed to quantify the turbulence modulation and particle responses in a turbulent particle-laden jet in the two-way coupled regime with an inlet Reynolds number based on bulk velocity and jet diameter $({D_j})$ of ~10 000. The investigation focuses on three cases with inlet bulk Stokes numbers of 0.3, 1.4 and 11.2. Special care is taken to account for the particle–gas slip velocity and non-uniform particle concentrations at the nozzle outlet, enabling a reasonable prediction of particle velocity and concentration fields. Turbulence modulation is quantified by the variation of the gas-phase turbulent kinetic energy (TKE). The presence of the particle phase is found to d the gas-phase TKE in the near-field region within $5{D_j}$ from the inlet but subsequently increases the TKE in the intermediate region of (5–20) D j . An analysis of the gas-phase TKE transport equation reveals that the direct impact of the particle phase is to dissipate TKE via the particle-induced source term. However, the finite inertia of the particle phase affects the gas-phase velocity gradients, which indirectly affects the TKE production and dissipation, leading to the observed TKE attenuation and enhancement. Particle response to the gas-phase flow is quantified. Particles are found to exhibit notably stronger response to the gas-phase axial velocity than to the radial velocity. A new dimensionless figure is presented that collapses both the axial and radial components of the particle response as a function of the local Stokes number based on their respective integral length scales.
Publisher: Elsevier BV
Date: 05-2015
Publisher: Elsevier BV
Date: 12-2014
Publisher: Elsevier BV
Date: 07-2008
Publisher: Cambridge University Press (CUP)
Date: 23-07-2015
DOI: 10.1017/JFM.2015.334
Abstract: A turbulent lifted slot-jet flame is studied using direct numerical simulation (DNS). A one-step chemistry model is employed with a mixture-fraction-dependent activation energy which can reproduce qualitatively the dependence of the laminar burning rate on the equivalence ratio that is typical of hydrocarbon fuels. The basic structure of the flame base is first examined and discussed in the context of earlier experimental studies of lifted flames. Several features previously observed in experiments are noted and clarified. Some other unobserved features are also noted. Comparison with previous DNS modelling of hydrogen flames reveals significant structural differences. The statistics of flow and relative edge-flame propagation velocity components conditioned on the leading edge locations are then examined. The results show that, on average, the streamwise flame propagation and streamwise flow balance, thus demonstrating that edge-flame propagation is the basic stabilisation mechanism. Fluctuations of the edge locations and net edge velocities are, however, significant. It is demonstrated that the edges tend to move in an essentially two-dimensional (2D) elliptical pattern (laterally outwards towards the oxidiser, then upstream, then inwards towards the fuel, then downstream again). It is proposed that this is due to the passage of large eddies, as outlined in Su et al. ( Combust. Flame , vol. 144 (3), 2006, pp. 494–512). However, the mechanism is not entirely 2D, and out-of-plane motion is needed to explain how flames escape the high-velocity inner region of the jet. Finally, the time-averaged structure is examined. A budget of terms in the transport equation for the product mass fraction is used to understand the stabilisation from a time-averaged perspective. The result of this analysis is found to be consistent with the instantaneous perspective. The budget reveals a fundamentally 2D structure, involving transport in both the streamwise and transverse directions, as opposed to possible mechanisms involving a dominance of either one direction of transport. It features upstream transport balanced by entrainment into richer conditions, while on the rich side, upstream turbulent transport and entrainment from leaner conditions balance the streamwise convection.
Publisher: SAE International
Date: 03-04-2018
DOI: 10.4271/2018-01-0246
Publisher: Elsevier BV
Date: 2013
Publisher: Elsevier BV
Date: 2011
Publisher: Elsevier BV
Date: 08-2004
Publisher: Elsevier BV
Date: 2021
Publisher: American Society of Mechanical Engineers
Date: 14-07-2013
DOI: 10.1115/HT2013-17221
Abstract: Investigations are underway around the world to make solar energy more competitive in the energy market [1–3]. One approach is to develop solar hybrid photovoltaic/thermal (PV/T) technologies which allow for maximal utilization of incident sunlight by integrating a PV cell and a thermal receiver in the same collector [4,5]. In this study, we will present a new PV/T design based on a compact linear Fresnel concentrator (LFC) coupled with a spectral beam-splitter. The beam-splitting approach avoids the efficiency drop in the PV cell while still obtaining high temperature thermal output. The design is analyzed numerically with respect to a worth factor which considers the intrinsically higher economic value of electrical energy at ∼3 times thermal energy. In order to predict optical performance, the geometry of this hybrid concentrating collector, which achieves 10–15 suns concentration, is modeled at various incident angles using the ray tracing software Zemax. Three different PV cells are considered (Si, GaAs and GaInP/GaAs). The reported spectral response of these cells is used to determine the optimal wavelength split for the fraction of the solar spectrum directed to the various PV cells. The results indicate that such designs can achieve 20–51% greater value of the power outputs — PV electrical power plus heat produced — relative to a stand-alone PV system.
Publisher: American Society of Mechanical Engineers
Date: 14-07-2013
DOI: 10.1115/ES2013-18147
Abstract: Portable energy storage will be a key challenge if electric vehicles become a large part of our future transportation system. A big limiting factor is vehicle range. Range can be further limited if heating and air conditioning systems are powered by the electric vehicle’s batteries. The use of electricity for HVAC can be minimized if a thermal battery can be substituted as the energy source to provide sufficient cabin heating and cooling. The aim of this project was to model, design, and fabricate a thermal storage battery for electric vehicles. Since cost and weight are the main considerations for a vehicular application — every attempt was made to minimize them in this design. Thus, the final thermal battery consists of a phase change material Erythritol (a sugar alcohol commonly used as artificial sweetener) as the storage medium sealed in an insulated, stainless steel cooking pot. Heat exchange to the thermal battery is accomplished via water (or low viscosity engine oil) which is pushed through a copper coil winding. A CFD model was used to determine the geometry (winding radius and number of coils) and flow conditions necessary to create adequate heat transfer. Testing of the fabricated design indicates that the prototype thermal battery module losses less than 5% per day and can provide enough heat to meet the demand of cruising passenger vehicle for up to 1 hour of full heating on a cold day. Other metrics, such as $/kJ and kJ/kg, are competitive with Lithium ion batteries for our prototype.
Publisher: Springer Science and Business Media LLC
Date: 28-05-2014
Publisher: Elsevier BV
Date: 02-2018
Publisher: Elsevier BV
Date: 12-2023
Publisher: Elsevier BV
Date: 10-2017
Publisher: Springer International Publishing
Date: 2016
Publisher: Elsevier BV
Date: 2019
Publisher: SAE International
Date: 04-2014
DOI: 10.4271/2014-01-1413
Publisher: SAE International
Date: 04-2014
DOI: 10.4271/2014-01-1259
Publisher: Elsevier BV
Date: 2019
Publisher: SAE International
Date: 09-2015
DOI: 10.4271/2015-01-1849
Publisher: Elsevier BV
Date: 2019
Publisher: Elsevier BV
Date: 12-2016
Publisher: AIP Publishing
Date: 06-2022
DOI: 10.1063/5.0097786
Abstract: The modeling of scalar mixing timescale remains a primary challenge in the transported probability density function (TPDF) method. The variation of scalar mixing timescale among species, i.e., differential mixing, results from the difference in molecular diffusivity and reaction-induced scalar gradient. Nevertheless, the vast majority of TPDF studies on turbulent non-premixed flames simply apply a single mixing timescale determined by the mixture fraction. In this work, a reaction-induced differential mixing timescale (RIDM) model for the mixing timescale of in idual species in turbulent non-premixed flames is proposed. The key idea of the RIDM model is to approximate the relative magnitude of the species dissipation rates by using their values in laminar flamelets. A direct numerical simulation dataset of a temporally evolving non-premixed ethylene flame is employed to thoroughly evaluate the model performance via a priori and a posteriori tests. Results show that specifying a single mixing timescale for all species results in a poor prediction of the species dissipation rate and thus the failure to predict the overall combustion process. By accounting for the difference in molecular diffusivity, a slightly better prediction can be obtained, but the improvement is very limited, illustrating that simply modeling the difference due to molecular diffusivities for differential mixing is not sufficient. In comparison, the RIDM model exhibits superior performance in both a priori and a posteriori tests. Moreover, all the components of the RIDM model are readily available in the TPDF method, making the RIDM model a promising candidate employed in practice.
Publisher: Elsevier BV
Date: 2015
Publisher: SAE International
Date: 17-10-2016
DOI: 10.4271/2016-01-2162
Publisher: Elsevier BV
Date: 2011
Publisher: Elsevier BV
Date: 2005
Publisher: Elsevier BV
Date: 2017
Publisher: Elsevier BV
Date: 10-2019
Publisher: Elsevier BV
Date: 11-2020
Publisher: Elsevier BV
Date: 08-2018
Publisher: SAE International
Date: 09-2015
DOI: 10.4271/2015-01-1852
Publisher: Elsevier BV
Date: 08-2011
Publisher: Springer Science and Business Media LLC
Date: 05-2016
Publisher: SAGE Publications
Date: 17-01-2017
Publisher: Cambridge University Press (CUP)
Date: 18-04-2011
DOI: 10.1017/JFM.2011.131
Abstract: This paper presents a numerical and theoretical investigation of the sound generated by premixed flame annihilation. Planar, axisymmetric and spherically symmetric flame annihilation events are considered. The compressible Navier–Stokes, energy and progress variable equations are first solved using simple chemistry simulations, resolving both the flame dynamics and the acoustics. These simulations show that the litude of the far-field sound produced by the annihilation events depends on the flame thickness, particularly for the axisymmetric and spherically symmetric flame annihilation events. The flame propagation velocity is also always observed to increase significantly prior to flame annihilation, which is in keeping with other reported experimental and numerical studies. A theory is then presented that relates the far-field sound to the flame annihilation event by using a previously reported and extended form of Lighthill's acoustic analogy. A comparison with the numerical results shows that this theory accurately represents the far-field sound produced by considering only the temporal heat release source term in Lighthill's acoustic analogy, as reported by others. Additional assumptions of an infinitely thin flame and constant flame speed are then invoked in an attempt to simplify the problem. In the planar annihilation, this theory results in good predictions of the overall pressure change. However, these assumptions lead to significant under-prediction of the litude of far-field sound produced for the axisymmetric and spherically symmetric annihilation events. Finally, dimensional reasoning supported by the simulations and theory is used to develop scalings of the far-field sound in terms of the flame parameters.
Publisher: Elsevier BV
Date: 11-2021
Publisher: Informa UK Limited
Date: 10-10-2018
Publisher: Elsevier BV
Date: 2007
Publisher: Springer Science and Business Media LLC
Date: 03-07-2018
Publisher: Elsevier BV
Date: 2009
Publisher: Springer Science and Business Media LLC
Date: 29-02-2016
Publisher: Elsevier BV
Date: 2021
Publisher: Elsevier BV
Date: 2013
Publisher: Springer Science and Business Media LLC
Date: 22-11-2020
Publisher: Elsevier BV
Date: 2013
Publisher: ASME International
Date: 31-01-2014
DOI: 10.1115/1.4026092
Abstract: Portable energy storage will be a key challenge if electric vehicles (EVs) become a large part of our future transportation system. A big barrier to market uptake for EVs is driving range. Range can be further limited if heating and air conditioning systems are powered by the EV's batteries. The use of electricity for HVAC can be minimized if a thermal storage system, a “thermal battery,” can be substituted as the energy source to provide sufficient cabin heating and cooling. The aim of this project was to model, design, and fabricate a low-cost, modular thermal battery for EVs. The constructed thermal battery employs a phase change material erythritol (a sugar alcohol commonly used as artificial sweetener) as the storage medium sealed in an insulated, stainless steel container. At a total prototype cost of ∼$311/kW-h, the system is roughly half the price of lithium ion batteries. Heat exchange to the thermal battery is accomplished via water (or low viscosity engine oil), which is pumped through a helical winding of copper tubing. A computational fluid dynamics (CFD) model was used to determine the geometry (winding radius and number of coils) and flow conditions necessary to create adequate heat transfer. Testing of the fabricated design indicates that the prototype thermal battery module can store enough heat and discharge it fast enough to meet the demand of cruising passenger vehicle for up to 1 h on a cold day. The battery is capable of storing nearly 100 W-h/kg and can provide a specific power density of 30 W/kg. The storage density is competitive with lithium ion batteries, but work is needed to improve the power density.
Publisher: Elsevier BV
Date: 2015
Publisher: Elsevier BV
Date: 06-2022
Publisher: American Chemical Society (ACS)
Date: 06-11-2013
DOI: 10.1021/EF401479S
Publisher: SPIE-Intl Soc Optical Eng
Date: 10-01-2017
Publisher: Elsevier BV
Date: 2021
Publisher: Elsevier BV
Date: 2013
Publisher: American Institute of Aeronautics and Astronautics
Date: 09-01-2006
DOI: 10.2514/6.2006-165
Publisher: Elsevier BV
Date: 06-2016
Publisher: Elsevier BV
Date: 07-2020
Publisher: Elsevier BV
Date: 07-2016
Publisher: Begell House
Date: 2015
Publisher: Elsevier BV
Date: 2007
Publisher: Elsevier BV
Date: 06-2014
Publisher: American Institute of Aeronautics and Astronautics
Date: 14-06-2011
DOI: 10.2514/6.2011-3586
Publisher: The Optical Society
Date: 09-05-2017
DOI: 10.1364/AO.56.004158
Publisher: Elsevier BV
Date: 10-2016
Publisher: SAE International
Date: 17-10-2016
DOI: 10.4271/2016-01-2303
Publisher: Elsevier BV
Date: 08-2001
Publisher: Elsevier BV
Date: 12-2013
Publisher: Elsevier BV
Date: 10-2022
Publisher: AIP Publishing
Date: 06-2011
DOI: 10.1063/1.3601483
Abstract: Three-dimensional compressible direct numerical simulation (DNS) data of freely propagating statistically planar turbulent premixed flames have been used to assess the accuracy of the isotropy- derived correction factors, which relate the two-dimensional projections of the different terms of the Reynolds averaged flame-surface density (FSD) transport equation with their corresponding actual three-dimensional counterparts for different values of Karlovitz number Ka, Lewis number Le, heat release parameter τ, and turbulent Reynolds number Ret. It is shown that the isotropic distribution of the surface area weighted probability density function (pdf) of the angle φ between the normal vectors on the measurement plane and on the flame surface provides a simple algebraic relation between the generalised FSDs evaluated in two and three dimensions (i.e., Σ2D and Σ3D), irrespective of the values of Ka,τ,Le, and Ret. Isotropic relations between two-dimensional and three-dimensional counterparts of the surface-averaged curvature and the FSD propagation term are also found to work well for all the values of Ka,τ,Le, and Ret considered in this study. However, the relations between the value obtained from two-dimensional projection and the actual three-dimensional value for the tangential strain rate and curvature terms in the FSD transport equation work well only for the high values of turbulent Reynolds number. The reasons behind the disagreement between the predictions of the relations derived based on isotropy arguments for both the tangential strain rate and curvature terms of the FSD transport equation are explained in detail. It is found that the threshold value of Ret above which the assumption of isotropy yields an accurate relation between two-dimensional projection and three-dimensional values for the tangential strain rate and curvature terms of the FSD transport equation depends on the values of heat release parameter, Lewis number, and the regime of the prevailing combustion process.
Publisher: Springer Berlin Heidelberg
Date: 2014
Publisher: IOP Publishing
Date: 2005
Publisher: Springer Science and Business Media LLC
Date: 28-01-2019
Publisher: IOP Publishing
Date: 23-01-2009
Publisher: Springer Science and Business Media LLC
Date: 05-01-2018
Publisher: Elsevier BV
Date: 2000
Publisher: SAE International
Date: 06-04-2021
DOI: 10.4271/2021-01-0527
Publisher: Elsevier BV
Date: 2019
Publisher: Informa UK Limited
Date: 12-2001
Publisher: Elsevier BV
Date: 2021
Publisher: SAE International
Date: 06-04-2021
DOI: 10.4271/2021-01-0526
Publisher: Elsevier BV
Date: 2005
Publisher: Cambridge University Press (CUP)
Date: 23-02-2021
Publisher: Springer Science and Business Media LLC
Date: 21-04-2015
Publisher: Elsevier BV
Date: 2015
Publisher: SAE International
Date: 28-03-2017
DOI: 10.4271/2017-01-0742
Publisher: Elsevier BV
Date: 08-2018
Publisher: Elsevier BV
Date: 07-2017
Publisher: Elsevier BV
Date: 11-2013
Publisher: Elsevier BV
Date: 10-2018
Publisher: American Chemical Society (ACS)
Date: 09-07-2018
Publisher: Elsevier BV
Date: 03-2017
Publisher: Elsevier BV
Date: 07-2017
Location: United States of America
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Evatt Hawkes.