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You searched for subject:(Tribrachial flame). Showing records 1 – 2 of 2 total matches.

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University of New South Wales

1. Krisman, Alexander. Direct numerical simulation of diesel-relevant combustion.

Degree: Mechanical & Manufacturing Engineering, 2016, University of New South Wales

Diesel combustion is a major contributor to global energy production. However, despite major improvements to diesel engine design, substantial gaps exist in the fundamental description of the in-cylinder combustion process. This impedes the development of simple, predictive models which are necessary for designing improved combustion devices. In particular, only an under-resolved description of ignition and lifted flame stabilisation exists, due to physical limitations of experimental measurements. Ignition and flame stabilisation govern the formation of pollutants and combustion efficiency, and so a refined understanding is required. In this thesis, direct numerical simulation (DNS) techniques are applied to idealised configurations that represent facets of diesel combustion. A particular focus is applied to representing the correct thermochemical conditions which result in multi-stage autoignition and a negative temperature coefficient (NTC) regime of ignition delay times. The results were broadly consistent with prior experimental studies, but the well-resolved information also revealed details of several novel combustion features that have not been previously reported. Simulations of lifted laminar flames at NTC conditions with detailed dimethyl ether chemistry observed that edge flame or hybrid edge flame/autoignition structures can exist even at diesel-relevant autoignitive conditions, which raises the possibility that edge flame propagation or a combination of edge flame propagation and autoignition are responsible for diesel flame stabilisation. The ignition of a two-dimensional mixing layer at NTC conditions in isotropic turbulence with detailed dimethyl ether chemistry was conducted. A complex ignition process was observed in which two-stage autoignition, cool flames, and hybrid edge flame/autoignition structures contributed to the overall ignition process. In particular, it was observed that the cool flame influenced the timing and location of the high temperature ignition. A three-dimensional ignition at NTC conditions with global heptane chemistry was conducted. The results were consistent with the two-dimensional mixing layer results. The results also emphasised the importance of mixing rates in determining the location and timing of high temperature ignition. Overall, this thesis complements prior experimental results, identifies novel combustion features and highlights the substantial modelling challenge presented by diesel combustion. Advisors/Committee Members: Hawkes, Evatt, Mechanical & Manufacturing Engineering, Faculty of Engineering, UNSW, Kook, Sanghoon, Mechanical & Manufacturing Engineering, Faculty of Engineering, UNSW.

Subjects/Keywords: Negative temperature coefficient; Direct numerical simulation; Diesel-relevant combustion; Triple flame; Two-stage ignition; Polybrachial flame; Tribrachial flame; Ignition; Cool flame; Edge flame

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APA (6th Edition):

Krisman, A. (2016). Direct numerical simulation of diesel-relevant combustion. (Doctoral Dissertation). University of New South Wales. Retrieved from http://handle.unsw.edu.au/1959.4/55498 ; https://unsworks.unsw.edu.au/fapi/datastream/unsworks:37862/SOURCE02?view=true

Chicago Manual of Style (16th Edition):

Krisman, Alexander. “Direct numerical simulation of diesel-relevant combustion.” 2016. Doctoral Dissertation, University of New South Wales. Accessed April 16, 2021. http://handle.unsw.edu.au/1959.4/55498 ; https://unsworks.unsw.edu.au/fapi/datastream/unsworks:37862/SOURCE02?view=true.

MLA Handbook (7th Edition):

Krisman, Alexander. “Direct numerical simulation of diesel-relevant combustion.” 2016. Web. 16 Apr 2021.

Vancouver:

Krisman A. Direct numerical simulation of diesel-relevant combustion. [Internet] [Doctoral dissertation]. University of New South Wales; 2016. [cited 2021 Apr 16]. Available from: http://handle.unsw.edu.au/1959.4/55498 ; https://unsworks.unsw.edu.au/fapi/datastream/unsworks:37862/SOURCE02?view=true.

Council of Science Editors:

Krisman A. Direct numerical simulation of diesel-relevant combustion. [Doctoral Dissertation]. University of New South Wales; 2016. Available from: http://handle.unsw.edu.au/1959.4/55498 ; https://unsworks.unsw.edu.au/fapi/datastream/unsworks:37862/SOURCE02?view=true


King Abdullah University of Science and Technology

2. Al-Noman, Saeed M. Experiment and Simulation of Autoignition in Jet Flames and its Relevance to Flame Stabilization and Structure.

Degree: Physical Science and Engineering (PSE) Division, 2016, King Abdullah University of Science and Technology

Autoignition characteristics of pre-vaporized iso-octane, primary reference fuels, gasolines, and dimethyl ether (DME) have been investigated experimentally in a coflow with elevated temperature of air. With the coflow air at relatively low initial temperatures below autoignition temperature Tauto, an external ignition source was required to stabilize the flame. Non-autoignited lifted flames had tribrachial edge structures and their liftoff heights correlated well with the jet velocity scaled by the stoichiometric laminar burning velocity, indicating the importance of the edge propagation speed on flame stabilization balanced with local flow velocity. At high initial temperatures over Tauto, the autoignited flames were stabilized without requiring an external ignition source. The autoignited lifted flames exhibited either tribrachial edge structures or Mild combustion behaviors depending on the level of fuel dilution. For the iso-octane and n-heptane fuels, two distinct transition behaviors were observed in the autoignition regime from a nozzle-attached flame to a lifted tribrachial-edge flame and then a sudden transition to lifted Mild combustion as the jet velocity increased at a certain fuel dilution level. The liftoff data of the autoignited flames with tribrachial edges were analyzed based on calculated ignition delay times for the pre-vaporized fuels. Analysis of the experimental data suggested that ignition delay time may be much less sensitive to initial temperature under atmospheric pressure conditions as compared with predictions. For the gasoline fuels for advanced combustion engines (FACEs), and primary reference fuels (PRFs), autoignited liftoff data were correlated with Research Octane Number and Cetane Number. For the DME fuel, planar laser-induced fluorescence (PLIF) of formaldehyde (CH2O) and CH* chemiluminescence were visualized qualitatively. In the autoignition regime for both tribrachial structure and mild combustion, formaldehyde were found mainly between the fuel nozzle and the lifted flame edge. On the other hand, they were formed just prior to the flame edge for the non-autoignited lifted flames. The effect of fuel pyrolysis and partial oxidation were found to be important in explaining autoignited liftoff heights, especially in the Mild combustion regime. Flame structures of autoignited flames were investigated numerically for syngas (CO/H2) and methane fuels. The simulations of syngas fuel accounting for the differential diffusion have been performed by adopting several kinetic mechanisms to test the models ability in predicting the flame behaviors observed previously. The results agreed well with the observed nozzle-attached flame characteristics in case of non-autoignited flames. For autoignited lifted flames in high temperature regime, a unique autoignition behavior can be predicted having HO2 and H2O2 radicals in a broad region between the nozzle and stabilized lifted flame edge. Autoignition characteristics of laminar nonpremixed methane jet flames in high- temperature coflow air… Advisors/Committee Members: Chung, Suk Ho (advisor), Roberts, William L. (committee member), Sarathy, Mani (committee member), Park, Jeong (committee member).

Subjects/Keywords: Autoignition; Flame stabilization; Lift off height; Ignition delay time; Tribrachial flame; Mild combustion; Jet flame; Coflow; Syngas; Methane; Dimethyl ether; n-heptane; iso-octane; Ethanol; Gasoline FACEs; Laser-induced fluorescence,; Formaldehyde

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Al-Noman, S. M. (2016). Experiment and Simulation of Autoignition in Jet Flames and its Relevance to Flame Stabilization and Structure. (Thesis). King Abdullah University of Science and Technology. Retrieved from http://hdl.handle.net/10754/615946

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16th Edition):

Al-Noman, Saeed M. “Experiment and Simulation of Autoignition in Jet Flames and its Relevance to Flame Stabilization and Structure.” 2016. Thesis, King Abdullah University of Science and Technology. Accessed April 16, 2021. http://hdl.handle.net/10754/615946.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7th Edition):

Al-Noman, Saeed M. “Experiment and Simulation of Autoignition in Jet Flames and its Relevance to Flame Stabilization and Structure.” 2016. Web. 16 Apr 2021.

Vancouver:

Al-Noman SM. Experiment and Simulation of Autoignition in Jet Flames and its Relevance to Flame Stabilization and Structure. [Internet] [Thesis]. King Abdullah University of Science and Technology; 2016. [cited 2021 Apr 16]. Available from: http://hdl.handle.net/10754/615946.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Al-Noman SM. Experiment and Simulation of Autoignition in Jet Flames and its Relevance to Flame Stabilization and Structure. [Thesis]. King Abdullah University of Science and Technology; 2016. Available from: http://hdl.handle.net/10754/615946

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

.