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Title: Development and application of the drop number size moment modelling sprays to engine simulations and application of combustion models
Author: Dhuchakallaya, Isares
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 2010
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This work presents the development and implementation of a spray combustion model based on the spray droplet number size distribution moments approach to spray modelling. In this spray model, the droplet size distribution of spray is characterised by the first four moments related to number, radius, surface area and volume of droplets, respectively. The governing equations for both the gas and liquid phases are solved by the finite volume method based on an Eulerian framework. These constructed equations and source terms are derived based on the moment-average quantities which are the key concept for this work. Regarding to the application in diesel spray combustion, the auto-ignition and combustion models are substantially required to be implemented. The model employed in the auto-ignition and combustion analysis here is the PDF-Eddy Break-Up (PDF-EBU) model. This scheme is developed in order to effectively validate both ignition and combustion phases. It is designed to compromise between the chemical reaction rate dealing with the ignition mode, and turbulence reaction rate dominating the combustion mode via a reaction progress variable which represents the reaction level. These average reaction rates are evaluated by a probability density function (PDF) averaging approach. In order to assess the potential of this developed model, the auto-ignition and combustion models are further required to be validated. In auto-ignition process, the predicted results from both the developed PDF-EBU and the Shell ignition models are completely satisfactory in predicting the ignition delay time. However, the ignition kernel location predicted by the Shell model is slightly nearer injector than that by the PDF-EBU model resulting in shorter lift-off length. In combustion mode, the PDF-Chemical Equilibrium (PDF-EQ) combustion model presents slightly stronger reaction rate than the PDF-EBU model results. So the combustion period of the PDF-EQ model is then slightly shorter due to the same amount of liquid fuel. Comparing with the experimental data obtained from the literature, the lift-off lengths of luminous flames are in reasonably good agreement with the simulation results of the PDFEBU ignition model. Furthermore, the power-law scaling of Siebers et al. [1, 2] generally employed for predicting the lifted flame provides corresponding lift-off lengths to the PDFEBU and experimental results as well. In overall, there are insignificant differences in predicting the flame areas and average surface flame temperatures by different ignition and combustion models. However, the PDF-EBU ignition model seemingly yields the predicted results in moderately good agreement with the experimental data. The performance of the developed PDF-EBU combustion model is comparable to that of the more complicated PDFEQ combustion model. The other CFD simulation results in literature employed for comparison are obtained from the detailed kinetic mechanism of n-heptane, which have high reliability and accuracy. Similar to the experiment comparison, the lift-off lengths predicted by a power-law scaling more corresponds to the PDF-EBU ignition model results than to the CFD simulation results. However, the simulation results of flame temperature predicted by any ignition and combustion models are relatively comparable to the complex CFD simulation results.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available