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Various sub models of a multi-zone phenomenological model are developed by incorporating Dec’s conceptual model and Siebers’ mixing limited theory and validated with experiments. The spray penetration model, liquid length model and lift-off length model are verified with experiment data. The ignition delay model is then validated with experiment data at different injection timings and loads. The air entrainment model is based on Siebers’ jet theory. Sub models for the premixed heat release rate and diffusion burn rate are also included. The overall phenomenological model is at first used to match the motoring pressure curve. The important sub models are well validated independently and the phenomenological model is useful in simulating diesel spray combustion. Future work is needed to integrate these sub models and to resolve existing issues in temperature profiles of the preparing zone and liquid zone.

To adhere to the current requirements for NOx and CO emissions in combustion systems, modern land and air based gas turbine engines often operate in the fuel lean regime. While operating near the lean blow out (LBO) limit does reduce some harmful emissions, combustor stability is sacrificed and extinction becomes a major concern. To fully understand the characteristics of lean operation, an experimental study was conducted to map the time averaged flow field in a typical industrial, counter-swirling, liquid fuel combustor. This study examined two steady-state operating conditions, both near the lean extinction limit for this swirl burner. Using an LDV/PDPA system, 2-D mean and fluctuating velocities, as well as Reynolds stresses, were measured throughout the combustor. These measurements were taken for both the non-reacting and reacting flow fields, enabling a direct analysis of the result of heat addition and increased load on a turbulent swirling flow field. To further understand the overall flow field, liquid droplet diameter measurements were taken to determine the fuel spray characteristics as a function of operating pressure and rated spray angle. Chemical composition at the combustor exit was also measured, with an emphasis on the concentrations of both CO and NOx emissions. This large database of aerodynamic and droplet measurements improves understanding of the swirling, reacting flow field and aids in the accurate prediction of lean blow-out events. With this understanding of the lean blow-out limit, increased fuel efficiency and decreased pollutant emissions can be achieved in industrial combustors, especially those used for thrust in the airline industry.

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Thesis (PH.D.)--Michigan State University. Mechanical Engineering, 2008. / Title from PDF t.p. (viewed on Aug. 28, 2009) Includes bibliographical references. Also issued in print.

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<p>Air, nitrogen, argon and carbon dioxide were used as the atomizing gas in an 'air-assist' spray nozzle to determine the effect of these gases on mean droplet size, number density, velocity and their distributions in kerosene fuel spays and spray flames using a two dimensional phase Doppler interferometer. Data have been obtained with these atomizing gases using a base, air assisted case as a reference, since this is the most commonly used atomizing fluid in almost all applications. Comparisons were made between the gases on a mass and momentum flux basis. Both burning and nonburning sprays were investigated. The results show significant differences in atomization characteristics from the atomizer with different gases and under conditions of constant mass and momentum flux of the gas. The results also show that the presence of oxygen in the air atomized sprays assists in the combustion process, since it produces smaller and faster moving droplets, especially at locations near to the nozzle exit. In nonburning sprays, droplets had similar size and velocity. Lighter gases such as nitrogen more effectively atomized the fuel in comparison to the denser gases. Argon and carbon dioxide produced larger, slower moving droplets than air and nitrogen assisted cases in both the burning and nonburning sprays. Flame photographs revealed the argon and carbon dioxide atomized flames to have greater luminosity than air or nitrogen atomized flames.</p> / Master of Science

In the recent past, LES methodology has emerged as a viable tool for modeling turbulent combustion. LES computes the large scale mixing process accurately, thereby providing a better starting point for small-scale models that describe the combustion process. Significant effort has been made over past decades to improve accuracy and applicability of the LES approach to a wide range of flows, though the current conventions often lack consistency to the problems at hand. To this end, the two main objectives of this dissertation are to develop a dynamic transport equation-based combustion model for large- eddy simulation (LES) of turbulent spray combustion and to investigate grid- independent LES modeling for scalar mixing. Long-standing combustion modeling approaches have shown to be suc- cessful for a wide range of gas-phase flames, however, the assumptions required to derive these formulations are invalidated in the presence of liquid fuels and non-negligible evaporation rates. In the first part of this work, a novel ap- proach is developed to account for these evaporation effects and the resulting multi-regime combustion process. First, the mathematical formulation is de- rived and the numerical implementation in a low-Mach number computational solver is verified against one-dimensional and lab scale, both non-reacting and reacting spray-laden flows. In order to clarify the modeling requirements in LES for spray combustion applications, results from a suite of fully-resolved direct numerical simulations (DNS) of a spray laden planar jet flame are fil- tered at a range of length scales. LES results are then validated against two sets of experimental jet flames, one having a pilot and allowing for reduced chemistry modeling and the second requiring the use of detail chemistry with in situ tabulation to reduce the computational cost of the direct integration of a chemical mechanism. The conventional LES governing equations are derived from a low-pass filtering of the Navier-Stokes equations. In practice, the filter used to derive the LES governing equations is not formally defined and instead, it is assumed that the discretization of LES equations will implicitly act as a low-pass filter. The second part of this study investigates an alternative derivation of the LES governing equations that requires the formal definition of the filtering operator, known as explicitly filtered LES. It has been shown that decoupling the filter- ing operation from the underlying grid allows for the isolation of subfilter-scale modeling errors from numerical discretization errors. Specific to combustion modeling are the aggregate errors associated with modeling sub-filter distribu- tions of scalars that are transported by numerical impacted turbulent fields. Quantities of interest to commonly-used combustion models, including sub- filter scalar variance and filtered scalar dissipation rate, are investigated for both homogeneous and shear-driven turbulent mixing. / text