M.Sc Thesis


M.Sc StudentLiron Hamelnick
SubjectInvestigation of the Characteristics Arrays of Polydisperse
Spray Flames
DepartmentDepartment of Aerospace Engineering
Supervisor Professor Emeritus Greenberg Jerrold
Full Thesis text - in Hebrew Full thesis text - Hebrew Version


Abstract

This study presents the characteristics of spray diffusive flames in multiple flames configuration. The way in which the flames from such burners interact is of paramount importance in determining the efficiency of the system. In addition, supplying the fuel as a spray of polydisperse droplets can exacerbate combustion inefficiency and pollution due the possibility of non-uniform heating on account of the droplet dispersion in the system.

The main goal of this research is to investigation the characteristics of multiple, laminar, spray and diffusive flames and the possible mutual influence between adjacent flames .In addition, the motivation behind this research was to find situations where a blockage in one of the fuel ducts and the interaction of a number of flames created a temperature field and flames (heights, types) which are different from the original combustion design and could decrease the effectiveness of the all system.

The sprays were modeled using the sectional approach in which the spray is divided into "size-sections" according to the droplets diameters. Each size section has its own conservation equation which is based on Williams's spray equation, describing the transfer of droplets between the sections, while the sectional vaporization coefficients are assumed constant. In addition, the conservation equation for the gas fuel phase and oxygen phase were solved. Two problems have been conducted using similar method and governing equations.

The first problem presents the characteristics of multiple spray flames when the chemical Damköhler number aspires to infinity. The mutual influence of spray diffusive flames was conducted for different characteristics of spray, flow and operating conditions in order to present when asymmetric combustion field is obtained.

In contrast, the results for finite chemical Damköhler number are presented in the second problem. The influence of chemical Damköhler number is significant and affects the characteristics of the spray flames. "Edge-Flame" is a result of diffusive mixing of the fuel vapor and oxygen which located somewhere downstream of the ducts exit and attached is a diffusive flame that trails downstream from it. The Conditions for stable or oscillatory flames was conducted for different system characteristics. Mass transfer between adjacent flames is the physical mechanism which contributes to the mutual influence between the flames, even to different oscillations and amplitudes of the "Edge-flames" and different temperature field (as design to).

The results in the two described problems are presented in a comparison between the characteristics of multiple spray flames configuration to the known characteristics of one spray flame problem.