| Summary: | 碩士 === 國立成功大學 === 航空太空工程學系 === 88 === ABSTRACT
Subject：Numerical Analysis on the Combustion Characteristic of
Heavy Fuel Oil Emulsion in Gas-Turbine Combustors
Student : Cheng-Sung Hsu
Advisor : Tsung-Leo Jiang
Combustion gas turbines have historically been a major source of NOx emissions. This is due to high combustion temperatures and pressures which accelerate thermal NOx production. In order to reduce the NOx emission levels to meet new environmental regulations, industrial combustion technologies have to be improved. It has been demonstrated by many literatures that the use of oil-water emulsions has significant effects on the improvement of combustion performance of liquid fuels, especially the reduction of particulate and NOx emissions. Different hypotheses have been postulated to explain these effects. The most widely accepted is the so-called "micro-explosions". Secondary atomization of the initial spray is produced as a consequence of the disruptive evaporation of the water droplets contained in an oil drop. This phenomenon has been extensively documented in several theoretical and experimental studies.Utilization of heavy fuel oil emulsion to control the NOx emission of gas turbine combustor is to be evaluated by using numerical simulation in this research. In addition, effects of the water content in heavy oil on combustion characteristics, combustion efficiency, and flame structure are to be investigated. In this study, a computer simulation program for the analysis of three dimensional multi-component spray combustion has been successfully developed. The computational and physical models adopted in the present study include: two-phase flow computation model, two-equation turbulence model, turbulent combustion model, oil/water emulsion drop vaporization model, and the models for the exchange of mass, energy, and momentum between two phases. The three-dimensional grids are generated adopting the concept of multiple block-structured mesh. The combustion flow simulated in the present study includes the spray combustion flow inside the liner, the inlet flow that is guided to flow through the passage between the casing and the liner and into the combustion zone through the inlet and dilution holes, and the exhausted flow in the rear pipe-section and mixing case. In the present study, effects of spray-angle expansion and droplet-size reduction, attributed to the secondary atomization of heavy oil-water emulsions, on the characteristics of spray flame have been investigated. The predicted numerical results show that the adoption of emulsified fuel helps reduce the emission of NOx. In addition, by using emulsified fuel more uniform distribution of fuel-air mixtures inside the combustion chamber can be obtained and the combustion efficiency is improved effectively.
|
|---|
