Sharif Digital Repository

In this thesis, combustion of liquid fuel spray under the condition of hot and diluted oxidizer, has been investigated. To this end, a novel type laboratory-scale test rig was designed to study the physics governing the MILD-Spray combustion conditions with an applied approach. The underlined test rig eliminates the operational problems of its predecessor test stands and is used for a heavier fuel with much more complex chemical composition (kerosene). The test section is axially symmetrical, in which the fuel is injected by a pressure-swirl atomizer in the direction of hot and diluted co-flowing air. With the use of the aforesaid test rig, the effect of variables such as oxygen... 

In order to improve performance and optimize design of high pressure combustion devices such as liquid rocket engine, gas turbine engine, and diesel engine there is a need for comprehensive understanding of injection, mixing and combustion in supercritical condition. Under this condition chamber pressure is higher than critical pressure of fuel and oxidizer. The characteristic of supercritical condition, include changing thermophysical properties such as density, CP, and compressibility factor. Therefore under this condition ideal state equation cannot correctly predict the mentioned properties. These characteristics make supercritical combustion different from other combustion regimes.... 

Moderate and Intense Low-oxygen Dilution(MILD) is the new member of combustion field. Highly preheated reactants and lowering the oxygen level in MILD combustion has some promising advantages. In this study the MILD burner, Jet-in-Hot-Coflow(JHC), is taken as the main test case. In this Research, Eddy Dissipation Concept combustion model ,introduced by Magnussen et al,is investigated in detail and governing equations are re-extracted. EDC combsution model due to moderate compuational cost in comparison with other combustion model and well prediction ability has drawn attention. Simulations on the Jet-in-Hot-Coflow(JHC) has shown the promising performance of the EDC combustion model. It seems... 

High swirl combustors with circulative structures in the flow field, have a highly flame stability with a wide range of operating conditions. In this study, Sharif Gas Turbine Model Combustor (SGTMC) which is a double high swirl burner, was investigated experimentally and numerically. In experimental studies, SGTMC with different settings of swirlers is investigated in terms of flame lean blow-out(LBO), wall temperature, the exhaust gas composition and pollutant and also flame geometry parameters. Setting of burner are changed by variations in air fraction between inner and outer air inlets or swirlers’ vanes degrees and flow rotation directions. The results indicate that the concentrations... 

In this thesis numerical investigation on the effect of injecting plasma into the MILD combustion regime which is based on the low oxygen dilution and high preheated temperature, were carried out. The burner which was utilized in this study is a co-flow burner, consists of three coaxial channels. From the center to the outside, there is a fuel jet at the center part, a co-flowing dielectric barrier discharge (DBD), and a preheated air section that is vitiated. The DBD that was used in this study is generated between two coaxial electrodes of which the outer one (conical copper electrode) is covered with a dielectric material made of quartz. The burner is modeled in a 2D-axisymmetric... 

In this study, the numerical simulation of MILD spray combustion of kerosene in preheated and oxygen-diluted air is conducted in the SMSTR combustion test rig at Sharif University of Technology. Considering the importance of understanding various aspects of this combustion regime, a numerical model has been developed, and using the EDC combustion model, the effects of parameters such as inlet oxygen concentration, inlet air temperature, chemical kinetics, and volume fraction/time scale constants on functional parameters like flame structure, flame lift-off height, temperature field distribution, and mass fraction ratio of combustion species in the reaction zone have been investigated. To... 

In this study, the effects of increasing the temperature of the air or oxidizer used in the combustion process were investigated. Additionally, the effects of oxidizer dilution through nitrogen gas injection into the inlet air of the combustion chamber were examined. The research was conducted experimentally on the Sharif model gas turbine combustion chamber. Moreover, LPG gaseous fuel, which is a mixture of propane and butane gases, was utilized. Data acquisition techniques such as imaging, bandpass-filtered imaging, spectroscopy, and thermometry were employed throughout the tests. The results are reported in four sections: base flame characteristics, preheating effects, dilution effects,... 

MILD combustion under high preheating and high dilution condition illustrates some interesting characteristics. Very low oxygen concentration in the reaction zone and reduced chemical reaction rates compared to conventional combustion are some of these features which make MILD combustion to be an unique type of combustion. In this work numerical investigation of a gas turbine model combustor (GTMC) was aimed to done using model of the EDC as turbulence-chemistry interaction combustion model. Modeling was performed by solving RANS equations and RSM equations for a 2D axisymmetric computational domain. The combustion chamber was investigated for both reacting and non-reacting conditions. A... 

In this study, the effects of using the co-flow air rotation on Kerosene combustion under air preheating and diluting conditions have been investigated. During this research, we have tried to achieve combustion under the MILD regime by simultaneous diluting, preheating, and swirling the co-flow air, which has also been achieved. To investigate the factors affecting the flame structure such as preheating temperature, dilution, swirl number, airflow rate, and also the type of fuel nozzle, the Sharif University MILD combustion test rig (SMCTR) has been upgraded in this research.The SMCTR has a symmetrically axial structure and provides a co-flow air with the desired temperature, swirl number,... 

High Swirl Combustors can provide stable flames in wide range of operating conditions. Double swirl combustors, as one of the newest designs in this field, have particular effects on improving the efficiency of combustion chambers in terms of flame stability, mixing process quality and reducing combustion pollutants. In this study, a double swirl gas turbine combustor, SGTMC, which is redesigned version of a German combustor (GTMC), has been investigated. According to experimental section of this study, lean stability limits, UHCs, CO and NOx has been measured and analyzed. Results show that this burner can provide a stable flame even in very low equivalence ratios. Also in some specific... 

In high-performance liquid fuel motors and space thrusters, the combustion chamber and nozzle walls are in contact with the gases caused by high temperature and pressure combustion, making severe thermal loads on the walls. Therefore, these systems require cooling mechanisms. The most common way of cooling in space thrusters is film cooling. This study is a numerical simulation of film cooling in the liquid fuel space thrusters. Numerical and empirical studies have been reviewed in this area and evaluated while conducting studies and results to select an appropriate model for ongoing project studies. Along this path, various fuel and oxidizing thrusters, including oxygen and hydrogen,... 

This project investigates the effect of plasma on diffusion flame. A Dielectric Barrier Discharge (DBD) plasma actuator has been used to generate plasma, which converts fuel-air non-premixed mixtures into plasma. Then, the effect of plasma on the shape and stability of the diffusion flame composed of fuel and air mixture has been evaluated. This study investigates the laminar flow regime for low calorific value fuels. For this purpose, natural gas fuel (urban methane) has been diluted with N2 and CO2 gases to reduce its calorific value. Then, the diffusion flame is formed from the fuel and air mixture in a laboratory stand. This stand consists of two coaxial tubes made of quartz, fuel flows... 

In this study, an Experimental investigation of plasma-assisted combustion using a DBD actuator has been performed. This actuator ionizes the fluid flow by producing asymmetric and cold plasma. Ionizing the flow of fuel or air in the combustion chamber reduces the combustion time scale. The test chamber consists of two coaxial quartz tubes that fuel passes through the central tube and the air pass through the side tube. In the case of fuel (natural gas) ionization, one rod as the electrode passes through the center tube, and the second electrode closes in a loop around the inner tube. One annular electrode is closed around the central tube during air ionization, and the second electrode is... 

MILD combustion can be a promising technology to prevent global warming. In this study, for the first time, the numerical simulation of MILD spray combustion of kerosene fuel with preheated and diluted air has been conducted in the faculty's SMSTR test stand. The modeling framework is based on the Reynolds averaged Navier-Stokes turbulence approach and the standard k–ε model, the DPM discrete phase model, and the EDC combustion model, using the skeletal chemical mechanism of Jet A POSF10325 kerosene with the air and droplet being tracked in Lagrangian coordinates. The simulation is done in a steady state and by an axisymmetric method, and the effects of inlet oxygen concentration, inlet air... 

In this study, the experimental study of kerosene mild spray combustion with the presence of the chamber has been investigated. The test rig that has been studied and improved is Sharif University of Technology's MILD Combustion Test Rig on a laboratory scale, which provides the possibility of studying spray combustion with preheating and high dilution. This test rig, while solving the problems of similar test stands, has the possibility of operating with liquid kerosene fuel, which is widely used in various industries. This test rig is axially symmetrical and provides the possibility of providing co-flow air with the desired temperature, swirl number and dilution rate for a liquid fuel... 

The Moderate or Intense Low-oxygen Dilution (MILD) combustion of liquid fuels has attracted attention to use its advantages in industrial burners and gas turbines applications. Here numerical investigation has been conducted on a research experimental MILD turbulent spray burner (Deft Spray in Hot Co-flow, DSHC). RANS approach has been adopted for modeling of the reactive turbulent flow field of continues phase with the Lagrangian approach for droplet modeling of pressure-swirl atomizer fuel spray. The EDC combustion model is used which has the ability to take into account the detailed chemical mechanisms. The accuracy of different turbulence and droplet injection sub-models are examined and... 

Presently, a wide range of devices operate at supercritical condition. In fact, supercritical condition refers to a condition in which both temperature and pressure of injected fluid exceed the critical point. In the case of modern internal combustion engine, the temperature and pressure of combustion chamber is high enough that can be considered as supercritical condition, whilst the fuel injected may be subcritical or transcritical.It has been widely accepted that in supercritical state, vaporization enthalpy is vanished and there is no distinction between gas and liquid. Hence, only a single state will remain which is neither liquid nor gas and referred to as fluid. Moreover, many... 

The present work is concerned with numerical simulation of spray flame for rocket combustor (MASCOTTE A-10 test case at 10 bar pressure) based on cryogen gaseous hydrogen and liquid oxygen at specific condition. This liquid oxygen and gaseous hydrogen single element combustor experiment has been the focus of many numerical studies which is representative of combustion in rocket combustion chamber condition. The purposed strategy relies on hybrid Eulerian-Lagrangian framework that continuous phase is evaluated by Reynolds average Navier-stokes (RANS) equation with quick discretization method and dispersed phase of combustion chamber atmosphere is evaluated by discrete phase method (DPM). To... 

This research introduces temperature measurement by a non-intrusive pyrometric method of the ratio of two colors of soot. For pyrometry, the spectral sensitivity of the Nikon D7100 camera was obtained by developing a neural network based on the results of photographing colored papers and their spectrum, and this camera was used for temperature measurement. Based on the dependence of soot radiation on temperature and the spectral sensitivity of the camera, a calibration chart has been extracted on the ratio of the green channel to the red channel of the camera with the soot temperature, which is used to produce the temperature contour using the flame image. The temperature contour of... 

The burners studied in the combustion principles have different types due to the configuration of different types of flames, each of them studies a specific phenomenon of combustion, so researchers need to design burners with the ability to: create different types of combustion flow regimes, changing in mixing rate and performance at critical points are felt more and more. This document describes the process of designing and manufacturing a turbulent jet burner with variable mixing ratio and the ability to create a diverse range of flow regimes and different flame configurations. Mixing rate is the most important characteristic in the stability of premixed flames, so the distinctive feature...