Sangsig Yun

High resolution temperature mapping of gas turbine combustor simulator exhaust with femtosecond laser induced fiber Bragg gratings

Femtosecond infrared (fs-IR) laser written fiber Bragg gratings (FBGs), have demonstrated great potential for extreme sensing. Such conditions are inherent in advanced gas turbine engines under development to reduce greenhouse gas emissions; and the ability to measure temperature gradients in these harsh environments is currently limited by the lack of sensors and controls capable of withstanding the high temperature, pressure and corrosive conditions present. This paper discusses fabrication and deployment of several fs-IR written FBG arrays, for monitoring exhaust temperature gradients of a gas turbine combustor simulator. Results include: contour plots of measured temperature gradients, contrast with thermocouple data.

Combustor deployments of femtosecond laser written fiber Bragg grating arrays for temperature measurements surpassing 1000 °C

Femtosecond Infrared (fs-IR) laser written fiber Bragg gratings (FBGs), have demonstrated great potential for extreme sensing. Such conditions are inherent to advanced power plant technologies and gas turbine engines, under development to reduce greenhouse gas emissions; and the ability to measure temperature gradients in these harsh environments is currently limited by the lack of sensors and controls capable of withstanding the high temperature, pressure and corrosive conditions present. This paper reviews our fabrication and deployment of hundreds of fs-IR written FBGs, for monitoring temperature gradients of an oxy-fuel fluidized bed combustor and an aerospace gas turbine combustor simulator.

High temperature measurement of a low emission, high pressure combustor using femtosecond laser written fiber Bragg gratings

Femtosecond Infrared (fs-IR) laser written fiber Bragg gratings (FBGs), have shown great potential for sensing in extreme environments. This paper presents the fabrication and deployment of two fs-IR laser written FBG temperature probes, for monitoring temperature gradients on the flame tube of a low emission burner, during a high pressure combustor test of an optically accessible combustor rig (OACR). Results of this work include: contour plots of measured internal and exhaust temperature gradients, contrast of FBG measurements with thermocouple data, discussion of deployment strategies, as well as comments on reliability and other important considerations.

High-resolution fast temperature mapping of a gas turbine combustor simulator with femtosecond infrared laser written fiber Bragg gratings

Femtosecond infrared (fs-IR) written fiber Bragg gratings (FBGs), have demonstrated great potential for extreme sensing. Such conditions are inherent to the advanced gas turbine engines under development to reduce greenhouse gas emissions; and the ability to measure temperature gradients in these harsh environments is currently limited by the lack of sensors and controls capable of withstanding the high temperature, pressure and corrosive conditions present. This paper discusses fabrication and deployment of several fs-IR written FBG arrays, for monitoring the sidewall and exhaust temperature gradients of a gas turbine combustor simulator. Results include: contour plots of measured temperature gradients contrasted with thermocouple data, discussion of deployment strategies and comments on reliability.

Combustion Emission Measurements With Preheated Jet Fuel

Jet fuel thermal stability at high temperature is receiving increased attention recently as advanced aero engines are being pushed to high power, high pressure and temperature regimes for improved engine cycle performance and low emissions. This paper describes the rig experimental tests to assess the high fuel temperature effect on combustor emissions. A special test rig facility has been designed and set up for emission measurements with preheated fuel. The purpose of the tests is to evaluate the combustor emission characteristics under nominal and elevated fuel temperatures. The scope of the project is two fold: (1) to design, procure and establish a dedicated hot fuel deoxygenation, fuel preheat facility that can reach temperature up to 600 °F (589 K); (2) to measure combustion emissions, mainly NOx, CO and UHC, at normal and elevated fuel temperature under representative engine operating conditions. The test rig has run for extended duration and proved reliable over the whole test campaign. Measured emission results show that fuel temperature effect on NOx, CO, UHC emissions are marginal, possibly due to the low emission capability of the sector combustor that is less sensitive to fuel inlet condition changes than other combustor designs. These results indicate a manageable risk for engine development with elevated fuel temperature from the emission viewpoint.Copyright

Experimental and Numerical Investigation of Spatial and Temporal Dispersion of Forced Fuel Oscillations

In lean premixed combustors of gas turbine engines, fuel-air mixing is considered vital for controlling pollutant emissions as well as combustion instability. Enhancement in mixing may be obtained by modulating the fuel flow rate. Modulation of fuel flow is also a useful technique to actively control combustion instabilities arising from the pressure oscillations in the combustor and thrust augmenters. Effectiveness of the forced oscillations depends on the level of dispersion present in the system. Knowledge of dispersion levels is also important in determining the degree of mixing and therefore, the effectiveness of a premixer. This paper presents the experimental efforts undertaken to study the spatial and temporal dispersion of fuel flow rate oscillation introduced at the premixer inlet. Effects of oscillation amplitude and frequency are investigated at different bulk flow rates and at various locations in the premixer. Also presented is a review of the in-house numerical work done towards this end, using three computational methods. Results show that the degree of dispersion in fuel flow rate oscillations depends on modulation amplitude and frequency as well as advective velocity of the bulk flow.Copyright

Harmonic Analysis of Jet Mixing

Development of low-pollution gas turbine engines has been calling for the development on new technologies. Lean premixed combustion is one of them but tends to be accompanied by combustion instabilities. Some instabilities are caused by coupling between the combustion zone and upstream fuel/air mixing chamber. Acoustic oscillations in the mixing chamber lead to variation of mixture distribution in the combustion zone. On the other hand, the instability itself may improve the turbulent mixing that mitigates these equivalence ratio fluctuations. The goal of this study is to gain knowledge of the fundamental mechanisms of harmonically perturbed jet mixing in air. A jet is considered as a system on which a harmonic analysis is performed. The input parameter is a modulated velocity to induce perturbation. The output parameter is the whole flow field, particularly the statistics of mixture fraction distribution. The tool is a high-order compressible direct numerical simulation code. It is demonstrated that the system can be qualified as a band-pass filter. The efficiency of mixing reaches a maximum for a modulation frequency comparable to the natural mode of a laminar jet. This study suggests that the characteristic frequency of the system to improve mixing can be inferred from the investigation of the natural mode of this system and vice versa.Copyright

Direct Numerical Simulation of Pulsating Jet Mixing

In lean premixed combustors, the fuel/air ratio oscillation can cause a serious problem since it can produce pressure and heat release fluctuations, and further, combustion instability if it is well phased with them. In order to design a system where such air/fuel ratio fluctuation is well suppressed, it is important to understand the mixing process and its interaction with the flow structures inside a premixer. In this study, the flow-field of a pulsating jet and the mixing of the jet with the co-flow are examined using direct numerical simulation. The effects of the frequency and amplitude of the imposed pulsation on the flow structures and mixing process are investigated in detail. It is found that the modulation amplitude has a favorable effect on mixing, but the dependency on frequency is more complicated.Copyright