In the field of energy production, there is a need for controls and instrumentation in areas such as the combustor where the environment is considered harsh. It is therefore important that the instruments used in the measuring of various parameters (combustor mapping) in such an environment be able to withstand extremely high temperature, high pressure and in some cases even ionizing radiation.
Inspiration for innovation in this area has come from UV laser-induced FBG (Fiber Bragg Grating) sensors because they have the following desirable features:
- They come in a small size
- Their nature is passive
- They are immune to electromagnetic interference
- They can directly measure particular physical parameters such as strain and temperature
In the recent past, gratings that hold stable in high temperature have been made using fs-IR (femtosecond pulse-duration IR laser processing). These are ideal for application in the energy production sector.
To get a better understanding of how it works, you need to understand that FBG is an optical filter that works using band rejection. Any light wavelength that does not resonate with the FBG is allowed to pass through, while those that do are reflected back.
FBGs work effectively as sensors and therefore have all the benefits of the various sensing approaches that are based on fiber optics. As such, they are sensitive to the environment that they are directly in contact with meaning that any changes in the mechanics or temperature will affect them directly. They respond by compressing or expanding, as well as through thermo optic and strain effects.
If the FBGs you are using have fs-IR lasers, they will be stable until they reach the transition temperature of the fiber glass. This makes them thermally stable and therefore ideal to use in combustion systems, power plants, the aerospace sector and turbines. They are manufactured using a ‘point by point’ or a phase mask approach.
If the oil recovery techniques in use are unconventional, the FBGs may be exposed to hydrogen gas at high temperatures. This hampers the fiber optic sensors due to optical losses caused by the entrance of the said gas. The effect is particularly felt if you are using standard telecom fibers that are doped with germanium. In order to reduce these effects, it is advisable to use core fibers made of pure silica instead. Even though this is a challenge if you use FBGs, it is relatively easy when you use fs-IR. By using these fibers instead, you will be improving the combustor mapping’s performance, the sensor and your ability to monitor the combustor.
If you still have any questions about innovation to combustor mapping through ultrafast lasers, contact us for consultation and services here.