TDL Sensor Technology for Gas Turbine Systems
Overview
The figure below is a schematic of a gas turbine engine depicting PSI's Tunable Diode Laser (TDL) Sensor Technology employed in advanced aeropropulsion applications. PSI's TDL based sensors are shown in red. Most of the sensors are also applicable to land-based gas turbines.
Schematic of gas turbine aeropropulsion engine showing existing sensor/controller variables with advanced TDL sensor configurations shown in red.
TDL sensors are superior to existing alternative technology sensors because:
TDLs are non-intrusive and thus can survive in harsh flows where intrusive sensors may not.
They have been demonstrated to exhibit continuous response bandwidths up to 500 Hz, much faster than many sensors (especially for exhaust gas analysis).
They can be configured so that one sensor has multi-component measurement capability (concentration, temperature, velocity, etc.).
TDLs are direct and absolute measurements of the target quantities, and are therefore very robust with respect to a stable calibration and lack of interference.
Since the measurement is integrated over the laser beam line-of-sight, TDLs provide a better sample of the total tailpipe flow than does a single-point sensor and may eliminate the need for instrumentation rakes commonly used to characterize the total exhaust flow, for example.
In the discussion below, PSI's TDL sensor technology descriptions are separated in exhaust, combustor, and inlet applications.
Exhaust Emissions Sensors
PSI's TDL sensor technology offers a unique ability to measure trace quantities of pollutants such as CO and NO in combustion exhaust gases. Unlike conventional exhaust sensors, PSI's TDL sensors integrate across the flow, providing a better sample of the total exhaust gas flow, and with thousandths of a second response time rather than seconds or minutes.
Example sensor response to CO emissions as a function of burner equivalence ratio.
Typical exhaust gas concentration detection limits are in the 1 to 50 ppm range, depending on the molecule and the exhaust gas temperature.
Combustion Sensors
Due to the mechanical complexity of the combustor and the extreme temperature and pressure conditions within, combustor sensors are one of the most challenging sensor applications, yet PSI TDL technology offers a mature platform for simultaneous temperature and combustion species concentration in gas turbine combustors.
No other sensors exist for measurements within this environment in production or research gas turbine systems. PSI's combustion sensors can be used to determine maximum turbine inlet temperatures, combustor exit temperature pattern factors, and overall uniformity of fuel injection/combustion. The temperature measurements would be useful in:
Turn-down monitoring
Optimization after fuel changes
Monitoring system health/aging components.
More development is underway at PSI to demonstrate this technology in gas turbine combustors. Typical temperature measurement range is 300 to 3000 K. Concentration measurements range from ppm levels to several percent.
Inlet Sensors
The inlet mass flux sensor is based on simultaneous measurements of oxygen density and velocity. The same basic principle can be applied to any gaseous species. PSI has achieved mass flux precision of ???2% over the full operational range of a production gas turbine engine in a ground test facility.
A fully autonomous flight version having a 10 Hz bandwidth is in the process of installation on an F-18 aircraft. We have also investigated its application to compressor stall sensing. No sensor for inlet mass flux or compressor surge/stall currently exists for production systems. Operating range is velocities from 1 to 10,000 m/s and air pressure from 0.1 to 10 atm.
velocity sensitivity y to ~1 m/s at atm pressure.
Measurement principles and installation of PSI's TDL mass flux sensor.
