High Spectral Resolution Emission Thermometry for Combustion Applications

Abstract

Several spectroscopic emission methods were investigated for the determination of combustion gas temperature. Spectroscopic simulations based on the HITRAN database were performed to aid in sensor design and data reduction. Four sensors were created, and limited testing was performed on three of the sensors.

The first sensor was based on a tunable spectroscopic filter being used to resolve the spectrum of the water emission band near 2.6 ?m. The measured water spectrum was compared to simulations to determine the temperature in a gas turbine combustor at Wright-Patterson Air Force Base.

The second sensor is based on H2O emission in the ?1 + ?3 bands. Two emission lines located at 1404 nm and 1405 nm were used in a ratiometric manner to determine gas temperature. A third channel near these lines was used to subtract background emission. Testing of this sensor was delayed due to lower than expected light detection levels.

The third sensor is based on CO2 emission from 4.2 ?m to 4.4 ?m. This region of the CO2 spectrum possesses the unique property of being optically dense over the engine operating range. The emissivity of this feature is unity, thus the slope of the feature can be compared to the Planck curve to determine temperature. This sensor was tested using an optically accessible engine based on the GM Triptane block.

The fourth sensor is based on a commercial optical spectrum analyzer (OSA). An OSA uses a scanning grating to direct light onto a detector. It is able to accurately resolve the wavelength and power of incoming light. The measured data is compared to simulations to determine gas temperature. Testing of the OSA sensor was performed on a hydrogen- oxygen flame and on a high-pressure, high-temperature test cell.

A high-pressure, high-temperature (HPHT) test cell was investigated and built to test a variety of sensors. The HPHT test cell consists of a heated, sealed quartz cell with a known quantity of the species under investigation inside of it. The cell is located in a pressurized vessel to keep the quartz cell from breaking. Windows on both ends of the pressure vessel allow for the testing of both emissions and laser-based sensors. The HTHP cell was tested with a commercial optical spectrum analyzer.