A Spectroscopic Study of the OH* Radical and its Application in Thermometry

Kurzfassung

There is a tremendous push to explore alternative fuels such as hydrogen or synthetic fuels to combat the effects of climate change. An important step in the development of alternative fuels is the characterisation of its combustion characteristics. There are various diagnostic tools which aid in the determination of flame properties. Optical diagnostics play a crucial role by providing a non-invasive form of measurement. In the current project the idea is to utilise the passive chemiluminescence from flames to determine flame properties. The focus is on the emission from the OH⁄ radical present in flames. This radical is responsible for radiation in the ultraviolet region ranging from 280 nm to 350 nm. This radical was also chosen as it is a radical common to both hydrocarbon as well as hydrogen flames. The objective of the project was to develop an emission spectra model of the OH radical and to test its feasibility in predicting flame temperature by comparing it with emission from a laminar premixed CH4 air Bunsen flame. The underlying physics regarding the various aspects of the project are discussed in detail in the initial part of the part. In the latter part, the work done for the project is explained. An emission model was developed for the OH radical in MATLAB. The model is capable of calculating the emission spectra at different temperatures and line shapes. Then a spectrometer was built to capture the radiation from the flames in the UV region. The obtained data was post processed to get the flame spectra. The flame spectra obtained from the flame was compared against the emission model to determine the best temperature fit. It was observed that the temperatures were much higher than the gas temperatures observed inCH4 air flames. This is attributed to a non thermal population distribution in the excited molecules. There however exists a unique mapping to the equivalence ratio which can be utilised for equivalence ratio determination when properly calibrated. There are many possible directions uncovered to take the work further by exploring the applicability of the tool for other fuels and flame regimes.