Estimation of combustion air requirement and heating value of fuel gas mixtures from flame spectra

This paper explores an optical method for evaluating the quality of fuel gases with uncertain composition. A spectrometer is used to acquire the radiation from flames generated with different fuel gas mixtures. Natural gas flame spectra are known to have features which vary with air/fuel ratio. In the current study flame spectra were collected from a number of fuel gas mixtures consisting of a reference hydrocarbon gas and varying amounts of a low calorific gas. During these tests the fuel flow rate was kept constant and the air flow rate was varied to generate flames with different air/fuel ratios. Analysis of the spectra showed that as air is decreased from a value greater than the stoichiometric requirement for the reference gas the OH band intensity goes through a maximum and decreases at lower air flow rates. The air flow rate at which the OH maximum occurs is correlated to the stoichiometric or combustion air requirement and the higher heating value, which are fuel quality parameters for that mixture. This observation suggests the basis for a method which has the potential to be designed and applied for estimating the combustion air requirement and heating value of gas mixtures with unknown fuel properties. To the best of our knowledge very little research is reported in literature on the application of flame emission spectroscopy for direct fuel quality evaluation. - Highlights: • Flame emission spectroscopy applied to evaluate the fuel quality of gas mixtures. • Spectra of reference hydrocarbon gas + low calorific gases mixtures presented. • Air flow at OH peak related to stoichiometric combustion air and heating value. • Method has potential with industrial waste gas evaluation.