Comparison of electrical and laser spark emission spectroscopy for fuel concentration measurements

Emission spectra from electrical and laser sparks in flowing methane–air mixtures of various compositions have been collected and analysed. The differences and similarities between the electrical and laser sparks in the context of their emission are discussed. The emission spectra from the laser spark were characterized by a weak continuum, onto which several strong atomic lines and some molecular bands were superimposed, in contrast to the spectra of electrical spark where a strong continuum, few atomic lines and several strong molecular bands were evident, making thus the laser spark spectroscopy a more accurate technique to measure hydrocarbon concentration. For both types of spark, the total intensity of the CN chemiluminescence around 388 nm was found to correlate almost linearly with fuel concentration in methane–air mixtures.