Investigation of the effect of colorless distributed combustion method on the flame of methane/hydrogen fuel mixture using image processing method

Abstract

In a period when zero-emission combustion studies are gaining importance, researchers continue their research on alternative fuels. Although different alternative fuels are tested in combustion studies, the production and storage capabilities of these fuels also affect industrial practices. For this purpose, in this study, the combustion characteristics and emission behaviors of methane gas enriched with H₂ at a volumetric ratio (20%), which can be transported in existing natural gas lines without any major changes, were examined. To solve the high flame speed problem caused by the hydrogen content of the fuel mixture, colorless distributed combustion conditions were proposed, and experiments were carried out. In the experiments, thermal power (5 kW), equivalence ratio (0.7), and number of vortices (0.4) were kept constant. The flame was exposed to external acoustic forcing frequencies in experiments under different conditions, and dynamic pressure oscillations were recorded. Additionally, in this study, flame image processing was performed with open-source software. The results showed that increasing the N₂ ratio in the oxidizing air increased the resistance to acoustic disturbances. While flame stability increased in the mixture containing 19% O₂ compared to standard air combustion conditions, when the O₂ rate was reduced to 18%, the flame experienced blowoff instability under strain. The change in stability varied in direct proportion to the flame thickness and length. On the other hand, while CDC combustion conditions reduced NO_X emissions in flue gas to almost zero, they caused an increase in CO emissions.