Flame patterns, heat distribution, and combustion characteristics of multi-hole nozzles

Abstract

Considerable research efforts have focused on improving combustion efficiency and reducing carbon emissions. This study examined the flame patterns, flame lengths, temperature distributions, and heat release properties within combustion zones produced behind bluff bodies and multihole nozzles. A circular bluff body, a three-hole bluff body, and a six-hole bluff body were employed to control the central and annular jet velocities. The methods utilized in this study included a digital photography conducted to characterize flame modes, a schlieren imaging system was adopted to visualize differences in flame field densities, and a thermocouple was used to obtain temperature distributions. The experimental results indicated that a swirling jet was generated behind the hole-containing nozzles. This jet increased turbulent fluctuation and enhanced the stability and occurrence frequency of coherent vortex structures. In addition, five flame modes were identified behind the six-hole bluff body: the jet-flame, flickering-flame, swirling-flame, bilayer-flame, and lifted-flame modes. The results also indicated that flames were shorter when annular flow was present, with the shortest flames occurring behind the six-hole bluff body. The six-hole bluff body enhanced the flame temperature and improved the temperature distribution. Moreover, it produced higher Reynolds numbers for both the central and annular jets, which contributed to higher combustion efficiency.