Comparative Analysis of Using Swirlers and Bluff Bodies on Flame Characteristics of an Adapted Coaxial Swirl Atomizer

Experiments were conducted on a coaxial swirl atomizer, transitioning from its widespread use in rocket propulsion to make it suitable for gas turbines and industrial burners. This study investigates the performance of swirl and bluff-body-stabilized flames while varying the stabilizer mean diameter ratio. Two types of flame stabilizers—three swirlers and three corresponding disc-bluff bodies—were investigated sequentially. It was found that the stabilizer mean diameter ratio is the dominant parameter controlling the observed combustion behavior. Consequently, this study focuses on the effect of changing the stabilizer mean diameter ratio on the flame characteristics of diesel spray. The methodology evaluates key operational metrics to optimize overall environmental and mechanical performance. The spray cone angle and the radial fuel spray distribution were measured. Interior and exterior recirculation zones were determined and found to interact with each other, yielding combined zones. The system achieved a peak thermal efficiency of 74.5% for the highest mean diameter ratio of the bluff bodies (DB = 8.3), representing a 57 % improvement over standard baseline models. Additionally, under optimal loads, the system exhibited the widest and longest recirculation zone, the highest sectional average gas temperature along the combustor tube, and the highest calculable heat released—in other words, the highest estimated combustion efficiency. Exhaust analysis revealed a reduction in carbon monoxide (CO) emissions from 300 ppm to 40 ppm and an increase from 1.8% to 3.7% in carbon dioxide (CO2) equivalents compared to current regulatory standards, matching the increased efficiency. The swirled flame became more convoluted, rotating and anchored, while the flame is much wrinkled, corrugated, incandescent and extended along the combustor tube for the corresponding bluff body stabilizer. Also, it is detected that the effect of swirl number alone is insufficient to describe and control the swirled combustion process, where it is found that impact of mean diameter ratio must be incorporated due to its significant influences.