Study of the Method of Mixing Oxidizing Agent and Fuel in the Combustion Process

This study investigates the combustion of natural gas in a simple 2 kW co-flow laboratory burner with the primary objective of identifying the most effective combination of interchangeable mixing-chamber nozzle and oxidizer swirler for achieving stable combustion, comparatively low CO emissions, and favorable NOx trends over a wide range of oxygen concentrations in the oxidizer (21%, 30%, 50%, and 75% O2). Interchangeable mixing-chamber nozzles were designed based on theoretical calculations to maintain flame stability under different oxygen concentrations, while five types of oxidizer swirlers (OZ-1 to OZ-5), selected on the basis of a literature review, were developed to intensify fuel–oxidizer mixing by disrupting the natural gas jet and inducing swirl within the mixing chamber. For comparison, experiments were also performed without a swirler (OZ-0). Experimental measurements were conducted in cylindrical combustion chambers, allowing simultaneous monitoring of the temperature distribution along the vertical axis, visual flame assessment, and flue gas analysis. The effects of oxygen concentration and swirler geometry on combustion characteristics were evaluated using thermocouple temperature measurements, CO and NOx emission analysis, thermal imaging, and qualitative CFD simulations of the cold flow field through the swirlers, performed for illustrative/screening purposes only and without quantitative influence on the experimental design or conclusions. The results demonstrated that swirler OZ-4, combined with the corresponding mixing-chamber nozzle, exhibited favorable overall combustion performance under the tested laboratory conditions, producing a stable flame with comparatively low CO emissions and favorable NOx trends throughout the investigated range of oxygen concentrations. The originality of this work lies in the development of a compact, structurally simple burner concept that enables stable combustion with comparatively low CO emissions under varying levels of oxygen enrichment while maintaining good flame stability, under the tested laboratory conditions. This work is presented as an introductory, screening-level study, intended to identify promising nozzle–swirler combinations and to establish a methodological and experimental basis for more detailed follow-up research, rather than as a definitive, fully validated characterization of burner performance.