Experimental characterization of a fuel-flexible burner with an integrated ultrasonic atomizer for low-carbon operation

The transition toward carbon-free combustion fuels such as hydrogen (H 2 ) and ammonia (NH 3 ) presents significant challenges related to flame stability and pollutant formation. Many carbon-free and low-carbon, fuel-flexible burners operate with either a gaseous or liquid-phase fuel, selecting only a single phase during stable operation. In this work, the newly developed HyMAm-Flex (v18) burner is experimentally characterized for multiphase, multi-fuel combustion at 18 distinct operating conditions, demonstrating stable flames of gaseous H 2 , liquid ethanol (C 2 H 5 OH), and their binary and ternary mixtures with gaseous NH 3 under stoichiometric conditions. A key feature of the additively-manufactured burner is the integration of an ultrasonic atomizer, which enables the generation of sprays with a narrow size distribution and low injection velocities. The atomizer performance is evaluated in situ, demonstrating the stable operation in a combustion experiment. The primary objective of the present study is to provide an initial experimental characterization of the HyMAm-Flex (v18) burner concept and its fuel flexibility. Chemiluminescence measurements in combination with visible flame luminosity are used to qualitatively assess reaction-zone structure and discuss the flame stability. Exhaust gas measurements of ternary-fuel combinations provide a quantitative baseline of the burner’s nitrogen-containing emissions and insight into the completeness of the combustion. Exhaust gas measurements showed nitrogen oxide (NO x ) ¡ 400 ppmv (wet), NH 3 slip ¡ 17 ppmv (wet), and nitrous oxide (N 2 O) ¡ 32 ppmv (dry). The addition of NH 3 is associated with reduced intensity in the central flame and increased N 2 O and ammonia slip, whereas alcohol addition is associated with enhanced NH 3 combustion within an optimal blending range. This study demonstrates the fuel flexibility of the novel burner concept and discusses potential improvements to the burner design aimed at enhancing flame stability and overall performance.