Two-Phase Flow Imaging and Spectral Characterization of Ammonia-Blended Methanol Spray Flames

Abstract This study investigates the spray formation and flame chemiluminescence of liquid methanol and liquid methanolammonia (NH3) gas blends under ambient conditions, focusing on phase transition, atomization, and emission from combustion species. Laser-induced exciplex fluorescence (LIEF) was employed to visualize the phase transition in sprays generated using a high-efficiency nebulizer fitted into a modified McKenna flat flame burner operating at room temperature and pressure. Higher concentrations of liquid were observed near the nozzle tip, while both liquid and vapor phases were present throughout the spray. Increasing the methanol flow rate while keeping the atomizing gas flow rate constant pushed the liquid spray further. It also enhanced spray penetration, broadened the vapor phase distribution and shifted phase change to higher parts in the spray. Using NH3 as the atomizing gas instead of nitrogen (N2), resulted in accelerated phase change and improved vaporization efficiency. When the liquid spray flame was supported by methane/air pilot flame, chemiluminescence analysis revealed that OH* radicals dominated in flames for both N2 and NH3 atomization. However, NH3 produced higher OH* intensities, indicating more efficient combustion. Lower CH* emission was observed in NH3 atomization, signifying reduced incomplete combustion. Trace amounts of NH* were also detected, reflecting the influence of NH3 decomposition in the combustion process. Beyond a critical methanol flow rate of 60 ml/hr, liquid and vapor-phase intensities in the spray saturated for N2 atomization while it continued to increase for NH3 atomization. Flame height and chemiluminescence exhibited minimal changes at higher flow rates for both atomization cases. The present study lays the foundation for investigating gaseous NH3 introduced into piloted liquid methanol spray flames when developing carbon-neutral renewable fuel blends based on NH3 as a hydrogen career.