Low-swirl effects on spray flames for compact jet-stabilised combustion systems

High-momentum jet-stabilised combustors promise fuel flexibility with low non-CO 2 emissions, yet compact integration with liquid fuels remains challenging. This study quantifies how low-swirl ( S N ≤ 0.3) air perturbations stabilise a pressure-swirl spray and the ensuing turbulent jet flame using seven additively manufactured swirlers. Spray atomization is characterised by shadowgraphy and phase-Doppler interferometry; combustion is analysed via time-resolved OH ∗ chemiluminescence and NO X emissions. Introducing low swirl seeds small-scale turbulence and suppresses coherent structures near the central injector, yielding thinner liquid brushes, d 32 < 10 μ m, and ∼ 50% more stable radial fuel placement relative to the no-swirl baseline. The resulting fuel distribution becomes more homogeneous in space and time, producing shorter, more symmetric flames (length reduced by up to ∼ 65%) with diminished heat-release fluctuations. Proper orthogonal decomposition and spectra indicate a progression from jet-stabilised to mixed-mode and swirl-influenced regimes with no dominant resonant peak. A local fuel-loading metric links stabilisation to fuel placement at the nozzle edge, connecting spray organisation to flame symmetry and intermittency, relevant to the formation of non-CO 2 emissions. While the axially compact flame incurs moderately elevated NO X (10–30 ppm at comparable load) in the present geometry, these increases are operationally manageable and can, for example in prefilming configurations, be translated into net emission benefits via symmetry-driven mixing improvements, outlining a clear optimisation pathway. Thus, embedding flow modulators such as low-swirlers can advance compact, liquid-fuel combustors for micro gas turbines and future hybrid aero-engine concepts. Novelty and Significance The current work investigates the implementation of additively manufactured low-swirl nozzles in a liquid-fuelled, high-momentum jet-stabilised combustor. Seven swirler configurations with vane angles | α v | = 0 , ± 15 , ± 30 , ± 45 ° (overall S N ≲ 0 . 30 ) are integrated into an in-house pressure-swirl injector. Introducing a controlled circumferential airflow seeds small-scale turbulence and, in the near-injector region, suppresses coherent wake structures; this centralises and stabilises the liquid sheet, improving atomization and fuel dispersion across the operating range. Quantitatively, the reorganised primary breakup yields d 32 < 10 μ m, a ∼ 50% increase in radial fuel-placement stability, and flames shortened by up to 64%, while spectra show no dominant resonant peaks. A practical design window emerges: effective suppression is achieved for S N ≳ 0 . 15 (i.e. | α v | ≥ 30 °), whereas diminishing returns and the onset of inner recirculation appear for S N , g > 0 . 28 . A local fuel-loading metric further links spray organisation to flame symmetry and intermittency. The concept therefore enables compact, robust combustors; the moderate increase in NO X (10–30 ppm) observed in the present non-prefilming geometry is operationally manageable and can be converted into net emission benefits in prefilming operation.