Pushing fuel flexibility with AM μ-slit injector for jet-stabilised combustion

The intensification of regulations on greenhouse gas emissions and pollutants has underscored the necessity for advanced injector concepts that ensure fuel flexibility and scalability, addressing critical demands within the thermochemical energy conversion sector. An additively manufactured µ-slit injector is proposed and evaluated across a wide range of operating conditions, including variations in jet velocity, fuel loading, air preheating temperature, and fuel type. Detached fuel film dynamics are analysed using machine learning-based object detection, revealing reduced film length with increasing jet velocity and decreasing mass flow rate, ensuring uniform radial distribution. Phase Doppler interferometry confirms the production of fine droplets, with an average diameter of 20 µm, inherently generated by the µ-scale fuel outlet design while maintaining a low pressure drop. Combustion performance, assessed via OH <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mo>*</mml:mo> </mml:math> -chemiluminescence for H <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:msub> <mml:mrow/> <mml:mn>2</mml:mn> </mml:msub> </mml:math> , CH <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:msub> <mml:mrow/> <mml:mn>4</mml:mn> </mml:msub> </mml:math> , ethanol, and Jet A1, shows excellent stability for H <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:msub> <mml:mrow/> <mml:mn>2</mml:mn> </mml:msub> </mml:math> across both low- and high-momentum jet regimes, attributed to enhanced turbulent mixing driven by the high density ratio. In contrast, CH <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:msub> <mml:mrow/> <mml:mn>4</mml:mn> </mml:msub> </mml:math> and Jet A1 exhibit similar lift-off trends. Ethanol and Jet A1 display significant pressure drop increases at high preheating condition, highlighting pre-vapourisation effects. Additionally, a correlation for gaseous fuels between the pressure drop and fluid property ratios is established, consistent with turbulent flow theory, and further extended by incorporating the injector discharge coefficient and compressibility effects. These results demonstrate that the µ-slit injector seamlessly accommodates both gaseous and liquid fuels, delivering exceptional fuel flexibility and scalability, and positioning it as a promising candidate for industrial burners, micro-gas turbines, and hybrid aero-engine systems.