Effect of Air-to-Liquid Mass Ratio on Global Combustion Characteristics of Jet-A Using Swirl Burst Injectors

Fine spray generation is the prerequisite for clean and efficient combustion due to the capability to vaporize quickly and mix with oxidizer homogeneously. Conventional airblast (AB) and pressure swirl (PS) injectors produce a liquid jet/core at the injector exit, which gradually disintegrates into ligaments and droplets further downstream of the injector exit, resulting in incomplete combustion of large droplets/ligaments. Our research group’s recently developed swirl burst secondary (SBS) injector generates fine sprays immediately at the injector exit, rather than an AB jet, irrespective of the viscosity of the fuels without preheating. The SBS injector thus has achieved clean, lean-premixed and complete combustion for conventional Jet A fuel and even high-viscosity fuels including sustainable aviation fuel jet C-3, vegetable oil (VO), glycerol and methanol blends that represent crude glycerol [1,2]. However, spray stability is hampered at a relatively high atomizing air to liquid mass ratio (ALR) across the injector. For the two-phase atomization, ALR significantly affects the spray characteristics thus the subsequent combustion performance. Our most recent Swirl Burst Primary atomizer (SBP) enhanced the internal two-phase flow interaction and achieved stable and rapid bubbly flow formation regardless of the ALR variation. Hence, it has discharged ultra-fine and stable water sprays immediately at the injector exit for a wide range of ALR. The current study aims to investigate the effect of ALRs ranging from 2.0 to 4.0 on the global combustion characteristics of conventional Jet-A by using the novel SBP injector in a 7-kW lab-scale gas turbine combustor, compared to the baseline SBS injector. The equivalence ratio is maintained at 0.75 throughout the experiment. Global combustion characteristics are studied in terms of flame lift-off height, flame length, combustion product gas temperature, concentrations of carbon monoxide (CO) and nitrogen oxides (NOx) to compare the combustion performance of SBS and SBP injectors. Results can be utilized to develop next-generation ultra-clean, efficient and fuel-flexible gas turbine combustors.