Experimental study on the effects of biofuels- Jet A-1 blends on flame morphology, stability, and emissions in a model gas turbine swirl combustor

Bio-derived fuels have long been used in IC engines, due to their low carbon and potential for production from sustainable sources. In recent years, there has been growing interest in using biofuels in gas turbines, particularly in the aviation sector. However, biofuels have different physicochemical properties than traditional jet fuels, which may lead to variations in energy density, combustion characteristics, and thermal stability. Thus, this study aims to shed light on how variations in the physical and chemical properties of sustainable biofuels, including their higher oxygen content, affect combustion performance, particularly when used as a blend with conventional fuels as a sustainable alternative. Here, the combustion performance of aviation Jet A-1 and its blends with 20% and 50% (by volume) of five different oxygenated biofuels (e.g., ethanol, acetone, butyl butyrate, iso -pentanol, and butanol), selected to test a wide range of properties, is experimentally investigated in a swirl-stabilized gas turbine combustor. Flame morphology, lean blow-off (LBO), exhaust temperature, and emissions measurement are carried out to compare the performance of the various tested blends relative to neat Jet A-1. The flame morphology, exhaust temperature, and emissions are tested at two equivalence ratios of 0.55 and 0.7. The results show that most blends have better LBO performance than Jet A-1, with maximum enhancements of 11%, 13%, and 15% at 50% blends of butyl butyrate, iso -pentanol, and butanol, respectively. The predicted (not measured) Sauter mean diameter (SMD), by the Lefebvre equation, and oxygen content closely explain the LBO trends. The blends exhibit a notable reduction in NOx emissions compared to neat Jet A-1, particularly for the biofuels, which have lower exhaust temperatures and smaller SMDs, resulting in maximum decreases of 60%, 72%, and 50% for 50% blends of ethanol, acetone, and butyl butyrate, respectively. This study demonstrates that the oxygen content of the biofuel blended with Jet A-1 is not the only factor influencing flame stability and emissions; instead, the testing conditions and thermal properties of the biofuels, including those that alter spray characteristics, vaporization, and mixing dynamics, also play a role.