Potentials of butanol and methanol blends as a replacement for Jet A in micro turbojet engines: Stability of transient regimes

• Seven Jet A blends with 10–30% methanol or butanol were tested experimentally. • Engine performance was evaluated under three steady-state regimes. • Transient responses revealed higher combustion stability for butanol blends. • Methanol blends increased specific fuel consumption and reduced stability. • All blends ensured safe operation, with no surge or flameout events observed. The use of alcohols as alternative fuels has generated increasing interest in the aeronautical sector. This paper investigates the behavior of a Jet A-fueled micro-turbojet engine, considering the impact of blending Jet A with methanol and butanol in concentrations of 10 %, 20 %, and 30 %, resulting in a total of seven tested fuels. Tests were conducted under three steady-state regimes: idle (30,000 rpm), intermediate (52,000 rpm), and near-maximum power (114,000 rpm). The engine operating line was plotted for each configuration, enabling a direct comparison of the thermodynamic behavior of Jet A and the six alcohol-based blends. Key parameters such as combustion temperature, fuel flow rate, and thrust were analyzed. Additional calculations were carried out for specific fuel consumption (SFC), combustion efficiency, and compressor efficiency. For instance, at maximum speed, the 30 % butanol blend showed a thermal efficiency increase of 2.8 % compared to Jet A, while the 30 % methanol blend increased SFC by 17.2 %. The second part of the study investigates transient processes, including startup dynamics, speed variation, exhaust gas temperature, and fuel flow rate evolution from ignition to idle. Rapid acceleration and deceleration phases were also analyzed to assess the performance differences between Jet A and the alcohol-based blends. Butanol blends exhibited better combustion stability and faster speed stabilization, while methanol blends caused delayed responses, especially at higher concentrations. For example, during rapid deceleration, the 30 % methanol blend caused a 12 % drop in turbine inlet temperature compared to Jet A. No surge or flameout events were observed during testing, confirming the operational safety of all blends. These findings highlight the potential of butanol and methanol blends to not only reduce the dependence on conventional Jet A fuel but also to enhance transient stability, which is critical for micro turbojet operation in UAV and distributed propulsion systems. The demonstrated improvements in acceleration response and surge margin confirm that such blends can contribute both to sustainable aviation goals and to the reliability of small-scale propulsion technologies.