Ahmet Alper Yontar

1. Heat engines are integral to daily life, particularly in road transport, which supports global economic and social development (Franco et al. 2013). Highways facilitate the movement of a wide ra...

Gelled fuels have emerged as a transformative class of energetic materials, bridging the operational gap between the high impulsive control of liquid bipropellants and the structural simplicity of solid grains. By immobilizing liquid fuels within a three-dimensional polymer matrix, problems inherent to liquid systems—such as leakage, catastrophic sloshing during high-G maneuvers, and rapid evaporative loss—are effectively mitigated. This study provides a thorough evaluation of the stabilization kinetics and droplet combustion behavior of ethanol-based gels formulated with carbomer (EtC1–EtC6) at concentrations of 1–6% by weight. Utilizing a single-pot mechanical mixing technique, the transition from Newtonian to non-Newtonian (shear-thinning) behavior was identified at a critical threshold of 3% carbomer. Static stability was verified through high-temperature thermal stress (65 °C) and dynamic centrifugal separation (1500 rpm), revealing that while higher gelant concentrations (up to 6%) ensure near-solid structural integrity, they introduce significant inhibitory effects on atomization. High-speed optical diagnostics and thermal imaging of individual fuel droplets demonstrate that EtC3 represents the "optimal rheological window," achieving the highest peak flame temperature (644 K) and a sustained extinction time of 4600 ms. Furthermore, while the burning rate generally decreases with gelation, EtC5 exhibited a localized peak of 1.37 mm2/s among gelled variants. These findings establish a fundamental basis for engineering "smart fuels" with tunable viscosity and predictable combustion signatures for advanced propulsion applications.

Pre-detonators serve as preferred shock initiators in aerospace applications, particularly when prioritizing power and weight over direct initiation with substantial energy demands. Strategically positioned obstacles within pulse detonation engines play a crucial role in shortening shock generation time while ensuring unimpeded blast passage. Enhanced turbulence within the duct contributes significantly to achieving elevated temperature, pressure, and velocity levels, resulting in more robust shock waves, particularly at heightened equivalence ratios. Accordingly, this study delves into the numerical investigation of hydrogen-oxygen, acetylene-oxygen, and kerosene-oxygen couples in two-dimensional configurations. The investigation encompasses obstacle heights ranging from 0.5 to 1.5 mm within tubes, evaluated at equivalence ratios of 0.5, 1.0, and 1.5 under identical initial conditions. The numerical analysis discerns variations in pressure, temperature, and velocity parameters induced by diverse fuels and obstacle ratios from shock wave inception to tube exit. Within our designed Ø10 × 210 mm pre-detonator, acetylene and hydrogen were observed to generate shock waves approximately 20 mm from the tube inlet. Specifically, hydrogen demonstrated the highest velocity among all fuel-oxygen mixtures, registering 1672.64 m/s at a 0.5 mm barrier height and 0.5 equivalence ratio. Acetylene at a 1.5 mm obstacle height and 1.0 equivalence ratio exhibited a peak average flame temperature of 8940 K. For kerosene, escalating obstacle heights at 0.5 and 1.0 equivalence ratios led to amplified temperature, pressure, and velocity values. These findings underscore the importance of tailoring blockage ratio and equivalence ratio levels, especially for highly reactive fuels like hydrogen, to optimize shock wave performance in pre-detonator applications.