Ahmed. F. Ghoniem

In this work, we performed a preliminary investigation on the redox behaviour of Sr2FeMo0.6Ni0.4O6-δ (SFMN) double perovskite in H2-H2O and CH4-H2O redox cycles in order to explore the potential use of this oxide as an Oxygen Carrier (OC) in fuel-assisted Chemical Looping Water Splitting (CLWS) processes driven by concentrated solar energy. The results were compared with our previous findings on the Reverse Water Gas Shift Chemical Looping (RWGS-CL) reaction. The improvement in performance due to the bimetallic exsolution on the OC surface is observed. This OC exhibits interesting activity and stability over CH4-assisted CLWS cycling. Future investigations are planned to examine the structural transformations that might impact the redox behaviour of this material in water splitting processes.

When using nanosecond repetitively pulsed discharges to actuate on dynamic combustion instabilities, the environment the discharge is created in is unsteady and changing on the timescale of the combustion processes. As a result, individual discharge pulses are triggered in a background gas that evolves at the timescale of combustion dynamics, and pulse-to-pulse variations may be observed during the instability cycle. Prior work has studied nanosecond pulsed discharges in pin-to-ring configurations used to control instabilities in lean-operating swirl-stabilized combustors, and observed variable discharge behavior. The focus of this work is on characterizing how the pulse-to-pulse discharge morphology, energy deposition, and actuation authority, evolve during the combustion instability cycle. This has important implications for designing effective plasma-assisted combustion control schemes. The discharge is observed in two distinct modes, a streamer corona and a nanosecond spark, with the occurrence of each regime directly linked to the phase of the combustor instability. Variation of pulse repetition frequency affects the total fraction of pulses in each mode, while variation of voltage affects the onset of the nanosecond spark mode. The transitions are described in terms of ratios of the relevant combustion and plasma timescales and the implications of this coupled interaction on the design of an effective control scheme is discussed.

Thermochemical redox cycles are a promising route to producing solar fuels. In this work, a novel reactor train system (RTS) is proposed for the efficient conversion of solar thermal energy into hydrogen. This system is capable of recovering thermal energy from redox materials, which is necessary for achieving high efficiency but has been difficult to realize in practice. The RTS overcomes technical challenges of high-temperature thermochemical reactors like solid conveying and sealing, while enabling continuous fuel production and efficient oxygen removal during metal oxide reduction. The RTS is comprised of several identical reactors arranged in a closed loop and cycling between reduction and oxidation steps. In between these steps, the reactors undergo solid heat recovery in a counterflow radiative heat exchanger. The RTS can achieve heat recovery effectiveness of 80% for a train producing 100 kg-H2/day with a 60 min cycle time. The RTS can take advantage of thermal energy storage to operate round-the-clock. Further, it implements waste heat recovery to capture the exothermic heat of water-splitting. If all auxiliary energy demands can be satisfied with such waste heat, the RTS base configuration achieves 30% heat-to-hydrogen conversion efficiency, which is more than four times that of current state-of-the-art thermochemical systems.

The precessing vortex core (PVC) is a self-excited flow oscillation state occurring in swirl nozzles. This is caused by the presence of a marginally unstable hydrodynamic helical mode that induces precession of the vortex breakdown bubble (VBB) around the flow axis. The PVC can impact emissions and thermoacoustic stability characteristics of combustors in various ways, as several prior studies have shown. In this paper, we examine the impact of centerbody diameter (Dc) on the PVC in a nonreacting flow in a single nozzle swirl combustor. Time-resolved high-speed stereoscopic PIV measurements are performed for combinations of two swirl numbers, S = 0.67 and 1.17 and Dc = 9.5 mm, 4.73 mm, and 0 (i.e., no centerbody). The bulk flow velocity at the nozzle exit plane is kept constant as Ub = 8 m/s for all cases (Re∼20,000). The centerbody end face lies in the nozzle exit plane. A new modal decomposition technique based on wavelet filtering and proper orthogonal decomposition provides insight into flow dynamics in terms of global modes extracted from the data. The results show that without a centerbody, a coherent PVC is present in the flow as expected. The introduction of a centerbody makes the PVC oscillations intermittent. These results suggest two routes to intermittency as follows. For S = 0.67, the VBB and centerbody wake recirculation zone regions are nominally distinct. Intermittent separation and merger due to turbulence result in PVC oscillations due to the destabilization of the hydrodynamic VBB precession mode of the flow. In the S = 1.17 case, the time averaged VBB position causes it to engulf the centerbody. In this case, the emergence of intermittent PVC oscillations is a result of the response of the flow to broadband stochastic forcing imposed on the time averaged vorticity field due to turbulence.

Minimizing energy consumption and reducing pollutant emissions during the carbon anode baking process are critically important for the aluminum industry. The present study investigates the effects of oxidizer inlet temperature, inlet oxygen concentration, equivalence ratio, refractory wall thermal conductivity, and refractory wall emissivity on the baking process using unsteady Reynolds-averaged Navier–Stokes (URANS)-based simulations in conjunction with the presumed probability density function method. Numerical results are combined with a response surface methodology (RSM) to optimize the anode baking process. The advantage of the coupled method is that it can adequately provide information on interactions of different input parameters. It is remarked that the significance level of the studied parameters varies drastically for different outputs. It is noted that diluting inlet oxygen concentration (from 23% in atmospheric air to 15%) at an elevated oxidizer temperature leads to enhanced furnace fuel efficiency, more uniform temperature distribution, and lower pollutant emissions. A linear model is detected to be adequate for response surface modeling of the anode baking furnace NOx formation. On the other hand, furnace soot formation is modeled with a higher-order model due to the quadratic behavior of the response.

In situ exsolution of nickel nano-particles on both sides of ceramic membrane reactors to accelerate the co-production of CO and synthesis gas through CO ₂ splitting and CH ₄ partial oxidation, respectively.