The sustainability issue has intensified interest in low-carbon alternatives to conventional hydrocarbon fuels for transport and power, where combustion is still expected to play a role. Ammonia is a promising carbon-free energy carrier, but it is difficult to ignite and exhibits slow early flame propagation, limitations that become more severe at low temperature and high pressure. Experimental data in this combined regime remain scarce, motivating this work to establish a validated basis for assessing ammonia and ammonia–hydrogen combustion under subzero conditions.

A custom constant-volume chamber was designed, commissioned, and validated for controlled subzero operation, with pressure-based diagnostics used to infer laminar burning velocity during early spherical flame growth. Results show that lowering the initial temperature from room temperature to \SI{-50}{\degree C} produces a strong penalty in neat-ammonia burning velocity across the investigated equivalence ratios, pushing the flame into a regime where losses and stretch effects become increasingly influential and ignition robustness is reduced. Hydrogen blending at \SI{-50}{\degree C} provides a marked performance recovery, with 20% and 30% H$_2$ producing substantial increases in burning velocity and restoring behaviour comparable to neat ammonia at room temperature near stoichiometric conditions. Minimum ignition energy could not be quantified reliably due to electrical signal variability, but ignition threshold settings indicate a strong increase in ignition difficulty as temperature decreases. Overall, the results show that subzero temperatures penalise neat-ammonia early combustion more strongly than predicted by kinetic models, while modest hydrogen enrichment can recover performance and improve robustness under cold-start-relevant conditions.

Bachelor Thesis: Design Synthesis Exercise 2023
Group 13: Electric General Aircraft
in collaboration with
Group 10: Mid-Flight Recharging System

Addressing the pressing need for sustainability amid climate change, the aviation sector is under pressure to mitigate its significant carbon emissions. As aviation accounts for over 2% of global emissions, achieving zero-emissions aviation by 2050 is crucial. The challenge lies in finding alternatives to jet fuel. One option is battery-powered electric aviation, but limitations such as range constraints and emissions during production and disposal must be considered.

This report proposes a solution to extend the range of all-electric passenger aircraft. The ElectriFly aircraft can currently fly 600km at 110m/s before requiring recharging. To achieve perpetual flight capability, a mid-flight recharging system is introduced using a drogue and probe system, similar to military refueling technologies. This approach not only increases range but also reduces turn around time at airports.

Powered by four parallel-connected solid-state batteries with an energy density of 600kWh/kg, the ElectriFly aircraft features 14 propellers using distributed propulsion and potential plasma actuators. This setup improves aerodynamic performance, reduces noise, and allows for regenerative braking, easing the burden on the recharging drone. Real-time data sensors enable predictive maintenance, minimizing downtime and providing pilots with crucial flight anomaly information.

This research presents a promising solution for electric aircraft limitations through mid-flight recharging. The proposed ElectriFly aircraft offers extended range capabilities and improved operational efficiency, supporting the goal of sustainable aviation.