UC Irvine

Hydrogen (H2) combustion and Solid Oxide Fuel Cells (SOFC) have the potential to mitigateaviation-induced greenhouse emissions in comparison to kerosene propulsion. This thesis describes a methodology to assess the performance and emissions trade-offs of retrofitting a short, medium, and long haul aircraft employing conventional kerosene powered propulsion, with H2-combustion and SOFC hybrid powered lower emission alternatives. The proposed framework employs a constant range approach analysis to design a liquid hydrogen fuel tank that meets insulation, sizing, center of gravity, and power constraints. These liquid hydrogen tanks are utilized to compare the performance of H2-combustion powered and SOFC hybrid powered aircraft, all flying the same range. A lifecycle assessment is conducted to evaluate the potential mitigation of carbon footprints through greenhouse gas emissions and contrail formation effects. Additionally, a cost analysis is modeled to examine the implications of implementing such retrofitting. In this thesis, three sample cases are presented to demonstrate the proposed framework on different aircraft models: Embraer 170LR (representing short haul), Boeing 737-800 (medium haul), and Boeing 777-300ER (long haul). The advantages of adopting the mentioned alternative fuel sources are evident, with an overall reduction in aircraft mass observed for medium and long haul configurations. However, for the short haul case, there is a slight increase in overall weight of 1.13% for H2-combustion and 1.39% for the SOFC hybrid system. Conversely, the medium haul case shows a substantial 27.73% decrease in overall weight for H2-combustion and a 0.4% decrease for the SOFC hybrid configuration. For long haul flights, H2-combustion and SOFC cases yield weight reductions of 38.51% and 2.85%, respectively, compared to conventional kerosene-powered aircraft. Moreover, considering the trade-off of removing cargo compartments to maintain fixed passenger capacity and range by making refueling stops, the lifecycle analysis of green hydrogen in H2-combustion and SOFC hybrid configurations results in an average reduction of 40% and 68% in CO2 lbs of emissions, respectively, compared to conventional Jet-A fuel emissions across all haul configurations. Fuel costs increase by 45% when replacing kerosene combustion with SOFC hybrid power using gray H2 for the short haul configuration, considering one refueling stop. In the case of long haul flights using green H2-combustion, the cost increases by 58.18% compared to conventional kerosene powered aircraft. However, for the long haul SOFC green H2-combustion case (ii), which includes 50% of passengers and their luggage, the total cost is estimated to be close to 33 million USD, representing a 98.90% increase compared to the cost of the long haul kerosene-powered aircraft. The results obtained through this methodology indicate that retrofitting all three aircraft to operate with these alternative fuels can significantly lower carbon emissions at a higher total cost, considering the trade-off of removing cargo compartments and making refueling stops to maintain the same fixed range as specified for each aircraft.