Life cycle assessment (LCA) calculations of greenhouse gases (GHGs) per revenue passenger kilometre for Ryanair flights under various scenarios are evaluated. Current state of art tends to focus solely on the LCA of the fuel; however, this work considers the entire lifecycle of flight operations and hence, gCO₂e/RPK (grammes of CO₂ equivalent per revenue passenger-kilometre) is the functional unit. Key parameters such as flight route, blend of hydrotreated renewable jet fuel (HRJ) and HRJ supply chain are assessed to understand the impact of each on the carbon intensity of the overall aviation activity.

The lifecycle of the HRJ and flight operations are broken into four sections: Feedstock Production and Procurement, Fuel Production, Airport Operations and Aircraft Operations. Feedstock Production and Procurement analyzes all activity involved with transporting the used cooking oil feedstock prior to the fuel production steps. Fuel Production includes all activity involved in the conversion of the feedstock into HRJ. Airport Operations includes all activity involved in transporting the HRJ from the refinery to the aircraft and the auxiliary activity necessary for the flight operation. Aircraft Operations determines the quantity and quality of fuel conversion due to the flight and uses logged flight data on a specific basis. In instances where specific data cannot be provided by external stakeholders, assumptions are made from the scientific literature and/or physical science relations to calculate the total GHGs from activities within the system boundary.

This work emphasises supply chain analysis particular to the specific aviation activity studied. It is found that existing LCA tools have limited compatibility with this paradigm as they do not allow full control or transparency over the mathematics behind the model. So as not to be constrained by existing assumptions or system boundaries, calculations are performed by hand, following rigorous physical science relations, and emphasising the use of data of the actual supply chain studied. Comparisons are made to equivalent results from existing LCA tools such as GREET and GHGenius. Key findings show that parameters such as location of HRJ feedstock procurement, mode of fuel transportation, and the carbon intensity of electricity generation, have a significant effect on the GHG emissions from the aviation activity and hence the specific flight emissions per revenue passenger-kilometre.

Mark Kelly

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