Life cycle greenhouse gas analysis of biojet fuels with a technical investigation into their impact on jet engine performance

• Bio-SPKs were determined to deliver “Cradle-Grave” GHG savings of 58–70%.
• Bio-SPKs exhibited improved thermodynamic behaviour at integrated system level assessment.
• Bio-SPKs are 3–3.8% more fuel efficient than Jet-A at flight mission level.
• Bio-SPKs deliver 5.8–6.3% less CO2 and 7.1–8.3% less LTO NOx relative to that of Jet-A.
• ALCEmB integrates regional water usage emissions which also accounts water-footprint.

Biojet fuels have been claimed to be one of the most promising and strategic solutions to mitigate aviation emissions. This study examines the environmental competence of Bio-Synthetic Paraffinic Kerosene (Bio-SPKs) against conventional Jet-A, through development of a life cycle GHG model (ALCEmB – Assessment of Life Cycle Emissions of Biofuels) from “cradle-grave” perspective. This model precisely calculates the life cycle emissions of the advanced biofuels through a multi-disciplinary study entailing hydrocarbon chemistry, thermodynamic behaviour and fuel combustion from engine/aircraft performance, into the life cycle studies, unlike earlier studies. The aim of this study is predict the “cradle-grave” carbon intensity of Camelina SPK, Microalgae SPK and Jatropha SPK through careful estimation and inclusion of combustion based emissions, which contribute ≈70% of overall life cycle emissions (LCE). Numerical modelling and non-linear/dynamic simulation of a twin-shaft turbofan, with an appropriate airframe, was conducted to analyse the impact of alternative fuels on engine/aircraft performance. ALCEmB revealed that Camelina SPK, Microalgae SPK and Jatropha SPK delivered 70%, 58% and 64% LCE savings relative to the reference fuel, Jet-A1. The net energy ratio analysis indicates that current technology for the biofuel processing is energy efficient and technically feasible. An elaborate gas property analysis infers that the Bio-SPKs exhibit improved thermodynamic behaviour in an operational gas turbine engine. This thermodynamic effect has a positive impact on aircraft-level fuel consumption and emissions characteristics demonstrating fuel savings in the range of 3–3.8% and emission savings of 5.8–6.3% (CO2) and 7.1–8.3% (LTO NOx), relative to that of Jet-A.