Techno-economic environmental risk analysis of advanced biofuels for civil aviation

Abstract

Commercial aviation has demonstrated its ability to be a key driver of global socio-economic growth to this date. This growth, resulting from an ever increasing need for air-travel, has been observed to be environmentally unsustainable. Any technological enhancements to the upcoming fleet of aircraft or operational improvements have been overshadowed by this very demand for air-travel. Any further investigation into innovative concepts and optimisation approaches bring in trade-off difficulties due to limitations in current technology. This creates a constraint on design space exploration. The need to mitigate civil aviation’s environmental impact has necessitated this sector to expand its frontier and seek radical technologies. Among a range of other technologies, advanced biofuels for civil jet engines have been claimed to be one of the most promising solutions. “Techno-economic Environmental Risk Analysis (TERA) of Advanced Biofuels for Civil Aviation” is a study that contributes to knowledge through conception plus application of quantitative/ qualitative approaches to assess the technical viability, financial feasibility and environmental competence of 2nd and 3rd generation biojet fuels, through their application into the existing scenario of civil aviation, against that of the fossil-derived conventional jet fuel (Conv.Jet fuel). TERA of advanced biofuels aims to accomplish the aforementioned through a holistic, multi-disciplinary study entailing life cycle studies, carbon-foot printing, sustainability analysis, fuel chemistry, virtual studies comprising combustion thermodynamic, engine/aircraft performance and emission prediction, economic studies entailing biofuel price prediction and business case analysis as opposed to earlier studies. TERA of Advanced biofuels study entails development of elaborate life cycle models, ALCEmB (Assessment of Life Cycle Emissions of Biofuels) and ALCCoB (Assessment of Life Cycle Cost of Biofuels) to predict life cycle emissions and costs, respectively, of the advanced biofuels from the point of raw material generation to the point of finished product consumption (a “cradle-grave” approach). A virtual experiment, to assess the impact of the “performance” properties of the advanced biofuels on a representative twin-shaft turbofan/airframe combination, relative to that of Conv.Jet fuel, was also undertaken through numerical modelling and simulation.Evaluation through ALCEmB revealed that Camelina-SPK, Microalgae-SPK and Jatropha-SPK delivered 70%, 58% and 64% savings in life cycle emission, relative to Conv.Jet fuel. The Net Energy Ratio (NER) analysis indicates that current technology for the biofuel processing is energy efficient and technically feasible. An elaborate post-combustion gas property evaluation infers that the Bio-SPKs exhibit improved thermodynamic behaviour. This thermodynamic effect has a positive impact on mission-level fuel consumption which reflected as fuel savings in the range of 3 - 3.8% and, therefore, emission savings of 5.8-6.3% in CO2 and 7.1-8.3% in LTO NOx, relative to that of Jet-A1. An economic feasibility analysis which entails prediction of hypothetical biofuel price prediction and its impact on direct operating cost (DOC) of an aircraft which infers that Bio-SPKs, over a user-defined medium-range mission profile, costs an additional 95-100% in terms of aircraft DOC, relative to that operated with conventional Jet-fuel, within short (2020) and medium (2020). However, the advanced biofuels are able to exhibit financial competence from 2020 onwards, relative to that of Conv.Jet fuel. However, the Bio-SPKs exhibit this economic feasibility only against a backdrop of persistent Conv.Jet fuel price volatility and severe environmental taxation between the analysis periods (2020-2075)