Sustainable aviation fuels (SAF) are widely recognised as a key component of aviation decarbonisation strategies. However, the introduction of new fuels into a safety-critical aviation system requires robust evaluation to ensure compatibility with existing aircraft, engines and fuel infrastructure. This review examines the qualification of synthetic aviation turbine fuels within established qualification and certification frameworks, with a focus on how the ASTM D4054 evaluation process operates in practice and how it interacts with broader factors influencing SAF deployment. The paper analyses how differences in fuel composition, including bulk properties, trace species and performance characteristics, are translated into proportionate evidence requirements through a structured, risk-based approach. It highlights that qualification is not a prescriptive sequence of tests, but a distributed evidence-generation and governance process involving fuel developers, testing organisations, original equipment manufacturers, standards bodies and other stakeholders. As the diversity and maturity of synthetic blend components increases, the performance of the qualification system is shaped not only by intrinsic technical uncertainty, but also by structural factors including testing infrastructure, representative fuel availability, data quality, OEM review capacity and stakeholder coordination. The review distinguishes clearly between fuel qualification and deployment. For several established pathways, qualification has not generally been the primary constraint on SAF uptake; deployment remains strongly influenced by feedstock availability, production scale, economics, infrastructure and policy certainty. However, the complexity, timescales and cost of evaluation can still influence pathway accessibility, particularly for more novel fuels, highlighting the need to improve qualification efficiency without compromising technical integrity or safety assurance. As policy ambition increases and more chemically diverse candidate fuels seek approval, qualification may become a more material constraint on the pace, predictability and diversity of future SAF deployment. Drawing on developments in pre-screening, distributed testing, Clearing House coordination, qualification-readiness assessment, data standardisation and proportionate evaluation approaches, the review shows that the qualification system is evolving to improve efficiency and scalability while maintaining the requirements of safety, operability and long-term system integrity. Overall, the paper positions fuel qualification as an enabling component of the SAF ecosystem whose future scalability will depend on earlier uncertainty reduction, improved data generation, coordinated testing infrastructure and continued expert review.
Jardson dos Santos Reis, Maria Fernanda S. Vieira, Florencia João Macamo, Jorge A. S. Tenório, Walter Ricardo Brito, Luiz Kleber C. De Souza
The growing demand for renewable energy has increased interest in the use of lignocellulosic residues for energy applications. Mallow (Urena lobata Linn.) stem residue is an underutilized Amazonian byproduct generated after fiber extraction, whose thermal degradation behavior remains poorly explored. This study evaluated the energy-related potential of mallow stem residue through thermogravimetric analysis, TG-MS, isoconversional kinetic modeling, thermodynamic assessment, and reaction mechanism analysis. The biomass was characterized by proximate and lignocellulosic analyses and subjected to non-isothermal thermogravimetric experiments under N 2 atmosphere at heating rates of 2.5, 5, 10, 15, and 20 °C min -1. The use of FWO, Kissinger-Akahira-Sunose, Starink, and Vyazovkin methods allowed the consistency of activation energy estimates to be evaluated and enabled the conversion-dependent reactivity of the biomass to be described without assuming a single reaction model. TG/DTG results revealed a multistage degradation process, with the main devolatilization occurring between 200°C and 400 °C. TG-MS indicated the release of H 2 O, CO 2, and light organic fragments, while minor m/z assignments were treated as tentative due to possible fragment overlap. The apparent activation energy decreased with conversion, ranging from approximately 133 to 104 kJ mol -1, with average values between 122.95 and 126.39 kJ mol -1. Thermodynamic parameters indicated a thermally activated and energy-demanding decomposition process, while reaction mechanism analysis suggested changes in the dominant mechanism throughout conversion. Overall, mallow stem residue showed thermal and kinetic characteristics comparable to other lignocellulosic feedstocks, indicating potential for energy-related applications. However, further product characterization, ash composition analysis, and reactor-scale studies are required to confirm its practical applicability in bioenergy conversion systems.
Ammonia (NH 3) has emerged as a promising carbon-free fuel for decarbonising internal combustion engines and power systems. However, its combustion produces elevated nitrogen oxide (NO x) emissions and ammonia slip, requiring effective exhaust aftertreatment. Selective catalytic reduction (SCR) is the leading technology for NO x control, but its application to ammonia-fuelled engines presents unique challenges, including NH 3 -rich exhaust, variable NO 2:NO x ratios, low exhaust gas temperatures (EGT), high water-vapour concentrations, and increased potential for nitrous oxide (N 2 O) formation. This review critically examines recent advances in SCR catalyst development and modelling for ammonia-combustion exhaust treatment. The performance of vanadia-based catalysts, transition metal oxides, and Cu- and Fe-exchanged zeolites (CuZ and FeZ) is evaluated in terms of activity, selectivity, durability, and resistance to deactivation under ammonia-rich conditions. Current understanding of NH 3 -SCR reaction mechanisms, catalyst ageing, and N 2 O formation is discussed alongside advances in microkinetic, reactor-scale, and computational fluid dynamics (CFD) modelling. Particular emphasis is placed on the strong coupling between combustion and aftertreatment, arising from the dual role of NH 3 as both fuel and reductant, and the need to integrate experimental observations with predictive modelling. Finally, key research priorities are identified, including catalyst development for NH 3 -rich exhaust, realistic experimental validation, improved prediction of N 2 O emissions, and integrated combustion–aftertreatment optimisation to enable efficient, low-emission NH 3 -fuelled power and propulsion systems.
This study investigates the potential for producing fermentable sugars from Prosopis juliflora stem biomass using an unique approach using microwave-assisted KOH pretreatment. Various operating parameters in the microwave-assisted KOH pretreatment involves KOH conc (1, 2% and 3%), biomass loading (1, 3 and 5 g), microwave power (150, 300 and 450 W) and irradiation time (3, 4 and 5 min) were optimized by response surface methodology (RSM) using Box-Behnken Design (BBD). Hydrolysis was also optimized using various concentrations of sulphuric acid (1, 3, 5, 7% and 9%) for 60 min at 120 °C to produce fermentable sugars which was compared with the liquid obtained after the pretreatment. The native and the pretreated P. juliflora stem biomass was characterized by scanning electron microscope (SEM). Under the optimized conditions (2% KOH, 5 g biomass loading, 150 W, 4 min, followed by 5% H 2 SO 4 hydrolysis at 121 °C for 60 min), a maximum reducing sugar concentration of 2.25 mg/mL (225 mg g -1 biomass) was achieved. The integrated microwave-assisted alkaline pretreatment significantly enhanced biomass deconstruction and fermentable sugar recovery while employing low chemical concentration and short processing time. These findings demonstrate that P. juliflora stem biomass is a promising lignocellulosic feedstock and that the proposed low-severity, scalable pretreatment strategy has considerable potential for sustainable and economically viable bioethanol production.
S. Aparna, S. Rahul, D. Dhanuprabha, S. Raaghavi, A. Arumugam
This study investigates a heterogeneous catalyst derived from calcined and NaOH-treated Madhuca indica (M. indica) shell ash for the transesterification of M. indica seed oil. Process parameters were optimized using a central composite design (CCD) within response surface methodology (RSM), resulting in a maximum biodiesel yield of 92.3% (GC-MS area-based ester content). The optimal conditions were a methanol:crude oil molar ratio of 22.5:1, a reaction temperature of 70 °C, a catalyst loading of 2.5 wt%, and a reaction time fixed at 6 h. Engine performance was evaluated on a single-cylinder diesel engine operating at 1,500 rpm, utilizing B10 and B20 biodiesel blends. Under full load conditions, B10 reduced hydrocarbon (HC), carbon monoxide (CO), and smoke emissions by 21.43%, 12.78%, and 5.97%, respectively. B20 reduced HC, CO, and smoke emissions by 27.55%, 20.3%, and 12.23%, respectively, relative to diesel. Nitrogen oxides (NOx) emissions increased by 8.37% for B10% and 17.1% for B20 relative to conventional diesel. A techno-economic analysis (TEA) was performed using an Aspen Plus economic analysis process model; results and underlying assumptions are detailed in the TEA section.
