An introduction to heat transfer

Plasma assisted combustion: Dynamics and chemistry

The development of kerosene-like drop-in alternative aircraft fuels is currently receiving increased attention. Using a range payload approach the need for drop in fuels is justified. The alternative fuels available can be categorised into two groups; depending on whether the product increases supply security of supply or provides a reduced environmental footprint. This paper uncovers this relationship through a review of commercially available process technologies (Transesterfication, Fischer–Tropsch (FT) and hydroprocessing (HRJ)) to produce alternative fuels. The lifecycle assessments available are reviewed to identify what are actually clean fuels or have the potential to be one. A summary of the recent alternative fuel flight test campaigns is given and there results evaluated along with ground based results. A review of combustion characteristics available for the alternative fuels including ignition characteristics are presented to demonstrate the effect the distillation curve has on combustion and how too narrow a distribution of components in the fuel could generate problems with high altitude relight. The effect alternative fuels have on gaseous emissions regulated by the International Civil Aviation Organisation (ICAO) Committee on Aviation Environmental Protection (CAEP) is discussed and shown to be engine hardware dependant. Experimental data, from an Auxiliary Power Unit (APU) engine, are provided showing how, although the Gas to Liquid (GtL) and Coal to Liquid (CtL) FT fuels may not reduce GHG emissions, even with Carbon Capture and Sequestration (CCS), the local air quality around airports will benefit through reduced particulate emissions. Finally the prospects for future fuel development are discussed.

Aviation gas turbine alternative fuels: A review

The fundamental combustion and emissions properties of advanced biofuels are reviewed, and their impact on engine performance is discussed, in order to guide the selection of optimal conversion routes for obtaining desired fuel combustion properties. Advanced biofuels from second- and third-generation feedstocks can result in significantly reduced life-cycle greenhouse-gas emissions, compared to traditional fossil fuels or first-generation biofuels from food-based feedstocks. These advanced biofuels include alcohols, biodiesel, or synthetic hydrocarbons obtained either from hydrotreatment of oxygenated biofuels or from Fischer–Tropsch synthesis. The engine performance and exhaust pollutant emissions of advanced biofuels are linked to their fundamental combustion properties, which can be modeled using combustion chemical-kinetic mechanisms and surrogate fuel blends. In general, first-generation or advanced biofuels perform well in existing combustion engines, either as blend additives with petro-fuels or as pure “drop-in” replacements. Generally, oxygenated biofuels produce lower intrinsic nitric-oxide and soot emissions than hydrocarbon fuels in fundamental experiments, but engine-test results can be complicated by multiple factors. In order to reduce engine emissions and improve fuel efficiency, several novel technologies, including engines and fuel cells, are being developed. The future fuel requirements for a selection of such novel power-generation technologies, along with their potential performance improvements over existing technologies, are discussed. The trend in the biofuels and transportation industries appears to be moving towards drop-in fuels that require little changes in vehicle or fueling infrastructure, but this comes at a cost of reduced life-cycle efficiencies for the overall alternative-fuel production and utilization system. In the future, fuel-flexible, high-efficiency, and ultra-low-emissions heat-engine and fuel-cell technologies promise to enable consumers to switch to the lowest-cost and cleanest fuel available in their market at any given time. This would also enable society as a whole to maximize its global level of transportation activity, while maintaining urban air quality, within an energy- and carbon-constrained world.

A review of the combustion and emissions properties of advanced transportation biofuels and their impact on existing and future engines

Biomass-derived jet (bio-jet) fuel has become a key element in the aviation industry׳s strategy to reduce operating costs and environmental impacts. Researchers from the oil-refining industry, the aviation industry, government, biofuel companies, agricultural organizations, and academia are working toward developing a commercially viable and sustainable process that produces a long-lasting renewable jet fuel with low production costs and low greenhouse emissions. This jet fuel, additionally, must meet ASTM International specifications and potentially be a 100% drop-in replacement for current petroleum jet fuel. In this study, the current technologies for producing renewable jet fuels, categorized by alcohols-to-jet, oil-to-jet, syngas-to-jet, and sugar-to-jet pathways are reviewed. The main challenges for each technology pathway, including conceptual process design, process economics and life-cycle assessment of greenhouse gas emissions are discussed. Although the feedstock price and availability and energy intensity of the process are significant barriers, biomass-derived jet fuel has the potential to replace a significant portion of conventional jet fuel required to meet commercial and military demand.

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Bio-Jet Fuel Conversion Technologies

The development of kerosene-like drop-in alternative aircraft fuels can be categorised into two groups, depending on whether the product increases supply security or provides a reduced environmental footprint. This paper uncovers this relationship through a review of commercially available process technologies (Fischer Tropsch and hydroprocessing) to produce alternative fuels, lifecycle results and recent flight test campaigns, before evaluating the prospects for future fuel development. Supply may be improved through the conversion of coal (with carbon sequestration) or natural gas using the Fischer Tropsch process. Refinement of these alternative fossil fuels, however, provides comparable total life cycle emissions to Jet A-1. The hydroprocessing of biomass feedstock provides for a reduced environmental footprint—approximately 30% reduction for sustainable cultivated feedstock, when blended 50/50 with conventional jet fuel. However, securing supply is a significant issue. Considering aviation is responsible for 2.6% of global CO2 emissions, converting 6% of arable land (representing 0.95% of the earth surface) to supply a 50/50 blend, thus offsetting 0.78% of global CO2 emissions, seems impractical based upon the current land use scenario. Furthermore, ground based sectors have significant environmental footprints compared to aviation, yet require little pre-processing of feedstock (i.e. power generation can burn raw feedstock), thus presenting a better biomass opportunity cost.

Sustainability of supply or the planet: a review of potential drop-in alternative aviation fuels

Aviation is an important contributor to the global economy, satisfying society’s mobility needs. It contributes to climate change through CO2 and non-CO2 effects, including contrail-cirrus and ozone formation. There is currently significant interest in policies, regulations and research aiming to reduce aviation’s climate impact. Here we model the effect of these measures on global warming and perform a bottom-up analysis of potential technical improvements, challenging the assumptions of the targets for the sector with a number of scenarios up to 2100. We show that although the emissions targets for aviation are in line with the overall goals of the Paris Agreement, there is a high likelihood that the climate impact of aviation will not meet these goals. Our assessment includes feasible technological advancements and the availability of sustainable aviation fuels. This conclusion is robust for several COVID-19 recovery scenarios, including changes in travel behaviour.

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Simon Blakey

Papers

Aviation gas turbine alternative fuels: A review

Sustainability of supply or the planet: a review of potential drop-in alternative aviation fuels

Evaluating the climate impact of aviation emission scenarios towards the Paris agreement including COVID-19 effects.

Performance evaluation of PACT Pilot-plant for CO2 capture from gas turbines with Exhaust Gas Recycle

A novel design for panel radiators