sustainability in aerospace: exploring alternative fuels/media/files/s/snc-lavalin/... · 2020. 10....

Sustainability in Aerospace: Exploring Alternative FuelsHow the commercial aerospace sector can adapt to pursue the world’s goals for sustainability and Net Zero.

By James Domone

Sustainability in Aerospace: Exploring Alternative Fuels

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ForewordThe time to take action to tackle the climate crisis is now.

This most important of issues is now intertwined with the shockwaves of the global Covid-19 pandemic; and both are forcing us to re-evaluate the effects of our lifestyles on the environment.

By minimising our extraction of raw materials from the earth to provide fuel and to manufacture products, and by changing our behaviour, we can move towards a carbon Net Zero circular economy. But the challenge is sizeable, not least for the aerospace industry.

So how can new technologies and fuel sources help? How can they sustain our desire to travel around the world in safety and comfort while supporting Net Zero CO2 ambitions?

In this paper we explore the options with a focus on new and alternative fuel sources, including batteries, hydrogen and sustainable aviation fuel.

The goal of all of these things being to move aerospace towards becoming a Net Zero industry, while still maintaining safety and performance standards.

“In June 2019 the UK became the first major economy to pass net zero emissions law. The new target will require the UK to bring all greenhouse gas emissions to net zero by 2050.”www.gov.uk news release, 27 June 2019

“The energy system is extremely complex and fluid. Decisions in one sector have a knock on effect in others… We believe that ultimately the energy system must be completely fossil-fuel free [including] heating, transport, electricity generation, industry, hydrogen, small advanced nuclear, smart grid and fusion.” The Road to Decarbonisation report, Atkins, 26 October 2017

“Net Zero by 2050 is achievable but not without substantial changes to the UK’s energy mix and requiring significant investment. This demands a 30-year complex programme. To achieve Net Zero the UK needs a flexible approach to ultimate system configuration; an energy system architect; clean, reliable, consistent nuclear power; a key role from carbon capture and storage; increased capacity from renewable energy sources, primarily offshore wind; greater investment in hydrogen projects; an optimal, reliable and balanced system.”Engineering Net Zero full technical report, Atkins, 2019

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ContentsForeword .................................................................................................................................. 2

Tackling the Challenge of Climate Breakdown ............................................................ 4

Options for Alternative Aircraft Fuels ............................................................................. 7

To achieve Net Zero the whole system must be Net Zero ................................................ 9

The Further Development of Battery Power ...............................................................10

Exploring the options for hybrids .....................................................................................10

Exploring the Role of Hydrogen Power ......................................................................... 12

Turbofan designs for hydrogen combustion ....................................................................14

Fuel cell technology for electric propulsion ....................................................................14

Hydrogen could become the fuel of choice for the future .............................................. 15

How harmful is releasing water vapour as an emission? ............................................... 15

A significant challenge in creating sustainable systems ................................................16

Sustainable Aviation Fuel .................................................................................................16

What is sustainable aviation fuel? .................................................................................... 17

The main challenges for sustainable aviation fuel .......................................................... 17

Sustainable aviation fuel is already in use ....................................................................... 18

What qualifies as sustainable aviation fuel? ................................................................... 18

Land availability and agriculture for production at volume ............................................20

The falling oil price also has an effect ............................................................................. 21

Turboelectric Propulsion ...................................................................................................22

Conclusions and Recommendations .............................................................................24

References and Further Reading ....................................................................................28


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Tackling the Challenge of Climate Breakdown In 2018 the Intergovernmental Panel on Climate Change (IPCC) issued a special report showing an average global temperature increase of 1°C to date, with a high confidence that this will reach 1.5°C by the middle of this century.

The report also forecasts the climate breakdown effects that will likely result from this heating – which include increased mean temperatures, increased extreme weather events, sea level rise, ocean acidification, biodiversity loss and increased risk to human food security. But, while the climate will change as a result of the emissions already released, collectively, we can play our part in preventing things from getting worse.

Globally, aviation accounts for approximately

2% of overallCO₂ emissions T

his

equa

tes

to

of CO₂ emitted

in 2018

918milliontonnes

according to the International Councilon Clean Transportation (ICCT)

There hasbeen a32%

in CO₂ emittedover the last

five years

incr

ease

1kg ofjet fuel burned

Taking the International

Civil Aviation Organisation (ICAO) assumption that

releases 3.16kgof CO₂

290 million

tonnes (Mt)

This equates to

of jet fuel burned during 2018

2018

ICAO has also forecast that emissions from flying aircraft will increase by anannual growthrate of 3-4%

However, the ICCT claims this figure is underestimated and is closer to

following a studyusing data from

20185.7%

And this suggests an increase of CO₂ emissions of afactor of

5.9from 2018 to 2050

Using the ICCT estimate, this would result

of t

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lca

rbon

bud

get

which they predict would account for around

5,500 Mt in 2050

in civil aviation CO2 emissions

of approx.

25%

This increase is driven by the increasing global demand forair transport

from countries currentlyconsidered‘low income’as their wealth increases over time and shown in Figure 1.

Aerospace CO₂ emissions in numbers

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A small number of people are causing the majority of the emissions

While a cursory glance at passenger volume statistics might indicate that a high proportion of the global population is flying and contributing to this CO2 release – this is not the case. Many people will fly a return journey, many routes will require a stop, and a change of flight, and lots of people are likely to fly more than once a year.

Atkins estimates the figure to be around 6% of the global population that are responsible for the majority of emissions resulting from flying (see Appendix: What percent of the world’s population will fly in an aeroplane in their lives or each year?). This disproportionately small number of people who are responsible for most aviation emissions helps to explain the predicted increase in demand for air travel as the world gets richer.

The International Civil Aviation Organization (ICAO) has published forecasts for fuel burn improvements in aircraft technology and air traffic operations management based on historical trends, that total 1.37% per year. Applying these improvement rates to the forecast CO2 emission output results in 3,500 million tonnes in CO2 per year by 2050. Despite these improvements, the overall result remains a large increase in CO₂ from aviation up to 2050 as shown in Figure 1.

Targets are not going far enough – why not Net Zero?

Many aviation industry bodies, including Advisory Council for Aviation Research and Innovation in Europe (ACARE) in Europe, are targeting reductions in CO2 which aim to achieve carbon emission reductions by 2050. While these are challenging targets, some representing a 75% reduction in CO2 emissions over 2000 levels (ACARE, 2011), they do not currently extend far enough to reach the carbon Net Zero targets being agreed by governments around the world. So, dramatic changes in the approach will be needed if the aerospace sector is to reach Net Zero and a complete elimination of greenhouse-gas emissions.

Any strategies not targeting Net Zero rely on other industries generating negative CO2 emissions – removal of atmospheric CO2 - and the use of market-based measures such as offsetting to account for this. While this approach could be considered, it should very much form a secondary plan. If many other sectors took the same approach it would be extremely difficult, if not impossible, to meet global Net Zero targets.

While CO2 is seen as a dominant exhaust product to reduce, aircraft produce other emissions: NOx, CO, SOx, unburnt hydocarbons, particulate matter and contrails due to water vapour. Whether these contribute to radiative forcing or lead to air pollution they are all targeted for reduction in much the same way as CO2.

Figure 1: Global CO2 emissions from commercial aviation 2010 to 2050

CO

2 Em

issi

ons

[Mt]

Year

2010 2015 2020 2025 2030 2035 2040 2045 2050

0

1,000

2,000

3,000

4,000

5,000

6,000ICCT Baseline

ICCT Baseline with Forecast Technology Improvements

ICCT Baseline with Forecast Technology & Operations Improvements


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This need to reduce harmful emissions was clear prior to the Covid-19 pandemic, which has temporarily reduced CO2 emissions and is forecast to delay air traffic growth. The effect is likely to be seen over the next few years, with growth rates returning to pre-pandemic levels within five years.

Due to difficulty in forecasting the effect of the pandemic, and that it is likely to help reduce emissions, its effects are not considered further within this paper. However, the economic effects could be more significant as government, industry and investors are likely to have less capital available to invest in the necessary research and development activities.

Why emissions must start declining from 2020

The urgent need to take action to help mitigate the effect of climate breakdown has become extremely prevalent in the public consciousness over the last couple of years, largely due to campaign groups such as Extinction Rebellion and individuals like Greta Thunberg. The UK has led the way amongst governments on this with its own 2050 Net Zero target now a legal requirement.

As is made clear by the IPCC, CO₂ emissions must start declining from 2020 to achieve Net Zero by 2050 and minimise the negative effects of climate breakdown. Increasing confidence in investment in sustainable technology, along with many commentators urging government Covid-19 recovery support in these areas could lead to the financial investment required. Indeed, recent announcements point towards this governmental support for a green recovery and an acceleration of Net Zero strategies, particularly in European nations. To completely eliminate CO2 emissions will require not only a re-think of aircraft, but also their place within a wider sustainable system.

Putting on the pressure to act NOW!

Political incentives and targeted legislation forcing the hand of the industry to act

Post-pandemic government support only available to organisations with clear routes to Net Zero by 2050

Increased public ‘flygskam’ or flight shame, reducing potential revenues, particularly in high-income countries

Increased commercial acceptance that business can successfully be conducted remotely

Traditional aviation fuel price uncertainty as oil reserves are reduced as peak oil is approached

Increasing costs and restrictions on the extraction and purchase of raw materials.

There are many promising areas of research that can help achieve the Net Zero goal, along with many that still need to be identified. This is starkly highlighted in aerospace – where feasible zero-emissions operations have been demonstrated for small payloads over short distances, but not for larger transport aircraft.

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Options for Alternative Aircraft FuelsAirbus estimates that 97% of greenhouse gas emissions from its aircraft occur during flight operations, see Figure 2. Eliminating the emissions from operating aircraft will make the biggest contribution towards CO2 reduction, but it also presents one of the biggest challenges; operating emissions are produced from the extraction, refining and burning of hydrocarbon fossil fuel with CO₂ being the most significant output for global heating.

Ground operations2%

Flight operations97%

Production1%

While the CO2 emissions resulting from production are small compared with emissions due to operations, the target is a Net Zero industry, so strategies to achieve this for production must be put into place too. One proposal for achieving this is to look to ideas provided by the circular economy concept. This is discussed further by Atkins in other papers and if fully embraced it can provide Net Zero production of aircraft.

Since the introduction of jet-powered flight in the 1960s, aircraft fuel burn efficiency has improved by 50%. However, this was greatest leading up to the end of the 1980s, and it has plateaued since as shown in Figure 3.

So the message is clear: to achieve Net Zero in aerospace operations the fossil fuel power source needs to be replaced, and the energy needed to fly and operate aircraft needs to be obtained from sustainable sources

Figure 2: Illustration of a typical commercial aircraft lifecycle greenhouse-gas distribution (Airbus, 2020)


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Converting the forecast use of aviation fuel into energy requirements provides a starting point for understanding the amount of stored energy that the global fleet will need to carry, which is shown in Figure 4.

Figure 3: Average fuel burn for new jet aircraft, 1960-2010

Figure 4: Forecast energy required for the global commercial fleet, 2010-2050

Average fuel burn for new jet aircraft, 1960-2010.* Large reductions in fuel burn are seen from 1960 up to the 1990s; however, since then any decrease has been modest, despite the development costs of new aircraft continuing to rise.

Fuel

bur

n at

spe

cifie

d ra

nge

(196

0+10

0)

1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010

25

50

75

100

Seat-km

1960s

1970s

1980s

1990sPost-2000

*www.theicct.org/blogs/staff/overturning-conventional-wisdom-aircraft-efficiency-trends

Glo

bal F

light

Ene

rgy

Dem

and

[TW

h]

Year

2010 2015 2020 2025 2030 2035 2040 2045 2050

0

1,000

2,000

3,000

4,000

5,000

6,000

ICCT Baseline

ICCT Baseline with Forecast Technology Improvements

ICCT Baseline with Forecast Technology & Operations Improvements

7,000

8,000

9,000

10,000

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Three ways for storing the energy needed for flight while achieving Net Zero

› hydrogen › batteries › sustainable aviation fuel

Figure 5: Net Zero aircraft energy storage options: hydrogen, batteries or sustainable aviation fuel

While it is clear that batteries are part of a trend towards the electrification of aircraft, hydrogen energy extraction through a fuel cell also provides electrical energy.

Hydrogen can also have its energy extracted through combustion, along with sustainable aviation fuel. Both could be used in the traditional sense to power a turbojet or in a turboelectric propulsion architecture to generate electrical energy.

All three options require significant energy inputs at various stages of their lifecycle in order to be useful energy stores for an aircraft: batteries during production and for charging during operations, hydrogen and sustainable aviation fuel during production and distribution. There is a challenge for this energy input to also be Net Zero.

H2OR OR

To achieve Net Zero the whole system must be Net ZeroFor all of the alternative fuel options to be considered Net Zero there is a challenge on the provision of the input energy required to create them, and recharge the batteries, to also be Net Zero – a challenge not unique to aerospace and one that must be addressed globally.

For aerospace, it is important to articulate the energy required and the form it is required in, to ensure consideration within wider energy strategies and systems. A high-level ‘system of systems’ approach that considers whole life energy costs is necessary to support this.

Atkins’ Engineering Net Zero provides the basis of such a study for the UK by considering the wider energy demands and how these can be met (Atkins, 2019).

The basis of such studies is also well-described by Ian MacKay in an easy to access book available for free online (MacKay, 2009).

www.atkinsglobal.com/EngineeringNetZero

ENGINEERING

TECHNICAL REPORT

http://www.atkinsglobal.com/EngineeringNetZerohttp://www.atkinsglobal.com/EngineeringNetZero


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The Further Development of Battery Power The main benefit of using batteries to power aircraft is that they are zero-emission during operation. The propulsor itself is also greatly simplified; it’s an electric motor or propeller – and so there are also options to employ novel aircraft architectures and distributive propulsion.

The feasibility of an aircraft powered using batteries is heavily dependent on the power-to-weight ratio, the gravitmetric density, of the batteries themselves. Current state-of-art lithium-ion battery systems are only likely to be able to power smaller classes of aircraft over the next 30 years to 2050.

These include aircraft grouped under the term eVTOL – meaning electric Vertical Take-Off and Landing – for the urban air mobility market (Uber Elevate, 2016) and potentially short-range, low payload, sub-regional aircraft carrying around 12 passengers, as proposed by companies such as Eviation (Eviation, 2020).

Larger aircraft require more powerful battery systems and these are very unlikely to available in the period up to 2050.

Many views exist on the likely development of battery energy density and much of the progress to date has been driven by the automotive sector. However, it is expected that volumetric density will drive much of the further improvement in this industry and therefore aerospace will have to continue the development itself for improved gravimetric density (energy per unit mass).

New battery formulations and chemistry will be required to achieve improvements; and continued battery research and development will still play an important part in the development of Net Zero aircraft. Batteries, as they do already, will increasingly provide power to non-propulsion systems on the aircraft. Increasing the gravimetric density will support this and therefore require less power to be taken away from what ever is used to power propulsion.

Exploring the options for hybrids

For larger aircraft, hybrid configurations have been proposed by some within the industry as a useful stepping stone towards a fully battery powered aircraft – and there are many options to configure these differently, depending on the aircraft and its power requirements; Figure 6 shows some examples of those considered the most feasible.

The power electronics and electric motors are common to all configurations including the all-electric power system, and by introducing and developing these components we can evaluate how efficient they are in-service – and use this data to inform designs incorporating fully electric architectures in the future.

Voskuijl (Voskuijl, 2018) and Pornet (Pornet, 2015) have published studies for the design of a regional hybrid transport aircraft operating short-range missions of around 1,500 km. Both studies concluded a significant increase in battery gravimetric density was required to make these architectures practical. Despite the potential for hybrids to form a stepping stone towards full battery power, for larger aircraft classes >30 passengers, they do not appear feasible by 2050.

Concerns about the sustainability of producing batteries

A further consideration with batteries is the carbon emissions resulting from their manufacture. A number of studies have found differing results, however Carbon Brief has compiled these and show that roughly half of the emissions result from electricity consumption during manufacture, and are therefore highly dependent on the energy mix of the country of origin (Carbon Brief, 2020). The remaining emissions result from the mining and transport of the raw materials required.

Another element is the human cost involved for the current means of mining for the required raw materials. Sources of the required materials such as Democratic Republic of Congo and South Africa have been verified to be associated with forced child labour and other environmental problems (Circular Energy Storage, 2019). So, there are serious socio-economic issues at play, too, which we should consider, alongside the environmental challenges.

Batteries also do not have infinite lifespans. At some point they must be reconditioned or recycled to ensure that any emissions occurring from the production of new replacement batteries, due to raw material extraction, are not repeated. This could involve a second life for the battery in a lower capacity requirement such as stationary energy storage.

While recycling batteries at scale is a relatively recent development, the increase in automative battery vehicles will grow this capability and reduce emissions compared with extraction of more raw material (ICCT, 2018).

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Figure 6: Three potential system architectures are shown with a progression from the ‘More Electric’ to ‘Full Hybrid’ to ‘All Electric’ (Atkins, 2018)

Turboshaft

Fuel

Generator

Powerelectronics

ElectricBus

Motor(s)

Aircraft systems

Battery

Turboshaft

FuelBattery

Generator

ElectricBus

Motor(s)

Aircraft systems

Powerelectronics

Battery

ElectricBus

Motor(s)

Aircraft systems

Powerelectronics

Turboshaft

Fuel

Generator

Powerelectronics

ElectricBus

Motor(s)

Aircraft systems

Battery

Turboshaft

FuelBattery

Generator

ElectricBus

Motor(s)

Aircraft systems

Powerelectronics

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ElectricBus

Motor(s)

Aircraft systems

Powerelectronics

Turboshaft

Fuel

Generator

Powerelectronics

ElectricBus

Motor(s)

Aircraft systems

Battery

Turboshaft

FuelBattery

Generator

ElectricBus

Motor(s)

Aircraft systems

Powerelectronics

Battery

ElectricBus

Motor(s)

Aircraft systems

Powerelectronics

MO

RE

ELEC

TRIC

FULL

H

YBRI

DA

LL

ELEC

TRIC


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Exploring the Role of Hydrogen Power The other option for Net Zero flight is hydrogen. Hydrogen as a fuel source for aeroplanes has been studied since the 1930s and in 1989 a Tupolev Tu-155 prototype was flown in Russia powered by liquid hydrogen fuel.

The most notable recent study into a hydrogen-powered aircraft was the European Cryoplane project which featured an extensive list of contributors and covered the full operating system in combination with the aircraft itself (Airbus, 2003).

Interest in hydrogen as an aviation fuel source has recently reignited following investment in the eVTOL sector by Hyundai and the French government via the European Union Clean Sky initiative (Clean Sky, 2020).

Hydrogen as a fuel source is attractive for a number of reasons

Figure 7: Tuplov Tu-155 hydrogen powered prototype aircraft

The main emission that results is water vapour and then, if the hydrogen is burnt in a turbine there would alsobe a small amount of NOx.

The gravimetric density of hydrogen is greater than jet fuel (whether hydrocarbon fossil fuel or sustainable aviation fuel). Indeed, it is used as a rocket propellant in part for this reason. Figure 8 shows a comparison of energy densities for some common fuel types and illustrates the relationship between hydrocarbon fuels, batteries and hydrogen.

H2

Hydrogen can be produced by electrolysis of water, or reformationof sustainable biomass, which canbe done globally but this must be powered by sustainable electricity.

Aircraft can be refuelled in similar time-frames to current aircraft. However, this is not without complication due to the handling of a high-pressure cryogenically cooled liquid.

1

4

2

3

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Figure 8: Fuel energy density comparisons

Hydrogen also presents some challenges

Hydrogen also presents some challenges; while it shows much greater gravimetric density than hydrocarbon fuels, it has notably lower volumetric density. Hydrogen must be cryogenically cooled to -253°C (20 K) into a liquid state, necessitating increases in aircraft system mass. However, the cryogenic system required could also be used to provide super-conducting electrical systems with near-zero resistance, improving efficiency. Even with cryogenic cooling a greater volume of storage is required, likely resulting in lower aircraft lift to drag ratios and increasing the energy needs to fly.

Also, liquid hydrogen must be stored under pressure making storage in wing fuel tanks very difficult to achieve efficiently and leading to fuselage storage. Additional system weight is unlikely to be compensated for by increased efficiency and therefore further structural optimisation is required along with potential range or payload reductions. The gas turbines or fuel cells which extract the energy from the fuel, require regular maintenance activities, with fuel cells needing new maintenance processes to be developed.

The infrastructure to produce and distribute liquefied hydrogen in sufficient quantities does not currently exist – and the majority of hydrogen production today is currently performed using natural gas (methane) reformation, releasing quantities of CO₂ equivalent to burning hydrocarbon fuel. Proposals for future generation of hydrogen by this process also require the implementation of carbon capture and storage, a low maturity technology, particularly at scale.

There are two routes to using hydrogen as an aircraft fuel which are shown in Figure 9: the direct combustion of hydrogen within a gas turbine, and the use of fuel cells to convert the stored chemical energy to electrical energy to power electric fans.

Volu

met

ric D

ensi

ty [k

WhJ

/L]

Gravimetric Density [kWh/kg]

0 5 10 15 20 25 30 35 40 45

0

2

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6

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Current and Future Batteries (2040)

Hydrocarbon fuels & sustainable aviation fuel

Hydrogen


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Turbofan designs for hydrogen combustion

Historical studies of using hydrogen as a fuel have focussed on the combustion route given the fundamental propulsion system remains very similar to existing hydrocarbon systems and the unavailability of fuel cell technology. This system would also allow aircraft to travel at similar speeds to current aircraft given the potential to use a turbofan design of engine.

However, this type of system is not completely emission-free; NOx would be produced as an emission in addition to water vapour as a result of the conditions within the engine combustion chamber. Different mission profiles with different thrust requirements, e.g. flight at different altitudes, fuel pre-mixing and development of combustor design to suit hydrogen are all expected to allow a reduction in NOx emissions calculated during feasibility studies or shown on system testing (NASA, 2002).

Fuel cell technology for electric propulsion

Thanks to advances in fuel cell technology, recent proposals for hydrogen-fuelled aircraft have focussed on this approach to powering the propulsion system.

Advantages from using fuel cells include:

› Elimination of NOx emissions; the only emission is water vapour

› Due to the use of chemistry rather than combustion to extract the energy, the thermal efficiency is increased, potentially leading to lower fuel volumes required as technology improves

› Simplified mechanical systems by replacing the gas turbine for an electric fan, reducing maintenance requirements

› A greater range of aircraft architectures is enabled because of relative ease of transfer of electrical energy from production site to motor, including distributed propulsion systems

› As electrical energy is produced, fuel cell output can be more easily combined with any other electrical energy output source.

However, they also have disadvantages:

› While fuel cell to propulsion efficiency is of the order of 40%, broadly similar to hydrocarbon fuel systems, overall system efficiency is notably lower than for batteries as illustrated in Figure 10 and notably highlighted by prominent automotive industry commentators (Cox, 2014).

› By replacing turbofan engines with electric fans, or propellers, flight speed will reduce.

Figure 9: Potential system architectures for hydrogen powered aircraft

Turbofan

Fuel

Fuel Cell

Fuel

ElectricBus

Motor(s)Power

electronics

Turbofan

Fuel

Fuel Cell

Fuel

ElectricBus

Motor(s)Power

electronics

HYD

ROG

EN

CO

MBU

STIO

NFU

EL C

ELL

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Figure 10: Approximate comparison on efficiencies for battery and hydrogen powered propulsion

Fuel cells powered by hydrogen could be a potential solution for larger aircraft classes – but, while feasible, the technological and operational challenges are high and could prove extremely difficult to overcome to make a difference by 2050.

Hydrogen could become the fuel of choice for the future

Although fuel cells may be unlikely to compete in terms of efficiency with batteries, and there are many challenges around using hydrogen as fuel regardless of energy extraction means (fuel cell or combustion), it may provide the only Net Zero solution that will be capable of providing range commensurate with economic payload. Achieving this within a 2050 timeframe is challenging but looks like a promising solution beyond 2050.

How harmful is releasing water vapour as an emission?

One concern with the use of hydrogen is the volume of water vapour emitted, whether a combustion or fuel cell route is followed. Specifically that this water vapour can form additional cirrus clouds when released in the stratosphere.

However, a robust position on this was defined by the IPCC in its 2013 reporting cycle. They state that “the amount of water vapour in the atmosphere is controlled mostly by air temperature, rather than by emissions. For that reason, water vapour is considered a feedback agent, rather than a forcing to climate breakdown. Anthropogenic emissions of water vapour have a negligible impact on the global climate” (IPCC, 2013). The effect of water vapour emitted in the stratosphere, where aeroplanes currently operate, is not well understood, but the conclusion is that human released emissions are probably negligible compared to natural processes in terms of radiative forcing. There is an admission that the confidence in this conclusion is considered “medium”, mainly due to difficulties in assessing the radiative forcing effect produced, which is extremely localised and short-lived.

Electricity

Create hydrogen η ≈ 70%

Charge Battery η ≈ 85%

Transportation η ≈ 90%

Fuel Cell Conversion η ≈ 60%

Power Flight η ≈ 70%

Power Flight η ≈ 70%

Batteries

ηtot ≈ 60%

ηtot ≈ 25%

Hydrogen


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Water vapour also has a fundamental difference when compared with other greenhouse gases, in that it can condense and precipitate. This results in released water vapour only persisting in the atmosphere for an average 10 days, where it does not contribute significantly to the overall greenhouse effect.

A significant challenge in creating sustainable systems

For either hydrogen combustion or fuel cells, the challenge of creating the hydrogen in a sustainable way is significant. This was a fundamental reason why studies into hydrogen for aviation during the 2010s were terminated (BBC, 2010); the lifecycle CO₂ output was deemed higher for hydrogen than for hydrocarbon fossil fuel. While the aerospace industry cannot tackle this challenge directly, it can support decarbonisation by only sourcing hydrogen from sustainable sources where possible.

Sustainable Aviation Fuel For a combination of reasons, batteries and hydrogen on their own are extremely unlikely to fully enable Net Zero aviation by 2050 without significant financial support. Mainly due to existing aircraft designs still being in operation at this time.

The solution which is receiving the most attention is the use of sustainable aviation fuel. This is biological or synthetic aircraft fuel which meets the requirements of existing aviation fuel but is produced from sustainable sources, and does not put demand pressure on its use elsewhere, such as for bioenergy.

Key drivers for the development and ongoing implementation of sustainable aviation fuel include:

1. It acts as a drop-in substitute for existing jet fuel; there is no change to the aircraft systems or ground based infrastructure is required.

2. It can contribute to life cycle emissions reductions for existing aircraft in-service, and doesn’t rely on a new aircraft type to be developed, produced and proliferate through global fleets.

3. Its energy densities and other performance properties are identical to hydrocarbon fuels, see Figure 8.

4. It can be mixed with hydrocarbon based fuel. Indeed, this is a requirement for the types of sustainable aviation fuel approved to date which restricts their use to up to 50% blend with conventional fuel. The industry intention is to allow 100% sustainable aviation fuel, but various technical details need to be understood and addressed to achieve this, however, test flights with 100% sustainable aviation fuel have been completed by Boeing using a 777 Freighter as part of its ecoDemonstrator programme (ICAO, 2019).

5. Implementation of sustainable aviation fuel does not change any development activities for zero emission alternatives such as batteries and hydrogen. Further, it is fully compatible with a turboelectric architecture.

6. It can be easily certified as properties of sustainable aviation fuel are mandated by existing airworthiness regulations and existing international standards define qualification processes.

7. There’s a lack of an alternative solution in the required time-frame.

The energy required for producing hydrogen by electrolysis is estimated as 50 kWh/kgH2 (Fuel Cells and Hydrogen Joint Undertaking, 2014)

The efficiency of fuel cell propulsion systems is around 42% (60% for a fuel cell (US Department of Energy, 2011), 70% for an electric fan (National Academy of Sciences, 2016).

This leads to a requirement for 1,340 TWh of electrical energy by 2050, to produce the quantity of hydrogen needed for the baseline case with technology or operations improvements considered.

For comparison, global electricity production from all sources was 25,600 TWh in 2017 (IEA, 2019).

2050

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What is sustainable aviation fuel?

For a fuel to qualify as sustainable aviation fuel under ICAO rules, it must demonstrate a whole-life reduction of at least 10% CO₂ (ICAO, 2019) versus a conventional fuel baseline. However, under the EU from 2021 the requirement is a 65% reduction in whole-life CO2, down from 60% before this date (EU, 2018). The whole-life distinction is important, because the direct emissions during operation resulting from the use of sustainable aviation fuel do not show a decrease in CO₂ compared with hydrocarbon fossil fuel.

The reductions come from the sustainable aviation fuel’s enablement of reuse and recycling of atmospheric carbon with the aim of a Net Zero effect. This process is directly comparable to the natural carbon cycle and contrasts with the single direction pathway currently followed through the use of hydrocarbon fossil fuels shown in Figure 11.

The main challenges for sustainable aviation fuel

1. It needs to demonstrate not just a CO₂ reduction, but life cycle Net Zero. This requires Net Zero along the full production chain and requires associated industrial sectors to decarbonise in support (energy, agriculture and transportation).

2. It needs to demonstrate its ability to be used 100% as sustainable aviation fuel without the need to blend with hydrocarbon fossil fuels. This mainly stems from the lack of aromatic hydrocarbons within sustainable aviation fuel, which are required, for example, by fuel gauges to ensure correct performance, and a lack of sulphur needed to ensure correct lubricity levels in seals (Sustainable Aviation, 2020).

3. The scaling up of sustainable aviation fuel production.

4. The relative cost versus conventional hydrocarbon based fuel.

Figure 11: Carbon life-cycle diagrams: fossil fuel and sustainable aviation fuel (ATAG, 2017)

CO₂

FlightFlight

CO₂

CO₂

CO₂

CO₂

CO₂

CO₂

CO₂

Distributionat airports

Distributionat airportsExtraction

Refining

Refining

ProcessingTransport

Transport

Transport

Feedstock growth

CO₂

CO₂

CO₂

Carbon lifecycle diagram: fossil fuels Carbon lifecycle diagram: sustainable aviation fuel

At each stage in the distribution chain, carbon dioxide is emitted through energy use by extraction, transport, etc.

Carbon dioxide will be reabsorbed as the next generation of feedstock is grown. Note: the diagram above does not demonstrate the lifecycle process of SAF derived from municipal waste.


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The technical issues around the compatibility of sustainable aviation fuel with existing aircraft systems is thought to be relatively easy to address through detailed design evaluation and fuel additives.

Many of the other challenges relate to the infrastructure and production of sustainable aviation fuel and are likely to require government policy and financial support to overcome cost barriers in the near term.

This is highlighted by the current use of sustainable aviation fuel accounting for less than 0.1% of total aviation fuel use in 2019 (IATA, 2019). ICAO forecasts that the available global production volume of sustainable aviation fuel will be 6.5 million tonnes by 2032.

However, there is uncertainty as to how much of this will be available for aviation over other forms of transport; this falls a long way short of the forecast demand for aviation fuel by 2050 of 11,000 million tonnes even when we consider improvements in technology and operations.

Sustainable aviation fuel is already in use

On the positive side, many airlines have been operating with sustainable aviation fuel in their fuel mix already and demand is growing quickly. ICAO now has a CO₂ reduction framework in place that fully acknowledges the role of sustainable aviation fuel in contributing to aviation CO₂ reductions, called CORSIA. This framework provides the basis for the aviation industry to consistently measure, reduce and then offset CO₂ emissions against a 2020 baseline targeting neutral CO₂ emissions growth from 2020 onwards. The use of sustainable aviation fuel is a central element of this CO₂ reduction, and a consistent method of taking the CO₂ reduction into account is applied.

What qualifies as sustainable aviation fuel?

A reduction of at least 10% of the whole-life cycle CO2 emissions are required for a fuel to qualify as a sustainable aviation fuel and also a variety of other criteria that ensure other UN sustainability goals are not compromised. These include non-sustainable changes in land-use and increasing local competition for food and water amongst others (ICAO, 2017).

There are currently five conversion processes certified to produce sustainable aviation fuel from a variety of feedstock sources which are listed in Figure 12. These feedstocks and processes are combined into pathways to produce sustainable aviation fuel summarised in Figure 13. Certification of new fuels and processes is lengthy and new routes are currently undergoing certification testing and accreditation following ASTM D1655 (Sustainable Aviation, 2020).

The most efficient and sustainable fuel for a particular country or airport depends on local feedstock and transformation methods – and this is an important consideration. Attempting to grow palm oil in northern Europe is unlikely to prove as efficient as rapeseed oil, for example. A number of feedstocks used in sustainable aviation fuel are waste products from other industrial or commercial sectors, such as municipal solid waste and used cooking oil.

Global sustainability trends are towards reducing and eliminating waste of any sort where possible and this could reduce future availability of these feedstocks. Using a waste product that itself may not be supporting emission elimination targets during its primary use may also serve to reduce the incentive for changing this. So, while the benefit to aviation is positive, the net global effect could prove negative.

In the case of municipal solid waste the conversion into useful sustainable aviation fuel is likely to be an attractive pathway due to the volume of material available and the need to reduce landfill usage. It’s very likely that this fuel source will be abundant for some time to come in generous quantities.

Agricultural residues

Forestry residues

Municipal solid waste (MSW)

Usedcooking oil

Tallow

SugarcaneSugar beetCorn grain

PoplarMiscanthusSwitchgrass

Palmfatty acid distillate

Cornoil

Soybeanoil

Rapeseed oil

Palmoil

Fuel Conversion Processes*Fischer-Tropsch (FT)

Hydroprocessed esters and fatty acids (HEFA)

Alcohol (isobutanol) to jet (ATJ)Alcohol (ethanol) to het (ATJ)Synthesized iso-paraffins (SIP)

*Reference: ASTM7566 and ASTM 1655 -ensures the technical specifications of the fuel

FEEDSTOCKS

FUEL CONVERSION

Figure 12: Sustainable aviation fuel feedstocks and certified conversion processes (ICAO, 2018)

19


One challenge is that the actual CO₂ emissions reduction for sustainable aviation fuel is not completely clear at present, and calculation methods suffer from a lack of consistency. An ICAO summary of studies from 2017 is (see Figure 14 ) indicates large differences for different pathways.

Different processes are at different levels of optimisation and there is likely to be great variability due to geographic location. However, much of the resulting CO₂ derives from transport and electricity usage, which can all be addressed and reduced over time.

Figure 13: Generalised view of sustainable aviation fuel production pathways (ICAO, 2017)

Oil Feedstock

Sugar Feedstock

Starch Feedstock

Lignocellulosic Feedstock S

usta

inab

le A

viat

ion

Fuel

(SA

F)

Lipids conversion HEFA-SPK

Thermochemical conversion

FT-SPK, FT-SPK/A

Biochemical conversion

ATJ-SPK, HFS-SIP

Pre treatment Oil production

Pre treatment Sugar Extraction

Pre treatment Sugar Production

Figure 14: Summary of life cycle emissions results from sustainable aviation fuel pathways (ICAO, 2017)

GH

G E

mis

sion

s (g

CO

2/M

J)

HEF

A -

Cam

elin

a

HEF

A -

Jatr

opha

HEF

A -

Mic

roal

gae

HEF

A -

Palm

HEF

A -

Rape

seed

HEF

A -

Soyb

ean

HEF

A -

Tallo

w

HEF

A -

Gre

ase

FT-C

orn

stov

er

FT-S

wtic

hgra

ss

ATJ

- Sug

arca

ne

HSF

- Su

garc

ane

ATJ

- Cor

n-gr

ain

0

100Lifecycle of CAF emissions

200

300

400

500

600

700

800

-200

-100

Results with LUC considerations

Results without UC considerations


20

Land availability and agriculture for production at volume

For agricultural feedstocks, the amount of available land is an important consideration. Land used for sustainable aviation fuel feedstock should not reduce the amount land that could be used for other, equally essentially purposes – such as fresh water and food, or conflict with local ecology and biodiversity. ICAO has included this in its consideration of sustainable aviation fuel and has forecast agricultural demands due to increased global population up to 2050 which is summarised in Figure 15 (ICAO, 2017).

The conclusion is that up to 0.2 billion-hectares of land would be needed from an available area of 1.41 billion-hectares. This would produce an estimated 55,500 TWh per year of sustainable aviation fuel; far above the estimated amount required for aviation shown in Figure 4. However, within this top-level global figure there are variations in the land available for individual feedstocks and the distribution of available land is not uniform across the planet.

Despite this, there is general consensus that the limiting factor in the use of sustainable aviation fuel is the infrastructure required to produce and transport the sustainable aviation fuel rather than availability of suitable feedstock (Sustainable Aviation, 2020).

Aside from a lack of current production volume, another key consideration preventing an increase in the use of sustainable aviation fuel is the cost relative to existing hydrocarbon fuels. ICAO estimates that sustainable aviation fuel from all sources is currently between 50% and 350% more expensive that hydrocarbon fossil fuels, based on average prices between 2013 and 2016, depending on the production pathway.

The cost ratio of raw feedstock to industrial processing to produce sustainable aviation fuel varies between the different pathways and typically follows an inverse relationship; that is, more expensive feedstock tends to require cheaper and simpler processing equipment and lower energy input, as shown in Figure 16.

Figure 15: Global land use for food and bioenergy (ICAO, 2017)

Forests, Deserts, Mountains and Urban

areas (B.1 GHa)1.41 GHa

Land available for non-food agricultural expansion, including

bioenergy

1.87 GHa0.05-0.2 GHa

1.61 GHa

Land required for feeding directly or

indirectly the world population in 2050

Land required for urban settlements and infrastructure expansion, forests, and protected areas for biodiversity

in the next decades

Land needed to expand bioenergy production to 100-200EJ/year

21


Figure 16: Feedstocks and relative position according to cost (ICAO, 2017)

Wastes & Residues

Lignocellulosics

Sugars

& StarchesOils

SAFTallow

Sugarcane Bagasseand Trash

Municipal Solid Wastes(MSW)

Algae (sucrose)

Used Cooking OilJatropha

Camelina

Cassava

Sweet Sorghum

Elephant Grass

Algae (waste)

Flue, Gas, CO, CO/H₂

EucalyptusPinus

SoybeanPalm

Sugarcane

Increasing costs of feedstockIncr

easing

technica

l efforts

The falling oil price also has an effect

As the base price of oil has fallen further during 2019 and 2020, and with the effects of Covid-19 temporarily reducing demand, the short-term financial case for sustainable aviation fuel is weakened further. Many in the industry are calling for government policy support, mainly in the form of incentives, to increase the usage of sustainable aviation fuel in the short-term. The resulting increased demand for sustainable aviation fuel is then expected to reduce costs as processes are optimised and scale effects become apparent.

However, due to the differences in lifecycle CO₂ emissions between the different pathways, details of how these incentives are applied are important. To achieve the elimination of greenhouse gas emissions the sustainable aviation fuel pathways that show routes to this elimination, along with consideration of other sustainability measures, should be the ones promoted.

As sustainable aviation fuel is heavily dependent on the whole process of production and supply, a coordinated approach to the whole system is required that links feedstock production with airports and aircraft operators.

The role of government in facilitating and supporting these systems, particularly where early investment costs are high with long waits for returns, is a factor that is likely to determine success on the timescales required for emissions elimination by 2050.

The overall challenge of introducing sustainable aviation fuel into aviation in large quantities remains high, although these challenges are largely political and economic rather than technical. ICAO notes that achieving the best case scenarios will require high levels of agricultural productivity and land availability for feedstock growth, conversion process efficiency improvements and large reductions in supporting utilities emissions.

ICAO forecasts that through the increased use of sustainable aviation fuel a CO₂ emission reduction in 2050 over 2020 levels is achievable, as shown in Figure 17. The CORSIA programme would then support further reduction or address shortfall in the availability of sustainable aviation fuel through market-based measures, such as carbon offsetting (ICAO, 2019).

A key criticism of offsetting is that while the projects which it supports are essential, many are only likely to provide the calculated CO₂ reductions over a long period. The reduction in emissions is needed over a relatively short timescale and offsetting alone will not support this.


22

Turboelectric Propulsion A turboelectric propulsion architecture extracts energy from its fuel source through the use of a gas turbine, which then drives an electrical generator and propulsive force is created through fans or propellers powered directly by this electrical energy.

While classed as electrical propulsion, it is distinct from a hybrid solution in that there is only a single source of propulsive energy which is not a battery or a fuel cell. Thus, hydrogen (combusted), fossil-fuel hydrocarbon or sustainable aviation fuel could be used as the energy source for this arrangement.

Figure 18: Turboelectric propulsion architecture

Figure 17: Forecast net CO₂ emissions to 2050 including the use of sustainable aviation fuel (ICAO, 2019)

Turboshaft

Fuel

Generator

Powerelectronics

ElectricBus

Motor(s)

TURB

OEL

ECTR

ICN

et 3

.16

CO

2Em

issi

ons

from

Inte

rnat

iona

l Avi

atio

n (M

t)

Analysis Year

20102005 2015 2020 2025 2030 2035 2040 2045 2050

0

1000

CAEP11 Baseline Including Fleet Renewal

Illustrative Alt Fuels Case

Range of 2020 CO2

Low Aircraft Technology Scenario

Additional Contribution of Technology Improvements

Additional Contribution of Improved ATM and Infrastructure Use

Range of Potential GHG Reductions with Alt Fuels

2000

3000

4000

Extrapolation beyond 2045

100% replacement of alternative jet fuel

23


These systems have the potential to improve fuel burn over the current state-of-art aircraft by 20% (National Academy of Sciences, 2016), which results from:

› operation of a gas turbine at a single operating condition in a shielded installation,

› potential for the use of a distributed fan arrangement,

› improvements in both gas turbine and fan technology given they are existing areas of research and development,

› opportunities to combine this approach with hydrogen or sustainable aviation fuel to offer further net zero benefits.

However, potential challenges with this approach include aircraft configuration regarding the location of the shielded gas turbine(s) given that it will still require an airflow, a suitable generator, cooling via a heat exchange of some type and development of high voltage electrical systems (which would also be required for any electrical propulsion system). These additional components, compared to current architectures, will result in increased structural mass and NOx will still be emitted even when sustainable aviation fuels or hydrogen are used.

The US National Academy of Sciences actually recommends a turboelectric architecture is the only feasible route to electrically propelled aircraft by 2050 and this is only up to short-haul sized aircraft (National Academy of Sciences, 2016). Turboelectric architectures are only likely to be required in a couple of scenarios:

› If hydrogen is the desired energy source and fuel cell technology has not progressed sufficiently to provide the necessary power, or a turboelectric architecture is shown to be significantly lower weight than that for a fuel cell system – accepting that this would not eliminate NOx emissions.

› If sustainable aviation fuel is taken as the desired fuel for next generation aircraft and production of this is limited to the extent where additional aircraft efficiency reductions are required to ensure there is enough fuel available for everyone.

The difficulty is that the decision on whether a turboelectric system is necessary will have to be fairly early in any aircraft development programme. As much development work as possible should cover all options until the point when these decisions are required to ensure the best configurations and technologies are taken through to service maturity.


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Conclusions and RecommendationsThe challenge of eliminating CO₂ emissions from commercial aviation is formidable. But now, it is also quantifiable; it has opened the door for solutions and strategies to enter.

Despite significant focus on the contribution of the aviation sector to global warming, it currently only releases approximately 2% of global CO₂ emissions.

However, as fully recognised by the industry itself, if nothing changes this share is predicted to rise due in large part to the efforts of other sectors and the significant forecast increase in demand for air travel over the years to 2050.

This increased demand will largely be the result of increasing global wealth as more people on the planet increase their living standards as a result of more basic needs such as food, shelter, sanitation and education being met.

The industry itself is targeting an emissions reduction against 2020 levels through a number of different initiatives. These approaches do not currently target an elimination of emissions, and rely on the long-term availability of market-based measures such as carbon offsetting.

For aviation to really meet the global Net Zero challenge it must look to eliminate lifecycle emissions without resorting to market-based measures, which simply move the problem elsewhere.

The majority of aviation CO₂ emissions are the result of burning fossil fuel to provide the energy needed to fly. Several potential energy storage technologies have been discussed that could provide Net Zero emission energy for flight; batteries, hydrogen and sustainable aviation fuel. Each option has advantages and disadvantages, but all have the potential to meet Net Zero.

Figure 20: Atkins view on sustainable fuel sources for Net Zero 2050 and beyond 2050

Aircraft Class Approx. PassengersFuel Source

By 2050 Beyond 2050

eVTOL 1-6 H2

Sub-Regional 4-30 H2 H2

Regional 30-120 H2 H2

Narrow Body Short Haul 120-200 H2 H2

Widebody Long Haul 200+ H2

25


Considering the need for immediate action and the availability of enabling technology some combination of the three options, dependent on aircraft class, is most likely to result in order to achieve the Net Zero target by 2050. Figure 20 presents Atkins’ view of the most likely mix of fuel types across the different aircraft classes to achieve Net Zero by 2050, and then beyond. This is based on the considerations discussed throughout, the different concepts being proposed around the world, and our consideration of technical feasibility.

In some classes, particularly the smaller ones, we expect a mix of different types depending on operational requirements. Over-time, as operational evidence is gathered and technology develops and matures, we predict there will be a convergence within each aircraft class, much like we see with current fossil fuel powered aircraft. Seeing where the journey leads will be interesting and exciting in equal measure.

New aircraft manufacturers are likely to emerge, some will disappear and many will adapt and embrace the necessary changes. New operating models are likely to evolve as aircraft capabilities change and the global population grows. The race to Net Zero presents some great challenges for engineers to tackle and it is imperative that we face them head on.

For true Net Zero and further increased sustainability, aviation also needs to address its energy use in production, and implement sustainable material usage. A shift to a circular economy model can support this change by aiming to reuse as much of its own material as possible in each successive aircraft rather than rely on other sectors to make good use of its waste.

Key recommendations

1

2

3

4

5

Significant government investment into developing and implementing alternative fuel aircraft technology and energy supply infrastructure is required to overcome the current industrial inertia and high initial costs.

Continuing development of batteries to increase gravimetric density, providing propulsive energy for smaller aircraft classes and onboard system power for larger aircraft classes.

A rapid increase in the volume and availability of Net Zero production of sustainable aviation fuels to move towards Net Zero within the current aircraft fleet as soon as possible.

A corresponding increase in the development of a Net Zero hydrogen creation and supply infrastructure.

Hydrogen fuel and propulsion system development, both for use in combustion and fuel cell architectures, but with a focus on longer term Net Zero goals beyond 2050.

HH22


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Appendix:What Percentage of the World’s Population Fly in an Aeroplane Each Year?

This is a question that not many individuals in high-income countries will necessarily consider. People in these counties, like the UK, USA, Canada, Japan, will most likely fly to go on holiday and possibly a couple more times during the year for work reasons.

If they don’t, then they know first-hand people that do. When you fly, particularly in Europe, most of the seats are full and during holiday periods airports are busy places. Through these optics it can be easy to come to the conclusion that most of the world’s population have experienced air transport.

A cursory glance at passenger volume statistics might indicate that a high proportion of the global population is flying and contributing to this CO₂ output, such as those produced by IATA and various other groups.

The International Air Transport Association (IATA) reports that there were 4,378 million passenger departures in 2018 (IATA, 2019). The World Bank estimates there were 7,594 million people on the planet at the end of 2018 (World Bank, 2020). This would suggest that 58% of the world population flew during 2018.

Every time an aeroplane takes-off and lands it is referred to as a segment. Many people will fly a return journey, many routes will require a stop and change of flight and lots of people are likely to fly more than once a year. Each of these elements are individual segments, so for example a return journey with a stop in each direction is four segments. It is the number of segments that are counted and reported to give the number of passengers flying each year.

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As there are many different situations and scenarios that would build-up a picture of how many people fly each year, we need a number of assumptions that take into account different factors for which there is very little, or any, public data. The assumptions taken to generate an estimate:

1. All journeys taken were return, which halves the number of passengers.

2. 20% of all trips were direct flights in both directions.

3. The remaining 80% involved 2 segments in each direction.

4. The frequent flyers account for 70% of journeys each year (UK value (FullFact.org, 2016)).

5. That 15% of travellers considered are frequent flyers who fly at least 3 times per year (UK Department for Transport, 2014).

This all works out indicating 464 million distinct passengers during 2018, which is 6% of the global population.


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Airbus. (2003). Liquid Hydrogen Fuelled Aircraft – System Analysis. Retrieved from https://www.fzt.haw-hamburg.de/pers/Scholz/dglr/hh/text_2004_02_26_Cryoplane.pdf

Airbus. (2020). Annual Report 2019. Retrieved from https://www.airbus.com/investors/financial-results-and-annual-reports.html#annualreports

Ashby, M. F. (2013). Materials and the Environment, 2nd Edition.

ATAG. (2017). Beginner’s Guide to Sustainable Aviation Fuel. Retrieved from https://aviationbenefits.org/media/166152/beginners-guide-to-saf_web.pdf

Atkins. (2018). The Challenges and Benefits of the Electrification of Aircraft. Retrieved from https://www.atkinsglobal.com/~/media/Files/A/Atkins-Corporate/Electrification%20White%20Paper%20-%20digital.pdf

Atkins. (2019). Engineering Net Zero Technical Report. Retrieved from http://explore.atkinsglobal.com/engineeringnetzero/

BBC. (2010). Aviation Industry ‘Ditches’ Hydrogen. Retrieved from https://www.bbc.co.uk/news/science-environment-11707135

Boeing. (2019). Commercial Market Outlook 2019 - 2038. Retrieved from Boeing Commercial Market Outlook: https://www.boeing.com/commercial/market/commercial-market-outlook/#/downloads

Carbon Brief. (2020). Factcheck: How Electric Vehicles Help to Tackle Climate Change. Retrieved from https://www.carbonbrief.org/factcheck-how-electric-vehicles-help-to-tackle-climate-change

Circular Energy Storage. (2019). Analysis of The Climate Impact of Lithium-Ion Batteries and How to Measure It. Retrieved from https://www.transportenvironment.org/sites/te/files/publications/2019_11_Analysis_CO2_footprint_lithium-ion_batteries.pdf

Clean Sky. (2020). Hydrogen-Powered Aviation. Retrieved from https://www.cleansky.eu/news/hydrogen-powered-aviation-preparing-for-take-off

Cox, J. (2014). Time To Come Clean About Hydrogen Fuel Cell Vehicles. Retrieved from https://cleantechnica.com/2014/06/04/hydrogen-fuel-cell-vehicles-about-not-clean/

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IATA. (2019). Retrieved from Airline Industry Economic Performance - December 2019: https://www.iata.org/en/iata-repository/publications/economic-reports/airline-industry-economic-performance---december-2019---data-tables/

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About the author

James DomoneSenior Engineer

James Domone is a senior engineer in aerospace design, security and technology for Atkins, a member of the SNC-Lavalin Group that is working to transform aerospace engineering for faster design, reduced downtime, and lower costs.

atkinsglobal.com/aerospace

Transforming aerospace engineering, for faster design, reduced downtime and lower costs.

© Atkins Limited except where stated otherwise.

ForewordTackling the Challenge of Climate Breakdown Options for Alternative Aircraft FuelsTo achieve Net Zero the whole system must be Net ZeroThe Further Development of Battery Power Exploring the options for hybrids Exploring the Role of Hydrogen Power Turbofan designs for hydrogen combustionFuel cell technology for electric propulsionHydrogen could become the fuel of choice for the futureHow harmful is releasing water vapouras an emission?A significant challenge in creating sustainable systemsSustainable Aviation Fuel What is sustainable aviation fuel?The main challenges for sustainable aviation fuel Sustainable aviation fuel is already in use What qualifies as sustainable aviation fuel?Land availability and agriculture for production at volumeThe falling oil price also has an effectTurboelectric Propulsion Conclusions and RecommendationsReferences and Further Reading

sustainability in aerospace: exploring alternative fuels/media/files/s/snc-lavalin/... · 2020. 10....

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