Department of Mechanical Engineering

Powertrain & Vehicle Research Centre

Dr James Turner

Professor of Engines and Energy Systems

University of Bath, UK

Department of Mechanical Engineering

Powertrain & Vehicle Research Centre

Low-Carbon Aviation – How can this be achieved?

“Prediction is very difficult,

especially if it's about the future.”

Niels Bohr

Overview of Presentation

Downsized engines

The historical link between aviation and automotive

Our need to change

The growth in transportation energy

The need for high energy density fuel in aviation

Pure hydrocarbons and the problem with everything else

Some options for decarbonizing fuel in aviation

Hydrogen, nuclear, ammonia

Another (blue sky) way

ZELTA

Carbon-neutral liquid fuels

Decarbonizing practical fuels

Concluding remarks

Downsized, Boosted Engines – the Link

Aviation pursued engine boosting to maintain power at altitude and then to

increase specific output significantly

Many of the engine technologies now employed in road vehicle engines

effectively came from aviation via racing

Twin-spark ignition

Double overhead cams (DOHC)

Four valves per cylinder (4vpc)

Supercharging (then turbocharging)

High octane fuels

Direct injection (DI)

Water injection (‘ADI’)

1923 Halford

Special Engine4vpc, DOHC 6-cylinder

The first turbocharged

car engine

Major Frank Halford designed all of de Havilland’s

engines and all of the Napier H-engines, as well as being

fundamental in the successful development of the gas

turbine (with ‘straight-through’ combustion chambers)

Major Halford was

President of the

RAeS in 1951

Automotive Engines are Architecturally-Frozen Aero Engines…

It could be argued that the template for the modern

automotive engine was actually laid down by Napier in

1916 with the Lion

4vpc, DOHC, narrow valve angle and a single cam cover

101 years old

Then general automotive engineering followed aero

engine technology after a 10-20 year delay…

However, in the 1940s/50s the gas turbine

comprehensively broke this delayed take-up link

…And the automotive industry never adopted the

sleeve valve as a result

Consequently the modern automotive engine shares

much in common with the Rolls-Royce Merlin, Daimler-

Benz 601 and Allison V-1710

Effectively it’s architecturally frozen at 85 years old

Napier Lion

Potential Transfer of Automotive Technology Back to Aviation

It has been attempted to use an automotive

engine in light aviation before – the Porsche

Flugmotor PFM 3200

Development started in 1981

212-241 bhp

Modern downsized, boosted, DI automotive

engines are light, reliable and fuel efficient, and

their control systems may well be more reliable

than current light aircraft avionics

Due to on-board diagnostics requirements

There are now several all-aluminium 2.0 litre DI

engines which deliver 200-350 bhp

Is this an option worth persuing?

This would be going full circle on engines…

UK Transport Energy Consumption by Mode, 1970-2014

Taken from: Energy Consumption in the UK (2015), DECC

Road

Rail

Water

Air

Air transport represents a particular problem:

How do you fully decarbonize an aircraft?

Change in UK Transport Energy Consumption, 1970-2014

Road

Rail

Water

Air

Taken from: Energy Consumption in the UK (2015), DECC

Air

: +

320

%

Long-range aircraft present a significant problem

Even hybrid aircraft propulsion systems can only

reduce CO2 while there is fossil carbon in the fuel

UK Road Transport Energy by Type of Vehicle, 1970-2014

LGVs

Buses

HGVs

Cars

Motorcycles

Taken from: Energy Consumption in the UK (2015), DECC

2008: Beginning of

EU CO2 legislationSimple: let’s just electrify the private road transportation fleet

Consumption of road transport is ‘only’ 40 Mtoe…

1 Mtoe = 41.87 PJ (41.87 x 1015 J)…

This is a continuous output of 1.33 GW over a year –

more than a good-sized nuclear power station (~ 1 GW)

UK Transport Energy Consumption by Mode, 2014

Taken from: Energy Consumption in the UK (2015), DECC

53 x 1 GW nuclear

power stations

17 x 1 GW nuclear

power stations

16.5 Hinkley Point Cs

5.3 Hinkley Point Cs

For perspective, in 2014 the average UK

electrical power demand was 34.4 GW

(or only half the total transport demand)

Peak demand in 2015 was 52.7 GW

To date, the only practical energy

system for transport has been fossil oil

The total design power of the two

Hinkley Point C reactors is 3.2 GW

Which, because we have developed fuel

supply together with transportation, has

developed symbiotically with it

By my reckoning, we pump oil at a rate

of 7.4% of the flow of Niagara Falls…

Long-Range Aircraft Battery Sizing Calculation

At take-off, a Boeing 787-9 has 50.7 tonnes of fuel on board for a 9000 km flight

This is 605 MWh of energy (2.18 x 106 MJ)

To convert to electric propulsion, we should allow an approximate factor of two

to allow for increased electric machine efficiency versus thermal engines

Implies energy at take-off for the electric version is 302.5 MWh (1.09 x 106 MJ)

• Or 3000 Tesla Model S P100D batteries (which are 700 kg each…)

Using 150-250 Wh/kg as a cell energy density, this gives a battery mass of

1210-2017 tonnes (cell level)

Current 787-9 fully-laden take-off

weight is 253 tonnes

Battery will be 5-8 times heavier

At 1.4 MW it would take 216 hours

(9 days) to fully charge it…

Calculation courtesy of

Dr Richard Pearson, BP

Plainly, this isn’t going to work!

0

5

10

15

20

25

30

0 5 10 15 20 25 30 35 40

Net gravimetric energy density / [MJ/kg]

Ne

t vo

lum

etr

ic e

ne

rgy d

en

sity / [M

J/l]

Gasoline

Diesel/Kerosene

E85

Ethanol

M85

Methanol

Liquid H2

700 bar H2

200 bar Methane

Batteries

On-Board Energy Density: Batteries v Everything…

Courtesy Lotus Engineering

Compared to liquid fuels batteries don’t really get off the origin…

This makes them really expensive and heavy

HTA

aviation

really

needs to

be hereRoad

transport

could

happily

live here

H2 is hardly

better than

batteries

Rider: at

automotive

scale Densities:

Liquid (cryogenic) H2 =

70.8 kg/m3

Kerosene (jet fuel) =

840 kg/m3

(or 11.8 times greater)

How do you Decarbonize Aviation?

Hydrogen Uranium Oxide

Ammonia (NH3) and

Hydrazine (N2H4) have also

been researched, as has…

NERVA Nuclear

Rocket Engine

General Electric

X211 turbojet:

nuclear core (!)

Requirement to

carry significant

energy makes

liquid hydrogen

viable here

Carbon-Neutral Ammonia

82% of power to

electrolysis

32.7% efficient

in terms of HHV

Allison PD-81 Ammonia

Research Engine

What could

possibly go

wrong?

Taken from RRHT Allison Branch

Newsletter, November 2011

Battlefield

Mobile

Compact

Reactor

Can Hydrogen Work? (1)

Liquid hydrogen has historically been investgated by the Lockheed Skunk

Works and Pratt & Whitney – Project ‘Suntan’

Hydrogen was considered attractive because of its high lower heating value and

the fact that a lot of energy would have to be carried

Suntan performed preliminary design work and P&W built a liquid H2 engine

The 304

But the idea was dropped because of the problem

of difficulties in hydrogen storage

The concept was rescoped and

became the SR-71

Pratt & Whitney 304

‘Suntan’ engine Taken from: “Advanced

Engine Development at

Pratt & Whitney” by

Mulready, R.C.

Can Hydrogen Work? (2)

Recently the EU-funded ‘Cryoplane’ project investigated the use of liquid

hydrogen to fuel long-range passenger aircraft

Combustion tests using hydrogen were conducted to establish engine control limits

Investigations into global warming potential were conducted

H2 was found to significantly better than kerosene

Water is a greenhouse gas too, but if the hydrogen cycle is closed then this is not

an issue – as long as ‘green’ hydrogen from e.g. electrolysis is used

Unfortunately the requirement for a

particular shape of tank – torospherical –

meant that the concept was not viable

There is also the need to derive lift from

the fuel energy in heavier-than-air aircraft

For the 787-9: 2.18 x 106 MJ = 18 tonnes of H2

Which occupies 254.2 m3

c.f. 60.4 m3 of kerosene – 4.2 times greater Cryoplane

Note impact of large

torospherical tanks

ZELTA

If the requirement for high-speed aerodynamic efficiency and the need to carry

the energy to generate lift can be removed, an interesting possibility arises…

– Zero Emission Lighter-Than-Air

A preliminary design study has been conducted at the University of Bath

Suggests that a 100-tonne payload, 100 knot airship with sufficient range to fly

from Cardington to San Francisco could be built and fuelled using liquid hydrogen

Note: helium would be the lifting gas, not hydrogen!

Exhaust ballast recovery and fuel cells to generate electricity and supply potable

water would also be incorporated

ZELTA

Richardson, A., ‘Study of design factors for rigid airships for long-

range, high-payload operation with zero in use carbon emissions’

LH2 Tank

Returning to the Actual Problem…

The real problem with transport is that we operate the vehicles on fossil fuels

Economically-affordable engines do not have to use such fuels: both Diesel and

Ford made their engines run on biofuels – we then made them run on fossil fuels

instead

But there is no shortage of carbon-free energy

We just need to find a means to convert it to a form usable in existing vehicles

Solving the Problem…

A pragmatic solution would be to use renewable

energy to synthesize drop-in alternatives to the

fuels we use now

These are known as ‘Carbon-Neutral Liquid Fuels’,

‘Electrofuels’ or ‘Synthetic Fuels’

Solving the Problem: the Sustainable Methanol-Based Cycle

electrolysis of water:

222O

2

1HOH +

Energy inHydrogen from

Carbon out

Synthetic

and productshydrocarbons

Carbon in2CO from fossil

fuel burningpower plants

Methanol synthesis:

OHOHHC3HCO 2322 ++

CO2 consumption

Atmospheric 2CO

CO2 emission

Fuel use:

23 O2

3OHCH +

OH2CO 22 +

Adapted from Olah et al., The Methanol Economy

Direct air

capture

of CO2

From Lackner, K.,‘Options for

Capturing Carbon Dioxide

from the Air’, May 2008

Gasoline, diesel and kerosene

can also be synthesized from

these feed stocks – with an

energy penalty (c. 8% point)Adapted from Olah et al.,

‘The Methanol Economy’

Courtesy Lotus Engineering

Feed stocks are water, air

and renewable energy

The price of these feed

stocks is free and a high-

value product is made

Provides the economic

driver to decarbonize and

a valuable buffer for

renewable energy

Available Upstream Energy…

Source: Dr Wolfgang Warnecke, Shell,

SAE PF&L, Baltimore, USA, October 2016

Available Upstream Energy…

The average solar load in deserts is 1000 W/m2

Therefore, assuming 20% solar panel efficiency, 12 hour days, and 50% land

area utilization, it would take 16000 km2 (a square of 127 km sides) to power

the entire European road transport fleet (400 GW)

This is only <0.2% of the area of the Sahara

25

30

35

40

45

50

55

60

0 100 200 300 400 500 600 700 800 900 1000

Energy for CO2 extraction / [kJ/kmol CO2]

Ele

ctr

icity-t

o-t

an

k e

ffic

iency /

[%

]

Thermodynamic limit is 20 kJ/mol CO2

‘A Gas Tank in the Sky’

CO2 is being extracted from the atmosphere now

In space ships and submarines

Done to provide a breathable atmosphere aboard

Values achieved in

practice to date

Using demonstrated performance, it is

possible to synthesize methanol at 45%

process efficiency (based on the HHV)

The biggest energy input – 80% – is the

electrolysis of water to get the hydrogen

needed

The other 20% is the CO2 extraction and

overhead to make hydrogen storable

UK DfT has consulted on synthetic fuels (and

continue to do so)

California ARB has just published draft standards

Example of Direct Air Capture: Climeworks

Climeworks, a spin-out from ETH Zurich, is one company that has built and is

operating functioning ‘direct air capture’ CO2 extraction equipment already

It has set itself the goal of capturing 1% of global CO2 emissions by 2025

Has a 50 tonne p.a. DAC plant operating at the moment

Is now building a 900 t.p.a. commercial plant to open next year

900 t.p.a. is equivalent to the CO2 produced by 40 people or 150 cars

The CO2 will be sold to food companies but the aim is to close the fuel cycle

Is already in partnership with Audi

So Who Is Actually Doing This?...

Many researchers are showing the feasibility of the approach, among them:

George Olah’s group at University of Southern California

Direct conversion of atmospheric-concentration CO2 to methanol with virtually no

catalyst degradation, at 79% conversion rate

Harvard University group showing the ‘Bionic Leaf’

UC Berkeley with their ‘Solar-to-Fuel’ system

The EU are funding the ‘Sun-to-Liquid’ project to decarbonize aviation

The project will be making aviation-grade kerosene directly from CO2, water and

solar thermal energy in a pilot plant using thermolysis driven by a heliostat

Sunfire with Climeworks – building a full synthesis system in Norway

DAC of CO2 in a commercial pilot plant using hydroelectricity to make 10,000 litres

/year of ‘blue crude’ to go into conventional petroleum refineries

Sunfire, like Climeworks, also have a relationship with Audi

The University of Bath – in the initial stages of feasibility project for gasoline

Illustrations courtesy of the

Institution of Mechanical Engineers

…And What Might These Plants Look Like?

Concluding Remarks

Aviation and automotive engineering are closely linked historically

Especially in the area of light aircraft

Modern automotive engine fuel-consumption technology could be applied to

aviation to reduce CO2 output from light aircraft

Could also use proven three-way catalysis to improve gaseous emissions

Long-range aircraft present a significant problem

The most practical way to use hydrogen might be to use it for propulsion in

airships… Not as a lifting gas!

However, for practical applications, the fuel itself needs to be decarbonized

This is really the only way to fully eliminate CO2 emissions from aviation

The technology exists to do this now

This would provide a means to monetize the direct air capture of CO2

The technology of electrofuels could then migrate to fuels for surface transport

Making it a disruptive technology for electric vehicles

THANK YOU FOR LISTENING

For further information on Direct Air Capture of CO2 and Electrofuels see also:

http://loker.usc.edu/methanolecon.html

http://www.climeworks.com/

http://www.sun-to-liquid.eu/

http://www.sunfire.de/en/company/press/detail/first-commercial-plant-for-the-

production-of-blue-crude-planned-in-norway

https://www.arb.ca.gov/fuels/lcfs/lcfs.htm