Ethanol as Aviation Fuel

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Ethanol as an Aviation Fuel

Technical Brochure No.51

BIOMASS

w Ethanol from biomass

w High octane replacement

for avgas

w Cooler, cleaner-burning fuel

w Less engine wear

HighlightsSummary

Aviation gasoline (avgas), the only

leaded fuel remaining in the United

States transportation fuel market, isto be phased out by mandate of the

1990 Clean Air Act Amendments

(CAAA). Baylor University in

Waco, Texas has set out to

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demonstrate that pure denatured

ethanol represents a viable, high-

octane alternative fuel in the field

of aviation.

Baylors Renewable Aviation Fuels

Development Center (RAFDC)

participates in airshows in the

United States and abroad to

Modified Pitts S2B flying over corn at an airshow.


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promote the fuels superior power

delivery, clean burning properties,

octane levels, costs and reliability.

Ethanol is usually produced from

corn; however, at some of the air

shows, ethanol has been sourcedfrom manufacturers who produce it

from other renewable biomass

resources such as orange waste or

sugar beets (see Table 1).

Project Background

The United States currently

consumes over 1,000 million litres

of avgas each year. Now that lead

has been phased out of othertransportation fuels, avgas has

become the countrys single

biggest contributor of lead to the

atmosphere. Although avgas has

been temporarily excused from

CAAA regulations, it is understood

throughout the US aviation

industry that the use of avgas in its

current form will soon be

discontinued.

Oxygenated alcohol fuels such as

ethanol meet the emission reduction

standards set by the CAAA. Ethanol

is cleaner and cooler in use than

avgas, prolongs engine life, delivers

more power, and is likely to present

a much cheaper option as supplies

become more readily available.

Ethanol has an oxidising effect on

aluminium, so corrosion inhibitors

are added to the fuel.

Ethanol supporters still must answer

those who make issue of the lower

energy content of the fuel and the

fact that engines must be modified

in order to use ethanol. Even so,

ethanol is poised to make a

significant impact in fleet transport,

especially in view of the CAAA

requirements that apply to vehicle

fleet operations in 22 non-attainment cities.

Work at the RAFDC involves

certification of engines and

airframes for ethanol use. To date,

the Center has certified two series of

Lycoming engines (one fuel injected

and one carburetted) and both the

engine and airframe of a Cessna 152

the worlds most commonly used

trainer. The Center has logged morethan 4,000 flight hours in nine

ethanol-powered aircraft.

The RAFDC is also evaluating

ethyl-tertiary-butyl-ether (ETBE) as

an aviation fuel. Preliminary

dynamometer tests are very

promising. An aircraft using ETBE

has performed at the worlds largest

airshow in Paris.

The Project

The RAFDCs ethanol-powered

aeroplanes were featured in

15 demonstrations during 1996.

During these events, information

was distributed and assistance

was given to pilots seeking more

information about converting

their aircraft to ethanol.

Up to $3,000 may have to be

spent to modify a Cessna 152 to

be able to use ethanol (where $ is

the US dollar). The Cessna was

fitted with a bigger carburettor jet,

a fuel pump, a fuel-flow meter and

a totaliser. A small avgas tank was

added to enable the engine to be

primed in temperatures below

210C. However, not all engines are

expected to need this level ofmodification.

The RAFDC is also certifying

agricultural aircraft, such as the

Piper Pawnee. The Centers

concentration on fleet aircraft

avoids initial fuel distribution

problems, since these planes are

commonly refuelled at fleet sites

where the correct refuelling can be

guaranteed. An ethanol

distribution system is presently

being implemented through the

US Department of Energys Clean

Airport Program.

Performance

A minor drawback of the use of

ethanol fuel is the slightly reduced

Table 1: Variety of biomass sources used at different

demonstration locations

Demonstration Location Biomass Source

Idaho, USA Potato waste

California, USA Waste oranges

Wisconsin, USA Waste cheese whey

Brazil Sugar cane

France Sugar beet

Italy Sugar beet


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range. A litre of ethanol produces

about two-thirds the heat of a litre

of avgas. However, the effect of

range loss is reduced by the

higher thermodynamic efficiency

of ethanol. A Cessna 152 fittedwith a Lycoming 235N2C engine

uses about 13.8 litres/100 km on

avgas and 15.7 litres/100 km on

ethanol.

The high octane level of ethanol

allows the use of higher

compression ratio engines that

deliver more power for the same

throttle setting. The lower Reid

vapour pressure of ethanol helps toprevent vapour locking. Ethanol is

cooler and cleaner in use than avgas

and is more resistant to detonation,

resulting in fewer vibrations and

longer engine life.

Economics

Americas farmers currently

produce 20 million m3 of corn per

year, about 6% of the total crop,

for use in ethanol production.

Increased use of ethanol in aviation

will also help to expand markets

for agricultural producers who

cultivate cellulosic energy crops,

an alternative category of biomass

from which the fuel can also be

made.

Ethanol has a tax advantage. Avgas

is taxed at $0.048/litre whilst

ethanol receives a tax advantage of

$0.14/litre. Avgas costs $0.53/litre

on average whilst ethanol costs

$0.34 to 0.37/litre. The US ethanol

industry provides 55,000 jobs and

$15.6 billion/year in net farm

income.

Avgas is slightly cheaper on a per-

kilometre basis than ethanol, but the

lower maintenance costs associated

with the use of ethanol ultimately

make it a cheaper fuel option for

pilots. Supporters of ethanol point

to the prospects of increased avgas

costs due to the need for an additive

that provides an adequate octane

level. They predict that ethanol

production costs will drop as the

base of sustainable biomass

feedstocks is expanded and

researchers discover new ways to

optimise its production.

Technical Brochure No.51

Farm show at Redwood Falls, Minnesota.

Table 2: Fuel consumption at various horsepower reference

points for a Lycoming IO- 540 D4A5 engine with a 10:1

compression ratio

Horsepower Avgas Ethanol % Increase in

(l/hr) (l/hr) Fuel

Consumption

180 77.2 85.2 10

210 73.1 95.4 18225 78.0 89.3 15

238 82.5 91.6 11

270 102.2 119.2 17

300 107.9 128.7 19

Note: Avgas delivered a maximum 300 hp with this engine, while ethanol delivered a

maximum 316 hp. In a Lycoming 0-235 engine running on ethanol, the RAFDC has

noted a horsepower increase of as much as 20% over avgas. When using ethanol-

based ETBE as an alternative fuel, fuel consumption is 5% lower than avgas at

225 hp, the most common power setting for cross-country flight.


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IEA

OECD

CADDET Centre for Renewable Energy

ETSU, Harwell

Oxfordshire OX11 0RA

United Kingdom

Tel: +44 1235 432719

Fax: +44 1235 433595E-mail: [email protected]

International Energy Agency

The International Energy Agency (IEA) is an

autonomous body which was established in 1974 within

the framework of the Organisation for Economic

Co-operation and Development (OECD) to implement

an international energy programme.

CADDET

CADDET was set up in 1988 as an IEA Centre for the

Analysis and Dissemination of Demonstrated Energy

Technologies. Today, there are two CADDET

operations: one is for energy-efficient technologies and

the other for renewable energy technologies. The

Centres co-operate with member countries in the

exchange of high quality information on energy

technologies.

Disclaimer

Neither CADDET, nor any person acting on their

behalf:

(a) makes any warranty or representation, expressed or

implied, with respect to the information contained in

this brochure; or

(b) assumes any liabilities with respect to the use of this

information.

US 97 504 First printed 1997

Printed on environmentally friendly paper.

Please write to the address below if you require more information.

Project Organisation

Baylor UniversityDepartment of Aviation SciencesRenewable Aviation FuelsDevelopment Center

700 S. University Parks Dr, Ste. 240Waco, Texas 76706,USAContact: Grazia Zanin/Max ShauckTel: +1 817 755 3563Fax: +1 817 755 3560E-mail: [email protected]

[email protected]

Information Organisation

National Renewable Energy Laboratory1617 Cole BoulevardGolden, Colorado 80401-3393, USAContact: David WarnerTel: +1 303 275 4373

Fax: +1303 275 3619E-mail: [email protected]

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Ethanol as Aviation Fuel