COMMENTARYWhile aviation diesels have low
specific fuel consumption (sfc), the
problem with them has been their
power and weight. They have not been
powerful enough for use in larger,
higher-performance general aviation
(GA) aircraft. And power-to-weight
ratio has been too low for them to be
usable in light helicopters.
This is changing, with ground tests
now underway of a new aviation diesel
replacing the turboshaft engine in
an Airbus Helicopters EC120 (see
photo). Flight tests of the HIPE AE440
high-compression engine (HCE) are
to begin by mid-year under Europe’s
Clean Sky research program. The
turbocharged V8 has been developed
by aviation-diesel producer Austro En-
gine and race-car engine maker TEOS
Powertrain Engineering.
A
viation gasoline has been the fuel of choice for lighter air-
craft for decades, but with leaded avgas becoming hardto find in some regions and environmentally unacceptable in
others, diesel-cycle engines burning jet fuel are gaining ground.
Fueling Change
Race-car technology brings high
power-to-weight diesel to aviation
Clean Sky is a €1.6 billion ($1.69
billion) public-private partnership
under which European Union research
funding is matched by industry and
other participants. Led by Airbus He-
licopters, the HCE program is one of
the major technology demonstrations
under the Green Rotorcraft project
within Clean Sky, which began in 2007
and runs to 2017.
Based in Austria, Austro already
is planning production of the 330-kw
(440 hp) AE440 for the fixed-wing
market, to meet demand for a jet-fuel
engine with higher power and lower
fuel consumption than ofered by its
in-production 125-kw AE300 diesel.
The light helicopter market may take
longer to penetrate, but a competitive
diesel-cycle engine could yet breathe
new life into the sector.Clean Sky’s goal is to demonstrate
reductions of 30% in sfc, 40% in
carbon-dioxide and 50% in nitrogen-
oxide emissions in the EC120’s turbine
engine. A 30% reduction in direct
operating cost and a doubling of range
with the same fuel are also targets.
The AE440 has a weight-to-power
ratio of 0.8 kg/kw (1.3 lb./hp) and a fuel
consumption of 235 g/kwh (0.386 lb./
hp-hr.) at takeof power.
The keys to the AE440’s perfor-
mance are its aluminum construc-
tion and fuel injection, both of which
come from the automotive industry.
Austro’s four-cylinder AE300 is based
on a Mercedes diesel and is a cast
steel engine. The AE440 is an all-new
engine made of lightweight, machined
aluminum. In production, this will be
changed to less costly but still lighter
cast aluminum, as used in race cars.
Common-rail direct fuel injection
operating at a 1,800 bar (26,000 psi)
provides precise injection of less fuel
at higher pressure for improved atomi-
zation and combustion, and reduced
fuel consumption. Two high-pressure
fuel rails feed individual injector valves
digitally controlled by the engine man-
agement system.
To enable it to directly replace the
faster-turning Turbomeca Arrius
turboshaft in the EC120 testbed, the
AE440 has a multiplier gearbox so it
can drive the rotors via the existing
transmission. For fixed-wing applica-
tions, the engine will drive the propel-
ler via a reduction gearbox.
With €9.3 million ($9.9 million) in
funding under Clean Sky, the research
program has not been without its chal-
lenges. Austro and TEOS have built
five engines and completed 300 hr. of
tests so far. Component failures have
caused delays, which is not unusual
in engine development. This and the
recent decision to add 100 hr. of flight
testing have stretched the program to
47 from 39 months.
But the AE440 is Austro’s first
clean-sheet engine, and the company
acknowledges that without Clean Sky
it would not have taken on develop-
ment of a powerplant that could be the
breakthrough needed to bring fuel-
efcient, low-emission aviation diesels
to a wider market. cLeading Edge
24 AVIATION WEEK & SPACE TECHNOLOGY/MARCH 30-APRIL 12, 2015 AviationWeek.com/awst
By Graham WarwickManaging Editor-Technology
Graham Warwick blogs at:
AviationWeek.com
[email protected]CLEAN SKY