A REVOLUTIONARY jet engine was unveiled at a Tokyo aerospace show last week.
Designed to power a new generation of commercial aircraft that will fly at five
times the speed of sound, the Hypersonic Transport Propulsion System (HYPR) is
the brainchild of Japan鈥檚 New Energy and Industrial Technology Development
Organization (NEDO), a branch of the Ministry of International Trade and
Industry.
The heavy industry divisions of Kawasaki, Mitsubishi and Ishikawajima-Harima
have teamed up to develop the engine, which is made up of two types of jet
engine mounted end to end: a turbojet in front and a ramjet at the back
(see Diagram).
At speeds under Mach 3, an aircraft鈥攁s yet
undesigned鈥攚ould be propelled by the turbojet. To provide the extra thrust
needed for higher speeds, the ramjet would kick in and gradually take over. An
ingenious network of ducts and valves handles the transition from turbojet to
ramjet mode.
In a turbojet engine, a turbine-driven fan draws in air, compresses it, and
pushes it through into a combustion chamber where fuel is injected and ignited
to produce a hot high-speed exhaust that creates thrust. A ramjet, however, has
no moving parts: the forward movement of the aircraft is enough to force air
into the chamber where fuel is ignited, producing the exhaust that creates the
thrust.
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Getting the two engines to work in tandem and designing materials to cope
with high engine temperatures were the main difficulties confronting the design
engineers. During tests, temperatures in the HYPR engine reached 1700 掳C
when simulating flight at Mach 3. Engines in subsonic planes don鈥檛 get any
hotter than 1500 掳C. When flying at its intended speed of Mach 5, the engine
will have to cope with temperatures of 1900 掳C.
The HYPR project began ten years ago as part of a long-term effort to build a
commercial passenger jet capable of flying from Tokyo to New York in just three
hours, at an altitude of 20 000 metres. 鈥淲e don鈥檛 know when that plane will be
built,鈥� confesses Mitsubishi Heavy Industries engineer Akihiro Tobita. 鈥淚t will
take a lot of international cooperation.鈥�
Foreign companies, including Rolls-Royce from Britain and General Electric
and United Technologies from the US, are already providing technical expertise
for the HYPR project. A spokesperson for Rolls-Royce confirms that it is taking
part in research for the programme, alongside United Technologies and the French
engine maker Snecma.
NEDO says that the HYPR engine could be quieter and less polluting than
conventional jet engines. Its next goal is to further reduce noise and pollution
in the engine and increase its energy efficiency, as well as doing the
groundwork for the body of the plane itself.