posted on Jun, 20 2004 @ 07:51 PM
DETONATION WAVE ENGINES
One option for a hypersonic vehicle might be four or six Pulse Detonation
Wave Engines (PDWEs), fuelled with liquid methane. As air breathers,
these PDWEs could theoretically propel a hypersonic aircraft towards
Mach 10 at an altitude in excess of 180,000 feet.
Used to power an trans-atmospheric vehicle, the same PDWEs might
be capable of lifting the craft to the edge of space when switched
to rocket mode.
Current theoretical operation of a PDWE
Liquid methane or liquid hydrogen is ejected onto the fuselage,
where the fuel mist is ignited, possibly by surface heating. The
PDWE works by creating a liquid hydrogen detonation inside a specially
designed chamber when the aircraft is traveling beyond the speed
of sound. When traveling at such speeds, a thrust wall (the aircraft
is traveling so fast that molecules in the air are rapidly pushed
aside near the nose of the aircraft which in essence becomes a wall)
is created in front of the aircraft. When the detonation takes place,
the airplane's thrust wall is pushed forward. This process is continually
repeated to propel the aircraft. From the ground the jet stream
looks like "donuts-on-a-rope."
Quoted below is a small description of how a PDWE would accelerate
a vehicle towards the hypersonic regime.
"...use a shock wave created in a detonation - an explosion that
propagates supersonically- to compress a fuel-oxidizer mixture prior
to combustion, similar to supersonic inlets that make use of external
and internal shock wave for pressurization."
Not much is known about Pulse Detonation Wave technology, but
there have been quite a few reports and sightings of mysterious
aircraft using propulsion technology unlike any heard or seen before.
On February 25, 26, and 27, 1992, there were night-time sightings
of an unknown aircraft with a "diamond-pattern" of lights at Beale
Air Force Base, which was thought to be the Aurora aircraft. The
aircraft had a distinctive engine noise, described as "a very, very
low rumble, like air rushing through a big tube." On the night of
February 26, what was thought to be a ground test of Aurora's propulsion
systems took place. A series of "booms" was heard and described
as similiar to "artillery fire" and "deep bass notes, not like sonic
booms." It was thought these were "light-off" tests of the engines.
It was speculated that the aircraft was using Pulse Detonation Wave
Engines. The noise and low frequency would, it was said, be consistent
with PDWE technology.
It has also been noted that despite the famous "Donuts-on-a-rope"
air contrails not being consistent with Aurora's propulsion system,
theses contrails can be produced by a PDWE operating outside of
its specified parameters.
Interpreting known information
Although the observations recorded of vehicles with an unusual
trailing contrail and noise are intriguing, they are also difficult
to reconcile with one another. While many observers agree on the
unusual sounds created by these vehicles, a range of descriptions
are provided as to the nature of these sounds. The pulsating tone
emanating from these sightings has been taken as an indication of
the use of some form of pulse detonation wave engine. Some observers
report a characteristic frequency as high as 60 Hertz, while others
suggest a frequency as low as 1 Hertz.
But a technical analysis of pulse detonation wave engines suggests
that engines operating at the thrust levels associated with military
aircraft would operate between 100 and 200 Hertz (pulses per second).
While doppler shifting may reconcile this value with the reported
50-60 Hertz pulsation, it is more difficult to reconcile this with
the reports of a 1 Hertz pulsation.
It is also difficult to reconcile a pulse rate of 100-200 Hertz
with the observed donut-on-a-rope contrails. The association of
these contrails with a PDWE would seem to be predicated on the observation
that each "donut" is a product of a single pulse detonation. Based
on published photographs, the "donuts" appear to be approximately
100 meters apart. Assuming a detonation pulse rate of 100 Hertz,
this would imply a velocity of 10 kilometers per second, roughly
Mach 36 which is 1½ times orbital velocity. While it is asserted
that the Aurora spyplane is a high-speed vehicle, this is at least
four times faster than the speeds normally associated with this
In addition, a closer examination of the published photographs
reveals a significant irregularity in the spacing between the donuts
on the rope. This would seem to be inconsistent with the normal
functioning of a pulse detonation wave engine.
(reprinted with permission)