Pulse Detonation Wave Engines

PULSE 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 aircraft. 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)

damn i knew that the US government had advanced aircrafts but one that goes mach 36. wow!

Mach 36, what a load of crap, that's above orbital speed, it would have to be made of unobtanium to survive that, yes they're developing PDE's, both in the white world and black world, but i've yet to see compelling evidence that these contrails are anything but conventional aircraft, i've seen puffy type contrails from commercial airliners before, its high altitude wind action.

Quite a bit of research and devleopment has been done with the PDE. The PDE pulse detonation engine and the "pulse jet" differ in how the fuel is ignited. With a PDE the fuel undergoes supersonic detonation, with a pulse jet it does not.

I ran across this link just now of research being conducted by Caltech on PDE propulsion at their Explosives Dynamic Laboratory or EDL. The site has some great images and even has filtered images showing the actual shockwave the detonation creates as well as a PDE in testing..
www.galcit.caltech.edu...

If this is all going on and being posted on a public sight it isn't too hard to imagine the government spending X amount of dollars for secret R&D of their own using black budget dollars. For all we know some aircraft already have this capability.

A while back I started a thread about a video I found on youtube of what some called proof of pulse detonation. It is a very specific contrail in the distance which very well could be proof of a PDE "technology demonstrator" in use by the military. But, honestly, they very well could be past that phase in the production of aircraft designed to use such technology we just don't know. Here's the link:
www.abovetopsecret.com...

Most of the generation 5 aircraft we have in the current inventory are extremely advanced but most of the research and development that has gone into stealth was done back in the sixties and seventies. There has been leaps and bounds in technology since then so it isn't so far fetched to imagine some pretty remarkable aircraft undergoing testing right now.

-ChriS

[edit on 26-5-2008 by BlasteR]

Originally posted by WestPoint23
damn i knew that the US government had advanced aircrafts but one that goes mach 36. wow!

The US has no advanced "aircraft" doing Mach 36 (Escape Velocity). That's a pipe dream, fantasy, sci fi...
Tech Demos doing Mach 5 to 8 on the other hand....
Quite plausible...

Demos doing Mach 5 to 8!

Sr 71's did Mach 3.2+ with 1950's technology. Did we only double that speed in the last half century?

Originally posted by MBF
Demos doing Mach 5 to 8!

Sr 71's did Mach 3.2+ with 1950's technology. Did we only double that speed in the last half century?

The keyword here is "aircraft'... an air breathing hypersonic USAF project


[edit on 5-27-2008 by intelgurl]

reply to post by intelgurl


That is what I meant. I kind of find it hard to believe that speed advancements were increasing at fairly rapid intervals and then all of a sudden only increase at a snails pace. I know that there are problems associated with going at those speeds, but I feel they could have worked most of them out in the last 50 years.

Originally posted by intelgurl
The US has no advanced "aircraft" doing Mach 36 (Escape Velocity). That's a pipe dream, fantasy, sci fi...
Tech Demos doing Mach 5 to 8 on the other hand....

Quite plausible...

Did we not have experimental aircraft (i.e. technology demonstrators) doing those speeds 40-50 years ago?

users.dbscorp.net...

-ChriS



[edit on 27-5-2008 by BlasteR]

[edit on 27-5-2008 by BlasteR]

Originally posted by BlasteR

Did we not have experimental aircraft (i.e. technology demonstrators) doing those speeds 40-50 years ago?

users.dbscorp.net...

-ChriS

X-15's were rocketplanes; rocketplanes are not "airbreathing aircraft", which is what I qualified my initial statement with.

The whole reason air-breathing aircraft have `stalled` at *only* mach 3 is physics , firstly the sr-71 uses a turbojet engine

www.sr-71.org...

very nice picture(s) especially of the moveable inlet cone , which is the crux of the speed limitation - the air coming into the engine has to be slowed down from mach3 to subsonic

Wouldn't PDE tech be more suited to sub-orbital recon vehicles and weapons platforms? Also I thought the term "Aurora" was used to umbrella many different programs within the black budget aerospace realm?

[edit on 27-5-2008 by djvexd]

Absolutely. Some PDE engines are being designed exclusively as rocket engines as well.
www.daviddarling.info...
Marshall Space Flight Cener is currently experimenting with rocket propulsion designs since a PDE application would create all kinds of new low-cost launch vehicles.

Is Air-breathing really even accurate when describing PDE's? It is largely a closed system in which the primary chamber, consisting of the fuel/air mixture, is ignited by a shockwave from a secondary chamber in which the pressures are vented through using a DDT or Deflagration to Detonation Transition. The DDT is basically a specifically designed tube used to introduce the shockwave it produces to the primary combustion chamber. Air is constantly being introduced into the cycle but not a whole lot is required. Wouldn't most of the air passing through the engine simply pass through while small amounts are being cycled through?

It's a completely different concept than what traditional air-breathing aircraft have done in the past..

-ChriS

reply to post by BlasteR


If your arguing simplicity then the ramjet would be even more so then the PDE systems. I don't fully get why a system that requires air wouldn't be classified as air breathing.

The typical PDE that most of us think of when we say PDE is an air-breathing engine. It takes air in the front, mixes in fuel, then burns it via a detonation instead of the more normal deflagration. Now, there's nothing saying that you can't carry your oxidizer onboard and inject it and the fuel into the combustion chamber, and in that case your PDE would not be air-breathing. It's even possible to envision a combination of the two, i.e. taking in oxidizer from the atmosphere at low altitudes and using an onboard supply at high altitudes or in space. The OP hints at this with the "when switched to rocket mode" comment.

Anyway the key point is the type of combustion (detonation versus deflagration) is what defines a PDE, and not where it gets the oxidizer from.

I'm just saying that it uses air in small amounts at a time for each detonation. Not exactly what we are used to with the more traditional "air-breathing" engines from years gone past. But I get what you are saying too. Technically, since it uses an air-fuel mixture it is an air-breathing engine. But a large majority of the air simply passes through the system. That's all I'm really saying.

The term "breathing", to me, implies inhalation and exhalation of air. The resulting shockwave is what is expelled, but would any air even be left to exhale after it is detonated within the chamber?

-ChriS

Realistically it makes no sense to use these engines below 60kft. Once SO then the contrail would be barely visible if visible at all. Only thing i can think of is if this vehicle is an attack vehicle and needed to get to speed quickly.

[edit on 27-5-2008 by djvexd]

Originally posted by BlasteR
Is Air-breathing really even accurate when describing PDE's? gh?

It's a completely different concept than what traditional air-breathing aircraft have done in the past..

-ChriS

"Air-breathing" is not an accurate term when describing rocket PDE's. Generally rockets bring their own oxidizer unless it is some kind of hybrid system that can breathe air from the atmosphere, but that would not be as efficient as the oxygen levels would not be as measured and precise.

I know that Pratt & Whitney has done and may still be doing PDE projects out at China Lake, I know nothing of what those projects are though.

What do you think of the shutter system vs the valved system. From what I understand a general electric prototype uses neither, but rather the pressure lows between detonations to maximize efficiency rather than having valves or shutters which would require all kinds of maintenance.

en.wikipedia.org...

In some PDE designs from General Electric, the shutters are even removed because the process can be controlled by timing on the periodic sudden pressure drops that occur after each shock wave when the "combustion" products have been ejected in one shot.

This article must have been edited sometime in the last few months because I've never heard of this before either:

DDTs occur far more readily if there are obstacles in the tube. The most widely used is the "Shchelkin spiral", which is designed to create the most useful eddies with the least resistance to the moving fuel/air/exhaust mixture. The eddies lead to the flame separating into multiple fronts, some of which go backwards and collide with other fronts, and then accelerate into fronts ahead of them.

I find this stuff fascinating!

-ChriS

Originally posted by BlasteR
What do you think of the shutter system vs the valved system. From what I understand a general electric prototype uses neither, but rather the pressure lows between detonations to maximize efficiency rather than having valves or shutters which would require all kinds of maintenance.

-ChriS

The GE type that uses neither the shutter nor the valve has fewer moving parts therefore it would be the most economically sound as long as the technique of transition is perfected. I agree, good stuff you're digging up.