The Naked Scientists

The Naked Scientists Forum

Author Topic: what is a rotary pulse jet?  (Read 8424 times)

Offline ifocoeur

  • First timers
  • *
  • Posts: 5
    • View Profile
what is a rotary pulse jet?
« on: 03/01/2015 13:18:01 »
A rotary pulse jet is actually a pulse jet engine (with a resonnant pipe) that rotates. In my view, a rotary pulse jet, rotary rectifier, and or a double duty augmenter are the only ways to improve a pulse jet fuel efficiency. a valveless pulse jet engine will consume as much as 5.5 lb of fuel for every pound of thrust that it generates per hour. A valved pulse jet engine will consume 3 lbs of fuel for every pound of thrust per hour. But a valved pulse jet is not reliable. the valves will fail in minutes. If you have a 55 lb thrust pulse jet (14 horsepower euivalent based on an actual propeller test----See discussion below), this engine will consume 302.5 lbs of fuel (49.8 gallons of gasoline) in the case of a valveless pulse jets for one hour of operation. But at high speed, fuel consumption will drop to 1.8 lb of fuel per pound of thrust per hour. See Gluharreff pressure jet or the US government sponsored "project Squid". The french snecma escopptte has a similar fuel consumption (1.8 lb of fuel per pound of thrust). But i believe the escopette has used "low pressure time fuel injection" along with a rectifier for the intake. remember that in direct fuel injection, as much as 50% of the fuel fed to the engine is being wasted. With timed fuel injection, this amount of fuel can be recovered (at least theorically). this would lower thrust specific fuel consumption. But this is difficult to do in practice. In practice, only a small percentage of the wasted fuel is being recovered. To improve fuel efficiency, a pulse jet designer can use thrust augmenter. Thrust augmenter is a larger tube place behind  the exhaust outlets of a pulse jet engine.  see US patent 3,206, 926 by Lockwood to see how to build an augmenter. Thrust augmenter can increase pulse jet thrust by 100% without consuming any extra fuel. But they have only been used at low speed. At high speed, conventional thrust augmenters create more drag than thrust. But i have recently design a new double duty augmenter for high speed vehicle. This double duty augmenter will perform as an augmenter and also create lift. Therefore, the faster the vehicle accelate, the more efficient is the augment.  With the double duty augmenter, fuel consumption will drop below 1.8 lb of fuel per pound of thrust (theorically 0.9 lb of fuel per pound of thrust). So far a pulse jet engine will take advantage of ram air at high speed (Gluharreff), timed fuel injection (escopette), and double duty augmenter (ifocoeur). But I believe we can do better than that. We can actually try to compress the fuel air mixture in the combustion chamber. We can do so by using a rotary pulse jet or rotary rectifier.

A rotary pulse jet engine (RPJE) converts jet power into shaft power or part of the jet power into shaft power. This is very important for several reasons. RPJE can power an axial compressor or centrifugal compressor like a turbojet engine. When a pulse jet is fitted with a compressor, it can compete with any other type of engine. Even without a compressor, a rotary pulse jet will improve pulse jet fuel consumption especially for low speed vehicles. A pulse jet engine is fuel efficient when it moves at high speed through the air. Therefore, it would not be wise to power a slow moving vehicle such as a gokart, a car, or a low speed ultralight aircraft with a conventional pulse jet engine. But a rotary pulse jet engine is ideal to power a slow moving vehicle. rotary pulse jet will move at high speed while the vehicle itself can move at low speed.  With RPJE, a 55 lb thrust pulse jet will generate 58.6 horsepower at 400 mph. Notice that I no longer use the expression "equivalent horsepower" because rotary pulsejet generates actual shaft horsepower when it rotates. When the engine rotates, it has a speed (also RPM). That's why I am talking about 400 mph. The speed can even be higher than 400 mph. At 650 mph (which is difficult to achieve in practice), a 55 lb thrust pulse jet would generate 95.4 horsepower. That is better than 14 horsepower equivalent. If you want to convince yourself that these numbers are acceptable, you need to search for the following aircrafts (the Jet Jeep and the Gluharreff EMG 300) on the Internet. With 2 20-lb thrust (40 lb thrust total) jet engines on the tip of an helicopter rotor blades, EMG 300 was able to lift 460 lbs. A piston engine would have to deliver at least 40 hp in order to power the same helicopter. And also with 2 35-Lb thrust pulse jet engines (70 lb thrust total) on the tip of an helicopter rotor blades, the jet Jeep was able to lift 705 lbs helicopter. A piston engine would have to deliver around 65 hp to power a similar helicopter. But notice that tipjets are dangerous. But RPJE is not dangerous. Notice that with RPJE, you can use various smaller engines to lower noise lever. Tipjets could only use 2 large engines. Notice also that the numbers quoted above are for RPJE without a compressor. In fact, you can use a an axial compressor or centrifugal compressor with RPJE. So these numbers are nothing in comparison to what actually can be achieved when we add a compressor to RPJE. A separate version of rotary pulse jet engine is what i called a pulse jet with rotary rectifier. the rotary rectifier is a pulse jet thrust augmenter that rotates. An augmenter will increase pulse jet thrust by 100%. But remember that this is a rotary rectifer. It is not moving forward. The rectifier can reach rotational speed above 400 mph. Don't think about rotary rectifier, the way you normally think of augmenter (good only for low speed application). The rectifier rotates (low drag); it is not moving forward (high drag). When a rotary rectifier is used to move a vehicle forward, forward speed of the vehicle will be much lower than the rectifier rotational speed. A rotary rectifier can power a propeller or the wheels of a vehicle via a gearbox. The gearbox will consume a small amount of power due to friction (less than 10%). So what. In theory, a rotary rectifier will be more efficient than rotary pulse jet (without a compressor of course). But the rotary rectifier has a larger frontal area. Therefore, a rotary rectifier will create more drag than a rotary pulse jet in high speed propulsion. One more thing about rotary rectifier, a rotary rectifier will allow a pulse jet designer to place both tail pipe and air inlet in the vehicle travel direction to capture ram air. Ram air will act as a piston on both the tail pipe and the air inlet to increase the pressure in the combustion chamber of the engine. Someone told me RPJE and rotary rectifier would have low TORQUE in comparison with tipjets due to the long lever arm (rotor blade) of tipjets and the short lever of rotary pulse jet and rotary rectifier. My response is that rotary pulse jet and rotary rectifier will have more shaft SPEED (more RPM). Shaft speed can be converted Torque. Torque can be converted to shaft speed. I even made a video to explain it. The video is listed below.
Here is a great video about rotary rectifier "PART 5 pulse jet with rotary rectifier" (
).
here is a youtube link for "PART 9 BEST rotary pulse jet engine and rotary rectifier" (
).
Here is a link about Torque of rotary pulse jet and rotary rectifier (
).
 Here is another link for "PART 2 rotary pulse jet" (
).
here is a link for rotary rectifier "PART 3 pulse jet with rotary rectifier" (
).
Here is a link for my double duty augmenter (
)(pulse jet augmentor for high speed aircraft).
Here is a link about pulse jet vs. turbojet (
)
Here is a link for high pressure pulse jet (
)
Here is a link on how to build a rotary rectifier (
)
« Last Edit: 10/01/2015 13:16:41 by ifocoeur »


 

Offline Bored chemist

  • Neilep Level Member
  • ******
  • Posts: 8655
  • Thanked: 42 times
    • View Profile
Re: what is a rotary pulse jet?
« Reply #1 on: 04/01/2015 13:21:01 »
Your numbers don't make sense.
When you say "a valveless pulse jet engine will consume as much as 5.5 lb of fuel for every pound of thrust that it generates." what do you mean?
5 pounds of fuel per second? per hour? Five pounds, but  then no more ever?

Similarly you say
"If you have a 55 lb thrust pulse jet (14 horsepower equivalent)"
Well, it's not equivalent.
One is a force and the other is a power.

It's related to a puzzle that lots of people get wrong.
Imagine a jet aircraft like a jumbo jet, just at the point where it's about to start rolling down the runway for take off. The engines are at full throttle and the pilot has just taken the breaks off.
What power are the engines delivering to make the plane move forward?


The answer is zero.
Once you understand why, you will understand why you can't equate thrust and power.
 

Offline alancalverd

  • Global Moderator
  • Neilep Level Member
  • *****
  • Posts: 4704
  • Thanked: 153 times
  • life is too short to drink instant coffee
    • View Profile
Re: what is a rotary pulse jet?
« Reply #2 on: 04/01/2015 14:55:18 »
I beg to differ. Power = energy per unit time.

The engines are accelerating the incoming air such that the exhaust gases have significant momentum, even if the plane isn't moving with respect to the ground. They are burning fuel at a rate of kilograms per second and since each kilogram produces about 50 MJ of energy, they are doing work on the air at a rate of joules per second = watts = power. The fan on your computer isn't moving the computer but it is moving air, and transferring power from the mains to the air in doing so. The catch, of course, is that the power of the engines is not being transferred to the plane at the moment of brake release.

However it is true that static thrust (what measurably comes out of a jet engine) is not power (what calculably goes in), and the figures quoted in the OP do not make sense at all.

With regard to the OP, it is true that bypass fans or rocket augmenters can improve static thrust and are effective at low speeds, but have an upper speed limit beyond which they create more drag than additional thrust, which is why modern airliners use high bypass fans for fairly constant subsonic cruising whilst fighters generally use little or no bypass as they have to accelerate from loiter to supersonic with the minimum of reconfiguration.
 

Offline Bored chemist

  • Neilep Level Member
  • ******
  • Posts: 8655
  • Thanked: 42 times
    • View Profile
Re: what is a rotary pulse jet?
« Reply #3 on: 05/01/2015 17:33:38 »
I didn't ask how much power they were using to push air around.
I asked how much power they were delivering to make the plane move forward.
Since, at that moment, the plane is stationary, the power is zero.
Power = work done /time.
Work = force * distance.
The distance =0 so the power =0.

In the same way, a test engine mounted on a test bench does zero work against the bench (though it might convert a few Watts into sound).
In any event, never mind the puzzle.
The OP has units that are shot to hell.
 

Offline alancalverd

  • Global Moderator
  • Neilep Level Member
  • *****
  • Posts: 4704
  • Thanked: 153 times
  • life is too short to drink instant coffee
    • View Profile
Re: what is a rotary pulse jet?
« Reply #4 on: 05/01/2015 22:35:50 »
I didn't ask how much power they were using to push air around.
I asked how much power they were delivering to make the plane move forward.

Newton says it's exactly the same. Pedantically, the power being used to  make the plane move is the power being delivered to the exhaust gas, but at the start of the takeoff roll it isn't being delivered to the plane - it's all going to the gas.
 

Offline Bored chemist

  • Neilep Level Member
  • ******
  • Posts: 8655
  • Thanked: 42 times
    • View Profile
Re: what is a rotary pulse jet?
« Reply #5 on: 06/01/2015 13:17:53 »
Newton didn't have a well defined understanding of power.
What you are saying is that two things are the same but that one- the power being delivered to the air- is very big, but the other - the power delivered to the plane- is very small (asymptotically, zero).
Would you like to think that through again?

What Newton said was that the forces are the same.
However to get the power you have to multiply the force by the velocity.
in the case of the air, the velocity is big.
In the case of the plane, the velocity is zero.
 

Offline ifocoeur

  • First timers
  • *
  • Posts: 5
    • View Profile
Re: what is a rotary pulse jet?
« Reply #6 on: 09/01/2015 18:50:59 »
My answer
Your numbers don't make sense.
When you say "a valveless pulse jet engine will consume as much as 5.5 lb of fuel for every pound of thrust that it generates." what do you mean?
5 pounds of fuel per second? per hour? Five pounds, but  then no more ever?

Similarly you say
"If you have a 55 lb thrust pulse jet (14 horsepower equivalent)"
Well, it's not equivalent.
One is a force and the other is a power.


I mean 5.5 lbs of fuel per pound of thrust per hour. When I say 14 horsepower equivalent, it is based on actual test of a propeller. I get this number from a Gluharreff paper. An actual test of a propeller (14 horsepower piston engine) would deliver 55 lb of propeller thrust. that is why I use the word equivalent. I know one is a force and the other is power.
 

Offline ifocoeur

  • First timers
  • *
  • Posts: 5
    • View Profile
Re: what is a rotary pulse jet?
« Reply #7 on: 09/01/2015 19:20:08 »

Once you understand why, you will understand why you can't equate thrust and power.


Rotary pulse jet actually generate shaft power. When a jet engine begins to move and reach a top speed, you can measure horsepower at that point. For example, if you place a pulse jet engine at the end of a lever arm like in a tipjet helicopter, the pulse jet will generate shaft power. a rotary pulse jet engine of my design has an extremely short lever arm. I use my own technique to make it rotate.
« Last Edit: 09/01/2015 20:41:43 by ifocoeur »
 

Offline ifocoeur

  • First timers
  • *
  • Posts: 5
    • View Profile
Re: what is a rotary pulse jet?
« Reply #8 on: 09/01/2015 19:35:23 »

With regard to the OP, it is true that bypass fans or rocket augmenters can improve static thrust and are effective at low speeds, but have an upper speed limit beyond which they create more drag than additional thrust

My point is to redesign pulse jet augmenter to increase the "upper speed limit beyond which they create more drag than additional thrust". let us say for example, current augmenter design create more drag than thrust at 100 mph. I want to redesign them to create more drag  than thrust (for example at 300 mph). But i want every reader to know that this post is more about rotary pulse jet and rotary rectifier than it is about the augmenter. please focus most of your energy on the second part (the one that talk about rotary pulse jet and rotary rectifier).
« Last Edit: 09/01/2015 20:55:42 by ifocoeur »
 

Offline ifocoeur

  • First timers
  • *
  • Posts: 5
    • View Profile
Re: what is a rotary pulse jet?
« Reply #9 on: 09/01/2015 19:40:55 »

The OP has units that are shot to hell.


which one? I will be able to explain them. I am sure.
 

The Naked Scientists Forum

Re: what is a rotary pulse jet?
« Reply #9 on: 09/01/2015 19:40:55 »

 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums