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Aside from early diesel engines, does anyone know of brayton-cycle engine that uses a positive displacement compressor rather than an aerodynamic one?
'Jet' engine with positive displacement compressor?
- Thread starter NateTG
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Discussion Overview
The discussion revolves around the concept of a Brayton-cycle engine utilizing a positive displacement compressor instead of a traditional aerodynamic compressor. Participants explore various engine configurations, including the integration of screw compressors and expanders, and share thoughts on the feasibility and design challenges associated with such systems.
Discussion Character
- Exploratory
- Technical explanation
- Debate/contested
Main Points Raised
- Some participants inquire about existing Brayton-cycle engines that use positive displacement compressors, noting a lack of widely known examples.
- One participant recalls a paper discussing a piston atop an axial compressor, suggesting that the compression may be supplemental.
- Another participant expresses interest in a configuration similar to turbo-fans but utilizing positive displacement, describing the concept as unconventional.
- A participant mentions a paper related to free piston topping for turbines, indicating a potential connection to the topic but acknowledges copyright limitations on the material.
- There is a discussion about the safety concerns associated with positive displacement outputs, with one participant referencing experiences with high-pressure systems in motorsports.
- Another participant points out that piston engines also have positive displacement outputs, questioning the safety concerns raised earlier.
- A participant shares a patent that appears to align with the discussed concepts, suggesting that there may be several designs in this area.
- Concerns are raised about the complexity of flow diagrams and the intuitive challenges of understanding certain compressor designs, particularly regarding pressure development and rotor bearing loads.
Areas of Agreement / Disagreement
Participants express varying levels of interest and concern regarding the feasibility and safety of positive displacement compressors in jet engines. There is no consensus on the practicality or existing implementations of such systems, and multiple competing views remain regarding their design and operation.
Contextual Notes
Participants reference specific papers and patents, but there are limitations in terms of access to copyrighted materials and the clarity of technical diagrams. The discussion reflects a range of assumptions about the engineering principles involved.
Who May Find This Useful
Individuals interested in advanced engine designs, compressor technologies, and the exploration of unconventional propulsion systems may find this discussion relevant.
- #2
FredGarvin
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You know, I vauguely remember a paper detailing an engine concept that did have a piston on top of an axial compressor. IIRC believe the compression was supplemental. Let me see if I can hunt it down.
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FredGarvin said:
I was actually wondering about something similar to turbo-fans, but with positive displacement. Still, that sounds zany.
- #4
FredGarvin
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It was on a turbo jet IIRC. I still haven't found it. Still looking.NateTG said:
EDIT: Now I recall what the heck I was thinking about. It had to do with free piston topping for turbines. I have a paper from the 2003 ASME Turbine expo on the topic, but it is copyrighted. Try doing a search on it and see what you can come up with. It's not what you were looking for, but it's kind of in the ball park.
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FredGarvin said:
Yeah, I was wondering if anyone had, for example stuck together a screw compressor, combustion chamber, and screw expander as a power plant.
Thanks for the response though.
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Danger
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Jeez, Nate... I thought that you were just asking about the intake side. A positive displacement output? I wouldn't want to be anywhere near it. I've seen a Funny Car shell its blower. Even with pop-off valves, it's not a pretty sight. I'd want an unobstructed exit for that combustion chamber.
I've seen quite a few 'turbojets' made out of surplus turbochargers, but that's about it.
I've seen quite a few 'turbojets' made out of surplus turbochargers, but that's about it.
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Danger said:
I don't understand why. Piston engines, for example, have positive displacement output in that sense.
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Q_Goest
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Hi Nate, I've always been amazed at what's been patented. I was saying to myself, "I've never heard of such a machine, though I can't think of any reason why not." So I checked. Sure enough, this one looks pretty close to what you suggested (screw compressor, screw expander).
http://www1.uspto.gov/web/patents/patog/week06/OG/html/1303-1/US06993897-20060207.html
I suspect there are quite a few of these designs out there. A quick Google search turns up a lot of hits.
Hey Fred - New avatar? Which one is Fred?
http://www1.uspto.gov/web/patents/patog/week06/OG/html/1303-1/US06993897-20060207.html
I suspect there are quite a few of these designs out there. A quick Google search turns up a lot of hits.
Hey Fred - New avatar? Which one is Fred?
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- #9
Danger
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That thing would be a hell of a lot easier to understand if I could get it all on the screen at the same time. Also, I'm not used to reading flow diagrams instead of blueprints. Looks sensible enough, if perhaps overly elaborate.
I guess that my objection might be more intuitive than based upon actual engineering principles. It's hard for me to envision a Roots-type blower, which is what I was thinking of, being easily reversible (like a worm gear set-up). Based upon the airflow through one, it seems that it would develop a lot of pressure internally as opposed to something that takes the flow axially. I suspect that the side-load on the rotor bearings must be incredible.
Thanks for the link, Q. Maybe if I print it out and get to look at the picture and text at the same time, it'll be easier to tell what's going on in it.
I guess that my objection might be more intuitive than based upon actual engineering principles. It's hard for me to envision a Roots-type blower, which is what I was thinking of, being easily reversible (like a worm gear set-up). Based upon the airflow through one, it seems that it would develop a lot of pressure internally as opposed to something that takes the flow axially. I suspect that the side-load on the rotor bearings must be incredible.
Thanks for the link, Q. Maybe if I print it out and get to look at the picture and text at the same time, it'll be easier to tell what's going on in it.
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- #10
FredGarvin
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Yeah. It's a new one. I need to change things around every once in a while. That's Lou and Andy from Little Britain. The best skit show EVER.Q_Goest said:Hey Fred - New avatar? Which one is Fred?
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FredGarvin said:
My brother and his wife are into that show...
Man I love the cake!