VALVED pulse-jets with turbines (turbocharged pulse jet)

Jets that defy normal classification

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d4nthrax
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VALVED pulse-jets with turbines (turbocharged pulse jet)

Post by d4nthrax » Mon Feb 22, 2010 6:53 am

Not currently an engineer here, but wanting some advice before I embark on a huge undertaking...

Start a common valved (reed-type) pulsejet. Add a turbine at the exit, and a compressor at the front, somehow mechanically connected, either inside or outside the engine.

Question 1: I know that for part of the cycle, the engine will need to suck in air from both ends. Will the fan assembly prevent this, or...

Question 2: Will the fan assembly render this unecessary, since, at operating rpms, there will likely be a SIGNIFICANT buildup of pressure on the compressor end, since the reed will be closed momentarily, which should (hopefully!) provide enough pressure to power the cycle.

Question 3: The BIGGIE: I've always comprehended pulsejets as an "air piston," "piston without a piston," or a "sort of reciprocating engine." Is it possible to make these function with the airflow going in one direction? To me, the pulsejet seems to depend on the elasticity of the air. With the reed valve closed, would the momentum of the turbine decrease the internal pressure enough to start the next cycle? Will their be enough air pressure on the compressor side to perpetuate the operation?

Question 4: Will the fan assembly simply "idle" along with the operation of the engine, or interfere with the airflow?

Question 5: Will we all just have to get together and build one to find out for sure?

racketmotorman
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Re: VALVED pulse-jets with turbines (turbocharged pulse jet)

Post by racketmotorman » Sun Feb 28, 2010 5:47 am


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Re: VALVED pulse-jets with turbines (turbocharged pulse jet)

Post by d4nthrax » Mon Apr 05, 2010 4:20 am

Mr. Wallis,

I saw your video a long time ago on youtube, very impressive. Have you ever considered using the turbine to power a compressor?

Dan

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Re: VALVED pulse-jets with turbines (turbocharged pulse jet)

Post by racketmotorman » Mon Apr 05, 2010 5:24 am

Hi Dan

I'm more into gas turbines these days , the PJ turboprop was just a bit of a diversion , it didn't produce any real shaft power even though i was able to spin the freepower turbine to ~20,000 rpm , my thoughts are that PJ's produce the bulk of their thrust "internally " rather than "externally" like a gas turbine jet engine does , thus limiting the power of a turbine wheel receiving the efflux downstream of the PJ .

Ideally, it would probably be better to duct the PJ exhaust "radially" towards the turbine wheel rather than axially as the requirement to turn the gases with an axial approach causes problems and losses , the requirement to power a prop in front of the PJ necessitated the placement I used , it would have been better to have fitted a scroll like a did on my turbine bike engine http://www.racketmotorman.turbinebuilde ... hp?album=3 .

Compressors are huge power consumers I doubt the PJ's freepower would have been up to the job , using a compressor to "supercharge" a PJ then using the PJ exhaust to drive the comps compressor is only going to produce an unduly complicated gas turbine engine that doesn't really perform as well as a common gas turbine , and then theres all that PJ noise and vibration .................best left as a pipe dream :-(

Cheers
John

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Re: VALVED pulse-jets with turbines (turbocharged pulse jet)

Post by d4nthrax » Wed Dec 08, 2010 7:35 pm

John,

HMMMMMM...... your argument is very plausible. I've been thinking about this for some time.

In a normal pulsejet configuration, you're saying that a scroll (did you mean bernoulli or centripetal) configuration would be the best way to extract energy as a free turbine?

Also, if I'm using a turbine so spin a compressor at the front of a valved pulsejet engine, wouldn't that increase the velocity of the outgoing gasses, and therefore the horsepower, and adding more torque to the turbine, and thus power to the compressor? Is the concept wrong here, or is it more of a 'numbers' game?

And thanks for responding! I do enjoy our little chats!

Dan

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Re: VALVED pulse-jets with turbines (turbocharged pulse jet)

Post by racketmotorman » Wed Dec 08, 2010 8:45 pm

Hi Dan

By "radial" , I meant coming at the turbine wheel in a direction 90 degrees from the turbine shaft axis , it would end up being more a tangential sideways glancing blow to the blades.

I doubt that you'd end up with enough horsepower to power a compressor sufficiently to make any great difference to the PJ's mass flow ..................but , I hope you can prove me wrong :-)

Cheers
John

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Re: VALVED pulse-jets with turbines (turbocharged pulse jet)

Post by d4nthrax » Thu Dec 09, 2010 6:03 pm

John,

I understand the "radial" concept--huge fan of early turbines!

My question was blade style. A bernoulli "furnace fan" type blower, or more of a turbocharger?

Definitely understand the need for radial--significantly more torque from a column of air moving at roughly 1/ 4 the speed of a turbine engine, riht?

Dan

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Re: VALVED pulse-jets with turbines (turbocharged pulse jet)

Post by racketmotorman » Mon Dec 13, 2010 9:26 pm

Hi Dan

Mmmmmm, I thought I'd answered this Post , guess I didn't ....duh :-(

Not a turbocharger type , it runs into "votex" problems requiring pressure drops etc , you need an axial turbine wheel that has impulse blading which doesn't require a pressure drop across the blades , the blades are best designed to run at half gas inlet speeds .

Cheers
John

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