gasturbine with turbocharger

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gasturbine with turbocharger

Postby segelfam » Sat Jan 08, 2011 4:45 am

Hi,
after building a very small but working pulse jet
http://www.youtube.com/watch?v=FX6hDPiWGDg
I want to try a gasturbine with a car turbo charger, but I don't have much experience with this kind of machines. Has anyone here advices what mistakes can be made. I want to make the machine as small as possible because I'm not interessted in high thrust, only a machine for demonstration.
Has anyone experience how big the combustion chamber should be at least for self substained operation. The turbo charger is a rather small modell for VW Jetta

Best regard and a happy new year

Thomas
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Re: gasturbine with turbocharger

Postby chrismb » Sat Jan 08, 2011 6:18 am

Is this for exhaust thrust, or torque to a prop-shaft?

I have no experience mechanically, but I have a watching brief on some of the latest 'range-extender' turbo-props for electric cars. Disclosable things in the public domain are, for example, an Israeli firm that has started offering turbo-gen sets for cars, and Jaguar has just unveiled a concept electric car with two 100kW or so turbo-prob gen sets in the boot (not sure if they are from that Israeli company!). They are very small devices. I have always considered this the way for cars to go, with some mods [that I can mention later].

I'll dig out some of those, just for interest (even if it doesn't quite help inform you, I think you may be interested in the tech).

I did also dig out a link to some guy who built some turbo-based thrust devices. I'll see if I can unearth it again. I was debating if I have the skills/ideas to make a lifting platform out of car turbos, and I think that guy had the same idea.
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Re: gasturbine with turbocharger

Postby segelfam » Sat Jan 08, 2011 7:24 am

Hi Chrismb
neither nor, at least for beginning, I don't want to extract any power, just being happy if the device turns with high speed without suppling pressed air.
There are a lot of videos about diy turbo charger turbines on Youtube, but they all use very large combustion chambers. I should like smaller ones.
I'm very interested in your links or papers

Thomas
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Re: gasturbine with turbocharger

Postby Joe Jarski » Sat Jan 08, 2011 11:22 am

A turbo uses a radial flow compressor and the compressed air exits the diffuser in one pipe which lends itself to using a single combustion camber for simplicity. A typical jet engine uses an axial flow compressor and the compressed air exits the last stage diffuser in an annular form. The annular combustion chambers are typical of current jet engines, but they sill use separate chambers for special applications like they did in the early days of jets. To use an annular or semi-annular combustion chamber you'll have to fabricate a new diffuser, which is a critical item but not impossible to make. Compressor surge (when the air stars flowing backwards) is a major issue with either compressor design that's why the diffuser is critical. The next problem with the normal layout of a turbo is that the airflow through the hot section is radial input to axial exit. So you have the same issues with changing the configuration of the turbine inlet to a distributed radial flow instead of the one pipe in. In general, the basic layout of a turbo doesn't make it an easy conversion to a gas turbine that looks "pretty". That's why most people just add a single combustor otherwise you're probably better off to build it from the ground up.
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Re: gasturbine with turbocharger

Postby Bill Fain » Sat Jan 08, 2011 1:59 pm

Joe, Hi. I have always wanted to make one of these too. I have a cummings turbo, oil, pump, fuel can, and a few braided steel hoses. I think I have the original AIEE turbo/jet design paper laying around here somewhere. I haven't built it yet because I don't have any welding/metalworking capability. And now any of that would go into fusors anyway. The biggest obstacle was going to be the burner can/flame holder deal. I have found a source of old burner cans, but I think they are too big for this application. I was going to buy one thinking they were titanium, but they turned out to be hi temp. SS. I can pick up one for $20, if you're interested before your impending visit. Might make a good pattern/ reverse engineering thing. I don''t know if they have a flame holder in them, but I'm pretty sure the injectors are not with them. Let me know soon because they are about an hour away. -bill
burner_cans.jpg
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Re: gasturbine with turbocharger

Postby Bill Fain » Sat Jan 08, 2011 4:45 pm

Hi, Well I blew this. Ready fire aim. I thought the post was started by Joe. My mistake. Well Thomas, do you need a burner can or the AIIE paper, if I can find it? -bill
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Re: gasturbine with turbocharger

Postby Doug Coulter » Sat Jan 08, 2011 5:19 pm

Being lazy at the moment, many people (one in Michagan and one in New Zealand I recall) have made working turbos with auto turbochargers. One was used on a go kart for thrust and was pretty successful, I think I found it searching, and movies on youtube. Various combustion chamber sizes have been used, they tend to be on the big side to work with a car sized turbo (say 4" diameter and over a foot long) and not melt. Most need compressed air or a leaf blower to start up, or some way to get the thing spinning in the first place so the fire doesn't just come back out the input compressor. However, once the big one I saw ran (turbo from a big diesel truck) it made that go kart really really go.

Google knows everything.
http://www.salvatoreaiello.com/main.shtml
http://www.diygasturbines.com/
http://pfranc.com/projects/turbine/top.htm (this one has links to other projects)
http://www.junkyardjet.com/links.html
http://www.aardvark.co.nz/pjet/faq.htm

Were the first five relevant ones that came up when googling "diy turbine engine".

And none are the ones I recall. There's a ton of this out there, it looks like fun.
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
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Re: gasturbine with turbocharger

Postby Joe Jarski » Sat Jan 08, 2011 9:23 pm

Bill, There was a time that I was contemplating building one of these too. I learned quite a bit of the little detaily type stuff when I was working for one of the big boys, but eventually shelved the project because I already have too many others and it wasn't going to be quickie.

Doug, you're right about about the size/cooling thing. A typical jet engine only uses about 30% of the air it takes in for combustion. The vast majority of the remaining 70% is used for cooling, and a lot of that is used reduce the combustion gas temperature to a reasonable level before entering the turbine. Another case for the large chambers is giving the fuel time to atomize and mix properly. I've seen combustion chambers and fuel injectors that were melted because the spray pattern wasn't exactly right.

The series of holes that go around the cans in Bills picture are used to keep the flame away from walls of the can and help cool the combustion gasses.
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Re: gasturbine with turbocharger

Postby Doug Coulter » Sun Jan 09, 2011 12:51 pm

I've sometimes traded stock in Capstone Turbine, a little company that seems to have a novel approach to all this, and I even considered buying one for backup power use here. Their thing has air bearings and eats a variety of different fuels, a do-all engine. They don't make ones small enough for me, though, and I'd guess there are scaling issues with making one both efficient and small, the old surface area to volume ratio thing again, or something like it.

Does anyone know offhand the basic efficiency of a gas turbine in say BSFC or pounds per horsepower-hour so I could compare it with a good IC engine? I know a small, high compression Honda fixed engine is really pretty good there with a little bit of tweaking, which is what I used in my high efficiency generator. Which needs repair next time the weather is permitting. Blew a head gasket (this time). Running one of these wide open to get the thermodynamic efficiency high means they tend to not have a super long service life, though. What usually does them in though is spinning the seals on the crank bearings (Honda uses ball bearings there!), or the doggone cam drive gear slips, it's only pressed on the crank, and it's not a clearance engine, so that's instant total destruction. Next one I buy, I might take apart and weld that sucker on, instead.

Of course, the basic objection to IC engines (other than wearing out) is the noise they make. It's very quiet here, and I like that. Diesels stink and sound like they are gargling rocks -- I prefer the swiss watch sound myself, and no water cooled auto/tractor type engines seem small enough to do well in efficiency for this application. And are picky about feeding -- gotta have the right fuel. Smallest one of those I've seen is about 20hp (and it's on my tractor) which is about 4 or 5x what my batteries can eat on charge easily.

Ideal in some ways would be a small, water cooled, fuel injected liquid fuel engine that made about 5-6 hp, but of course no one makes that. I'd guess one reason is that with the small displacement, the surface area to volume ratio in the cylinders gets high and heat losses from that kill the efficiency. But such a thing could probably be made to eat almost any liquid fuel and live. BillF sent me a link once to a home made engine that used solenoids for the valves, so you could effectively adjust compression ratio on the fly with valve timing!

Some alcohols have syntheses that mainly need heat to make them go, which makes them solar-power-able. That would make for an unlimited capacity "battery" which would be super nice to have. Till then, gotta get out that vanadium pentoxide and try to make that redox battery, but the membrane they need is super expensive and not found on street corners. It's not that I don't get enough kilowatt hours out of my PV panels, it's that they don't come when I need them. Storage is the issue there.
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
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Re: gasturbine with turbocharger

Postby Bill Fain » Sun Jan 09, 2011 2:05 pm

Hi, BTW, I think my cummings turbocharger exhaust impeller is only good for 900 deg F. I need lots of bypass air for that. The higher temperature the exhaust turbine impeller can stand, the less bypass air needed, thus better efficiency. IIRC some of the new engines get up to over 2000 deg F and I believe some use ceramic materials in their turbine impellers.
I was wondering if anyone has thought of taking a micro turbine and coupling it to a gearbox and then take the microturbine exhaust and feeding it to the input of an IC engine. Maybe it would be more of a hot air engine? The IC engine would have to be really big volumetrically as compared to the output of the turbine? Both the micro-turbine and the IC would be geared together. Heck, maybe take the output of the IC and run a stirling engine. Oh, yes, and add a thermoelectric pile somewhere in that loop. If this could be pulled off at all, would all the mechanical losses negate any gains? -bill
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