parkland
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Joined: February 2015
Posts: 57 
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Post by parkland on Feb 1, 2015 14:24:11 GMT -5
Hello everyone !
I have for years thought turbocharger jet engines were interesting and neat, but failed to see any useful purpose to the average person.
For some reason, I recently started thinking about it again, and decided maybe I will give it a shot.
And I'm not talking a turbocharger jet engine display, I mean an actual engine that does something.
As redneck as it might sound, a friend has a riding mower with a blown engine, and I am thinking it could be an ideal vehicle to horse
around with jet power. It is small enough to not need huge power, but beefy enough to carry some weight and equipment that would bolt on.
While not practical compared to the v-twin briggs and stratton that was in it, it might find occasional use as a towing yard tractor.
Most importantly, it is free, so hopefully the project won't cost a fortune to build.
Some goals I have so far:
-As fuel efficient as possible. I know these can burn a ton of fuel, but want to try and keep it as "sane" as possible.
-Self contained. No leaf blower or external tanks to start, everything on-board.
-Reliable. Able to run and run, without melting down or over heating.
-Versatile fuel - Able to burn a variety of fuels, including waste oils.
So far, I've read a lot of things, and have a few thoughts on how to do things.
The general design I was thinking, would be a turbocharger jet engine, either driving a sprocket or gear for power, or use a 2nd turbo with the compressor removed, and drive gear attached.
That design seems to work for many people, would there be a benefit to driving a load directly from the turbine shaft, instead of a second drive turbine?
For the combustion chamber, I think I would use a design similar to what many use already, but incorporate a fuel coil in the chamber, so once ignition is obtained, any type of fuel can be pushed through
the coil, where it will vaporize and burn. I originally thought this might cool combustion and reduce efficiency, but then I realized any heat soaked up, would be transferred to the fuel, so it should net a null result.
I was thinking a spark igniter and gasoline injection would get things going initially, then switch to oil after temperature is up.
I would spray the gasoline though an atomizer nozzle, and use a small electric pump, nothing huge, as it would only be used for starting, not highest flow rates.
For oil injection into the coil, Maybe an electric pump, or mechanical, connected to the output shaft.
Not sure on oil pump yet.
For cooling, I was thinking a pipe could be installed over the exhaust, so that as the engine expels hot air, it sucks air through the outer pipe. The other end of the
outer pipe would have a small radiator, like a transmission cooler, with the oil flowing through it. So the harder the engine ran, the more airflow would go through the cooler.
OK So now the hard questions....
Normal turbocharger, or VNT/VVT/VGT turbo?
Shouldn't a variable vane unit allow much better idling and lower fuel consumption?
Maybe the actuator could be connected to an air actuator and spring, so that the vanes open more as combustion pressure rises?
Or maybe somehow open the vanes as RPM increases?
It seems like this would allow for more throttle response without waiting for RPM to change as much.
Also, what about 2 turbochargers, and compounding them?
I read that it could save fuel, but it is basically not worth the hassle, as an intercooler would be required. My question about that, is we don't use an intercooler
with a single turbo engine, why would we use one on a double turbo engine?
I realise the temperature would be higher, but isn't that a requirement to make power?
Compounds used on trucks only have a single intercooler, but on a jet engine, why would you want to reduce the temperature after the compressor?
Wouldn't that just throw energy away, and waste fuel?
I realise that there is a temperature limit, but if it means making less power to keep temperatures safe, wouldn't a compound setup run more reliably, and
be more responsive and fuel efficient? I am not after maximum possible power, rather a well running unit.
I'm not sure what the answer is for what I want, maybe it's compounds, maybe a single, maybe a VVT.
What size turbochargers should I be looking at, 1 ton truck? semi? what kind of power can be extracted using an exhaust driven turbine?
20-60 hp would be cool. Since I'm so concerned with fuel usage, and jet engines use so much fuel at idle, I suppose it would be better to go smaller
rather than the biggest one that will fit?
Finally, what kind of fuel burn rate can be expected?
I've read all kinds of stuff, from about a gallon an hour, to several gallons an hour.
It would be nice to have an hour or 2 run time without refilling.
Also, with heat management, I notice a lot of videos of cooling down turbocharger engines with a blower, after shutting down.
I am wondering what the purpose is of this, as vehicles can shut off and not bother with a cool down period, and turbochargers seem to do just fine,
and EGT's can be super high was well. For EG my 6.4 ford diesel, among others, might regularly see 1300*F.
Is this because of oil temperatures in these jet engines?
Is a cool down method going to be a necessity, or are people doing that hoping for longevity or dealing with seal leaks?
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parkland
Junior Member
Joined: February 2015
Posts: 57
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Post by parkland on Feb 1, 2015 15:04:39 GMT -5
And also,
Sorry I forgot to touch on this...
I mentioned I wanted it self contained.
For starting, I noticed there are electric motors that can start the engine by direct shaft engagement.
I have to say I am not a fan of that setup.
I am thinking between 2 options....
If the power is taken from the engine turbine, maybe use a lower speed electric motor to drive the gear reduction wheel, to increase speed to the shaft....
Or if it ends up being an exhaust driven turbine without a mechanical linkage to the main shaft, maybe use an air injector to the exhaust housing, and a 12v air pump to build up pressure?
Even a little cheap 12v air pump, and make an air resevoir, and a valve to dump the air pressure to the exhaust housing to spool it.
Downside there, is that you would have to wait several minutes for pressure to build before attempting to start.
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Post by racket on Feb 1, 2015 18:50:33 GMT -5
Hi Welcome to the Group :-) You're attempting a very ambitious project .................checkout RC Don's Site for some pointers www.rcdon.com/html/experimental_projects.html . For a "vehicle" its best to use the 2 shaft system with a freepower turbine to produce the shaft power , single shaft engines aren't really suitable . Forget compounding , theres simply too many problems to overcome , especially for a first build , you'll save some fuel but not a huge amount, it'll still be thirsty unless run at max rpm/pressures. Fuel burn rates will be > 1 pound of fuel per horsepower per hour at full power , expect that to increase by >50% if at low power settings , so 60 hp will need >60 pounds of fuel per hour or >1 pound per minute . You won't be needing anymore than 20 hp, so a decent sized automotive turbo will do the job , something with >50mm inducer on the comp . The post shutdown cooling is because our idling temps are still much higher than a diesel engines idling temps , most auto manufacturers advise not to shutddown a turbo'ed engine from high power settings without a few minutes at idle first to cool the turbine and reduce heat soakback and coked bearings , unless the turbo has a watercooled bearing housing, but even then its best to have a few minutes at lower power settings . Cheers John |
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parkland
Junior Member
Joined: February 2015
Posts: 57
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Post by parkland on Feb 1, 2015 19:07:17 GMT -5
Hi Welcome to the Group :-) You're attempting a very ambitious project .................checkout RC Don's Site for some pointers www.rcdon.com/html/experimental_projects.html . For a "vehicle" its best to use the 2 shaft system with a freepower turbine to produce the shaft power , single shaft engines aren't really suitable . Forget compounding , theres simply too many problems to overcome , especially for a first build , you'll save some fuel but not a huge amount, it'll still be thirsty unless run at max rpm/pressures. Fuel burn rates will be > 1 pound of fuel per horsepower per hour at full power , expect that to increase by >50% if at low power settings , so 60 hp will need >60 pounds of fuel per hour or >1 pound per minute . You won't be needing anymore than 20 hp, so a decent sized automotive turbo will do the job , something with >50mm inducer on the comp . The post shutdown cooling is because our idling temps are still much higher than a diesel engines idling temps , most auto manufacturers advise not to shutddown a turbo'ed engine from high power settings without a few minutes at idle first to cool the turbine and reduce heat soakback and coked bearings , unless the turbo has a watercooled bearing housing, but even then its best to have a few minutes at lower power settings . Cheers John OK So then I really want the free power turbine then. I agree I won't need over 20 hp. At least I can narrow things down a bit, and get a clearer vision of what needs to happen. That is a crapload of fuel haha, good thing these can run on lots of fuel sources. Has anyone ever installed a water jet, post turbine, to cool it off some as it spools down? Otherwise I suppose equipment would be needed to circulate air somehow. |
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Post by racket on Feb 1, 2015 20:18:05 GMT -5
Hi
Its always possible to install an electric RC ducted fan setup to blow some air through post shutdown.
Another alternative is to have a "dump valve" between the gas producer and freepower turbine that can be opened at idle to reduce backpressure on the gas producer and minimise temperatures for a few minutes before shutdown .
Cheers
John
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mitch
Senior Member
Joined: August 2014
Posts: 285
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Post by mitch on Feb 1, 2015 20:22:02 GMT -5
Parkland, your project sounds similar to what I am currently working on- I use a GT3788VA turbo ( which you might be familiar with if you drive a ford 6.4) but I leave the VNT vanes open all the way, as I had trouble starting the engine when I actuated the vanes with a 12v power supply. I am no expert and don't have nearly the knowledge or experience that many other members on here have. But as far as your question about intercoolers, I think I understand the idea. Try to think of the intercooler in terms of density, not temperature. More dense= more fuel, which is why roots blowers are less efficient that turbochargers on automotive applications, due to the far greater temp rise across the screw type compressors compared to the centrifugal compressor. As far as your free power goes, I am using an ST-50 turbocharger, using my gas producer's oil supply to also supply oil to the bearings on the free power, and I am using a sealed ball bearing on the end of the turbo shaft by where the gear will be mounted to prevent radial thrust loads due to the loading and tension from the change drive.
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Post by racket on Feb 1, 2015 22:41:23 GMT -5
Hi Mitch
The intercooler is used between compressor stages on a compound engine ( 2 stage compression) to not only minimise the power required to compress the air going through the second stage , cool air compresses more easily than hot air , but also to save the alloy second stage comp wheel from exploding due to its tensile strength degrading from the high compression temperatures , if your first stage compresses to 3:1 PR at 72% effic theres an ~148 deg C temp so a T2 going into the second stage will be ~163 deg C or ~325 deg F , do another 3:1 PR through the second stage and you'll have an outlet temp of 386 C - 728 F , that second stage alloy wheel ain't gunna survive .
No intercooling required with a single stage compression .
Cheers
John
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parkland
Junior Member
Joined: February 2015
Posts: 57
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Post by parkland on Feb 1, 2015 23:40:24 GMT -5
Parkland, your project sounds similar to what I am currently working on- I use a GT3788VA turbo ( which you might be familiar with if you drive a ford 6.4) but I leave the VNT vanes open all the way, as I had trouble starting the engine when I actuated the vanes with a 12v power supply. I am no expert and don't have nearly the knowledge or experience that many other members on here have. But as far as your question about intercoolers, I think I understand the idea. Try to think of the intercooler in terms of density, not temperature. More dense= more fuel, which is why roots blowers are less efficient that turbochargers on automotive applications, due to the far greater temp rise across the screw type compressors compared to the centrifugal compressor. As far as your free power goes, I am using an ST-50 turbocharger, using my gas producer's oil supply to also supply oil to the bearings on the free power, and I am using a sealed ball bearing on the end of the turbo shaft by where the gear will be mounted to prevent radial thrust loads due to the loading and tension from the change drive. That's the 6.0 turbo.. the 6.4 has compounds with vVT on one of them. The 6.4 turbo would be tempting to try since the regen heat is so extreme that there must be some great materials in them. I have a spare f250 with a 6.4 that I bought to do an engine swap but I was thinking of keeping the compound turbos to use on the mechanical engine that's going in there...maybe. |
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parkland
Junior Member
Joined: February 2015
Posts: 57
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Post by parkland on Feb 1, 2015 23:48:39 GMT -5
Hi Mitch The intercooler is used between compressor stages on a compound engine ( 2 stage compression) to not only minimise the power required to compress the air going through the second stage , cool air compresses more easily than hot air , but also to save the alloy second stage comp wheel from exploding due to its tensile strength degrading from the high compression temperatures , if your first stage compresses to 3:1 PR at 72% effic theres an ~148 deg C temp so a T2 going into the second stage will be ~163 deg C or ~325 deg F , do another 3:1 PR through the second stage and you'll have an outlet temp of 386 C - 728 F , that second stage alloy wheel ain't gunna survive . No intercooling required with a single stage compression . Cheers John Ok... What about changing configuration radically here... What about the compressors both feeding the combustion chamber separately, but the exhaust turbines are compounded ? In essence, would that not change the effective turbine performance ? |
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Post by racket on Feb 2, 2015 0:23:23 GMT -5
LOL.............it would certainly change it :-)
The first stage turbine wheel would have to be oversized to cope with double the flow and would "overspeed" before its comp wheel produced the required pressure ratio , the second stage turb wheel would be even further oversized due to the reduced density , more problems again :-(
One thing we must remember with turbine engines that differ considerably from turbochargers is there ain't no pistons forcing gases through the turbine stage at pressures higher than the compressor discharge pressure ( P2) , with a turbo based gas turbine the P2 leaving the comp wheel is the highest pressure within the engine , the pressure continues to drop for every inch we move away from the comp wheel through the engine, the turbine stage has to "voluntarily" swallow the gases , they can't be "forced" through it, try to force them, and the compressor/s will surge .
Cheers
John
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parkland
Junior Member
Joined: February 2015
Posts: 57
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Post by parkland on Feb 2, 2015 11:03:14 GMT -5
LOL.............it would certainly change it :-) The first stage turbine wheel would have to be oversized to cope with double the flow and would "overspeed" before its comp wheel produced the required pressure ratio , the second stage turb wheel would be even further oversized due to the reduced density , more problems again :-( One thing we must remember with turbine engines that differ considerably from turbochargers is there ain't no pistons forcing gases through the turbine stage at pressures higher than the compressor discharge pressure ( P2) , with a turbo based gas turbine the P2 leaving the comp wheel is the highest pressure within the engine , the pressure continues to drop for every inch we move away from the comp wheel through the engine, the turbine stage has to "voluntarily" swallow the gases , they can't be "forced" through it, try to force them, and the compressor/s will surge . Cheers John John, You seem very knowledgeable with this stuff. Let me ask you an off the wall, off topic question, haha. Feel free to correct me on anything here, if I say something like I know what I'm talking about, I don't haha. OK, basically, a gas turbine jet engine runs from an increase of pressure between the compressor and exhaust turbine, created by heat, and expansion of air and gasses. If a compressor and exhaust turbine had the same vane size, and angle, it would never run, because the force would act equally on both turbines, so no work could be done at all. So we rely on the exhaust turbine being designed to flow more than the compressor, so that expanded air takes the path of least resistance, causing the compressor to spin, and the engine to run. Now heres my "what if" question... What if, the combustion chambers were changed from "free flowing", as they are now, into "controlled flow" combustion chambers? Here is what I'm thinking; Compressor pushes air to 2 combustion chambers, each with a set of intake valves, on springs. So the air would be pushed into whatever chamber has less pressure. Each combustion chamber would take a turn firing, and expelling gas to the exhaust turbine, after travelling through an exit exhaust valve, so that one chamber can't force exhaust into the other chamber. So if one chamber is always burning and expelling exhaust, the other chamber would always be filling with air, as it's internal pressure would be less, and the compressor would fill it. The intake valves would probably work fine with little springs, and wouldn't need much engineering behind them. The exhaust valves I am not sure, it would need to stay closed when filling with air, and open during combustion... maybe springs as well, and big valve off a train engine or something. Why all the trouble? The way I see it, in a jet engine, if the combustion chamber is running at 10 psi, the compressor must force air through at 10 psi, meaning it is working to push xxx cfm of air @ 10 psi. If controlled chambers were used, it would not have to push air against 10 psi, for the same given power, as the "10 psi" number is the combustion pressure, not the intake pressure, although with the current design, combustion pressure IS intake pressure, because there is no valve or control, we rely on the velocity of the gas itself, to make it run. That is the point I am trying to make, if if the compressor didn't need to push air against the combustion pressure, wouldn't performance be a lot better? The way I see it, with a few valved combustion chambers, we could still have the same combustion pressure driving the exhuast turbine, but since the compressor no longer has to push against combustion pressure, intake velocity should be much improved, and power would be better. We would need something like a small diesel 2 cylinder injection pump, and diesel injectors in the combustion chambers. Or some type of fuel pump, and a system to inject in one chamber, then the other, never both at the same time, or else it would stall and act like a normal jet engine, but with added restriction of valves and smaller flow paths. I think this would give way more power, and allow way better spooling, as the engine would run much better on lower efficiency part of the turbo map. What problems can I see? Exhaust pulses shouldn't really be an issue, these turbochargers live fine behind engines, which deliver steady exhaust pulses all day long. Back pressure from one combustion chamber, lasting too long, causing it to not "empty" all the way, before the other one fires, causing pressure buildup in both combustion chambers, and performance decrease.... This would be a fuel timing issue, the injection is lasting too long. A bigger injector would be needed, to deliver the fuel quicker, and run a lower operating frequency with the combustion chambers, so that they have the chance to expel all pressure on the exhaust turbine. What size combustion chamber? I don't know, it would depend on operating frequency, either small ones firing more often, or larger ones operating less often. I don't really know what would be best. I am sure there is a performance gain to be had here, as we are saving energy by not compressing air against combustion pressure. |
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mitch
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Posts: 285
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Post by mitch on Feb 2, 2015 11:05:20 GMT -5
Racket, thank you for clarifying!
I was more so trying to get at the usage of an intercooler on single turbo automotive engines.
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Post by enginewhisperer on Feb 2, 2015 11:16:17 GMT -5
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parkland
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Joined: February 2015
Posts: 57
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Post by parkland on Feb 2, 2015 11:38:06 GMT -5
OK I did, Interesting stuff, but not what I was thinking at all though. When I said "2 combustion chambers", I meant basically little hollow tanks, in which fuel would spray and ignite. No moving parts. Very similar in operation to a current combustion chamber. The only difference operationally, would be that instead of a constant fill, burn, expansion to do work, mine would fill an empty chamber, and burn and do work while isolated from the compressor, to save energy. The combustion chambers would just take turns doing work, and while one is fueling and doing work, the other would be empty, so the compressor does not have to work as hard to force air in. I know it sounds complex, but the way I'm picturing it seems very simple. EDIT: OK I know I said no moving parts, that isn't correct. The moving parts would be the valves. Each combustion chamber would have an intake valve, so that when burning, combustion gasses are forced to the exhaust turbine, not back into the compressed air, and also have exhaust valve, so that when one combustion chamber is burning, the exhaust is forced over the exhaust turbine, and not back into the other chamber which would be filling with fresh air at the time. |
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Post by enginewhisperer on Feb 2, 2015 13:42:38 GMT -5
If you have valves but no secondary form of compression you may be able to have more of a mismatch between turbine inlet and compressor outlet pressures, but they will still have to be fairly close (otherwise residual pressure on the turbine side will always be higher than the compressor outlet pressure and you won't be able to fill the combustion chamber with air)
A free piston engine allows a much higher compression ratio, which can extract more energy from the fuel and give higher overall efficiency.
If it's built like a two stroke engine, it can perform the valve functions with minimal parts, as well as increasing the compression ratio.
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