Variable geometry turbo

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Markproa

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My converted engine is a Peugeot 1600cc DV6 Turbo diesel. I have just realised the original turbo is variable geometry so hence no wastegate and the actuator electronically controlled. My problem is that I've done away with all the electronics and I'm running a mechanical distributor pump instead of the common rail. That leaves me without control for the variable geometry vanes.
I've been advised I can run a manual control cable back to the instrument panel so I can choose say 1.5 atmospheres on take-off and 1 atmosphere for fast cruise.
Does anyone have knowledge around this to advise of any issues I should look out for? Is it possible to overboost a VG turbo?
 

Jay Kempf

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Sounds like you need a small single board computer and a pressure sensor. Raspberry Pi, Arduino, PCduino, etc... Lots of hobbyists building little control servo systems like that. I am sure one can be co-opted for a single point controller like that but if you want more you have to put sensors back on the engine so you can measure and adjust.
 

galapoola

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You could also use your throttle control to simultaneously adjust engine RPM and vane angle. Not sure if it's been done. The FADEC boys laud a single control lever and let the CPU do the rest. So if you have a lever style throttle, figure out the position for take off max RPM. Do the same for fast cruise and lowest flying RPM. You'd need to figure out where in the arc of movement to attach the second push pull cable for the blower. In the graphic below the outside cable would move more than the inside cable with the same rotation of the lever. Not sure which would need more or less range of movement at the end but that would be one way to have a single lever do both. It would be an interesting mechanical puzzle to figure out, that is if such an idea is even a best practice.
Untitled-1.jpg
 

TFF

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I would say yes, you can overboost. You can either lock it at some position and live with it or put it on a control. Control would be the best, but if your rules do not allow extra control, you will probably lock it at around 1/3 closed and fly.
 

wsimpso1

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My converted engine is a Peugeot 1600cc DV6 Turbo diesel. I have just realised the original turbo is variable geometry so hence no wastegate and the actuator electronically controlled. My problem is that I've done away with all the electronics and I'm running a mechanical distributor pump instead of the common rail. That leaves me without control for the variable geometry vanes.
I've been advised I can run a manual control cable back to the instrument panel so I can choose say 1.5 atmospheres on take-off and 1 atmosphere for fast cruise.
Does anyone have knowledge around this to advise of any issues I should look out for? Is it possible to overboost a VG turbo?
If you want to stay electronics free, finding a conventional turbo, wastegate, and manifold pressure controller for that engine might be your best option.

Second best is going with manifold pressure sensors, a dedicated controller, and dedicated actuator to run the geometry, but then you have to figure out how much is automatic, get the gains and actuators right to make it respond correctly, control manifold pressure and turbine speeds smoothly, do the Failure Mode Management work, and figure out when to cancel electronic control and give manual control to you.

I think my last choice is to set manifold pressure by looking at the manifold pressure gauge and moving a lever by hand while keeping up as you change altitude, etc.

It would be great if Ross at SDS were to weigh in.

Billski
 

Puggo1

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hi, I am interested as I've also a DV6 destined for an aircraft here in UK. There are plenty of diesel aircraft in France with your engine mods. www "Dieselis" for a start.
before I reply a little more information would be helpful?
- goal ?? fast spedster or economic STOL aircraft, desired hp/rpm
- psru or direct drive
- torque pulse limiting device
- fixed or variable pitch
- coolant limitations
regards
Puggo1 (ex Albury, NSW now UK)
 

PMD

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My first thought would be to go with a properly sized turbo with no variable vanes, no wastegate. Airplanes are really constant speed engines (or nearly so) and performance off peak (i.e. takeoff and cruise power range) is not that important. As you have lost the advantages of HPCR, you are now in the world of 20 years ago tech for fuel injection (and I am saying that with understanding that is adequate for you goals). BUT: since you already HAVE the VVT turbo, and it is bought and paid for, mounted and functional the idea of controlling it is not all bad. At the most basic level, running it on a test stand (airplane on ground) and adjusting the gate position for clean exhaust at takeoff power will give you a setting you could just lock permanently and be done with it. Adding a control cable, using it to bring boost up after setting TO power is workable, but I don't see how it is going to be of any real advantage vs. just "set and forget".

What are you using for injectors and injection pump, if you don't mind me asking?
 

Geraldc

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This sort of controller might work but I am unsure about the vacuum on a Diesel
 

Hephaestus

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Back in the 90s... A few of the vdub frankenmotors (1.6/1.9 mix and match) got built with the newer VGT.

You'd manually set/lock the vanes - and install a wastegate. Don't just drill/tap directly - pretty sure the consensus was do a copper?brass? Insert...
 

Markproa

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hi, I am interested as I've also a DV6 destined for an aircraft here in UK. There are plenty of diesel aircraft in France with your engine mods. www "Dieselis" for a start.
before I reply a little more information would be helpful?
- goal ?? fast spedster or economic STOL aircraft, desired hp/rpm
- psru or direct drive
- torque pulse limiting device
- fixed or variable pitch
- coolant limitations
regards
Puggo1 (ex Albury, NSW now UK)
The engine is in a Gazaile 2 designed by Serge Pennec who also designed the Dieselis you mention.
Goal-Economical/fastish 135knot cruise. Around 95HP 3800rpm
PSRU- tooth belt 1.66 reduction (same as Dieselis)
Torque limiting device: Flexible rubber coupling
Fixed pitch
- coolant limitations-none that I know of.
 

Markproa

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At the most basic level, running it on a test stand (airplane on ground) and adjusting the gate position for clean exhaust at takeoff power will give you a setting you could just lock permanently and be done with it. Adding a control cable, using it to bring boost up after setting TO power is workable, but I don't see how it is going to be of any real advantage vs. just "set and forget".
What are you using for injectors and injection pump, if you don't mind me asking?
Set and forget sounds good: I don't have any experience with turbo diesels* and I'd want to know that locking the turbo vanes without a wastegate won't risk an over-boost situation. I've got more than enough HP with this engine so not scrounging for the last ounce: I'm more interested in economy. My hope is to cruise at 135knots using 10 litres/hour (155mph@2.6usgph): Gazailes in France are getting that. The aircraft designer suggested a manual control from the cockpit, I've asked him to elaborate on how this would be set up and work. The pump is a Bosch VE and the injectors are from a Rover 400 series, Bosch KBAL70P46.

*I've spent a lifetime playing around with petrol engines and now find myself with three diesel cars in the driveway and a diesel aeroplane!
 
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PMD

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Mark: to start with, I suppose we should consider your altitude aptitude (sorry, couldn't resist that one). Set-and-forget I would try by making a screw-adjustable linkage starting with open vanes, run to TO power in fuel supply, increase MP by closing vanes with the turnbuckle or screw until you have a clean exhaust and/or your target MAP then lock down the adjuster. The downside of doing this is that you will have max power only at your setup airport altitude and temperature, and if you want to go to greater altitudes, fuel supply will continue as per pump delivery, but MAP will drop off, giving lack of air. The solution for moderate altitude would be to adjust the TO power to excess air to target the original MAP setting at cruise altitude (which will give you clean burn and best climb at that altitude). Since power is defined by fuel delivery, the air is just there to make it burn fully BUT: lack of sufficient air will result in soot (from exhaust and into oil) and excessively high EGT, so you do have to look at it carefully.

If you want to make the big numbers in middle altitudes (I like 15,000+/- feet for long distances as it happens) you really want to maintain some MAP control. The other thing to consider is that the turbo is designed for the kind of density altitudes that a car is expected to encounter, and you may need more compressor wheel/scroll to keep airflow at aviation altitudes.

I too started off as a gasser gearhead (motorsports) but "discovered" diesels 42 years ago. It seems the passion grows with one's ability to think logically.
 

wsimpso1

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Mark: to start with, I suppose we should consider your altitude aptitude
LOL! I am going to use that one.

The downside of doing this is that you will have max power only at your setup airport altitude and temperature, and if you want to go to greater altitudes, fuel supply will continue as per pump delivery, but MAP will drop off, giving lack of air.
We are used to having an engine that starts and idles only if a little rich, has a throttle valve to control air flow, we keep the valves in it by running rich at high power, it makes peak torque (at any given airflow) around stoich, EGT peaks around stoich. Leaner than stoich, power drops slowly and EGT's come down, then we get into lean roughness.

But with a Diesel and atmospheric manifold pressure, we start out really lean at low power and we enrich the mixture to make more power until we get to the smoke point. Now we are at or above stoich and excess fuel flow without enough air to burn it pulls power down. Since we want enough power to fly, we pump in more air so that we can run the right amount of fuel for that power. At some point in adding more air and more fuel, our EGT's get higher than we would like to see for durability of things like exhaust valves and the turbine. How to to keep those temps down? Two things: Cooler inlet air and more air. Great thing about this is a bigger intercooler is usually less restrictive, allowing higher manifold pressures at less turbo speed. Now the fuel charge is diluted in more air (leaner of peak again), the combustion starts at lower temps, so ends at lower temps, and our exhaust valves, piping, and turbine live much longer because they run at more reasonable temps.

Standard turbochargers run with a wastegate that is somehow controlled to adjust the exhaust gas split through and around the turbocharger. Old school is a mechanical controller referencing manifold pressure, newer cars use sensors and the ECU with a map of desired MP versus RPM and fuel flow (or some other power indication) and an electric actuator. Go with variable configuration turbo, and the ECU controls the config based upon the sensors and MP map through an electric actuator. True, the automakers go to all this effort to meet emission regs while giving good useable power over the entire range of engine speed and altitudes, etc. In an airplane we only want full power for take-off and good cruise over our cruise altitude range. Trouble with that is at 8000 feet we have lost a quarter of our sea level inlet air density, and we have commonly used airports around the civilized world that are higher than that... OH, and I think we want to manifold pressure to go atmospheric when we pull the power for descent and landing.

So, anyone considering being the developer of this new engine - this is no longer copying someone else's successful engine - this IS a new engine scheme. The job is to deliver enough power for comfortable take-off and climb and good cruise power at your cruise altitudes while always keeping Turbine Inlet Temperature low enough and turbocharger within its usual speed range. You get to figure out your targets and how to do all that. With the configuration set for standard temperatures and pressures and takepoff power the turbo is effectively choked to not overboost you there. I suppose you could add a blowoff valve to prevent overboost. Then you climb, and you get what you get from the turbo with it choked for sea level and power. Yeah, turbine speed will float to different rpm at your fuel flow as gas densities and flows change, but they may not go where you want.

Frankly I do not know if altitude and reduced fuel flows will cause the power to drop way down or if the turbine/compressor will choke or overspeed. You get to figure all this out. Hugh MacInnes has a nice book on applying turbos, selecting them, reading the maps, manifold pressures, intercoolers, control strategies, and so on. Variable geometry compressors came after his publication. There are other books.

I do urge anyone considering this path to get the maps for your turbine and your compressor and become educated on how these gadgets work so you will have an idea if your selected turbo, will behave on one setting over that range of air densities and power needs.

I suspect that the lowest fuss solution will be an identical turbocharger and controller to the ones already in reliable use with this same engine.

Billski
 

pictsidhe

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If I we're doing this, I'd find a conventional turbo with a bigger hot side. As has already been pointed out, you don't need low rpm torque. Depending on your fuel injection pump, you may not even need a wastegate. Some big constant speed diesels run with no wastegate. But, that may not work well for altitude.
 

wsimpso1

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This sort of controller might work but I am unsure about the vacuum on a Diesel
The lowest manifold pressure you will get in a Diesel is usually local atmospheric pressure - no vacuum - then we boost, but pressures below atmospheric is unlikely. No throttle plate at all on a Diesel, so no vacuum.

The video, well, he is using a electronic controller, which the OP is trying to avoid, and he did talk about actuating the variable geometry turbine with electric and with air operated actuators. Then he told us he did not know how he was going to make it all work. Then, well, he drinks Heineken, has his Glock on the bench, with his salvaged and new parts for his Honda, while also showing us an actuator taken from his BMW motorcycle... I guess somebody had to do all those things simultaneously.

Billski
 

Geraldc

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Until this post I was unaware that this technology existed.So I did an internet search and found lots of information on how to do this.
But as is the case these days you have to sort the wheat from the chaff.
The bit I thought might work was the dual air cylinder type with one end hooked up to boost pressure and the other to manifold pressure.
This could possibly be done with an off the shelf pneumatic cylinder.
Or even one with 2 different size pistons in one unit.
 

PMD

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LOL! I am going to use that one.

I suspect that the lowest fuss solution will be an identical turbocharger and controller to the ones already in reliable use with this same engine. Billski
You are forgetting what you just explained (and I mentioned in my post): the turbos and controllers in use with this engine are not likely expecting to be a 0.5 Bar, so the compressor wheels are too small. Since one can get the VE pump to deliver any quantity of fuel regardless of Atm, MAP, etc. there is potentially as much engery in the exhaust at altitude as at sea level, so the turbo can overspeed - thus the need to go with more compressor to add load to the exhaust turbine to limit RPM. We do it in the little car diesel world all of the time - but to get more airflow for the sake of airflow (which is about that using more compressor at altitude is doing). There are some very simple, low cost solutions such as installing fancy billet wheel in stock housing that can work small wonders on this count.
 

Markproa

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If there is one thing I've learnt about diesels over the last couple of days it is to forget everything I know about petrol engines. Thanks Bilski and PMD, you have increased my understanding 100 fold, along with a load of other reading I've done.

I also received a reply from Serge. He says at take-off to have a maximum pressure which does not make you lose engine revs at take-off throttle, so no more air than needed. At cruise, you do the same thing, set the cruise revs then reduce the turbo pressure to just above where revs decrease. So from this I gather I would find a setting (distributor pump and boost) that gives maximum HP (little smoke) that can be used for take-off at sea level (most of Australia). When flying I would reduce throttle (a misnomer) to cruise speed then back off the turbo until it starts to decrease in revs. As altitude increases, I dial in more boost keeping an eye on revs and EGT. Have I got that right?

I guess there will also be a setting I could use to 'set and forget' that will give me enough boost for adequate take-off power and OK in cruise, one that can be used by other pilots without special instruction, similar to a non-variable turbo.

BTW, my basic medical doesn't allow cruising at altitudes above 10,000 feet in Oz and our highest airport is 4000ft with a vast majority being less than half that. though it can get very hot.

Mark
 
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wsimpso1

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The bit I thought might work was the dual air cylinder type with one end hooked up to boost pressure and the other to manifold pressure.
The output of the turbo is boost pressure, and manifold pressure is essentially boost pressure - no pressure difference between them. The exception is in using an intercooler, then the manifold will be slightly lower pressure than turbo out - only by the pressure drop through the intercooler. That is a pretty small difference and will be a function of how much air is flowing - it will not be a useable signal for control of manifold pressure.

Ideally, you have a gadget that senses absolute pressure in the manifold, and then either mechanically compares that to desired pressure and drives a servo to move the wastegate to maintain a set manifold pressure or an ECU reads the sensor, consults its map of intended manifold pressure as a function of other inputs, and then electrically drives the wastegate to maintain the mapped manifold pressure.
 
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