What changes that anyone has done has kept at least the base performance on a 617 turbo but has made a noticeable improvement in fuel milage.

change ip time to 28 degrees BTDC

drip method is best

Do you want to try this on mine Mike?

2.47 rear end, timing advance, no acceleration on the uphill, slooooow acceleration from stop, time stoplights so you roll through rather than stopping, never touch the brakes, coast whenever possible, make your idle low (like 600-650rpm). If you really wanna get good mileage, the #1 thing to do would be to improve aerodynamics of the car. Front air dam, side skirts, wheel covers, boat tail, underbody panels and fairings behind the rear tires. Also removing mirrors, improving the shape of the front of the car, and removing all exterior trim would help.. I have been really tempted to try all these things.

What is this "timing 27°BTDC" and how do you do that????

thx

I have noticed that turning the ALDA out seems to improve mileage. If you go too far you have smoke and mileage goes back down. Anyone else noticed this?

What is this "timing 27°BTDC" and how do you do that????

thx

Do a search for "drip method" or look in the DIY links under timing for a writeup on how to adjust the timing via the drip method. You will need to purchase or make a drip tool.

As for the ALDA, I have mine gutted (the housing is on as a dust cap but there are no parts inside of it) and I have noticed that if I stomp it from a stop, it will smoke a little bit, but if you go easy (and I mean eeeeeeeaaaassy) on the go pedal it will respond in kind. Removing the ALDA gives you direct control of the rack. Just keep this in mind when you are driving and you will be able to control fuel delivery how you want it, whether it be only a little fuel or a lot.

300CD-
valves set very carefully,
bye bye EGR,
247 diff,
AAZ injectors @150 bar with 265 nozzles,
vogtland springs lowered it quite a bit & ought to reduce wind resistance some, alda 1 turn cc -no smoke except a very little when just starting from cold.

What changes that anyone has done has kept at least the base performance on a 617 turbo but has made a noticeable improvement in fuel milage.

Although I have yet to complete the work, removal of the trap cat from 617.952 engines (California version of the '85 300D and SD cars) has been claimed on this forum as well as documented in M-B specs to improve both power and fuel economy.

A couple of horsepower and a couple of mpg are said to result from replacing the cat with a straight pipe for testing purposes only. I plan a long test, say 200,000 miles, to get good data.

Jeremy

I plan a long test, say 200,000 miles, to get good data.

Jeremy

LOL!!!:bowrofl:

On an SD a cherry bomb muffler helps a little. I have also replaced my turbo with one from an OM603 engine (not exactly a drop in replacement) which is of newer design and all indications are that this too is an improvement in mileage and power.

Although I have yet to complete the work, removal of the trap cat from 617.952 engines (California version of the '85 300D and SD cars) has been claimed on this forum as well as documented in M-B specs to improve both power and fuel economy.

A couple of horsepower and a couple of mpg are said to result from replacing the cat with a straight pipe for testing purposes only. I plan a long test, say 200,000 miles, to get good data.

Jeremy
I don't think I've ever seen a catalytic converter on a diesel. Course I'm pretty new to diesels - this is only my second one, and both of them are OLD (84 & 86). Got a picture of it? Mine has a muffler-looking exhaust piece just ahead of the rear axle, but from what I've been told it is a resonator - not a catalytic converter....

And like Greasy Beast, I drive like a geezer and time lights to avoid stopping as much as possible. I also don't carry any extra weight (junk in the trunk), and I have blocked off my EGR too...

So maybe I should be aware of what is "normal " city and highway mileage for these cars. I had a 80' sd that consistently got 26 in town and 29-31 on the freeway. No diesel since then has done that good.

I don't think I've ever seen a catalytic converter on a diesel. Course I'm pretty new to diesels - this is only my second one, and both of them are OLD (84 & 86). Got a picture of it? Mine has a muffler-looking exhaust piece just ahead of the rear axle, but from what I've been told it is a resonator - not a catalytic converter.....

It is not a true catalytic converter but rather a soot trap that collects soot when the engine is cold and tending to be a little smoky. When the engine and everything around it heats up, the soot is supposed to burn off. It was installed in the 617 engines for the 300D and SD 1985 California cars only. At first Mercedes used a "trap oxidizer" that was replaced every 30,000 miles on warranty; in the early 90s they changed to a "trap catalyst" that was a one-time replacement.

The trap was installed between the exhaust manifold and the turbocharger. (See the attached pictures.) Many people replace the entire manifold assembly to get rid of the trap; I have chosen another route.

Jeremy

300CD as well.

On an SD a cherry bomb muffler helps a little. I have also replaced my turbo with one from an OM603 engine (not exactly a drop in replacement) which is of newer design and all indications are that this too is an improvement in mileage and power.

Any reduction in backpressure should help fuel economy AND power a little.

How does it sound with the cherry bomb? I am looking to make mine sound more powerfull but not loud when I eventually replace my exhaust.

I seem to have gained a bit over 2 MPG with my VGT. I believe this is due to lower turbine inlet (back) pressure when cruising.

THAT's worth the mod. Nice benefit.

I believe this is due to lower turbine inlet (back) pressure when cruising.

Right. I can basically turn my turbo off when cruising, it makes only 0-2psi of boost and has little more restriction than a non-turbo engine.

What changes that anyone has done has kept at least the base performance on a 617 turbo but has made a noticeable improvement in fuel mileage.
I'm making 20hp, 46lb-ft more than stock (dyno verified) and still average 26mpg in mixed city+highway driving and 29mpg on highway trips.

...29mpg on highway trips.
How fast do you drive?

Right. I can basically turn my turbo off when cruising, it makes only 0-2psi of boost and has little more restriction than a non-turbo engine.



I am at 5-6 psi when crusing on the freeway. I could probably get a bit more economy by further opening the vanes at cruise, but for now I will stick with my simple actuator system. I just got 27.5 MPG on a highway trip at 65 MPH, up from 25 or so. I also still have the 3.69 rear end. :o

How fast do you drive?

70mph. I know for sure I can break 30mpg if I can keep it under 60mph.

Covert to run on waste veg oil. 80-113 MPG if you drive 50 miles to work. (summer or longer distances will improve MPG)

covert to run on waste veg oil. 80-113 mpg if you drive 50 miles to work. (summer or longer distances will improve mpg)

False, waste fryer crap will reduce base performance as well as the lifespan and long term performance.

I think he means MPGD as in miles per gallon diesel(warmup/shutdown cycles; not counting the "free" wvo

Any reduction in backpressure should help fuel economy AND power a little.

How does it sound with the cherry bomb? I am looking to make mine sound more powerfull but not loud when I eventually replace my exhaust.

Mine is fairly quiet still as I kept the resonator. It is not much louder than stock. Most noise comes from the engine compartment. I do have an 85 Cali car that has an Ox cat and that also contributes to muffling the noise however.

I think he means MPGD as in miles per gallon diesel(warmup/shutdown cycles; not counting the "free" wvo

The same way this guy claims his 400hp mustang gets 100MPG because it burns E85. :rolleyes:
This

He would be getting 100mi/gal of paid fuel if he was distilling his own E100 and blending. However, the difference is he is paying for 100% of the fuel he burns, not 15%.

No, the difference is he actually gets 16.5mpg.

Not bad, my mustang(before the engine seized) was getting 12-15mpg

Right. I can basically turn my turbo off when cruising, it makes only 0-2psi of boost and has little more restriction than a non-turbo engine.

I'd think that a change of turbo settings or geometry would improve your MPG then.

If your boost is zero at cruise, then you're not using the 'free' exhaust energy to overcome the less-than-100% VE, correct?

In another post, someone mentioned running around 5psi at cruise. That sounds like about the optimum point for best economy.

Since I drive almost all rural 2-lane, in mountain-country; I spend a lot of time at very low throttle...i.e. just maintaining say, 40mph, against wind-resistance...because there's another curve coming up soon where I'll have to brake.

So I've always been interested in setting things up to get boost at very low power-settings. Yet I need a turbo system that works well at near full power as well; because every 10 curves there's another mountain to climb... :D

In lieu of the $$$ VGT's that I can't afford, I've often wondered about experimenting with a tandem turbo setup. Something tiny from a sub-2L, in tandem with either a stock 617 turbo, or even a slightly larger one (to keep backpressure down at the upper-end of the power/rpm range).

My first guess is to use backpressure to control the gates that'd switch between the two turbos...but I've really not thought it all out in detail yet.

So many experiments to try, so little time.... :D

If your boost is zero at cruise, then you're not using the 'free' exhaust energy to overcome the less-than-100% VE, correct?

Boost isn't free, it causes backpressure in the exhaust that makes the pistons work harder to push exhaust out of the cylinders.

The 617 is good for 88hp without the turbo and it only takes around 20hp to push the car down the road at a constant 55mph. The lower the boost the less work the engine is doing to make that 20hp.

If you have the $$ for a second turbo, you have the $$ for a $100 VGT off of eBay. :D

Boost isn't free, it causes backpressure in the exhaust that makes the pistons work harder to push exhaust out of the cylinders.

The 617 is good for 88hp without the turbo and it only takes around 20hp to push the car down the road at a constant 55mph....

True, but that's irrelevant....i.e., the power required to push a certain car at speed 'X' isn't relevant to the efficiency of boost vs. no-boost.

No matter -what- the power-level is, the engine operates more economically if the exhaust energy is captured and used to replace pumping-losses which otherwise come out of crankshaft-power.

You're correct of course that back-pressure adds workload to the pistons, but you have to recognize that the -level- of that pressure is -proportional- to the power-level of the engine.

I.e., at the 20hp output level you mentioned, the BP in the exhaust system is a lot less than at 88hp.

It's proportional....at lower output, less HP of boost-pumping is needed AND less HP of backpressure-pumping-work is generated at the pistons.

Also, it's not the case that a turbo has to add a lot of backpressure in order to pump air. A turbo extracts most of its energy from the -heat- of the gases; not from the pressure.

If you take a look at power-output and BSFC curves for both turbo and NA versions of the same engine, you'll see that the turbo version is always more efficient (i.e. bsfc) even in the lower regions of power-output.

I can't claim that every single engine ever made acts this way; but we do a lot of genset, pump, and mine-haulage overhauls and retrofits here, and I've yet to see a single make or model engine whose charts did not show such an across-the-board efficiency advantage for the turbo version.

In any case, I'll stand by what I posted....if he has set up his turbo system so that it's not pumping air at cruise, then he's not getting the best-possible MPG yet, imho.

Of course, I don't know precisely what "zero boost" meant....was the turbo not pumping at all, and there was actually a -vacuum-, which didn't register on a unidirectional gauge?

Or was it pumping just enough to overcome VE losses and truly was literally zero psi at the intake manifold ?

If the latter, then the turbo actually -is- producing 'boost' (i.e. performing pumping work) even though the gauge read 'zero'.

But to overcome port and valve losses, I think one would want to see more than that 'zero'...perhaps 2-3 psi at the manifold?

Even with 2-3psi, it may still be an -overall- benefit to pump to, say, 5psi, and have a bit of excess air. It's possible that more complete combustion would produce more output than the accompanying (if any) increase in backpressure would cost.

There's a balance-point for that, which can only be found by actual measurements....i.e. either dyno testing or long-run fuel and output tracking.....easy with a genset....hard with a car.... :D

If you have the $$ for a second turbo, you have the $$ for a $100 VGT off of eBay. :D


very true...NOWadays..... :D

but when I first started thinking about it, VGT's were pretty uncommon at the boneyard...

very true...NOWadays..... :D

$150 for my new toy. :D
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&rd=1&item=130241303955
I would have disassembled and cleaned it anyways so the price is right.

$150 for my new toy. :D
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&rd=1&item=130241303955
I would have disassembled and cleaned it anyways so the price is right.


ok, I'm jealous, I admit it... :D

well, I don't have my -engines- yet....so I guess I can wait a bit on the turbos.... ;)

As it happens, I don't currently own any MB cars....got rid of the 300TD in December.....but am preparing to do a pair of conversion-projects for which I'm currently searching for engines.

I will be reading your many excellent posts/threads very carefully when it comes time to select, adapt, and control the turbos for them... :)

A turbo extracts most of its energy from the -heat- of the gases; not from the pressure.

Not true. What really does the job is the aerodynamic flow of the expanding gasses across the turbine, not the heat itself. The exhaust gets cooler as it exits the turbine in the same way that refrigerant gets cold as it exits the expansion orifice, rapid expansion. Thats what confuses people into thinking that the exhaust heat is doing the work.

Think of a wind farm, they don't work by heat but by the flow of air across the blades.

Thats how VNT/VGT turbos work, they increase the potential energy of the exhaust by increasing its velocity and expansion ratio across the turbine.

Back pressure is a natural result of gasses slowing as it contacts the working surface (turbine).

Not true. What really does the job is the aerodynamic flow of the expanding gasses across the turbine, not the heat itself. The exhaust gets cooler as it exits the turbine in the same way that refrigerant gets cold as it exits the expansion orifice, rapid expansion. Thats what confuses people into thinking that the exhaust heat is doing the work.

Think of a wind farm, they don't work by heat but by the flow of air across the blades.


No, that's not correct, in two senses....

First, it's not like a wind-genny; which works solely from lift over a wing; and extracts pretty much the same energy >>regardless of the temp of the gases flowing through it<<.

(important point/difference there)

Secondly, I think you're looking at it backwards; because it is the heat that CAUSES the gases to expand. It is the HEAT energy at work here....not the minimal pressure-differential across the expander.

The exact same kind of turbo-expanders are also used as "energy-recovery" machines in all sorts of industrial processes that handle -hot- gases......like refineries, ammonia-manufacture, etc..

Obviously, there does have to be -some- delta-P, to get the gas through the turbine in the first place; but the majority of the rotational power comes from the heat-energy stored in HOT gas....rather than the minimal mechanical-energy in the typically small delta-pressure across the turbine.

As a thought-experiment, imagine putting the same paltry low psi/delta-P of -cold- gas (i.e. ambient temp) into your turbo-turbine...

Even if the in/out pressures and flow-rate were identical to your engine exhaust, you'd hardly get any shaft-power at all.....simply because there just isn't any energy to speak of in 70F gas vs. 1000F gas.

hope I was coherent with the above...it's 1am here... :D

Heat is only what is making the gasses expand. Its the aerodynamic flow of the gasses across the turbine that does the work, not the heat.

A turbine is a turbine, they all work by the push of gasses flowing over the work surfaces, the temperature makes very little difference. Thats why a turbo will make the same boost just as easily with 600*f exhaust as it can with 1600*f exhaust.

Heat is only what is making the gasses expand. Its the aerodynamic flow of the gasses across the turbine that does the work, not the heat.

A turbine is a turbine, they all work by the push of gasses flowing over the work surfaces, the temperature makes very little difference. Thats why a turbo will make the same boost just as easily with 600*f exhaust as it can with 1600*f exhaust.

No offense intended by the following wording FI....I just want to be very clear:

The above is flat-out incorrect.

I think that by insisting on that 'windmill' view, you're holding yourself back from even greater turbo-mastery than you already have.

The turbine absolutely will NOT "make the same boost just as easily" with 600F gas as with 1,600F gas.

In fact, it will require -considerably- more mass-flow at 600F than at 1600F; to produce the same shaft-power (psi x cfm of boost, or compressor-massflow)

Again, a turbo-turbine is NOT just a windmill....NOT just a simple propeller...it IS a HEAT ENGINE.

....so you gotta remember your Carnot... :D

I sense that you're (reasonably) resisting changing your view of how turbos work just on my word....so I urge you to look it up in any turbomachinery textbook, and verify for yourself that what I'm saying here is true.

It's clear that you already know a ton of good stuff about turbos from the practical/usage side; so I think that if you give yourself the advantage of correctly viewing them as heat-engines instead of as simple 'fans', you'll find the use and tuning of them more intuitive, and even more rewarding. :)


PS; the Carnot numbers also imply that not only can more shaft-power be extracted from hotter gas, but also that a higher -percentage- of that higher energy can be extracted. (i.e. higher efficiency too)

That's why the output-power of heat-engines (including turbos) tends to rise NON-linearly with input temp. Double the temp, get four times the power....roughly that sort of relationship....and with much higher efficiency at the same time.

That first-order relationship between temp and both power and efficiency is why the jet-turbine guys are always pushing the limits of materials so they can raise the turbine-inlet temp just another 100 degrees.

It's also a partial factor in why adding an intercooler tends to reduce the boost a few psi at the same engine conditions as before.

It's not just the added flow-resistance of the IC....it's also the lower energy-content of the cooler exhaust, plus the reduced efficiency of the turbine at that new lower temp....it's a double-whammy on the turbine power output.

The same factor is why it's an advantage to wrap the headers....i.e., to maintain the gases as hot as possible going into the turbine.

Again, a turbo-turbine is NOT just a windmill....NOT just a simple propeller...it IS a HEAT ENGINE.

I'm sorry but the above is flat-out incorrect. If that were true then a turbo would not be able to make any boost if run immediately after a cold start. The simple fact I can make 5+psi with my VNT by revving the engine right after starting disproves your heat engine idea.

verify for yourself that what I'm saying here is true.
I'm sorry but it isn't. They are simple fans.

It's also a partial factor in why adding an intercooler tends to reduce the boost a few psi at the same engine conditions as before. It reduces boost a few PSI because the air is more dense for the same amount of airflow as well as less boost is needed. Measure before and after an intercooler and you can see the drop.

The same factor is why it's an advantage to wrap the headers....i.e., to maintain the gases as hot as possible going into the turbine. No, its to maintain the gasses velocity. As the gasses cool they slow down, wrapping headers keeps heat in to keep the exhaust from slowing inside the pipes and causing restriction.

I'm sorry, but you study up a little bit more on the fundamentals of how these things work.

Very interesting thread. :)
FI, you have loads more experience with turbochargers than I do and I'm chiming in with the utmost respect for said experience but I have to throw in with dozer here.
The expansion valve analogy isn't appropriate because the refrigeration in that case comes primarily from the phase change.
And, to say all turbines work from the flow of gasses across the work surfaces is definitely incorrect. Steam turbines extract a massive amount of heat energy from the steam, otherwise we could just use air pressure.
Turbos are similar. If the exhaust gas is cooler at the turbo outlet than the inlet, where did the energy go? This is a reason exhaust driven superchargers are more efficient than engine driven superchargers. You are using leftover heat energy from the combustion process to compress the inlet charge instead of new mechanical energy (requiring more fuel consumption) from the crank. If it was purely a gas pressure-driven scenario, the pumping losses through the exhaust side of the turbo would not offset the gain from the increased inlet airflow.
Keep the dialogue going. I'm learning from everyone here.:D

If the exhaust gas is cooler at the turbo outlet than the inlet, where did the energy go? As said before, if a compressed gas rapidly expands it releases energy and gets cooler. Basic physics. Thats why moisture in compressed air can form ice as it exits a nozzle and steam gets cool as it expands.

If it was purely a gas pressure-driven scenario, the pumping losses through the exhaust side of the turbo would not offset the gain from the increased inlet airflow.
There is a huge pumping loss in turbochargers. The only reason they work is because the exhaust contains a much larger gas volume from the combusted fuel, the same way steam engines work by using the expansion properties of water.

If heat was the driving force of turbos then remote turbo systems like what is sold by STS Turbo ( http://www.ststurbo.com/ ) would not work either because in the distance the exhaust has traveled it has cooled significantly. They maintain the exhaust velocity by using small exhaust pipes.

Wow.

Steam is used to drive turbines because heating the water into steam causes the water to expand 1600 times! Heating air comes nowhere close. The water to steam transition carries with it the pressure of expansion, that pressure drives the turbine. It is a very simple and efficient way to turn heat into pressure and then into mechanical power.

You keep the turbo wrapped/hot to keep the air from cooling and thus contracting, as FI said, the contracting air would then have less pressure & thus less flow. I always wrapped the turbo and exhaust pipes to it on my Cats, keep the energy in!

Cooling the air through an aftercooler/intercooler will cause less boost pressure at the intake because you have decreased the volume of the incoming air by cooling it, thus the volume, although the mass-flow is the same. It is also because of the resistance of flowing through the tubing and cooler.Exhaust temps will drop somewhat also simply because of the cooler intake air.

Think of creating steam, the expansion causes a massive outflow from the boiler, if it hits a cooler before the turbine it would contract, if cold enough to re-condense there would be no flow left to get to the turbine (I have a working axial-flow steam turbine here on my desk, hot stuff).

Steam is a gas, air is a gas, just a huge difference in the thermal coefficient of expansion.

Although I respect and strongly agree with all else that Dozer has said, and not just because he's a Cat man, I find myself disagreeing with the turbine being a heat engine. The turbocharger is all about geometry, and coatings/materials that have been experimented with or are in use to control heat in turbines are to avoid absorbing the heat into the turbine and to pass it harmlessly through to the exhaust or into another turbine. Materials are always being experimented with that will withstand the tremendous forces and heat in gas turbine engines so that more heat can be introduced, the more heat the more expansion (pressure) and the more compression the more heat & pressure, heat is necessary only to keep the pressures up. The more heat and thus expansion and pressure you can put into the turbine, the more power per cubic foot of engine or lb of engine weight.

What about a cabin-adjustable wastegate? You could dump exhaust through the wastegate for low-power cruising if you wanted to decrease the boost.

So I've always been interested in setting things up to get boost at very low power-settings. Yet I need a turbo system that works well at near full power as well; because every 10 curves there's another mountain to climb... :D

In lieu of the $$$ VGT's that I can't afford, I've often wondered about experimenting with a tandem turbo setup. Something tiny from a sub-2L, in tandem with either a stock 617 turbo, or even a slightly larger one (to keep backpressure down at the upper-end of the power/rpm range).

My first guess is to use backpressure to control the gates that'd switch between the two turbos...but I've really not thought it all out in detail yet.

So many experiments to try, so little time.... :D

just vent the boost line.
Btw. ALDA enrichment should be the the negative effect on economy while cruising in my opinion.
A switch to operate an electro valve venting the boost line could help.

Tom

The ALDA enrichment won't make a difference, your right foot ultimately controls the fuel rate while cruising. If you vent it you'll just have to give it more throttle to maintain speed and it will still consume the same fuel rate.

Very interesting thread. :)
FI, you have loads more experience with turbochargers than I do and I'm chiming in with the utmost respect for said experience but I have to throw in with dozer here.

The expansion valve analogy isn't appropriate because the refrigeration in that case comes primarily from the phase change.
....

....If the exhaust gas is cooler at the turbo outlet than the inlet, where did the energy go?

This is a reason that exhaust driven superchargers are more efficient than engine driven superchargers. You are using leftover heat energy from the combustion process to compress the inlet charge, instead of new mechanical energy (requiring more fuel consumption) from the crank.

If it was purely a gas pressure-driven scenario, the pumping losses through the exhaust side of the turbo would not offset the gain from the increased inlet airflow.

Keep the dialogue going. I'm learning from everyone here.:D

thanks CJ....those are all good, correct, and nicely put, points.

(except that one -can- refrigerate/chill without a phase-change or a liquid-to-gas expansion valve...by simply expanding gas itself. In this case, the 'valve' is a 'throttle', and the process is called 'throttling', and it's not so efficient.)

I wish I had thought of that one simple question that you asked, since it hits the nail on the head so well....

"since the output gas from the turbine is much cooler, where did all that heat-energy go ??"

Or to put it another way, if it isn't mainly heat-energy that's being extracted as shaft-power, then why is X grams of gas per second suddenly 200 degrees cooler just 2" further along at the outlet of the turbine? Where else did that heat GO?....if not to shaft-power?

Obviously, the answer is that the shaft-power DID come from that heat-energy.

A turbo-expander IS a heat-engine. Or, to perhaps put it more precisely, it's the expansion-half of a Brayton heat-engine cycle.

In the case of our TD's, the piston-engine itself is acting as the compressor and 'burner' portions of this 'outer loop' Brayton-cycle heat engine.

The turbo's turbine is the expander half of this
'outer loop' heat-engine cycle; and the turbine's shaft, where it drives the turbo-compressor, is the mechanical-power extraction point.

But even if the output air from the turbo's compressor wasn't even being fed to the piston-engine, but was used externally to, say, blow up tires :D ; it would STILL be a Brayton cycle heat engine.

(The mechanical-work extraction point would now be the compressed-air output of the turbo-compressor)

In fact, the compressor half of the turbo isn't even -necessary- for this heat-engine/cycle to be complete. ANY load on the turbine-shaft will do.

You could instead hook an alternator to the turbine-shaft and charge batteries with it.....and this combination of piston-engine compressor/burner and turbo-turbine expander would STILL be a complete Brayton cycle heat-engine.

It is further illuminating to recognize that if you -don't- put a mechanical-load on that turbine-shaft, it will NOT cool the gases!

Which makes totally intuitive sense if you're properly viewing a turbo-turbine as a heat-engine expander instead of a simple fan.

It's clear that, without a load, you're not extracting any energy, right?

Right....and exactly as you'd expect from heat-engine and turboexpander theory, the usual 200F temp-drop simply -disappears- when you disconnect the shaft-load !

(of course, a very short time later, your turbine hits 400krpm and goes into orbit... :D )


hey Babymog, glad to hear from a fellow Cat-man! :)

I have to correct that steam-turbine thing tho....

The expansion-ratio between water and steam isn't relevant to the operation of the steam-turbine itself. The large volume-difference between water and steam that you mentioned is true, but it does not take place within the turbine. The turbine never sees liquid.

Rather, as CJ correctly noted, a steam-turbine works by converting the HEAT energy content of the steam to mechanical shaft-power; which of course has the effect of -removing- that heat and thereby chilling the steam.

If this wasn't true, then as CJ also noted, why would we need to burn so much coal to heat the damn stuff up in the first place? :P

The steam to the inlet of a turbine is -superheated- to add energy to it; well above the temp where water first evaporates. Inlet steam temps are rarely less than 500F...and up to 1000F are typical.

Water is used not because of the volume-ratio between its liquid and vapor; but simply because it's the cheapest and safest of the various HEAT-energy-carrier gases available to us (e.g., butane, ammonia, freon, sulfur dioxide, etc. etc).

In any case, FI still doesn't believe me, and nobody can say I haven't given it my best shot, right? :D ....so I'll admit defeat and give up now, while we're all still friends.... :P

FI: a pleasure debating with you....and I still urge you to get yourself a good turbomachinery handbook and look up turboexpanders and brayton cycles, just for your own satisfaction. :)

"since the output gas from the turbine is much cooler, where did all that heat-energy go ??"

Or to put it another way, if it isn't mainly heat-energy that's being extracted as shaft-power, then why is X grams of gas per second suddenly 200 degrees cooler just 2" further along at the outlet of the turbine? Where else did that heat GO?....if not to shaft-power?

Obviously, the answer is that the shaft-power DID come from that heat-energy.

A turbo-expander IS a heat-engine. Or, to perhaps put it more precisely, it's the expansion-half of a Brayton heat-engine cycle.
The above is false information, a turbo is NOT a heat engine. Where did the heat go? Two places, some is dissipated as the gas expands and some is absorbed into the turbine and housing as it contacts their surfaces.

It is further illuminating to recognize that if you -don't- put a mechanical-load on that turbine-shaft, it will NOT cool the gases! This is also incorrect. If it were true then the exhaust gasses would stay hot well after it exits the exhaust pipe.

Which makes totally intuitive sense if you're properly viewing a turbo-turbine as a heat-engine expander instead of a simple fan. However, it IS a simple fan.

It's clear that, without a load, you're not extracting any energy, right? No, aerodynamic energy is being used to spin the turbine even if its not producing work (boost). Take the inlet off your turbo and start the engine, notice its spinning even with no significant heat in the exhaust stream.

Right....and exactly as you'd expect from heat-engine and turboexpander theory, the usual 200F temp-drop simply -disappears- when you disconnect the shaft-load ! Incorrect. There is still a temperature drop, although it is reduced because the velocity of the gasses is not changing as dramatically.


The expansion-ratio between water and steam isn't relevant to the operation of the steam-turbine itself. The large volume-difference between water and steam that you mentioned is true, but it does not take place within the turbine. The turbine never sees liquid.
Thats because steam is a vapor. If it sees liquid then the system is not operating efficiently.

Rather, as CJ correctly noted, a steam-turbine works by converting the HEAT energy content of the steam to mechanical shaft-power; which of course has the effect of -removing- that heat and thereby chilling the steam.
Incorrect again. The steam is just an efficient large volume working medium moving from a high pressure environment to a low pressure environment.

If this wasn't true, then as CJ also noted, why would we need to burn so much coal to heat the damn stuff up in the first place? :PBecause it takes lots of energy to raise the water temperature.

The steam to the inlet of a turbine is always -superheated-, well above the temp where water first evaporates. Inlet steam temps are rarely less than 500F...and up to 1000F are typical.
That is to keep the steam from condensing and maintain it at its maximum expansion ratio. Freshly boiled steam is still wet, it has liquid vapor suspended in it (This is the white steam people see). A superheater boils any remaining liquid.

Water is used not because of the volume-ratio between its liquid and vapor; but simply because it's the cheapest and safest of the various HEAT-energy-carrier gases available to us (e.g., butane, ammonia, freon, sulfur dioxide, etc. etc). Incorrect again. See above.

I'm sorry to repeat it again but, I'm sorry, you study up a little bit more on the fundamentals of how these things work.

ps; I'm so used to my old textbooks that sometimes I forget there's google! ...lol...

Which I just tried...and found that anyone who wants to be sure of their facts can do so in less than 5 seconds.

A google of "centrifugal turbine expander heat engine", and variations on those terms, instantly provided the following facts; among thousands of others.....

(underlines are mine)

Brayton cycle: Definition from Answers.com
1791 - John Barber received the first patent for a heat engine in which a bellows (compressor) and a turbine (expander) were connected...
www.answers.com/topic/brayton-cycle

Heat engine - Patent 6336316
6134876, Gas turbine engine with exhaust expander and compressor, Hines et al. ..... 4 comprises, as an example, a centrifugal turbine T 32 ,

(turbo-turbines are heat-engine turboexpanders)

"Elliott Company • Products • Steam Turbines/Expanders
The TH power recovery expander turbine is available to utilize the energy in high temperature, low pressure gas streams to drive..."

http://en.wikipedia.org/wiki/Steam_turbine
A steam turbine is a mechanical device that extracts thermal energy from pressurized steam, and converts it into useful mechanical work.

(it's the heat, not the pressure, producing the majority of the shaft-power)

etc. etc..

it's the heat, not the pressure, producing the power.

Incorrect, again. A turbine is a simple fan.

Dozer, it's clear that we've each brought a knife to a gunfight here. ;)
I'm just chagrined that much of what I learned in my mechanical engineering tech bachelors degree and nearly 20 years at an anhydrous ammonia manufacturing facility (where we generated and used about 800,000 #/hr of steam per unit) is totally false and incorrect. :D
Guess I'll go look for a new book of steam tables because I now know that the old one (that's been in use for many years) is wrong. :rolleyes:

Dozer, it's clear that we've each brought a knife to a gunfight here. ;)
I'm just chagrined that much of what I learned in my mechanical engineering tech bachelors degree and nearly 20 years at an anhydrous ammonia manufacturing facility (where we generated and used about 800,000 #/hr of steam per unit) is totally false and incorrect. :D
Guess I'll go look for a new book of steam tables because I now know that the old one (that's been in use for many years) is wrong. :rolleyes:

Apparently so CJ....and dinky little knives at that... :D

An ammonia-guy huh? A rare-breed these days! I'll call you brother; as I cut my heat-engine teeth on ammonia-systems in ice-cream plants in the 60's; working with my dad, who was a refrigeration engineer.

I look forward to joining you in future threads on fuel-economy and other ways to usefully extract the surplus heat-energy via the turboexpander. :)

Its just a fan. Get over it.

wow. an incredible volley.

Isn't it fair to say that you could never make any major positive gains without the heat that dozer alludes to?

although, 'heat' is not what spins the turbo. Turbos are efficient b/c they make gains off otherwise wasted energy: The heat from combustion is going to happen regardless, it is going to get dumped, regardless. After combustion there is still more potential energy in that exhaust gas than before it went through the turbo. That potential is now harnessed by the turbo shaft to pressurize the next batch of fresh air. What was waste is now more potential energy in the cylinder in the form of compressed, combustible gas. The turbo makes a profit off of its very own work - compounding interest.

true, the fans suck more air in via the exhaust stroke on the crank, but that is used, additional energy. Almost the the same as a supercharger. If the a turbo is no more than a supercharger, why do they consistently produce higher gains?

And it isn't about the engine being hot. There's an explosion happening in each cylinder, and that air is hotter than before, independant of the chamber it is in.

not that I have extensive experience with what I'm talking about though. Just looking for clarity.

Dozer's argument is that a turbo is just a heat engine and that the heat is all that drives it. What really happens is the physical push of the high velocity gasses is what drives it, heat only increases the efficiency by making the gasses expand to a larger volume.

kinda seemed like he just wsn't saying it right. But what was almost said is a crucial part of the turbo-compression process.
??

Dozer's argument is that a turbo is just a heat engine and that the heat is all that drives it. What really happens is the physical push of the high velocity gasses is what drives it, heat only increases the efficiency by making the gasses expand to a larger volume. The ideal gas laws

This law has the following important consequences:


If temperature and pressure are kept constant, then the volume of the gas is directly proportional to the number of molecules of gas.
If the temperature and volume remain constant, then the pressure of the gas changes is directly proportional to the number of molecules of gas present.
If the number of gas molecules and the temperature remain constant, then the pressure is inversely proportional to the volume.
If the temperature changes and the number of gas molecules are kept constant, then either pressure or volume (or both) will change in direct proportion to the temperature.

There you go. :)

There you go. :) Woohoo 1500th post! lol. I like what youve done with your profile forced :) Very diesel giant style lol.

oh maaan...

I was trying so hard not turn this into a chem lecture.

thanks again Cervan

PV=nRT does implicate the things Cervan suggested, but without considering Work, it means nothing in this context.

A tactile description:

If the turbo was just a simple fan, according to Cervan's "Laws" it would produce boost in proportion to engine speed (I.E. gas volume flow). However, if you look at your EGT guage on a transition from level to an uphill grade, with CONSTANT fuel pedal position maintained, you will notice that the EGTs rise, and a corresponding boost pressure rise occurs as well. All this with a decrease in RPM....

HOW COULD THIS BE POSSIBLE IF THE TURBO WAS NOT A HEAT ENGINE?

Its both, but you cannot have one without the other.

Furthermore, that has nothing to do with the actual work being done, in order to maintain the same speed the injector pump adds more fuel as boost comes up, causing a higher egt.

However, if you look at your EGT guage on a transition from level to an uphill grade, with CONSTANT fuel pedal position maintained, you will notice that the EGTs rise, and a corresponding boost pressure rise occurs as well. All this with a decrease in RPM....

HOW COULD THIS BE POSSIBLE IF THE TURBO WAS NOT A HEAT ENGINE?

The load on the engine is changing and more fuel is being injected per cycle which increases the exhaust volume per exhaust stroke.

No, the amount of fuel injected per cycle remains constant. Pedal position constant means the same amount of fuel is injected per cycle. Cruise control is not on guys...

read the question again, it says constant pedal position not constant speed.

so let me rephrase the same question in a different way:

Since the fuel volume per cycle is constant, due to constant rack position, the increased load only causes the engine speed to decrease. So why does the boost pressure rise and hold steady?

I italicized the "hold steady" part because that is evidence that the boost rise encountered upon transition from level cruising to an uphill grade is not related to inertia of the turbocharger's rotating assembly.

Once we have found a reason for this phenomenon we will see whether the turbocharger is a heat engine or not.

I believe the answer can be seen here:

YouTube - Beer+old turbo=home made jet engine

Im actually missing the point of this debate.. If i have it right, your saying that the turbocharger is spun, by the heat the engine produces, not the exhaust pressure? Well we can test that pretty easy. Just take the exhaust impeller off leave the shaft in there and see how fast the intake impeller spins. Or are you saying that the turbocharger simply increases the combustion chamber temperatures?

Man, I need one of those. Even if only to make my neighbors mad.

Found what I'm going to do with my T3 after the VNT install. :D

Im actually missing the point of this debate.. If i have it right, youre saying that the turbocharger is spun, by the heat the engine produces, not the exhaust pressure?

Thats the flaw with their "side" of the debate, they are taking the words "heat engine" literally.

Turbine
n.
Any of various machines in which the kinetic energy of a moving fluid is converted to mechanical power by the impulse or reaction of the fluid with a series of buckets, paddles, or blades arrayed about the circumference of a wheel or cylinder.

Brakes are heat engines too, but all of us know that when (most types of) brakes get hot they actually loose performance.

Thats the flaw with their "side" of the debate, they are taking the words "heat engine" literally.

Turbine
n.
Any of various machines in which the kinetic energy of a moving fluid is converted to mechanical power by the impulse or reaction of the fluid with a series of buckets, paddles, or blades arrayed about the circumference of a wheel or cylinder.

Brakes are heat engines too, but all of us know that when (most types of) brakes get hot they actually loose performance. ahh, i see. But what befuddles me, is that if this were to be an actual heat engine like a sterling engine as example. We wouldnt have any actual energy being transmitted by means of physical interaction. It would be like, brake pads stopping a car by means of friction creating heat and slowing the car down. But on a turbocharger you have exhaust gasses being "scooped" by the impeller and turned into physical energy, like a windmill. Or even more similar, a water turbine.

Yes, a sterling engine is about as close to a true "heat engine" that I can think of. Even in that the heat isn't doing the actual work, its the expansion and contraction of air/fluid pressure as it transfers between the hot and cool pistons.

Brakes work by making heat. The heat is just a byproduct of operation, the friction does the actual work even though brakes are "heat engines".

Im actually missing the point of this debate.. If i have it right, your saying that the turbocharger is spun, by the heat the engine produces, not the exhaust pressure? Well we can test that pretty easy. Just take the exhaust impeller off leave the shaft in there and see how fast the intake impeller spins. Or are you saying that the turbocharger simply increases the combustion chamber temperatures?

That's OK Cervan......I can't even remember now what the original point was myself.... :rolleyes:

First, FI has been misquoting me all along....using words like "just", and "only", and "all".....when what I actually said was that the >majority< of the shaft-power produced by the turbine was from the extraction/conversion of the heat, not simply from pressure like a 'fan'. I never said "all" or "only".

I also didn't say that the heat was 'doing' the work. I said that the shaft-power was mainly derived from conversion of the heat-energy into mechanical work.

Second, to answer your question....yes, exactly, the turbo IS mostly powered by the heat-energy contained in the compressed gas.

The turbine-portion of a turbo is technically known as a "turboexpander"; and contrary to FI's assertion, the 150-200 degree drop in gas-temps across the turbo is mostly NOT caused just by heat radiating off the turbo. It IS caused mainly by the heat-energy stored in 1000F gas being usefully -extracted-, i.e. converted into mechanical shaft-power via the process of "expansion" in heat-engine terms.

As I posted earlier, nobody has to take my word for it....you can confirm all this yourself -easily- with just a simple 5-second web-search; or a 5-minute consultation of any turbomachinery handbook ever written.

And no, a brake is not a heat-engine. That's just plain silly. A brake is nothing but a dissipative load. -Exactly- like a resistor in electronics. Nobody would claim that a resistor is a generator.

"Heat Engine" is a specific term defining a machine which converts heat-energy to mechanical work; or converts mechanical-work to cooling.

The extraction of mechanical energy from a gas -requires- expansion. Expansion is how you get work out of any engine.

Thus, any heat-engine -requires- a compression phase -prior- to adding the heat-energy that we want to turn into mechanical work later in the expander.

So, a basic combusting heat-engine requires compression; then the burning of fuel to heat that compressed gas, and finally the expansion of that hot gas (to convert that added heat-energy into useful mechanical work).

Now you know all about heat-engines...it's that simple.

It can be done with pistons and cylinders...or it can be done purely with simple turbomachinery, like that great example that Greasy just posted of a 'jet' engine made from nothing but a car-turbo and a burner (I love that thing! :D )

That's nothing but a compressor, a burner, and an expander. You'll note that the expander is a turbo turbine... :cool:

(in fact, the very first jet-engine ever made WAS a centrifugal engine, not an axial-flow like today's jet turbines)

In our TD cars, besides the self-contained Diesel-cycle of the piston-engine, there IS an additional "outer loop" heat-engine cycle going on too....which involves the turbo.

This is essentially a Brayton Cycle (which involves compression and expansion being done in seperate devices) heat-engine.

The piston-engine is the compressor/burner half of this "outer loop" Brayton cycle.....and the turbo-turbine is the expander (energy-extraction point) of it.

Again, a 5-second web-search will turn up the definition of heat-engine, description of turboexpanders, and will confirm all of the above; including the fact that the large temp-drop across a turbo is mostly caused by the -work extracted-. Only a small fraction of that temp-drop is from radiation off the housing, etc..

I'm sure this all must've had -something- to do with optimizing fuel-economy on our TD's...but for the life of me, I can't recall what right now... :D

But in lieu of remembering what started all this, I'll just summarize heat-engine understanding into turbo-system design aspects for best economy...

- Since heat and expansion provides the turbo-power, keep the gases as hot as possible between the head and turbo. Which means, don't expand them (keep the runners narrow) and if the runners have much length, insulate them...or at least shield them from the fast-moving underhood air.

- Conversely, -after- the turbine, provide as much expansion-room (exhaust size) as possible.

- Design the turbo-system so that it's providing at least several psi boost at common cruise-power levels. Even if that's only 1/4 throttle or 30hp, you DO want the turbo to be at least overcoming VE (intake resistance) losses.

Remember, if the turbo (running on otherwise wasted heat-energy) doesn't push that air into the engine, then the crank/pistons (running on fuel you gotta pay for) has to do that vacuum-pumping work.

- Vary the boost proportional to fueling (i.e. to the power-level being demanded). Any excess-air beyond that needed to combust cleanly at your current fueling-level will cause wasted mechanical-energy in the piston-engine.

- Since the turbo is producing mechanical work from normally-wasted heat energy in the exhaust, the best economy comes from replacing as much of the piston-engine's pumping/compressing workload as possible.

In other words, besides replacing the intake-resistance losses with a few psi of boost from the turbo-compressor, also replace as much of the mechanical piston-performed compression-ratio as possible with turbo-compression instead.

Lower the engine's comp-ratio to 17-18 and crank up the boost to 30+ psi. The goal would be to achieve the same total cylinder pressure (BMEP) but with the waste-heat in the exhaust-gas doing as much of the total compression work as practical.

Such a change in engine-CR will have the effect of making starting more difficult; and will also somewhat reduce torque/power prior to the turbo spooling up. However, it will provide the lowest possible steady-state specific fuel-consumption at power.

- Consider adding a 2nd turboexpander to recover more of the substantial remaining heat-energy in the exhaust. This may seem 'exotic', but I've been thinking about it off and on for a few years and I think it's both practical and doable.

Looking at it as HP, and assuming engine eff. of 33%, with another 33% of fuel-value wasted as heat in the radiator and the last 33% of the fuel-value wasted via heat in the exhaust (typical numbers); then when you're running down the freeway at 70, using, say, 30hp, there is >30hp< of heat-energy going right out the tailpipe!

Your primary turbo is recovering a few hp of that; but in a power regime where the turbo-inlet gas is running 900F and the exit-gases at perhaps 700F, there's obviously still a LOT of energy left to capture there.

As one way to capture it, add a 2nd turboexpander sized for the lower-temp gases (it will be larger and lower-rpm) and drive a high-speed alternator from the turboexpander-shaft. The output of the Alt. will be rectified and used to power a DC motor coupled to the engine or drivetrain.

If this secondary turboexpander also recovers several HP while the car is using 30hp to maintain speed, that would be a 10% fuel savings right there.

With good design, it may be possible to recover as much as 5-6hp.....which would be a 20% improvement in MPG. Perhaps not significant to some folks, but us engineers go ga-ga over that kind of efficiency improvement in anything... :D

A large lag in such a larger turbo wouldn't really be significant in any steady-state driving regime. So, freeway and any steady rural 2-lane driving would see the mpg gains.

To reduce the weight-impact of such a system, an alternator could be modified to serve as both alt. and brushless-DC motor. (remove internal rectifiers and bring out the 3-phase winding leads; and control it with a 4-quadrant 3-phase PWM bridge).

Obviously, there are limits to both belt-capacity (2-5 hp per B belt perhaps?) and HP capacity of the alt/motor itself. It may be difficult to get more than 2hp out of an auto alternator.

Although I've brought out alt-windings and used the alt as a high-power "stepper motor" in the past, I've never tried running one at high speed/power...so I've never happened to measure the output as HP, or gotten an idea of what the thermal issues with a regular car-alt as motor might be.

One could of course source a high power-density brushless-DC motor instead of using a car-alt. That too can operate as an alt. when needed, by using that 4-quadrant PWM controller.

Most of the thinking I've done on this concept has been related to my F350 (7,000 lbs, 7.3L) and I'd thought that the PTO port on the tranny was the ideal place to put a DC-motor. But in using my crane-truck, I've noticed that if I forget to disengage the PTO, then the trans shifts a lot harder (stick trans). Perhaps the PTO-port on the T-case could be used without impacting driveability.

On a 300 series, I can't really think of any easy spot to drive, other than at the engine. Perhaps adding a shaft to the crank-pulley and driving there would be best. It would be a necessity if one was successful in developing 5-10hp from this system.


Anyway, to address the original point of the thread, those are my turbo-related fuel-economy throughts... :P

Ok, so lets say that you put a second remote turbo down stream. Its still going to take more fuel to burn in order to incorporate this second turbo. allthough if it were a smaller turbocharger, you could reduce spool up times drastically by compounding them, or adding a supercharger. but this would not be done for millage gains. With a supercharger, you could lower the C/R alot and only use the S/C to keep it at idle like the two cycle detroit diesels. By raising the pressure and filling the cylinder with enough air to create higher compression. This would also be good to compound with a turbocharger virtually removing spool time. And as an added benefit you could completely remove the turbo by opening the wastegate at cruising speeds furthermore, you could remove the S/C from the equasion as well by putting it on a clutch and disengaging it at highway speeds.

First, FI has been misquoting me all along....using words like "just", and "only", and "all".....when what I actually said was that the >majority< of the shaft-power produced by the turbine was from the extraction/conversion of the heat, not simply from pressure like a 'fan'. I never said "all" or "only".
Not even the majority, none of the shaft power comes from the actual heat.

The turbine-portion of a turbo is technically known as a "turboexpander"; and contrary to FI's assertion, the 150-200 degree drop in gas-temps across the turbo is mostly NOT caused just by heat radiating off the turbo. It IS caused mainly by the heat-energy stored in 1000F gas being usefully -extracted-, i.e. converted into mechanical shaft-power via the process of "expansion" in heat-engine terms. The above is false information. Read what was posted above, "kinetic energy of a moving fluid".

And no, a brake is not a heat-engine. That's just plain silly. A brake is nothing but a dissipative load. -Exactly- like a resistor in electronics. Nobody would claim that a resistor is a generator.
The above is false information as well. Take your own advice, search the web on it. http://www.google.com/search?q=brakes+heat+engine
Look at the first result: "Brakes are a heat engine, they convert kinetic energy (motion) into thermal energy or heat."

"Heat Engine" is a specific term defining a machine which converts heat-energy to mechanical work; or converts mechanical-work to cooling.False again. The turbo is a heat engine because of this: "Heat engines can generate heat inside the engine itself or it can absorb heat from an external source."
http://en.wikipedia.org/wiki/Heat_engine

The extraction of mechanical energy from a gas -requires- expansion. Expansion is how you get work out of any engine.
The flow of a fluid from a high pressure region to low pressure. This is how the turbo works.

Now you know all about heat-engines...it's that simple.
Sorry, but you need to learn more about these things before you try to teach about them.

That's nothing but a compressor, a burner, and an expander. You'll note that the expander is a turbo turbine... :cool:
And it works by, guess what, the high velocity exhaust gasses from the burner pushing the turbine which drives the compressor wheel.

Again, a 5-second web-search will turn up the definition of heat-engine Use the link I posted above, its clear you don't even know what "heat engine" means.

I'm sure this all must've had -something- to do with optimizing fuel-economy on our TD's...but for the life of me, I can't recall what right now... :D It was going great until you thought that restricting the exhaust by making boost that isn't needed somehow can increase efficiency.

- Since heat and expansion provides the turbo-power, keep the gases as hot as possible between the head and turbo. Which means, don't expand them (keep the runners narrow) and if the runners have much length, insulate them...or at least shield them from the fast-moving underhood air.

- Conversely, -after- the turbine, provide as much expansion-room (exhaust size) as possible.
That is common knowledge in every turbo system design.

- Design the turbo-system so that it's providing at least several psi boost at common cruise-power levels. Even if that's only 1/4 throttle or 30hp, you DO want the turbo to be at least overcoming VE (intake resistance) losses. 1-2psi is more than enough, more than what is needed to burn the fuel completely only restricts the exhaust.

then the crank/pistons (running on fuel you gotta pay for) has to do that vacuum-pumping work. The above is false as well. The pistons do not suck in air, the atmosphere pushes it in.

- Consider adding a 2nd turboCHARGER to recover more of the substantial remaining heat-energy in the exhaust. This may seem 'exotic', but I've been thinking about it off and on for a few years and I think it's both practical and doable. A second turbo is only useful if you need to get pressures higher than one turbo can produce or in a Vee engine with one turbo for each bank.

Anyway, to address the original point of the thread, those are my turbo-related fuel-economy thoughts.
A lot of wind. You could have put a turbo on that and recoverd some of that 30 minutes. :rolleyes:

And it works by, guess what, the high velocity exhaust gasses from the burner pushing the turbine which drives the compressor wheel.

Forced, rather than guessing, can you prove this statement (hint: math)?

EDIT: Another hint: which has more energy? a hot gas at x velocity or a cold gas at x velocity? How are you measuring velocity? Where are you measuring velocity? Does velocity in this whole thing really mean what you think it means?

That is all the information you should require to figure this "puzzle" out scientifically, rather than just guessing. Or you could save yourself some time and mental strain and just read a bit about turbo machinery theory and the physics involved therein.

Perhaps a way you might expose your mind to this concept would be to think of heat giving a gas velocity? why might that happen?

Forced, rather than guessing, can you prove this statement (hint: math)?

EDIT: Another hint: which has more energy? a hot gas at x velocity or a cold gas at x velocity? How are you measuring velocity? Where are you measuring velocity? Does velocity in this whole thing really mean what you think it means?

That is all the information you should require to figure this "puzzle" out scientifically, rather than just guessing. Or you could save yourself some time and mental strain and just read a bit about turbo machinery theory and the physics involved therein.

Perhaps a way you might expose your mind to this concept would be to think of heat giving a gas velocity? why might that happen?


you are missing a crucial element again. Referring to Cervan's laws: neither has more 'energy' per volume of gas. The heated one has more energy per molecular mass which takes up more volume which destroys your ability to test the two comparitively by volume.

A heated gas has less 'material' or mass and is therefore less dense. The resistance it provides is less than that of a cold gas. This means that cold gas per volume can most likely push a propeller with more strength than a heated gas... the other side is that per mass of the same gas, the heated one will have greater volume. Perhaps the balance b/w these two characteristics determines the design for a specified application of a turbo.

Turbos need heat to make gains or they are no more than a supercharger.

That's OK Cervan......I can't even remember now what the original point was myself.... :rolleyes:

First, FI has been misquoting me all along....using words like "just", and "only", and "all".....when what I actually said was that the >majority< of the shaft-power produced by the turbine was from the extraction/conversion of the heat, not simply from pressure like a 'fan'. I never said "all" or "only".

I also didn't say that the heat was 'doing' the work. I said that the shaft-power was mainly derived from conversion of the heat-energy into mechanical work.

Second, to answer your question....yes, exactly, the turbo IS mostly powered by the heat-energy contained in the compressed gas.

The turbine-portion of a turbo is technically known as a "turboexpander"; and contrary to FI's assertion, the 150-200 degree drop in gas-temps across the turbo is mostly NOT caused just by heat radiating off the turbo. It IS caused mainly by the heat-energy stored in 1000F gas being usefully -extracted-, i.e. converted into mechanical shaft-power via the process of "expansion" in heat-engine terms.

As I posted earlier, nobody has to take my word for it....you can confirm all this yourself -easily- with just a simple 5-second web-search; or a 5-minute consultation of any turbomachinery handbook ever written.

And no, a brake is not a heat-engine. That's just plain silly. A brake is nothing but a dissipative load. -Exactly- like a resistor in electronics. Nobody would claim that a resistor is a generator.

"Heat Engine" is a specific term defining a machine which converts heat-energy to mechanical work; or converts mechanical-work to cooling.

The extraction of mechanical energy from a gas -requires- expansion. Expansion is how you get work out of any engine.

Thus, any heat-engine -requires- a compression phase -prior- to adding the heat-energy that we want to turn into mechanical work later in the expander.


Here we go.

As the HOT exhaust leaves the high pressure area and enters low pressure - it is given the space it needs to release potential energy. By expanding it cools down. It is the place whrere this expansion ocurrs that allows a turbo to harness the otherwise wasted engergy (heat energy) in exhaust.

by expanding the gasses across impellers of different ratios and vector fields (quote FI here), the basic fans (impellers) capitalize on TWO DIFFERENT VOLUMES of A gas body at different temperatures as it (gas body) changes across them (simple fans)

turbos need heat (or an available means of pressure differential)
turbos need simple fans

I'd think that a change of turbo settings or geometry would improve your MPG then.

If your boost is zero at cruise, then you're not using the 'free' exhaust energy to overcome the less-than-100% VE, correct?

In another post, someone mentioned running around 5psi at cruise. That sounds like about the optimum point for best economy.

So I've always been interested in setting things up to get boost at very low power-settings. Yet I need a turbo system that works well at near full power as well; because every 10 curves there's another mountain to climb... :D




in an effort to finish this..

It is safe to assume that a turbo-ed engine is more efficient than a non-turbo-ed.

But it is only 'kinda free' exhaust energy

It sounds like Forced pays really close attention what he is doing, although some serious mathematical analysis may help further maximize his turbo settings.. his mileage is pretty impressive already.

Cervan, if the turbo (either primary or secondary) is of the proper size and geometry, it extracts far more HP from the exhaust-heat than the pumping-work it adds to the piston-engine.

FI, thank you!! Yes, that was the point that got it all started.

You claimed that having the turbo doing zero pumping-work at cruise-power (20hp as I recall) was more efficient.

I pointed out that even at partial-output like 20hp, the piston-engine would run more efficiently if the turbo (using wasted heat-energy) was set up to do the work of overcoming intake-resistance; rather than using the pistons (whose work comes from burning additonal fuel).


JT, I think you summed it up well....

turbos need heat.....and obviously, turbos need a 'fan'... :D

I said "turbos need heat" OR another available source of PRESSURE DIFFERENTIAL.

...and I just realized everything I have said was already stated by FI. - sorry

JT, I didn't see an "or".

ps; I'd be interested in hearing your thoughts on the original question/point:

Is a TD running at partial-load (say, 20-30hp) more efficient if the turbo isn't providing any pressure; or if the turbo is set up to provide enough boost (say, 3psi) to overcome intake-resistance losses?

thanks

"since the output gas from the turbine is much cooler, where did all that heat-energy go ??"

Or to put it another way, if it isn't mainly heat-energy that's being extracted as shaft-power, then why is X grams of gas per second suddenly 200 degrees cooler just 2" further along at the outlet of the turbine? Where else did that heat GO?....if not to shaft-power?

Obviously, the answer is that the shaft-power DID come from that heat-energy.

A turbo-expander IS a heat-engine.


NO. The gas cooled by expanding. As a by-product, it pushed on the vanes as it left. The work the heat did was carry potential energy, the pressure did the work. Heat=Potential Pressure

Ok, I promise not to return to this thread.

Mike, I hope you get better gas mileage

Here we go.

As the HOT exhaust leaves the high pressure area and enters low pressure - it is given the space it needs to release potential energy. By expanding it cools down. It is the place whrere this expansion ocurrs that allows a turbo to harness the otherwise wasted engergy (heat energy) in exhaust.

by expanding the gasses across impellers of different ratios and vector fields (quote FI here), the basic fans (impellers) capitalize on TWO DIFFERENT VOLUMES of A gas body at different temperatures as it (gas body) changes across them (simple fans)

turbos need heat (or an available means of pressure differential)
turbos need simple fans


^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

JT, I didn't see an "or".

ps; I'd be interested in hearing your thoughts on the original question/point:

Is a TD running at partial-load (say, 20-30hp) more efficient if the turbo isn't providing any pressure; or if the turbo is set up to provide enough boost (say, 3psi) to overcome intake-resistance losses?

thanks


to be perfectly honest, I do not have enough information on that. I was trying to learn more about turbos. Thank you for the excellent dialogue.

My belief is that a turbo-ed engine is more efficient than a n/a. pretty lame.

JT, I didn't see an "or".

ps; I'd be interested in hearing your thoughts on the original question/point:

Is a TD running at partial-load (say, 20-30hp) more efficient if the turbo isn't providing any pressure; or if the turbo is set up to provide enough boost (say, 3psi) to overcome intake-resistance losses?

thanks

I dont think the backpressure that a turbo imposes is ever a loss at the crank.
partial load boost can't be bad

I don't think the backpressure that a turbo imposes is ever a loss at the crank.
partial load boost can't be bad

It is. Thats how exhaust brakes work, backpressure.

to be perfectly honest, I do not have enough information on that. I was trying to learn more about turbos. Thank you for the excellent dialogue.

My belief is that a turbo-ed engine is more efficient than a n/a. pretty lame.

My thanks back your way JT...appreciate your posts and input.

It is. Thats how exhaust brakes work, backpressure.


I don't know much about exhaust brakes, clarify. (use of expanding gases, or backpressure to crank?)

it doesn't make sense that a turbo could be beneficial to an engine if it didn't make use of more than one form of energy at all times.

you said it yourself. The expansion of the gases is the important part of a turbo's ability to compress air. As long as you put some exhaust into that turbo, you gain from the natural tendency of that gas to expand in your turbo and, in turn, compress air on the incoming side.

How could the push of the piston forcing hot air into another chamber that now captures an additional form of energy return a loss at the crank that would have completed its revolution w/o that captured energy?

It is. Thats how exhaust brakes work, backpressure.


Back pressure on crank = belt driven supercharger on crank.

Compressing the intake air from energy stolen at the crank is even worth the gains from a simple supercharger.

A turbo does this job AND harnesses expanding exhaust gasses across the turbine shaft through aerodynamic propagation.

An exhaust brake works by causing backpressure in the exhaust manifold. That makes the pistons work harder to push the exhaust out of the cylinders.

A turbo or supercharger does not add any power to the engine. The additional power comes from more fuel being burned per cycle because the turbo/SC provides extra air.

Thats why a turbo added to a 240D or non-turbo 300D with an otherwise unmodified engine does not add any power. Its only after the injection pump settings are changed that it can get a change in output. The same applies with making the turbo produce more boost than the engine receives fuel for, it adds restriction and actually reduces power.

A turbo or supercharger does not add any power to the engine.

right, it adds EFFICIENCY (turbo only)


Thats why a turbo added to a 240D or non-turbo 300D with an otherwise unmodified engine does not add any power. Its only after the injection pump settings are changed that it can get a change in output. The same applies with making the turbo produce more boost than the engine receives fuel for, it adds restriction and actually reduces power.

Its hard to imagine that even with the valve totally open, and no energy being spent on creating boost, that your turbo isn't also restrictive. I see no straight sections as wide as the exhaust pipe.

With the turbo creating even a little boost (or just enough), it is providing enough extra efficiency to negate its comprimising effects on the engine. (-a belief)

I do not mean to be antagonizing and I apologize if you have already gone the hoops of trial and error finding the exact spot where efficiency and fuel consumption meet. Would this would mean that the exhaust being passed through the turbo is small enough to get by w/o backpressure, and that the corresponding fuel usage is just enough to keep you coasting?

right, it adds EFFICIENCY (turbo only)

Incorrect. A turbo only adds power.

damn.

Any suggestions for where I can read up on turbos?

--on a NIN kick, huh?--

http://www.turbobygarrett.com/turbobygarrett/tech_center/turbo_tech101.html

been there

Turbo adds air to be burnt, thus power. it takes away less power at the crankshaft than a supercharger (supposibly a supercharger leeches 1/3 the power at the crankshaft).

Although I have yet to complete the work, removal of the trap cat from 617.952 engines (California version of the '85 300D and SD cars) has been claimed on this forum as well as documented in M-B specs to improve both power and fuel economy.

A couple of horsepower and a couple of mpg are said to result from replacing the cat with a straight pipe for testing purposes only. I plan a long test, say 200,000 miles, to get good data.

Jeremy



can i see some picture please, where to find trap cat place and what its lookof this. and one thing more how to remove it. hope that you could me out. thanks a lot sir:)

http://www.mercedesshop.com/Wikka/OM617CalToFed