Supercharger,Turbocharger Question.

[espeefoamer]

What is the difference between a supercharger some people put on thier cars to increase performance,and a turbocharger used on diesel locomotives?[?]

[espeefoamer]

Thanks! There was some really cool info in there[:)]!

[Modelcar]

....Another web site is "how stuff works"....go to google and take a look.

[Modelcar]

....Oops, didn't see Mark's listing of "how stuff works" before I posted it...Sorry.

[Overmod]

Not to be Mr. Wiseass here, but a very important detail about EMD turbocharging vs. supercharging seems to have gotten left out of the discussion so far, namely that many of EMD's turbochargers are actually of hybrid design for better performance.

One problem with *locomotive* turbochargers from the Buchli days onward is that they have to deliver fairly large volumes of compressed air at low engine rpm/exhaust volume/heat. This traditionally means that the big 'wheels' have substantial inertia and are slow to spool up... the principal reason why Alco 244s have that 'honorary steam engine' column of black smoke is that they HAVE to be overfuelled to get the engine up to the rpm that provides enough exhaust volume to spin the turbo up to boost.

EMD engineers (IIRC from the SD24 onward) thought they were smarter. They put a mechanical connection, with an overrunning clutch, on the turbo shaft. At slow engine speeds, the mechanical drive spins the turbo wheel, providing enough compressed-air volume to keep the engine relatively 'smokeless' at high starting loads. As the exhaust volume builds up, the turbo starts spinning faster than the mechanical drive, which the overrunning clutch freely permits.

All this is good in theory. When it starts to break or leak, evil things can happen (doubtless Randy Stahl has some excellent Turbo Surprise stories related to the care and feeding of these clutches, and the interesting consequences from their, ah, compromised operation.

I am still waiting to see a proper discussion of 'nonmechanical charge enrichment' via the use of molecular diffusion filters -- now easily packageable on locomotives. At least one recent study indicates that the most efficient gains from this technology (for emissions) come with only slight oxygen enrichment of the intake air. But it's also possible to separate essentially ALL the nitrogen out of the feed-air stream (this is at the heart of some of the "pure oxygen" clean-coal technology that purports to recover the CO2 from combustion exhaust for zero-emissions). Now, when people start discussing recovery of combustion CO2 'cost-effectively', I join Randy in humming a mantra and thinking about the Matrix. But... what if it is, in fact, possible, and not just a convenient marketing scam?

[Anonymous]

And don't forget, when you use a supercharger or turbo and increase the airflow into the engine, you have to increase the amount of fuel also to maintain a proper fuel to air ratio.

[Overmod]

Imho, not exactly, BRF:

You are throwing away some theoretical efficiency if you underfuel, but some additional oxygen over 'stoichiometric' charge won't hurt the engine's operation. That's a key difference between throttled automobile engine operation (Otto cycle) and compression ignition...

Diesels always want to operate with an 'excess' of combustion air, because the ignition transition energy is supplied implicitly in the hot compressed charge air at the time of fuel injection. There is no reliance on rich kernels or torches to light off the fuel charge, no need for weird stratified charge, etc. (IDI with Ricardo swirl is a bit of a different case, dealing with preheat and effective pre-quench mixing of injected fuel and air when less-than-ideal atomizing, fuel charge mass, etc. are used).

The turbo lets you burn more fuel per stroke without an overfueling (smoke, etc.) penalty. Underfueling is as simple as injecting less fuel... what you do inject will still go substantially to 100% even if effectively very lean. This is a major contributor to the 'fuel efficiency' of compression-ignition motors...

[Anonymous]

Now, The Turbocharger on my Grand national pushed 24 PSI... At that I am running 100 octane race gas, no you 87 pump gas, If i wanted to run 93(Premiem) I would have to tune down the Turbo, and ALKY....

[Modelcar]

...That's above the stock charge for a Grand National turbo isn't it...?

[Anonymous]

Indeed, It is.

[Anonymous]

QUOTE: Overmod Posted: 08 Aug 2004, 23:48:08
Imho, not exactly, BRF:

You are throwing away some theoretical efficiency if you underfuel, but some additional oxygen over 'stoichiometric' charge won't hurt the engine's operation. That's a key difference between throttled automobile engine operation (Otto cycle) and compression ignition...

Diesels always want to operate with an 'excess' of combustion air, because the ignition transition energy is supplied implicitly in the hot compressed charge air at the time of fuel injection. There is no reliance on rich kernels or torches to light off the fuel charge, no need for weird stratified charge, etc. (IDI with Ricardo swirl is a bit of a different case, dealing with preheat and effective pre-quench mixing of injected fuel and air when less-than-ideal atomizing, fuel charge mass, etc. are used).

The turbo lets you burn more fuel per stroke without an overfueling (smoke, etc.) penalty. Underfueling is as simple as injecting less fuel... what you do inject will still go substantially to 100% even if effectively very lean. This is a major contributor to the 'fuel efficiency' of compression-ignition motors...

I had my mind on Otto instead of compression.

[adrianspeeder]

Yes, both use a fan to force air into the engine, the only difference is in what drives it. Like said above, a supercharger is spun off of the engine. Another way to think of a turbocharger is just like a waterwheel is spun by a stream of water, a turbo impeller is spun by exhaust gasses on their way out of the engine.

I have seen some pretty insane numbers for turbo boost. My truck maxes out at 25psi stock, but guys have put in liquid cooled ball bearing turbos to get up to 40psi for their diesel trucks.

Im sure somebody has a pic of a loco turbo because i would like to see one. In the meantime here are some pics of my turbo.

The exhaust side of the turbo is on the left and the fresh air side is on the right with a small shaft connecting the two

http://www.supermotors.org/getfile.php?id=133989&toggle=fullsize&filename=Turbo left

The fresh air side of the turbo

http://www.supermotors.org/getfile.php?id=133990&toggle=fullsize&filename=Turbo right

Adrianspeeder

[Anonymous]

Overmod,
could it be that by accepting only the part of air that is oxygen, the total amount of air needed to run an engine would be greatly increased?

I'm assuming that you are saying that there is some way to extract oxygen from the atmosphere in real time for the intake of an engine. For example, if air is 20% oxygen, then to accept that 20% only, 500% must be "filtered" to get 5 x 20% - %100 of the gas needed to fill the cylinder, and filling the cylinder whatever the gas is, is pretty important if we're going to get the heat we need for combustion.

Maybe what would be truely efficient is an "optimized" mix of gasses, that gives us the volume we need and the best amount of oxygen.

Maybe, there is an inert gas that has a high specific weight that can be added to give a greater pressure for a given volume.

[Anonymous]

QUOTE: Originally posted by Lehigh Valley Railroad

Now, The Turbocharger on my Grand national pushed 24 PSI... At that I am running 100 octane race gas, no you 87 pump gas, If i wanted to run 93(Premiem) I would have to tune down the Turbo, and ALKY....

Diesel fuel goes by Cetane rating, not octane rating. I wish I could tell you the diference, but it is a hundred degrees here and I don't have air conditioning and my brain is malfunctioning. I'm sure somebody can chime in,

[Allen Jenkins]

It's difficult to imagine that on every compression stroke of a Diesel engine, the air temp reaches one-thousand degree's F, as starting a cold motor. Also note that the lobes of a roots blower never touch, and are a specific gauge distance apart. acj.

[Anonymous]

QUOTE: Originally posted by Allen Jenkins

It's difficult to imagine that on every compression stroke of a Diesel engine, the air temp reaches one-thousand degree's F, as starting a cold motor. Also note that the lobes of a roots blower never touch, and are a specific gauge distance apart. acj.

Blower shafts are driven by helical cut gears. The lobes are "timed" by adding or subtracting shims to each gear.

[Anonymous]

QUOTE: Originally posted by jruppert

QUOTE: Originally posted by Lehigh Valley Railroad

Now, The Turbocharger on my Grand national pushed 24 PSI... At that I am running 100 octane race gas, no you 87 pump gas, If i wanted to run 93(Premiem) I would have to tune down the Turbo, and ALKY....

Diesel fuel goes by Cetane rating, not octane rating. I wish I could tell you the diference, but it is a hundred degrees here and I don't have air conditioning and my brain is malfunctioning. I'm sure somebody can chime in,

Indeed, You are correct, Diesel burns at a much higher tempurture... You could toss a match into a can if diesel... and it would go out, while around gasoline, it would ignite.

[oltmannd]

QUOTE: Originally posted by Overmod

Not to be Mr. Wiseass here, but Mark left out a very important detail about EMD turbocharging vs. supercharging, namely that many of EMD's turbochargers are actually of hybrid design for better performance.

Not quite. An EMD is a two stroke engine and has to have a blower to provide scavenging air. The problem is there is not enought energy in the exhaust stream at idle to provide enough scavenging air, so the compressor must be shaft driven. At full speed and load, there is plenty of energy in the exhaust to provide scavenging air at a nice boost pressure. In between, the compressor is partially powered by shaft and turbine (actually, it "lifts off" the shaft around notch 6)

Another solution to this problem is to use both a roots blower and a free running turbo. The DD 149 series engine does this.

[Overmod]

With respect to 'reference hydrocarbons', octane is an eight-carbon chain, and cetane (name derived from original source, whale oil) is a sixteen-carbon linear chain. The rating systems are different and have different purposes.

The 'octane' tests are indications of knock propensity, and nominally represent a mixture of straight-chain heptane (7-carbon chain, with lousy knock characteristics) and isooctane (more 'globular' in shape, 8-carbon chain) which has relatively good characteristics). Of course, avgas people and fans of Moroso Octane Booster will recognize that octane ratings of 108, 114, etc. are extensions of the scale proportioning ABOVE iso-octane...

Cetane rating, on the other hand, represents the propensity of the fuel to ignite MORE spontaneously on exposure to heat.

It's always amusing to test 'ordinary' folks out by asking them what happens when gasoline gets inadvertently run into a diesel engine. Everyone knows gasoline is almost explosively combustible, but diesel is notoriously hard to light. So they start thinking gasoline will grenade the diesel, or at the very least cause backfires, flashbacks in the intake, etc. What ACTUALLY happens is that the engine won't run...


With respect to Mr. Ruppert's excellent questions:

The technology to separate oxygen from nitrogen is quite well advanced... interestingly enough, it was originally developed to separate NITROGEN for packaging processing (discarding the oxygen)! A quick Google search will give you more than enough information on how the technology works, how big the devices have to be, etc. (There were links from one of the recent Trains Magazine weekly update features to a discussion of this technology specifically applied to diesel locomotives). One thing this discussion noted was (implicitly) that there ARE 'optimized' mixes of oxygen and nitrogen that produce best results, in particular engines for particular purposes. (Remember that overall cost-effectiveness, not 'thermodynamic efficiency', is probably the correct measure to use when assessing this kind of technology...)

Yes, you'd need about 5 times the air volume to produce an equivalent volume of 'pure oxygen' in the cylinder (it's a bit more complex for a variety of physical reasons uninteresting to almost everyone). Normally, you don't need pure oxygen in a motor cylinder, as it produces way more heat energy than you can use for practical pressure expansion (which is the thing that makes the horsepower)

The principal thing about the 'inert gas' is that it subsequently goes out the exhaust... this rules out most of the logical contenders that might apply. The already-present neutral nitrogen already qualifies as a reasonable inert gas, except for its unfortunate predilection to combine with oxygen under higher heat and pressure... CO2 can be made to work, but its characteristics aren't particularly better than nitrogen and it's been tarred with a reputation as an Environmentally Evil Greenhouse Gas.

Note that one of the better 'inert' materials to improve pressure performance in diesels can be water. Water injection, properly timed and modulated, can use much of the 'excess' heat of internal combustion to produce (steam) pressure expansion. There are things to watch out for, of course, ranging from hydraulic lock (easy and catastrophic!) to increased rusting of components in the exhaust system (particularly if high-sulfur fuel is involved). But with reasonable care this is a logical and effective means of increasing output torque even in fairly high-speed motors...

[adrianspeeder]

Right on overmod.

Gas in a diesel wont run if the engine is cold, heck it is even tricky to get diesel to run in a diesel when it is cold. Glowplugs and blockheaters eliminate any cold weather starting issues for cars and light duty trucks though.

Gas in a warm diesel on a hot day = cool story.
Last summer a woman was filling her VW diesel car at the local truck stop. Brand new golf TDI. Only problem was she was filling it with gas. Attendent and other truckers said thats a diesel engine, not gas. She flipped out with a major attitude and said she knows its a diesel engine, and though shes blonde, she doesnt need to be told every simple thing. Then she drove off, and that thing roared away, and prolly made about 500horsepower for about 3 seconds. Then the head exploded. We all helped push her car back in the lot off of the road.

Adrianspeeder

[Overmod]

oltmannd, I'm perfectly aware of the need for positive-displacement scavenging on GM 2-stroke diesels. I'm referring to the BOOST supercharging, not anything to do with the presence or absence of Roots blowers.

There is at least one other recent thread that addresses the combination mechanical/exhaust superchargers used on many EMDs. Since what is used is a turbocharger with auxiliary mechanical drive (much like some of the 'electric-boosted turbochargers' recently designed by Caterpillar et al. for use in heavy road vehicles), I thought I could be relatively confident in calling the thing a 'turbocharger' rather than a 'supercharger' although of course it can be either one depending on how it's driven.

Hopefully someone can give us a link to pictures -- I remember at least one Kalmbach article that had a pretty good shot in it, many years ago when the technology was new -- I might also add that this would address adrianspeeder's request to see what a locomotive turbo looks like.

BTW, there is a partly disassembled turbocharger in the ex-EL SDP45 at the Virginia Museum of Transportation in Roanoke... you can get a nice look right at the intake side with no air filter or duct in the way...

[oltmannd]

Overmod-

I'm not trying to argue, but the point I was trying to make was that there is nothing magical in the performance of EMDs turbocharger design - it was a matter of necessity. The turbocharger's performance curve was a poor match for the engine's air requirement, so the gear drive supplement was a nice design choice.

EMD has a nice crossection of a turbocharger in their engine manuals.

Technically, the term "turbocharger" is slang - albeit a common term these days. It is more correctly a exhaust turbine driven supercharger.

Conrail actually removed the overrunning clutch and pinned the drive "solid" on a couple of GP35s and derated to 2000 HP (to avoid the turbine from driving the crankshaft) as a poor-man's way of making a "GP38" out of some otherwise useless GP35s. At least one was leased out to a short line in the mid 90s but I don't know what ever became of it.

[AntonioFP45]

From a simple viewpoint:

As a railfan, I've always enjoyed hearing the sound of turbocharged EMDs on SD40-2s zipping by!

[espeefoamer]

QUOTE: Originally posted by adrianspeeder

Right on overmod.

Gas in a diesel wont run if the engine is cold, heck it is even tricky to get diesel to run in a diesel when it is cold. Glowplugs and blockheaters eliminate any cold weather starting issues for cars and light duty trucks though.

Gas in a warm diesel on a hot day = cool story.
Last summer a woman was filling her VW diesel car at the local truck stop. Brand new golf TDI. Only problem was she was filling it with gas. Attendent and other truckers said thats a diesel engine, not gas. She flipped out with a major attitude and said she knows its a diesel engine, and though shes blonde, she doesnt need to be told every simple thing. Then she drove off, and that thing roared away, and prolly made about 500horsepower for about 3 seconds. Then the head exploded. We all helped push her car back in the lot off of the road.

Adrianspeeder

This one would be perfect for the humor forum[}:)][:)]!

[Anonymous]

interestingly enough, NASA has built an engine for VERY High Altitude Long Duration use (running a recip. engine at FL950 or so for high-atmospheric weather and chemical research) that actually recycles a portion of its exhaust for the "inert" portion of the intake charge. The aircraft brings LOX with it for oxidizer and is roots blown and aftercooled. Saw a blurb on it in Popular mechanix and one other mag (scientific american?) about 10 years ago.

with this whole "molecular sieve" process to provide more oxy per stroke, I have to wonder if the increased pumping and parasitic losses don't cut back efficiency too much to be worth the effort. Does anyone know if the idea is better volumetric specific power, or is it an attempt to cut down NOx and CO emissions?

water injection was used both as a power boost and anti-detonant in fighters in WWII, notably on FW190s and sometimes on P47's. I don't know about the rest of you, but the idea of needing an additional anti-detonant when running 145 octane Avgas just scares me.)

modern aero-derivitive gas-turbine electrical powerplants use water injection to reduce firing temperature (to reduce NOx) and to improve mass flow on hot days.

one other thing about water injection: engines run regularly with water injection don't suffer from carbon deposits or stuck rings. . . the steam removes any deposits before they harden.

So i think the complaints about rust, etc. are a little overblown- I can see the problem occuring in poorly /rarely operated and maintained (think "consumer") engines but given some minor engineering and a few lines in the ECU code for proper shutdown, I don't think it's a show stopper.

[Anonymous]

I had a SD-40 slip the turbo clutch more than once. It sounds like someone through a hand full of marbles in the turbo, then the engine died.

[Anonymous]

>Gas in a warm diesel on a hot day = cool story.
>Last summer a woman was filling her VW diesel car at the local truck stop. Brand new golf
>TDI. Only problem was she was filling it with gas. Attendent and other truckers said thats a
>diesel engine, not gas. She flipped out with a major attitude and said she knows its a diesel
>engine, and though shes blonde, she doesnt need to be told every simple thing. Then she
>drove off, and that thing roared away, and prolly made about 500horsepower for about 3
>seconds. Then the head exploded. We all helped push her car back in the lot off of the road.
Not a good thing! Similar happened to a guy I used to work with, but under slightly different circumstances. He actually USED the diesel pump, not knowing that the tanker driver had put unleaded into the diesel holding tank. He made it a few feet out of the lot before the injection manifold blew off the engine. Needless to say, the station owner wasn't happy to have to buy us a new Ford Power Stroke Diesel.
Tim

[Anonymous]

QUOTE: Originally posted by Overmod

With respect to 'reference hydrocarbons', octane is an eight-carbon chain, and cetane (name derived from original source, whale oil) is a sixteen-carbon linear chain. The rating systems are different and have different purposes.

The 'octane' tests are indications of knock propensity, and nominally represent a mixture of straight-chain heptane (7-carbon chain, with lousy knock characteristics) and isooctane (more 'globular' in shape, 8-carbon chain) which has relatively good characteristics). Of course, avgas people and fans of Moroso Octane Booster will recognize that octane ratings of 108, 114, etc. are extensions of the scale proportioning ABOVE iso-octane...

Cetane rating, on the other hand, represents the propensity of the fuel to ignite MORE spontaneously on exposure to heat.

It's always amusing to test 'ordinary' folks out by asking them what happens when gasoline gets inadvertently run into a diesel engine. Everyone knows gasoline is almost explosively combustible, but diesel is notoriously hard to light. So they start thinking gasoline will grenade the diesel, or at the very least cause backfires, flashbacks in the intake, etc. What ACTUALLY happens is that the engine won't run...


With respect to Mr. Ruppert's excellent questions:

The technology to separate oxygen from nitrogen is quite well advanced... interestingly enough, it was originally developed to separate NITROGEN for packaging processing (discarding the oxygen)! A quick Google search will give you more than enough information on how the technology works, how big the devices have to be, etc. (There were links from one of the recent Trains Magazine weekly update features to a discussion of this technology specifically applied to diesel locomotives). One thing this discussion noted was (implicitly) that there ARE 'optimized' mixes of oxygen and nitrogen that produce best results, in particular engines for particular purposes. (Remember that overall cost-effectiveness, not 'thermodynamic efficiency', is probably the correct measure to use when assessing this kind of technology...)

Yes, you'd need about 5 times the air volume to produce an equivalent volume of 'pure oxygen' in the cylinder (it's a bit more complex for a variety of physical reasons uninteresting to almost everyone). Normally, you don't need pure oxygen in a motor cylinder, as it produces way more heat energy than you can use for practical pressure expansion (which is the thing that makes the horsepower)

The principal thing about the 'inert gas' is that it subsequently goes out the exhaust... this rules out most of the logical contenders that might apply. The already-present neutral nitrogen already qualifies as a reasonable inert gas, except for its unfortunate predilection to combine with oxygen under higher heat and pressure... CO2 can be made to work, but its characteristics aren't particularly better than nitrogen and it's been tarred with a reputation as an Environmentally Evil Greenhouse Gas.

Note that one of the better 'inert' materials to improve pressure performance in diesels can be water. Water injection, properly timed and modulated, can use much of the 'excess' heat of internal combustion to produce (steam) pressure expansion. There are things to watch out for, of course, ranging from hydraulic lock (easy and catastrophic!) to increased rusting of components in the exhaust system (particularly if high-sulfur fuel is involved). But with reasonable care this is a logical and effective means of increasing output torque even in fairly high-speed motors...

I recently started reading "Diesel's engine" by Lyle Cummins, and thought it would be interesting to note that Rudolf Diesel used water injection in his first engine to control combustion temperatures when he tried higher compression ratios before settling on lower ratios (serious explosions!). He so believed in Carnot's perfect heat cycle, that he insisted on isothermal expansion, even if the resaulting indicated hp curve "IHP" of a pressure-volume diagram was so small the engine barely ran if at all.

I also learned an interesting fact, indicated horsepower goes back to the earliest days of steam, when a paper drum would reciprocate by linkage to the piston and then a marker would move axially by cylinder pressure plumbed to a small cylinder, creating a P-V diagram

He also managed to get his first engine to run on a variety of fuels gas, liquid, and solid. If anybody has read the thread about air starting, I should also say the first diesel engine was air started by admitting compressed air into the cylinder !

[Overmod]

I didn't think there was anything 'magical' about EMD's mechanical drive, only that it eliminated the problem with turbo spoolup at low engine power. Think of the fun Alco could have avoided with a drive and sprag clutch to the 244's turbo wheel... I enjoy the smoke show as much as anybody, but all that soot could have been horsepower. And now the EPA is watching...

Strange that you mention proper nomenclature... I was thinking about commenting on that in the last post. I always called these things 'turbosuperchargers', because that's what they were called when developed and applied to military aircraft in the 1940s, and it neatly describes what they are (turbine-driven superchargers). I had the impression it was tacitly assumed that these would be 'exhaust-driven' rather than use separate powered gas turbines (although the Russians apparently tried to use a single monster compressor to feed boost to multiple engines at one point). I don't remember what Buchli (no easy umlauts on this computer) called his exhaust-driven pressure chargers, but he is one of the pioneers in this field and may have 'discoverer's naming rights' on some of the designs used...

The 'eureka moment' for the general public appears to be the introduction of the famous, or infamous, Porsche Turbo, with all the publicity that accompanied it, in the disco era. Apparently this is the origin of the word 'turbo' as a general adjective to be applied to things that marketing guys wanted to give the cachet of 'modern extreme speed' -- examples of this whizzardry include a Turbo Competition Swimsuit, the "turbo" button as a kind of awful standard for the high-speed switch on a personal computer, and the use of 'turbo' for a high-powered engine in too many science-fiction stories.

On the other hand, I think the difference between 'supercharger' (meaning a shaft-driven compressor, whether positive displacement, centrifugal, or otherwise) and 'turbocharger' (meaning an exhaust-driven device that performed supercharging, by definition not a positive-displacement device) was made clear early on in automotive practice, with the shorter name becoming rapidly understood and accepted in that area. Since the word 'turbocharger' is now in common use, meaning in general exactly what we expect a term to mean and imply, I see no problem in using it here; while I'm a fan of "historical" terms used to describe evolving technology (such as 'touching a spring' in the 19th-Century sense, or 'scorching' -- which has a good railroad provenance, like 'hot rod' -- for speeding) I think that insisting on a longer, multi-word term every time this device is mentioned may be counterproductive.

[CSSHEGEWISCH]

We're all familiar with the results of turbo lag on an Alco 539 or 244 engine, but I found it rather amusing to see the same thing happen on a Mercedes-Benz on I-294 within the last year. He was cruising at about 60 MPH and then apparently floored the accelerator to gain speed and left a small cloud of smoke behind him. It wasn't like an Alco but it still isn't something you'd expect to see from a luxury sports sedan.