What is the difference between a supercharger some people put on thier cars to increase performance,and a turbocharger used on diesel locomotives?[?]
Thanks! There was some really cool info in there[:)]!
…Another web site is “how stuff works”…go to google and take a look.
…Oops, didn’t see Mark’s listing of “how stuff works” before I posted it…Sorry.
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 purp
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.
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…
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…
…That’s above the stock charge for a Grand National turbo isn’t it…?
Indeed, It is.
I had my mind on Otto instead of compression.
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
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.
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,
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.
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.
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.
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,
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