A friend of mine who is a diesel mechanic was explaining the operation of a turbo yesterday. I understand that hot exhaust gasses drive the vanes on a shaft that has a separate set of blades (compressor) on the opposite end of the shaft. This makes sense. However, I thought that the compressed air is pre-cooled by the charge cooler just before it enters the combustion chamber through the intake valves. My friend says, no, that after compression, the air enters the charge cooler (he says that's why it's also called an "after-cooler") and then returns to enter the engine for ignition. I guess that makes sense too, but when I look at my turbo and it's arrangement, I am confused again. :-(
The big silver pipe in the picture (below) is connected to the charge cooler. Is the air going to the charge cooler or FROM it? What about the brown portion of the turbo? Seems like that would be receiving the hot exhaust gasses to drive the turbo. I must be missing a third pipe that returns the cold, denser air to the engine, correct?
I know I'll never rebuild or take one of these apart, but I like to understand how these things work.
I didn't even mention the wastegate. Mine had a hole in it and I had no boost for the first 3 years I owned the coach and never realized it till Cummins detected the problem. If you've never had a turbo, you don't know what you're missing. I do now!!! So how does the wastegate fit into all of this? ???
Thanks in advance to all of you techies who will clue me in. :)
Don,
Air flow to your engine-- intake side:
Air intake on the side/top of coach, air filter, turbo (yes, driven by a shaft "powered" by exhaust gas), CAC (Charge Air Cooler= After-Cooler= Inter-Cooler. All the same thing) then the engine intake manifold.
The CAC is important, as intake air temperature coming out of the turbo can be over 300 degrees F. The CAC gets it back down to within a few degrees of ambient temperature.
You can trace out the plumbing on your intake system to see how each of these pieces fit in the overall scheme of things.
Brett
Hi Don,
Maybe this will help.
Raymond
So, Brett, engine intake manifold is on the passenger side near the injector pump? And the air in the intake manifold has been compressed and cooled (denser) by the turbo and CAC, respectively? If so, "daylight in the swamp"!! :) Thanks!
Raymond,
That diagram really helps! But what does the wastegate do? From its location in the illustration it's not really clear. Thanks.
The waste gate allows exhaust gas to bypass the turbo. By doing so, it limits intake manifold boost to that prescribed by your engine manufacturer. Think of it as an air bleed around the turbo's compressor blades.
Brett and Raymond: Thanks for filling in one of the many holes in my understanding of engine operation. :}
Don,
No problem. Just need help in making up a bumper sticker: "Will Work For Diesel"
Know anyone in the sign business?
RE: need help in making up a bumper sticker: "Will Work For Diesel" Know anyone in the sign business? Brett Wolfe
Try James Stalling at Xtreme Graphics in Nac. His shop may be able to make your bumper sticker.
I know probably inexpensive way to get that made for you if you want, will do so and mail to you. Just give me the go ahead (i.e. you really want it) and will not cost you anything. What size you want it to be? Email me address. May take a few days, but friend here in Nacogdoches I am fairly sure would do it. Mike
Thanks to Don, Brett, and Raymond for this great topic, explanation and diagram.. This really helps me...
Dave Abel
not exactly our systems but the principles are reviewed at this site.
How a turbo works (http://www.youtube.com/watch?v=vGhlgphrBxA#)
Mike,
Excellent video and very close to what we all have in our Caterpillar and Cummins powered coaches (not Detroit 6V92's).
Will send you a PM as well.
Brett
Other than the charge air cooler is after the turbo, and the roots blower. What is different on he 6/8v92's
Yup, you have a supercharger in addition to the turbocharger.
Bill, your water aftercooler is located down in the vee of the engine, if you look at your engine, the discharge from the turbo enters the roots blower, when boost is over 5 psi, the bypass valve (round vertical cylinder with small rubber hose on top of roots blower) opens, unloads drag from roots blower (30+hp), the hot air continues through a radiator looking cooler that is located below the roots blower, cooling the air before it enters the airbox / then cylinders.
The truth is the engine runs a lot more free / more power if you remove that cooler,
however keep close watch on EGT as it will surely go up quicker.
The roots blower on a turbo Detroit is only needed to start engine and get turbo up to the 5 psi. Being a 2 cycle engine.
Just part of the old hot rod in me, been there-done that .
Brett.....at long last, the bumper sticker is made and will be in the mail Monday (3/12) to you. I kept getting bumped in the order line by larger orders from major customers, but finally the sign folks got 'er done. Mike