The DRGW milled out the air intake ports of its Roots equipped 567’s to solve this problem. This would be the so-called “normally aspirated” 567 model engines prior to the GP 20 which was the first EMD I know of to have a turbo.
Union Pacific turbocharged over 30 GP9s before the first GP20 was built. See my previous post on this thread for reference by Don Strack. The UP experimentation led to the EMD’s own turbocharger equipped units: SD24 and GP20. First Turbo GP9 was in 12/55! [:)]
I would like to know the brand of diesel truck in the original question. If it is a Ford with the International v-8, this engine suffers from the same problem that has plauged every v-8 made by International-running 8 cylinders with only 5 main bearings, making the crankshaft too weak to handle the increase of compression ratio that would come from using a turbocharger big enough to supply the air required to compensate for the altitude density loss. If the truck in question is a Dodge with the cummins inline 6, I think that a dealer could make an adjustment. I know nothing about GM Duramax, but if it is also a v-8 , the crankshaft could again be the limiting factor. When International tried to produce a v-8 farm tractor, the 1468, the farmers tried to turbocharge this naturally aspirated engine with crankshaft failure following not to far behind.
Increase of what?
Compression ratio doesn’t change when you increase the volume compressed through the turbo to compensate for high altitude/low density. All you’re doing is compressing a larger volume of air that was at a lower pressure, so the MAP would be reading what it would “see” in normal operation. Of course, it would help to have a larger wheel on the turbo’s compressor, so you move more air rather than reach higher final pressure… the place to put this larger wheel is on the secondary turbine in a sequential setup, so you get the larger mass flow going into the primary (which would be the one with the fancy variable vanes).
Yes, you can use twins on a PowerStroke or Duramax. Granted, you can boost a Cummins 6BT more extravagantly – but is the difference between 700hp and 1100hp important in this context???
Oh, yes: exactly how would you propose to make a V-8 that has nine main bearings without forging the *** crank so long, and making the engine so long, that it runs like a dog? The GM 2-stroke locomotive diesels all use common journals for pairs of cylinders (fork 'n blade on the 567s) and I don’t think anyone questions that they produce more unit power than any feeble little big-cam Cummins or tiny Cat 3206… It’s the SIZE of your mains – the journal diameter and the area of the bearings – that determines how much “compression” you can run without compromising your engine life. The GM 6.5TD, for example, is limited by the crank strength, not the bearings; the crank fails in torsion, which has little to do with the number of mains.
I’ve said it before, and I’ll say it again, if you don’t care about NOx you want to get as much boost into a diesel as you can possibly manage, but NOT intercool the charge air. Naturally you need really strong rotating parts, and stout mains, block, etc. to make this trick work right. You get effectively all the energy used to compress the hot air back during the power stroke, so the engine runs with much mo
The poor turbochargers were the reson for the failure of the Budd built Rio Grande Prospectors. They had a great deal of difficulty breathing at the high altitudes found on the Rio Grande mainline. If the two two car trains had been operated on almost any other railroad in America they probably would have been extrememly successful. The Hercules diesels they were equipped with were very successful. It was the small turbos that were the downfall of the original Prospectors.
Just for the sake of laughs on the main bearing questions above… radial aircraft engines do some amazing things! At the far extreme end – the P&W 4360 Wasp Major produced up to 4,000 HP on 5 main bearings, 4 crank throws! (28 cylinders)…
Don’t forget that alot of high altitude operations also include many sharp curves and tunnels, not to mention steep grades. D.&R.G.W.'s & S.P.'s SD-40t2 & SD-45t2’s were splendid power in that environment. Walking your train in Moffat with 30 minutes of air in your s.b.a. isn’t fun.
I question Overmod’s statement regarding intercooling. The aim of turbocharging is to increase the MASS of air getting into the cylinder. Increasing the pressure on air raises its temperature. Raising the temperature of a gas decreases its’ density. Using an intercooler increases the density of the incoming air, in essense turning the single stage turbocharger into a two stage compressor. The result is that an intercooler puts a greater mass of air into the cylinders than the turbocharger would otherwise provide while operating at the same boost pressure.
Adding an intercooler may not increase the gas mileage of a vehicle because developing more horsepower means burning more fuel. However, in terms of thermal efficiency, which measures the the amount of power developed per unit of fuel burned, the effect is beneficial. You are litterally getting more bang for your fuel buck. The only downside is that higher fuel efficiency results from higher pressures and temperatures being developed inside the cylInders (a.k.a. BMEP). This means that the engine parts are subjected to higher stresses and may have to be beefed up.
EMD and GE still test the new protoype units at Raton Pass (Elev 7800+), Pueblo AAR/TTC (Elev 5000’+/-), Winter Park (Moffat Tunnel) and Palmer Lake (Monument Hill, Elev 7200+) on a regular basis. The new EMD’s still appear on a regular basis for high altitude tests with EMD’s Test Car No. 800…On the older engines, rack setting helped with the power curve / combustion issue as well.
(At La Junta, Pueblo or Denver on ATSF it was rare to see anything without a turbo used as power…GP38’s were rare, GP 39’s were common. CF7’s and GP-7/9’s were unusual to see, GP20R’s were everywhere in Yard service. (Exception was GP9 slug mother 1312 and slug 109 at Pueblo and later at La Junta …later , in the 1990’s we saw herds of demoted GP-30m’s, GP35R’s and B23-7’s in yard service)
[banghead][banghead][banghead]
Mr. Silverman would be correct on an engine not employing compression ignition. Not intercooling at high boost on spark-ignition gas engines, for example, could easily be a ticket to interesting detonation. Diesels are a bit different in that you can recover the compression energy in the subsequent power stroke up to comparatively high nominal boost pressure, and so long as you have a stoichiometric amount of oxygen in the charge air mass, and your rings, etc. can take it, the absolute mass of charge air isn’t as significant (and, in fact, higher mass can become detrimental at high flow rates (and can contribute to stronger torque peaks in the stroke). Remember, the part of the heat energy that makes a difference in these engines manifests itself as pressure; higher pressure ‘in’ will produce higher pressure out, especially on engines with good ceramic components and thermal coatings; you’re getting the additional boost pressure ‘free’ through the magic of heat drop through the turbocharging system at the price of proportionally low back pressure in the exhaust.
Remember that I’m not talking about the peak power you can squeeze out of the engine, either – for that, you’ll benefit from intercooling because (as he indicates) you can at least in theory provide a denser charge at any given manifold pressure if the charge is cooled (either before or after the injection of the fuel).
“In terms of thermal efficiency” any time you are using energy to do compression, and then subsequently throwing the heat away, you’re using energy derived from the fuel to no purpose. If you run the numbers, you’ll find that proportionally you’re using more fuel (measured as specific fuel consumption per hp/hr or similar units) for an intercooled engine. The advantages of intercooling lie in other places: for instance, you can often use a smaller and lighter engine to make a specific required horsepower, lightening the vehicle beyond what the added mass of the intercooler and pipes requires.
In 2 stroke diesels, some of the boost is used to scavenge the cylinders. At low rpm/low boost, the intake ports and exhaust valves need to be open long enough to do this. Would variable exhaust valve timing be more beneficial in achieving higher cylinder pressures at full power/high boost than a larger turbo? Do any 2 stroke diesels do this?
At the risk of starting another hare – there is a seemingly unrelated issue involved in high altitude operations, which is one of the major reasons why mudchicken sees units under test: cooling. Without bothering with all the details, suffice it to say that a radiator of a given size can’t cool an engine as effectively at high altitude as at sea level, all other things being equal, and most manufacturers worry that maybe, just maybe, at full power things may get too warm… Not usually a problem in automotive applications (automotive/truck radiators are moderately to hilariously oversize, in most applications) but very much a problem with a railway engine.
That is the reason that SP had EMD make the Tunnel Motors. After two SD 40/45’s transit a tunnel or snow/rock sheds in the Cascades or Sierras, the units behind the lead two start to overheat. Then they shut down and this causes all sorts of bad things to start happening. And this is happening at altitudes 1/2 as high as Rollins and Winter Park. Tunnel Motors have a larger radiator as well as air intakes down where the air is cooler.
To answer up829 question about variable valve timing; variable valve timing will not supplant the benefits of a larger turbo, which presumably would also provide a higher boost. Cylinder air has mass. This means it also has inertia and momentum. Increasing valve timing (duration and overlap) allows an engine to develop more power because it can breathe easier at high rpms. The increased valve timing gives the cylinder air more time to exit the cylinder by givng the air mass more time to get moving out of the cylinder ),overcoming its’ inertia. The increased overlap (simultaneous opening of exhaust and intake valves) sucks more fresh air charge into the cylinder due to the siphoning effect of the fast moving exhaust gases. The momentum of the incoming air continues to add mass to the cylinder even after the piston has reached the bottom of its stroke. To take advantage of this, the intake valves are not closed until after the piston starts to move up again. This effect is usually not noticed until an engine reaches or exceeds about 3,000 rpm.
The downside of this effect is that when use a cam timing that develops high horsepower at high rpms, you have a relatively unresponsive engine at low speeds) off the line. Conversely, an engine set up to hit its’ torque peak at low rpms will be very responsive in stop and go traffic but is weak passing cars at highway speeds.
Variable Valve timing gives you the best of both worlds . You wind up with an engine that is responsive at both high and low rpms.
Diesel engines utilize a heavy construction in order to withstand the high compression ratios. This heavy construction limits the maximum rpms that the engine can safely operate at. Diesel engines develop a lot of torque at low rpm because they are generally large displacement engines. Changing valve timing so that a diesel can operate at higher rpms is a waste of time unless you can also reduce the weight of the reciprocating masses (pistons, crankshafts, and connecting rods)
A rough rule of thumb for piston engines is a 7% loss in hp for every 1000 feet gain in altitude. For instance, your 300 hp normally aspirated truck drops down to about 200 hp at 5,000 feet. At 10,000 feet… Well, it’s gasping for air, right?
A turbo CAN negate this, if it has a gate on it that normally liimits the pressure boost under normal altitude operation. At high altitude the turbo would then be used at 100% of its capacity to keep things humming along. If that 4400 hp locomotive normally has 30% of the turbo output bypassed, then at roughly 5,000 feet the bypass would close down and you’d still get 4400 hp out of it. At 7,000 feet you’d get maybe a 15% reduction in power.
I personally don’t know how the locomotives have their turbos set up. More turbo can give you better performance at altitude, but costs more and takes up more space.
Mark in Utah
Of course it would be impossible to make a 9 bearinf V-8, and I am well aware that locomotive V-s use “common” or paired mains. I was merely pointing out that the crankshaftin the IH v-8, as manufactured, would not accept a greater amount of turbo boost without failure. Therefore, the Cummins equipped Dodge would be easier to set to overcome altitude loss of natural air density.
In trucking we had computers on our engines that understood what the “outside” was like and understood what needed to be done to create the power.
When I came thru Eisenhower (over 12,000 feet) in colorado I did not detect any “driveability” issues with the Cummins I had under my hood. Even though I was suffering from oxygen problems being that high up from sea level. (Dont smoke like I did for many years)
I have flown in private planes at 13,000 feet and can attest to the loss in performance both at the wing and engine. Never mind the threat of sleep that kills. (Hypoxia? -spelling)
There is always a limit somewhere at a point above land on the earth that a desiel will fail to run.
This remains true for all “Airbreathing” engines and people.
Large desiels are my personal favorites when it gets VERY cold. You need to keep it lit and the fuel warm. As long you have warm fuel and able to keep it lit then you will survive.
Since my trucking days in the rockies are over, I am quite content to remain near sea level. On a recent flight on southwest I could tell the cabin pressure was “Higher” in altitude than what I am accustomed to being at.
They aint big enough. You will learn this when you try to cross the dead valley to the western areas of Nevada in summer. My problem with older cars and some trucks was actually radiators that were too small and did not contain enough evaporative area to get the heat out.
There are two kinds of cooling. RAM air cooling is helpful when a vehicle is at speed the pressure of the air flowing into the vehicle’s front and the “pass thru”
The other form of cooling is simple radiating. This happens when you are in hot traffic stuck idling at gridlock stop and go. All vehicles have a limit.
Some of the aircraft engines such as the Pratt and Whitney are marvelous in not needing radiators other than what air cooling already provides. Although I venture that they operate in atmosphere that is quite freezing and that helps alot.
I sniff a cornbinder hater. Perhaps he hasn’t heard of every frikin powerstroker like me that mod the heck out of our fords and get waaaay over stock boost and never snapped a rod. It will take a lot more than just high boost to brake something on any engine. Lots of air is useless if there ain’t enough fuel to use it. Next on my list is propane injection to get that ford up to the modded cummins slayer level. My V8 will whooop your I6… [:D][:D][:D]
And what is with this anti intercooler stuff? The increased heat from compressed air will offset increased boost. The only thing an intercooler hurts is turbo lag time. That can be solved with a heavier foot when reving before dumping a clutch, or a higher stall torque converter for the slushbox fans.
Adrianspeeder
[quote]
QUOTE: Originally posted by Leon Silverman
To answer up829 question about variable valve timing; variable valve timing will not supplant the benefits of a larger turbo, which presumably would also provide a higher boost. Cylinder air has mass. This means it also has inertia and momentum. Increasing valve timing (duration and overlap) allows an engine to develop more power because it can breathe easier at high rpms. The increased valve timing gives the cylinder air more time to exit the cylinder by givng the air mass more time to get moving out of the cylinder ),overcoming its’ inertia. The increased overlap (simultaneous opening of exhaust and intake valves) sucks more fresh air charge into the cylinder due to the siphoning effect of the fast moving exhaust gases. The momentum of the incoming air continues to add mass to the cylinder even after the piston has reached the bottom of its stroke. To take advantage of this, the intake valves are not closed until after the piston starts to move up again. This effect is usually not noticed until an engine reaches or exceeds about 3,000 rpm.
The downside of this effect is that when use a cam timing that develops high horsepower at high rpms, you have a relatively unresponsive engine at low speeds) off the line. Conversely, an engine set up to hit its’ torque peak at low rpms will be very responsive in stop and go traffic but is weak passing cars at highway speeds.
Variable Valve timing gives you the best of both worlds . You wind up with an engine that is responsive at both high and low rpms.
Diesel engines utilize a heavy construction in order to withstand the high compression ratios. This heavy construction limits the maximum rpms that the engine can safely operate at. Diesel engines develop a lot of torque at low rpm because they are generally large displacement engines. Changing valve timing so that a diesel can operate at higher rpms is a waste of time unless you can also reduce the weight of