Diesels & altitude

[chad thomas]

On another thread it is stated that deisels do not loose power as altitude increases.

If that is so why do diesel engines in pickup trucks loose power?

What is the real deal?

[Anonymous]

LOSE power! ONE "o"! Anyway, I don't know but air IS less dense at higher altitudes so even with a turbocharger packin' it in there the mix will be a little richer in fuel.

[CopCarSS]

Diesels do lose power at higher altitudes. However, forced induction engines (spark ignition, and combustion ignition) have a much shallower power loss curve than naturally aspirated engines. Since almost every diesel on trucks and trains is turbocharged these days, its not that big a deal.

Unfortunately, my LT1 is naturally aspirated...so when climbing Trail Ridge Road, she's pretty lame![xx(]

[GP40-2]

Ok Chad, I'll be nice this time.

While it is true that air gets thinner at altitude, the key is to design a system that allows enough oxygen in to to cylinder to let the proper amount of fuel to burn to reach the desired performance level.

Let's say you want a particular engine to have at least 4400 hp available for traction at all possible operating conditions that your customers could subject the locomotive to. You find the parameters needed (i.e. the amount of oxygen/fuel in this case) in the worst possible situation, add an additional margin to make sure the objective will always be met, and engineer accordingly.

So in simple terms, you supply the locomotive diesel with a large enough turbo and fuel injectors to handle any condition it may come across in the operating environment to maintain at least 4400 hp.

The simple answer to your truck question is that the particular engine was operating outside its design parameters, so it lost power at altitude. The fix may be as simple as buying an aftermarket computer chip to redefine the operating parameters of the engine. Or it may be more complicated--depends on the inital design of the engine.

Back in WW2, fighters and bombers used turbocharged piston engines at altitudes up to 35,000 feet while maintaining high performance.

[mvlandsw]

Can the computer controlled locomotive diesel engines adjust for this automatically?

[GP40-2]

Yep, they take into account environmental conditions such as temperature and pressure and adjust accordingly.

[selector]

GP40-2, I think you meant 'supercharged' when dealing with WWII radial engines. [:)]

[GP40-2]

They were exhaust driven, so they are technically turbochargers. Superchargers are mechanically driven from the engine.

Many of the planes in WW2 were not radial engined. Most of the "modern" designs used in line or V engines instead.

My favorite WW2 plane was the Lockheed P38 Lightning. It was equiped with two 1,500 HP V-12 Allison engines equiped with General Electric turbochargers.

It could maintain 420 mph in level flight and reach 44,000 ft altitude. They had enough firepower to sink a ship.

[Anonymous]

all this sounds about right. Automobile and light truck engines use a waste gate turbocharger which would need to be tuned for a higher altitude either mechanically or electronically depending on the year of the engine.

Another factor would be fuel rack limiting devices that limit smoking during acceleration. These devices limit fuel rack position when air becomes limited for the amount of fuel being injected at the time, normaly during acceleration when a turbocharger can momentarily lag behind engine demands. If available air falls below the capacity of a turbocharger, this device will limit the fuel system and power of the engine to maintain a clean exhaust. Disabling this system for more power is a mistake. I have seen this common practice in poorer countries, and all the black smoke is nothing more than wasted fuel. I one saw valves from such an engine that had carbon deposits on the stem that literaly modeled the shape of the entire port! no wonder the owner complained of lost power!

[Randy Stahl]

Older locootives had a fuel limiter on the governer. A small air line runs directly into the air box. Newer engines use Barometric pressure sensors that do the same thing... Reduce fuel = reduce horsepower.
Randy

[selector]

Yes, the P-38 is my all-time favorite. The Allison, unfortunately, killed man pilots due to failure on take-off. By the way, it WAS turbocharged as you say, but the Pratt-&Whitney R-4360 Wasp Major was gear-supercharged (don't know if it was used in WW II). Also, the inverted V-12 in the German Me-109 was gear-supercharged.

Sorry, [#offtopic].. I'll get out. [:I]

[SSW9389]

Go here to read about early efforts to turbocharge EMD engines because of power loss: http://utahrails.net/webpubs/up-gp9-turbo.php Don Strack gives a good account of the how and why it was done.

[jchnhtfd]

Having flown some of these puppies... well, on the whole I'd take the Corsair (Twin Wasp or Wasp Major (eek!!!) in one late version) or the Spitfire (Rolls-Royce Merlin). There were versions of the Wasp Major R-4360 which were turbocharged, used on the B-36 and B-50 bombers. It and the Wright Turbocompound engines were really and truly the peak of aircraft piston engine desigh. The Wrights were supercharged (a two speed geared centrifugal affair) but used the exhaust through 3 turbines to boost engine power directly -- the turbines were geared to the crankshaft. The DC-7C and L-1049 used them, among others.

The relationship of turbocharging or supercharging to engine power is rather complex, though. The first thing one has to do is distinguish between engine installations which are turbo-normalized and turbo-charged. I the first instance, the turbocharger is being used to maintain a certain rated maximum BMEP (and hence, horsepower) up to a certain altitude. In the second, the turbocharger (or supercharger) is used to increase the air pressure -- and hence the amount of air taken in and the amount of fuel burned and therefore the horsepower) at any altitude, from sea level up. You can, of course, have combinations of the above! For example, you could have a turbocharge set up to maintain, say, 50 inches manifold pressure from sea level to, say 15,000 feet, but above that the manifold pressure would start to drop off. You can do the same sort of thing with geared superchargers, too -- which is why the two speed gearing on the Wright Turbocompounds.

There is a very definite limit to the maximum manifold pressure, though, above which the engine will dissassemble itself astonishingly rapidly. In aircraft, pilots (or flight engineers) are trained to watch this, as the turbocharger or supercharger used to be manually controlled. Nowadays, most installations are automatic -- but it is best to watch it anyway, as waste gates have been known to stick shut.

Then there is the additional problem of heat. Compressing air raises its temperature quite a bit. Some aircraft, and a lot of land or marine applications, use intercoolers to reduce the intake air temperature, which also increases ultimate power output.

Sort of off-topic, but... if you ever want to see something really truly scary, try a Wright Turbocompound at takeoff power with a blown piston. The flame coming from the related blow-down turbine can reach well past the tail section of the bird...

[chad thomas]

So it sound to me like they derate themselves at lower altitudes then.?????

[jchnhtfd]

QUOTE: Originally posted by chad thomas

So it sound to me like they derate themselves at lower altitudes then.?????

Yes -- either the pilot or flight engineer 'derates' them manually (the guys on the ground are not pleasant if you come back and say 'oh by the way, I overboosted # 2 on takeoff'[:D]) or the derating is done automatically, by various barometric controllers (see Randy's post) or other contraptions.

[CSXrules4eva]

One thing I've got to say that wasn't mentioned here about diesel engines and "thin air". One of the problems you'd run into with any diesel is the oxygen and air tempature. Sometimes if you start a diesel in cold or "thin" type air a condition, in which I call "no start" occurs. Since a diesel is a compression ignition engine, it must crank fast enough to produce sufficient heat for combustion. You can't compress cold air. Ususally a slow cranking speed will result. This is about the only thing I can say since jruppert, lol stole most of my answer to this question. hehehehe

[espeefoamer]

Diesel HP loss at high altitudes was the reason that the Colorado & Southern kept a steam engine on the Leadville to Climaxc branch until Oct. 1962.

[adrianspeeder]

Have no fear.... Adrian"diesel"speeder is here...

What is the truck in question?

Adrianspeeder

[selector]

Actually, you can compress cold air, and I know this because that is the only way to get diesel-equipped tractors running up in the arctic. The slow crank is more likely a function of crankcase oil viscosity and/or battery condition. Of course, spray ether helps, but if you have enough juice, you just crank the diesel over until the compression warms up the piston top and cylinder head. The fuel is especially formulated for arctic ops, so atomization is not an issue. Once the cylinders get hot enough, they fire.

No one said it was pretty, but it works.

[rvos1979]

QUOTE: Originally posted by selector

Actually, you can compress cold air, and I know this because that is the only way to get diesel-equipped tractors running up in the arctic. The slow crank is more likely a function of crankcase oil viscosity and/or battery condition. Of course, spray ether helps, but if you have enough juice, you just crank the diesel over until the compression warms up the piston top and cylinder head. The fuel is especially formulated for arctic ops, so atomization is not an issue. Once the cylinders get hot enough, they fire.

No one said it was pretty, but it works.

Just don't shoot ether into an engine with an intake manifold heater, unless you want to replace the manifold......

Randy

[kenneo]

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.

[SSW9389]

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! [:)]

QUOTE: Originally posted by kenneo

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.

[Anonymous]

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.

[Overmod]

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 more jerk, but higher thermal and mechanical efficiency. Intercooling throws away energy!

[passengerfan]

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.

[jchnhtfd]

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)...

[Anonymous]

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.

[Leon Silverman]

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.

[mudchicken]

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]

[Overmod]

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.

An interesting point is that pressure goes up seemingly out of proportion to temperature, which is why you see Cummins boost up there in the 50 to 60lb range even on streetable trucks -- if you look at the mass flow at the higher pressure, Mr. Silverman is again correct in noting that an intercooled charge at a lower pressure will allow the same, or higher, horsepower output from an engine of given displacement. Indeed, to get very high horsepower output out of a given engine, at some point it becomes imperative to use *some* intercooling on the charge air.

As another aside, it might be interesting to speculate on whether a diesel engine running at high altitude, pressure-turbocharged *with minimal heat loss* to nominal sea-level MAP, would actually produce a bit MORE power (net of the additional turbo action) since there is lower back pressure on the exhaust, and that will in turn allow a bit better heat drop (and hence energy recovery) across the turbo. (One might note by analogy that steam locomotives can perform much better at high altitude than at sea level -- their exhaust being freer, and the required higher airflow for combustion being easily assured up to quite high altitudes.) What you would expect to see, however, is a VERY large turbo wheel and intake plenum; something which if used as the only turbocharger would make 244 smoke look puny! (And cost way, way too much for something used in the ranges closer to sea level...)