Diesels & altitude

[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

[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.

[chad thomas]

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

[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...

[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.

[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]

[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

[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!

[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.

[selector]

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

[GP40-2]

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

[mvlandsw]

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

[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.

[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(]

[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.

[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?