Curious as to how much negative effect there is on rated horsepower output of diesel locomotives operating at higher altitudes? I know there is less oxygen but with turbocharging wouldn’t that almost eliminate any HP loss at the altitudes of the transcons in Wyoming, Montana, Idaho, etc.?
Correct. The turbo just spins faster. Roots blown engines do suffer some HP loss (and smoke like crazy!)
So I’m wondering if electric locs have an advantage on those long, high grades?
They are air cooled so I wonder too. I remember reading about testing P47’s at over 40,000 ft and that even at subzero temperatures at that altitude the pounds of air going through the oil coolers wasn’t enough to keep from overheating. But in the continental US with a maximum of 8,000 ft I don’t think it would be a factor.
Older turbocharged locomotives (SD40-2 era) did lose a few percent horsepower at high altitude; for all I know maybe newer engines can fully compensate for the thin air, but I’m betting they don’t quite. If anybody has a service manual, a graph in the back might give the altitude correction to be applied when load-testing the engine.
The Moffat Tunnel line, which is a main line for the UP and the primary route for Rio Grande from the 30s to the 90s, is 9239 feet ASL. This is also the highest altitude on the Amtrak system with the route of the California Zephyr. The Tennessee Pass route, also in Colorado, was mothballed by UP in 1997. At the time, it was the highest main line route at 10,225 ft ASL. With grades of 3%, it certainly required more diesels than other lines, but I’m unsure of the ratio of engines to tonnage or the HP necessary. I will say that in the 80s, it was not uncommon to see seven to twelve units per train with middle and end of train helpers.
observed HP = corrected HP * 1/(0.933212 +0.0023142 * barometer in “Hg) (for AAR std conditions = 1000 ft elevation = 28.86” Hg) Going from 1000 ft to 10,00o feet, you lose less than 2% brake HP.
On which locomotive?
I can tel you this from an OTR driver viewpoint. Going over Sherman Hill is Easier than Eisenhower Eastbound. Why Lower Altitude my poor old 430 Detroit was gasping up Ike and did a max of 29 MPH at 80K. Now up Sherman hill at 80K it was 38 MPH and a full gear higher. I can tell you this however the next truck I ran over both was a 565 testbed and even that monster had issues with the high Altitudes. Above 12K and Ike is that high at the summit any engine will have trouble getting enough air even with a Turbo on it. Called there is NOT ENOUGH AIR to breathe.
Read this Don Strack article about turbocharging the GP9 http://utahrails.net/articles/up-gp9-turbo.php . Union Pacific research back in the day showed that its EMD units were losing up to 14% of their power at high altitude. This led to experimentation with turbochargers on thier EMD locomotives.
The graph in the SD60 manual says 100% power at 1000 ft altitude, 96% at 8000 ft. (At the same temperature, no doubt-- i.e. not ISA.)
16-645E3 engine
Would altitude significantly increase fuel consumption? My only direct knowledge is driving on I 84 paralleling the UP mainline in WY. My VW has a 1.8 TDI. The effect on power was not noticeable but my mpg’s decreased from 48 normally to 45. Confounding this, however, is the rather high, sustained speed on that road (75 - 80 mph).
Fuel consumption should not be significantly affected by altitude. The decrease in fuel mileage you see with your VW is most likely due to increased speed.
SD60 controls system is different from an SD40-2. SD40-2 runs on the governor fuel rack setting regardless of HP output. SD60 runs constant HP. The SD60 should just keep squirting more fuel until the HP output is reached. Something else is going on…
SD45T-2 manual says 100% power at sea level, 93% at 8800 feet; GP40-2 manual (6/79 edition) says 100% at sea level and 98% at 8850 ft.
While I don’t claim to be up to speed on locomotive turbochargers, I have worked on turbocharged aircraft engines (the reciprocating variety) for the past thirty years, and I would think the two are quite similar in both function and operation.
Bear in mind the aircraft engine has fewer cubic inches per engine than the prime mover has per cylinder, and a much smaller turbocharger, but is capable of maintaining sea level manifold pressure, and full horsepower to VERY high altitudes. I can’t imagine diesels giving up that power at altitudes below 10,000 feet. There is a controller that prevents over-boosting the engine and causing internal damage. I would tend to think all engines have a similar setup. Pilots tend to have a heavy hand on the throttle, and the controller is the only thing that saves their bacon.
If locomotive turbos are set up like aircraft engines they should be able to maintain full power at all elevations.
I may be wrong, but those are my thoughts.
Diesel turbos don’t have waste gates like spark ignited engines do, so back to the drawing board.
Creepy
I beg to differ. Diesels have had waste gates for years. There is a thing called over-boost. I have worked on engines that have blown the turbo off the exhaust manifold. Most commonly is the exploded compressor wheel sending shrapnel in every direction. Most waste gates are set to open at around 35 PSI. I have dynoed trucks that boosted to 50+ PSI but those engines did not live long. Cowboy truck tuners could really soup up the old mechanical fuel pumps. I pride myself on reliability when I rebuild. Some of my engines are over a million miles.
Turbos have helped a lot at the high altitude / thin air. It is still not a cure all. Electronic controls have helped some also. The engine designers have to strike a balance between fuel economy, longevity, and smog/soot at most operating conditions. Setting up an engine for one condition would be detrimental in others. Fairbanks Morse OP engines worked great in marine applications but placed in a loco frame they did not fair so well. In boats and subs they were run at a fairly constant speed and few hours at idle. In a loco they were idling for hours than full throttle then notched down and had varying loads placed on them.
Pete
No medium speed diesel in rail application had a waste gate. The load/speed points are fixed so none is needed.