Question, I work with baby GM diesels (6V-92 & 8V-92s), in the forums I notice people saying that turbos are removed and roots chargers are put on instead, my question is do the bigger GM 2 strokes not need the roots charger when they have a turbo. I thought that they had to have the roots charger even if they have a turbo, it just blows through.
Thanks for the info.
super charge a sd70? OH YEA i can see it now. 75 cars of grain Im leaving a siding go to notch 8 …200mph in 5.3secs conductor loses mirror ( again) railroading at its finest.
same thing only a ge engine put it in the 8th notch fire comes out of the stack 3miles down the road and 5mph. somethings never change
Non-turbocharged EMD diesel engines use two Roots-type blowers, gear driven off the crankshaft (only one is provided for the the 6-cylinder engine). The blower is necessary to scavenge exhaust gases from the cylinder: it supplies a large volume of air at a low pressure, about 4 psi. It’s not enough pressure to provide a horsepower increase, and these are considered normally-aspirated engines, not supercharged in the sense you would find on a automobile.
If an EMD engine is turbocharged, it has no Roots blowers. The turbocharger supplies air at about 15-18 psi, increasing horsepower by 50% in the same displacement. The turbocharger is gear driven at low rpms; once exhaust flow builds to sufficient volume a clutch disengages the gear train and the turbo is freewheeling.
Alco and GE turbochargers run in the 18-26 psi range, as far as I know.
Bronco, the BNSF has been down grading some of their SD40s to SD38s. What they are doing is removing the turbo and putting a roots on. Then the locomotive is used mostly in the yard. There is no advantage to having a turbo on a yard engine. It always appeared to me yard work tended clog up the turbo and increase maintenance.
EMDs SD 90s has the new H Block diesel it is a 4 stroke engine and has two true turbos. No gear drive at low RPMs.
Boy you all stole my glory. Being an ex-machinist I couldn’t have said it better myself.
Thanks for the info. With regards to the conversion of sd40-2 to a sd38-2 it looks like UP is also doing this too. Thought I saw a couple of converts in the Roseville yard, Missouri Pac style with 4 stacks. Can anyone confirm.
2 strokes are cool…twice the work same RPM!
broncoman,
There is perhaps a little more to add to the editor’s comments about EMD turbochargers. They are driven from the crankshaft by a train of gears at the generator end of the engine, the same gears as used to drive the roots blowers. The gear ratio is changed because the centrifugal blower turns faster to produce the same pressure than the lobes in the roots blowers.
The gear drive means that at lower power, the turbocharged EMD engine runs exactly like one fitted with the roots blowers. This is what gives the EMD the faster response at lower engine power, and avoids the black smoke on throttle change so familiar with GE (and for those who see them, ALCOs).
The turbocharger doesn’t free wheel until fairly high up the power range, about notch 7, by which time quite a bit of power was being used to drive the blower. Once the clutch releases, this power is available for use in the alternator, and this causes the change in the specific fuel consumption figures that we mentioned in the discussion about SD80MACs. Above this point, the EMD is competitive with the GE on fuel consumption, below, with the blower still mechanically driven, the EMD uses more fuel.
For yard switchers, which might not often get into notch 7, a simpler roots blower engine is a better proposition, because it will spend much of its time idling or in low power, where the fuel consumption of blower and turbocharged engines is similar. The clutch for the turbocharger is a relatively high maintenance item, and if the locomotive was frequently going to high power for short periods, the clutch would wear out more quickly. The simple roots blower still gives you a fast throttle response for switching, but a higher fuel consumption for a given power at high power settings (notch 7 and 8).
It is the drive train to the turbocharger that gives turbocharged EMD locomotives their distinctive sound, mentioned by our English member 45144, particularly while they are idling. I think it may
Peter, I assume in the Perry-class frigates the Detroit Diesels are for electrical power? While the LM2500 gas turbines are purely for propulsion? Do I understand you correctly that these have 149s have both Roots-type blowers AND turbochargers? Or either but not both? I appreciate you pointing out the “step” in the fuel economy at the point where the turbocharger disengages. That’s only obvious when you stop to think about it!
It’s of interest that EMD has been arranging engines the same way for over 60 years now: blowers or turbocharger on the rear end (turbocharger end), along with the starter motor(s) geared to the flywheel and the auxiliary generator, and water pumps, lube oil scavenging pump, lube oil pressure pump, and governor on the front end (accessory end) – which is in the rear of the locomotive. So the engine is “backward.” But the air compressor can be on either end – today, as far as I know, it’s always on the front end, that is, in the back of the unit, but on F units it was on the rear end of the engine, driven off a flex coupling from the front of the generator. This is a very ugly connection. I foolishly thought it could be unbolted to replace it, but in truth you sort of rip the thing apart piecemeal with the liberal use of cheater bars and oxacytylene torch.
To quote from the EMD 645E3 Engine Maintenance Manual:
"The turbocharger assembly is primarily used to increase engine horsepower and provide better fuel economy through the utilization of exhaust gases. It has a single stage turbine with a connecting gear train. The connecting gear train is necessary for engine starting, light load operation, and rapid acceleration. Under these conditions there is insufficient exhaust heat energy to drive the turbine fast enough to supply the necessary air for combustion, and the engine is actually driving the turbocharger through the gear train assisted by exhaust gas energy. When the engine approaches full load, the heat energy in the exhaust, which rea
The Seaboard Coast Line Railroad had a problem with EMD GP 40’s related to the turbo. Johnny Moore, an engineer who worked the road, whom I met through my church, told me about overheating, probably bearing falure which occures from oil overheating to the point of viscosity loss, starving the bearings,resulting in a costly bit of downtime for turbo failure. This, he asserted, was from using to much throttle during switching moves. I believe he said the turbo freewheels at or by the sixth notch. His respected advice was to use low throttle speed while running locals on a GP40. In perspective the location was Lakeland, FL, which is 197ft above sea level with “hilly” terrain, or ripwrap profile, with two roads diverging ACL/SAL=SCL in the ‘70’s topping the hill from four directions. In the days of first generation power and 150 car trains men would approach Lakeland, the top of the hill, wide open. GP7’s and RS3’ worked locals, So the GP40’s, replaced on road freights by U36B’s, became turbo training ground. This, I belive prevented the GP/SD39,49,59’s from a future with SCL Ind. The Coast Line removed the turbo from the SD35, calling it an H-15. EMD Leasing(gmemd.com) rates SD38 and SD40 starting TE and max con TE pretty close. Just available HP is 1,000 less than the “turbo.” The NS has taken to replacing two GP38’s with one SD40 on locals around Rome, GA these days, now that was Different! Even so, you would observe, they work it easy, only using the real power when they need it. So Easy Does It! remember-it’s not your dad’s GE! Enjoy Your Hobby!
Mark,
Yes the Perry class use four Detroit Diesel 16V-149 engines rated at 1000kW each for auxiliary power. There are plans, both here and in the USN to replace them with Caterpillar 3516 engines, retaining the same alternators.
Since the Perry class has only a single screw, they have two retractable and trainable electric “auxiliary propulsion units” which can be used for manouvring in harbour, or as emergency propulsion (up to maybe 5 knots). That is the only way the diesels get to propel the Perry class.
And yes, the engines each have two roots blowers sitting down in the vee, and four turbochargers, each driven from four cylinder exhausts. These originally sat above the engine (I think) but were moved lower to reduce the engine height, and sit alongside the rocker covers on the outside of the engine now (on the Navy versions). The blowers run all the time, and draw air past the standing turbochargers until the power gets to the level when the turbochargers compress the air fed to the blowers. I think the intercooler is located between the turbochargers and the blowers.
There are versions of the engine sold without the turbochargers, and these rely on the roots blowers to provide the positive pressure. They are rated at a lower power, of course.
Turbocharged versions of the Fairbanks Morse engine had the same arrangement of a turbocharger feeding a roots blower. None were fitted in locomotives in the USA, but a large number of Russian built locomotives fitted with copies of FM engines used a turbo feeding a roots blower.
In fact, the only locomotive engine built in really large numbers outside the USA was the turbocharged version of the FM engine, which was built right up to the end of the Soviet era in 1990.
Peter
I think it’s cool to be discussing the Detroit Diesel line in the same context with the EMD two cycle engine, since both share an extrordinary amount of simular traits. two piece crosshead pistons, port type cylinder liners, rack controlled injectors, excluding the heads, the '71 series Detroit cross sectioned resembles a scaled down 710 Series, including two bolt together v8 crankshafts to make the V16. My favorite motors have always been V12’s, probably 'cause of the 12VSeries. Detroit Diesel General Motors carried the motto,“Standardization, Is The Key!” So,the inline '6 and 12V71Series share the same 6cyl head, for years. Iv’e seen Uclid dump trucks lift front wheels off the ground, using the motor to"help" dump the load! God, I love this country! PT109(as well as PT73), used three Packard V12 Diesel engines during WWII. Also both the EMD and Detroit Diesel Roots blown engines will not run without the blower, or turbo, attached, since every down stroke is a power stroke, and the motor starves for air. The lobes inside the blower mesh, but do not touch one another, for which there is a gauge made to assure clearence. 'Ole Lefty Scott back at Polk Vo Tech taught us “the nastiest thing in the world is the inside of a Detroit Diesel!” Thanks for the info on the 149 Series in the Perry class Frigates. Iv’e heard of the 110 Series marine Diesel, but not much about the 149. Marine, industrial, power unit, automotive, generator set, MADE IN AMERICA!
the reason for the sounds like we are taking it easier with the sd40 comparied to the gp-38 is because in notch 3 of the sd40 we are doing the same amount of work in that notch as you would be doing in notch 6-7 with a 38. the gearing and power of a sd40 allows for less throttle at switching than with the good ole gp38. and one other thing being a sd40 is a 6axel unit there are restrictions in spur tracks usually of 5mph. with these units.
The conversion of SD40’s to SD38’s by replacing the turbo with a roots blower is hardly uncommon. BNSF has done it with its SD38P’s, although some of those started out as SD35’s, UPY SD38’s are mostly rebuilt from SD40’s and SD40-2’s, although some are originally SD38-2’s. BRC has done the same with its 560 & 570 series.
In a similar vein, IC rebuilt a number of ex-UP and ex-SR SD24’s into SD20’s by removing the turbocharger (among other things). Precision National did a similar thing with a batch of SD24’s that eventually wound up on C&NW.
Allen – good point about turbocharged engines in switching service. The bearings in the turbo take a horrible beating. I’ve never been sure, though, whether it was so much overheating and thinning of the oil, as a plain ordinary pressure drop when the engine is returned to idle from a high power. At high power, that turbo is really winding! I do know in aircraft engines that the quickest way to kill a turbo is to go from say cruise power to idle without letting the turbo spin down – takes about three or four minutes to do.
From my understanding of turbos, its the oil pressure drop causing the overheating. The oil pump is belt or chain driven off the engine. As RPMs go up pressure goes up. Turbos are very dependent on oil flow. When you drop the throttle to idle, oil pressure drops tremendously. The turbo is still spinning at high speed when most of the oil goes away. Heat builds up quickly as the bearings wear against each other. The bearings will only take so much of this before they fail.
Derrick
Mark and/or Peter,
Do the bigger series xV-149 and xV-645, 710 have accessory gear drives at both ends of the engine as well.
Peter,
We had a GM engineer tell us that although there is a reduction in efficiency with the blower, it had the benefit of keeping the turbo spinning during on the throttle, off the throttle situations since there is a pressure drop on the compressor side of the turbo, turbo lag is reduced. Seems logical, only heard this from him and no where else.
broncoman,
I don’t have any data with me on the accessory drives, but my recollection is that the 645 and 710 have all the gear drives, blower/turbo and camshafts at one end (the end the generator connects). As Mark said, there is a driveshaft at the other end for the air compressor, and this drives the radiator fan in older switchers and some exporrt units.
While the 149s are basically two crankcases connected, I think the accessory drives are at one end only, with all the shafts running through with bolted connections. But when I get a chance, I’ll check.
Having thought about the EMD Turbo drive and the reasons for its adoption rather than EMD taking the Detroit Diesel solution of a turbo and a roots blower in series, I feel sure that the fuel economy advantages caused the selection of that design.
The cost of diesel was becoming an issue in the late 1950s, and UP were testing diesel locomotives on heavy marine fuel oil (which they used in their gas turbines, and had used in steam locomotives). ALCo were still in business, the 251 was very economical and fairly reliable, and GE were expanding their export business and looking to build locomotives for the US Domestic market. So the same (big) customer who was pressing for more power also wanted better fuel economy, and EMD selected a design that would keep them happy on both counts.
Peter
The UP has rebuilt about 10 ex MP SD40-2s into “SD38-2s” de-turbocharging them, adding paper air filters, but leaving the SD40-2 style carbody…damn with those bigger radiators they outta cool themselves well!!! They are assigned to North Little Rock, Roseville (I think) North Platte, and maybe St. Louis last time I was there 2 were there.
It’s a heat thing. It all points to the practice of lugging. Now there are factors that are not published about the EMD V-type two cycle Diesel that are not relavant to the application of platform-mounted, power-generation prime movers, now that you mention it, such as peak-torque rpm, which with a compression-ignition engine is at the bottom of the operating range. The whole theory of lugging an engine is dropping below advertised peak-torque rpm speed. After diesel engines drop below peek tor. speed, the governor automaticly reduces fuel injection. On automotive Diesels, this can be noted by drop in tubo speed. At that point, you downshift, and Not before! This is how you save fuel. However, the major principal to be learned is, oil pump speed is directly related to throttle speed. If you need power, graduate it to the work. If by principle, of power application half the distance to the stopping point, the question would be do I need to exceed notch four? Can I accompli***he work without hitting the mark like Napoleon over the Alps? Johnny Moore stongly advocated and taught and evaluated performance in notch 6 or less. Then the heat accumalated would be transfered to the oil flow, as designed. Sudden, quick throttle-ups, raise operating temps., then dropping back to idle speed, (as in branch line daily local service), results in overheating the oil, which breaks down viscosity. O.K., do I get an honorary dergree? Enjoy Your Hobby!
Allen – sounds great! And all of that (and more) is why the newest engines (whether from EMD or GE – and I don’t want to get into that!!!) are computer controlled (so is your car, for that matter) – the designers have gone to a good deal of trouble to figure out what is the best combination of rpm and injector pressure and timing for a given power demand, over the whole power range, for best economy, lowest emissions, and best reliability – and then equipped the engine with sensors to find out what it’s really doing, and adjust things to stay on the best point (and not incidentally, tell the maintenance folks what’s going wrong, before it’s obvious). Lets the guy in the front office decide how much power he needs, and not worry about the rest of it…