I was watching a Youtube vid on starting up an old E unit. They were filming the prime mover from all angles. On the front of the engine behind the cab compartment, there was something that sure reminded me of a GMC diesel super charger like semis have. Anybody know anything about this? I know some locos are turbo diesel, but this looked like a blower.[%-)]
I believe what you are referring to is a Roots Blower
which is a type of supercharger, high volume but low psi
gain.
loather this was a roots type blower, we removed the two on our BL2 at the Kentucky Railway Museum 2 years ago and had them rebuilt. They are used on the exhaust side of the engine not the intake side. Here is a link to a photo taken at IRM http://www.irm.org/gallery/cnw411paintproj/acz
Dale
The EMD 567 diesel engine (567 cubic inches per cylinder) is a two-stroke design. In the E-unit most likely a 12-567-B or C. The air is forced into the piston through ports in the side walls, and the fuel is injected from the top. The 4 exhaust valves are on the top. These engines require a pressure to force the air in. The Roots supercharger does the trick. On turbo engines, the turbo is geared, so that the pressure is formed until the engine is wound up to clutch out gears and the turbo freewheels.
Quite the opposite sorry, a super charger is geared/belted to the engines crankshaft so that when the engine is running there is boost, compared to a turbo charger which has a turbine spun by the engines exhaust, and they only spool up when there is enough exhaust passing thru, which can cause whats known as ‘turbo lag’. Variable turbine blades can make them operable at lower engine speeds, but a super charger imo is the way to go no matter what.
I agree with this post. All the turbos I have ever encountered were driven only by the exhaust gas flow leaving the engine and all the superchargers (blowers) were all mechanically driven thru the use of belts or gears.
Each has their own pros and cons. At lower idle speeds the turbo has little power drain on the engine while at the same time it contributes almost nothing. At higher engine speeds the exhaust gases turn a turbine which is conected via a shaft to an impellor which forces air into the engine. A blower, while consuming upwards of 10-15% of the engines horse power, relys on a the engine to mechanically turn it while supplying forced air thru out its rpm range.
WSOR 3801 Thanks for the info. I did not know that 567’s were built upside down but now the setup makes a lot more sense to me. Guess I better stick to small block Chevys. But this explains why they keep me in the car shop most of the time and helping the steam crew out occasionally. Also explains why I couldn’t find the carbs.
Dale
From the EMD 645E manual here: http://www.rr-fallenflags.org/manual/emd645-s08.pdf
TURBOCHARGER
DESCRIPTION
The turbocharger assembly, Fig. 8-I, is primarily used to increase engine horsepower and provide better fuel economy through the utilization of exhaust gases. As shown in cross-section, the turbocharger 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 reaches temperatures approaching 1000° F., is sufficient to drive the turbocharger with-out any help from the engine. At this point, an over-running clutch in the drive train disengages and the turbocharger drive is mechanically disconnected from the engine gear train.
The EMD 567C manual, as in an E-unit, is here: http://www.rr-fallenflags.org/manual/emd567-gen.html
EMD engines are termed either “normally aspirated” or “turbocharged” but technically are not either. Normally aspirated EMD engines are Roots blown (supercharged). The Roots blowers (there are two except on the 6-567) are gear driven off the back of the engine (the engine is backward in the locomotive), achieving a pressure in the air boxes of about 4 psi. That pressure is sufficient to scavenge the cylinder of exhaust gasses and recharge it with combustion air in the small amount of time that’s available in a 2-stroke engine.
EMD turbochargers are gear-driven at low engine rpms. When the engine accelerates to approximately notch 7 there is sufficient exhaust gas pressure to drive the turbocharger without the assistance of the gear train, and an overriding clutch uncouples the gear train and the turbocharger free wheels. The EMD turbocharger develops about 15-18 psi in the air boxes at full load. The result is 50% more horsepower compared to the same displacement in a naturally aspirated engine.
All Alco and GE engines are turbocharged, producing about 18-26 psi to the engine.
RWM
Sounds like the boffins at EMD have combined the turbo and supercharger.
The low-speed direct gearing of the turbocharger is to reduce the smoking problem caused by turbo lag, which is why Alco’s smoke heavily when the throttle is advanced.
Also, the 567, 645 and 710 engines are all two-cycle diesel engines, and a Roots blower or turbocharger is an absolute necessity for the engine to operate.
Alcos smoke heavily??[%-)][:D]
Drafterdude-That’s them! Thanks for the pic! Learn something new every day on these forums.
EMD actually began using turbochargers on its diesel electrics after the Union Pacific began to experiment with a retrofit package applied to some GP9 units. Union Pacific was always looking for a solution to the dropoff in power that “normally aspirated” diesel electrics experienced at higher temperatures and altitudes. They needed locomotives that were capable of sustained high horsepower while moving trains over the very long steady grades between Laramie and Ogden as well as throuth the lot deserts between Salt Lake City and Los Angeles. Steam locomotives didn’t have a problem here but early diesels certainly did. In fact, the gas turbines were built precisely for service between Ogden and Laramie because they performed better (comparatively) than diesels in this service.
As I remember the story, Union Pacific first retrofitted some GP9 units with aftermarket turbocharger packages, I believe made by AiResearch and later Elliot. These units were sometimes called Omaha GP20s. Then EMD took this suggestion to heart and came out with their own “turbocharged GP9” called the GP20, and the SD24. Once these units were available, Union Pacific bought quite a few of these, too. This was really the first time turbocharging had proven itself in heavy mainline rail service, and of course it was only the beginning. The full and complete story (without my memory errors) can be found in the “Diesel Spotter’s Guide” by Pinkerpank as well as in several good on-line articles.
I remember those early EMD units as well as UPs other attempts to solve the horsepower problem on this difficult route. There were GE U50 and U50C units, Alco C855 as well as EMD DD35, DD40 and DD40X types. Finally, the growing horsepower capability of more conventional turbocharged Geep type units made this horsepower battle unnecessary, and virtually all of UPs locomotives for this service are now turbocharged.
Starting with the GP20, EMD used a combination Turbo/Supercharger design. The unit was attached to the drive shaft with a centrifical clutch. As the RPM’s increased, the clutch disengaged the unit from the drive shaft and it was then a freewheeling exhaust driven turbocharger. The advantage of this design was that ‘boost’ was available at low RPM’s, and raw fuel was not shot out of the exhaust(remember the famous Alco black exhaust when the throttle was moved fast?). Ge engines also suffered this issue in the early days. Starting with the ‘Dash 8’ engines, the computer controls can limit the fuel to the injectors if there is not enough air volume in the cylinders. I am not sure if the current EMD SD70ACe engines still have the clutch or are ‘computer controlleed’…
Jim
WSOR 3801 is on target here
From working on EMD and GM detroits one has to remember that they are two-stroke engines and will not start unless there is sufficient air pressure in the air box (normaly asparated is with forced air, ie blower), forcing air through the scavinging ports of the piston liners. If memory serves me, both the GM truck and EMD roots have the same CC clearence of .002 between the blower lobes so they tightly pumped air. (A roots blower, contrarly to one of above ansers is only on the intake side of the engine) regardless of the application, train, truck, dragster or drag boat.
The GP20 that WP had were both roots (starting) and turbo for added forced air. When we got the GP35s it was turbo only. One had to wait a few minits before starting them to let the turbo oil pump supply oil up into the turbo bearings as it took to long for the engine scavaging pump and oil pump to deliver oil, thus preventing turbo start failure from excessive exhaust heat. When setting the govenor RPMs, one could hear the turbo kick out as we set the different notch speeds(throttle positions).
Here is a prime mover from a SD40-2. The turbo is front and center. Air intake is the round part. Exhaust out the top. The ductwork from the turbo feeds the air box. There is a gear train behind that spins the blade at lower speeds.
Down on the bottom is I believe the turbo lube pump. This turns on before the engine starts, and should stay running for 30 minutes after engine shutdown, to prolong turbo bearing life.