• GPF39-3

  • Discussion of Electro-Motive locomotive products and technology, past and present. Official web site can be found here: http://www.emdiesels.com/.
Discussion of Electro-Motive locomotive products and technology, past and present. Official web site can be found here: http://www.emdiesels.com/.

Moderator: GOLDEN-ARM

  by mxdata
Since two-stroke cycle diesels have no intake stroke, they require an external means of forcing air into the cylinders. This can be done with a roots blower (used on many makes and models of diesels), a centrifugal blower (used on the Detroit Diesel 6-110), or a turbocharger with an external drive gear train (as used on EMD turbocharged engines).

A freewheeling turbocharger by itself will not work well, as there is no exhaust energy available at startup, but it can be connected in series with a roots blower. The roots blower provides the air flow for starting, when the turbo has no exhaust energy available to drive it. As load is increased on the engine it powers the turbo which precompresses the air going into the roots blower. This roots blower plus turbo system was used by Detroit Diesel, Cleveland Diesel, Fairbanks Morse, and was also applied to a few EMD engines in experimental installations.

Unlike the others, the EMD engine has the blowers mounted over the generator, and having freewheeling turbochargers and aftercoolers stacked on top of two roots blowers was a nightmare installation, particularly in a locomotive carbody. EMD's unique gear train assisted turbocharger took far less space to do the same job.

  by Justin B
Interesting.... I stand corrected.

  by crij
The turbo 2 cycles, are not really true turbocharged engines.

In a 4 cycle engine that is turbocharged, the exhaust is enough to pressurize the intake, due to the fact that the intake and exhaust ports of the cylinder open at 2 different times. (The exhaust gas spins a turbine, that is connected to another turbine in the intake side, by a shaft. By spinning the turbine in the intake side, it forces additional air down the intake, in proportion to the speed of the engine.

The problem with 2 stroke engines is that the intake and exhaust ports are both open at the same time, at the bottom of the stroke to purge the exhaust from the cylinder, so the turbo cannot compensate for the loss in pressure, especially when accelerating. EMD got around this problem by coupling the turbocharger's shaft to an electric motor with an over speed clutch. basically the electric motor runs at a defined speeds depending on the notch position, when there is enough exhaust pressure to spin the turbos faster then the set point, the clutches slip, allowing to spin as fast as the engine needs.

The advantage of the Roots Blower (supercharger) is that there is always a few pounds of pressure to completely purge the cylinder at the bottom of the stroke, so that the engine is compressing pure air, and not air contaminated with burnt gasses.

I could be wrong in my statements, but this is how the whole situation was explained to me.

Take care,


Personally I would rather be blown then charged, especially when it comes to my diesel engines.

(if you need a hint (blower vs. turbo), not necessarily the other thing)

  by Railpac
The GP9 used the 567C series block, not the 567D. The D series crankcase was itroduced with the GP18/20 models.

Also, from what I understand, and diagrams I have seen, EMD turbos for the 2 stroke (567, 645, 710) use a two step method. The turbo is gear driven at low RPMs, and is exaust driven at higher RPMs. A centrifugal clutch allows the turbo to switch to exaust at the proper speed. As said before an all gear, or exaust driven turbo on a 2 stroke diesel would be highly inefficient.

  by mxdata
In building up a few hundred EMD engines over a span of 35 years, I never found the one that had an electric motor inside the engine, driving the turbocharger. All of them I worked on, had the turbo driven by the turbocharger drive gear assembly which is part of the #2 idler in the rear timing gear train. Guess I must not have been looking in the right place. The only motors I found were the starters (or the DC generator on units that motor the generator for starting). Gosh, you learn something new every day! We have a 16-645E3 taken apart right now, I will have to go and look for that motor! :wink:

  by dave76
I think on the turbocharged EMD engines the turbo is clutch driven at the lower RPMs to provide combustion air. When the RPMs rise the clutch disengages and the turbo operateds normal, off the the exhaust pressure.

  by EDM5970
Dave76 and Railpac, you are both correct on how an EMD turbo works; nice, short explainations, too.

Now, I have a question for someone like mxdata. I recall reading about "de-turboing" GP-30s and GP-35s, by replacing the clutch with a block or a plate of steel, so the turbo is aways gear-driven.

Did I remember this correctly? Does this really work, or would the gears get worn out early, taking the turbo revs up above the point where it would normally be free-wheeling? It seems like a cheap way to get scavenging air, rather than going with a pair of Roots blowers.

(Of course, the 30 and 35 would also benefit from a major rewiring, ripping out the multi-stage shunting and turning them into roughly 2000HP GP-9s or -18s, but that is another story-)

  by mxdata
There have been a number of instances where engine owners have applied "locked-up" turbochargers to 567D2, 567D3, and 567D3A engines, primarily in applications where the engine has been derated. The parts for doing this exist from some marine applications where the clutch is in the gear train rather than in the turbocharger. This turns the "turbocharger" into an "exhaust assisted supercharger", and eliminates the clutch. If this is going to be done, you have to pay some attention to the rating and loading of the engine because the turbo drive gear train was designed to transmit power to the turbo in the DRIVING direction. If you load up the engine too much, the turbo gear train tries to drive back to the engine, and the bushings in the planetary gears were not designed for that, they only have about 1/4 as much bearing surface in the OVERRUNNING direction.

The turbocharger clutch is not centrifugal, it is a direction of motion device which has rollers in pockets in a camplate. If the engine gear train is going faster than the turbo would be turning on exhaust energy, the motion between the camplate and the support drives the rollers to the narrow end of the pockets and the clutch engages. If the turbo has enough exhaust energy to go faster than the engine gear train is turning, the motion between the camplate and support drives the rollers to the wider end of the pockets and the turbocharger is free to seek whatever speed the available exhaust flow allows it to achieve.