GP20
EMD GP20
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| Performance figures |
| Power output |
2,000 hp (1.5 MW) |
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| Performance figures |
| Power output |
2,000 hp (1.5 MW) |
An EMD GP20 is a 4-axle (B-B) diesel-electric locomotive built by General Motors' Electro-Motive Division between November 1959 and April 1962. Power was provided by an EMD 567D2 16-cylinder turbocharged engine which generated 2,000 horsepower (1,500 kW). EMD was initially hesitant to turbocharge their 567-series diesel engine, but was spurred on to do so following successful tests made by Union Pacific in the form of UP's experimental Omaha GP20 units. 260 examples of EMD's production locomotive model (with the EMD turbocharger) were built for American railroads.
The GP20 was the second EMD production locomotive to be built with an EMD turbocharged diesel engine, sixteen months after the six-axle (C-C) model SD24. Power output of the turbocharged SD24 was 33 percent higher than the 1,800 hp (1,340 kW) of the concurrent Roots blower-equipped SD18s with the same engine displacement, 400 hp (298 kW) per axle, but the power output of the turbocharged GP20 was only 11 percent higher than the 1,800 hp (1,340 kW) of the concurrent Roots blower-equipped GP18s with the same engine displacement 500 hp (373 kW) per axle, due to the limitations of the traction motors then available (this limitation was eliminated in the 40-Series). Nevertheless, the turbocharged GP20 provided full rated power at all altitudes, which the Roots-blown GP18 could not provide.
The turbocharger was the then-new EMD mechanically assisted turbo-compressor. During engine startup, and at lower power levels, during which there is not sufficient exhaust heat energy to drive the turbine fast enough for the compressor to supply the air necessary for combustion, the engine drives the compressor through a gear train and an overrunning clutch. At higher power levels, the overrunning clutch is disengaged, and the turbo-compressor operates as a true turbocharger. It is possible for the turbo-compressor to revert to compressor mode momentarily during commands for large increases in engine power. Turbocharging provides higher horsepower and good running characteristics at all altitudes. Turbocharging also improves fuel consumption and reduces emissions.
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