An EMD GP20 is a 4-axle 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 A cylinder (from ) has traditionally been a three-dimensional solid, one of the most basic of curvilinear geometric shapes. In elementary geometry, it is considered a prism with a circle as its base. A cylinder may also be defined as an infi ...

turbocharged engine which generated . 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 The Union Pacific Railroad , legally Union Pacific Railroad Company and often called simply Union Pacific, is a freight-hauling railroad that operates 8,300 locomotives over routes in 23 U.S. states west of Chicago and New Orleans. Union Pac ...

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 In an internal combustion engine, a turbocharger (often called a turbo) is a forced induction device that is powered by the flow of exhaust gases. It uses this energy to compress the intake gas, forcing more air into the engine in order to pro ...

diesel engine, sixteen months after the six-axle ( C-C) model SD24. Power output of the turbocharged SD24 was 33 percent higher than the of the concurrent Roots blower-equipped SD18s with the same

engine displacement Engine displacement is the measure of the cylinder volume swept by all of the pistons of a piston engine, excluding the combustion chambers. It is commonly used as an expression of an engine's size, and by extension as a loose indicator of t ...

, per axle, but the power output of the turbocharged GP20 was only 11 percent higher than the of the concurrent Roots blower-equipped GP18s with the same engine displacement per axle, due to the limitations of the traction motors then available. Nevertheless, the turbocharged GP20 provided full rated power at all altitudes, which the Roots-blown GP18 could not provide.

EMD-type Turbo-Compressor (Turbocharger)

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 a

freewheel Freewheel mechanism In mechanical or automotive engineering, a freewheel or overrunning clutch is a device in a transmission that disengages the driveshaft from the driven shaft when the driven shaft rotates faster than the driveshaft. An ov ...

. At higher power levels, the freewheel 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. Previous Union Pacific experiments with turbocharging had utilized multiple Elliot or

Garrett AiResearch Garrett AiResearch was a manufacturer of turboprop engines and turbochargers, and a pioneer in numerous aerospace technologies. It was previously known as Aircraft Tool and Supply Company, Garrett Supply Company, AiResearch Manufacturing Compa ...

turbochargers feeding the usual pair of Roots blowers. EMD's mechanically assisted turbocharger eliminated the need for the pair of Roots blowers and also integrated the turbocharging function from two (Elliot) or four (AiResearch) smaller add-on turbochargers into one much larger, turbo-compressor (turbocharger) with intercooling. The introduction of the EMD-type turbocharger was successful and all subsequent GP series were offered with this turbocharger, although not all models within a series were offered with turbocharging (e.g., the ''38'' models were Roots-blown).

Original buyers

Preservation

*Western Pacific 2001, the very first GP20 built, is preserved at

Western Pacific Railroad Museum The Western Pacific Railroad Museum (WPRM) in Portola, California, known as the Portola Railroad Museum until January 1, 2006, is a heritage railroad and archives that preserves and operates historic American railroad equipment and preserves d ...

at Portola, CA. *KLIX 2003, originally Cotton Belt 815, is being stored at the Arkansas Railroad Museum in Pine Bluff, AR. *Midland Railway 4079, originally Southern Pacific 7229, is on The Midland Railway in Baldwin City, Kansas.

References

* * * * http://www.trainweb.org/jaydeet/gp20.htm Robert Sarberenyi roster with phase information and fuel tank size

External links

photos of EMD GP20s
''rrpicturearchives.net'' {{Authority control GP20 B-B locomotives Diesel-electric locomotives of the United States Railway locomotives introduced in 1959 Freight locomotives Standard gauge locomotives of the United States