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What Is the Anatomy of a Diesel Locomotive? By Danielle Abram Print

What Is the Anatomy of a Diesel Locomotive?

Locomotives have developed a great amount over the years. One great revolution in the train world is the diesel locomotive. The diesel locomotive consists of a prime mover and a method of transmitting that power to the tracks, and there are many different versions of this engine with different mechanical powers and transmission types that are used for different purposes. Let’s get into it, shall we?

What are the different parts of a Diesel locomotive?

  • Headlight - Projects the light at the front of the locomotive.

  • Number Board - Displays the train or locomotive number, depending on the railroad.

  • Horns - Clear the way! The horns act as a warning for animals and people to stand clear of the tracks. 

  • Porthole Window - Windows on the train. 

  • Ventilators - Also known as exhaust fans, these cool the locomotive's engine and dynamic braking grids.

  • Coupler - Device at the front and rear of the locomotive for connecting locomotives and rail cars together.

  • Pilot - Also called the cowcatcher, the pilot is installed on the front of the locomotive to clear debris or obstacles from the track. 

  • Cab - This is where the operators stay put, including the drivers, engineers, and the fireman. This crew department is also where the controls are located. 

  • Fuel Tank - Surprise surprise… The fuel is kept in this tank which is located under the frame. Typically the tank holds 1,000-5,000 gallons of fuel. 

  • Stirrup - The stirrup (shown just behind the truck's swing hanger) acts as a step to get into the locomotive

  • Truck - The trucks are a cast or welded framework holding the wheels, axles, gears, motors, and brake cylinders and support the locomotive. 

What Are the Different Transmission Types?

  • Diesel-mechanical - Uses a mechanical transmission like a car’s gearbox, most common in low-powered and low-speed locomotives. 

  • Diesel-electric - Drives either an electrical DC generator or an electrical AC alternator-rectifier. There is not a mechanical connection between the wheels and the diesel engine. 

    • Diesel-electric Control - The locomotive’s power output depends on the road speed. Also, it is important that the unit generator current and the voltage limits are not surpassed.

    • Transmission Methods:

      • “Field shunting”/”diverging” or “weak fielding”

      • Generator/rectifier transition

      • Series/parallel or “motor transition”

    • Electro-diesel - This engine is a dual-mode locomotive where it can be powered from an electric supply line or using its onboard diesel engine. New Haven, and later Amtrak, use electro-diesels in the emission-restricted approach to New York City.

  • Diesel-hydraulic - This engine is less efficient than diesel-electric locomotives. To help convey the power to the wheels, this engine uses torque converters with a mechanical final drive. 

    • Hydrostatic transmission - The engine turns a pump that pressurizes hydraulic fluid which then powers a motor on the drive side.

    • Hydrokinetic transmission - also called hydrodynamic, uses a torque converter 

  • Diesel-steam - Here you can use the steam that has been generated using a boiler or a diesel to power a piston engine.

  • Diesel pneumatic - This locomotive can be converted using an existing steam engine and transitioning to diesel operation.

What are the Advantages of Diesel Locomotives over Steam Locomotives?

Diesel locomotives are simply more advanced than steam engines. In the 1930s, diesel started to replace steam power and in the 1950s, diesel took over almost entirely because they are easier to maintain. 

Not only do diesel engines require less maintenance, but they have a longer run time between services. Granted, diesel engines are more expensive upfront, but factoring in the cost savings of abandoning turntables, water towers, ash pits and requiring fewer men made the diesel inevitable.

Another positive of using a diesel loco is that they cost less to run. They have a higher thermal efficiency and require fewer crew members to run the locomotive. Once motive power planners stepped away from the steam engine mentality of powerful single-unit locomotives and adapted to the building block nature of diesel, motive power rationalization swept through the industry. No longer were there big-drivered Pacifics to haul passenger trains, slow speed switching engines for working yards, or dual-purpose 4-8-4s for hauling long distance. A single GP7 could switch a yard, and two or more operating in multiple (many engines controlled by a single engineer) could handle any length of rolling stock coupled up. 

What were the 1946 Steam Versus Diesel Road Trials?

During these trials, six locomotives were chosen by Paul W. Kiefer, their designer, in 1946 to see which engine came out on top. The 6,000 hp Niagaras were compared to 4,000 hp diesels and were run from New York to Chicago, via Albany, Syracuse, Rochester, Buffalo, Cleveland, Toledo, and Elkhart before they returned. The locomotives traveled 9281 miles total and the results were close! 

What do you think?

Do you think diesel locomotives are better than steam engines? Did you know there were that many transmission types?

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