LEC Fuel Systems & Injection 2 — Questions and Answers
Question 1: What is the primary purpose of the fuel injection pump on a diesel locomotive?
- To cool the fuel before combustion
- To meter and pressurize fuel for delivery to injectors (Correct answer)
- To filter contaminants from the fuel supply
- To recirculate excess fuel back to the tank
Correct answer: To meter and pressurize fuel for delivery to injectors
The fuel injection pump meters precise amounts of fuel and raises it to the high pressure needed for atomization in the cylinders.
Question 2: What condition is indicated when a locomotive's exhaust appears black and sooty during operation?
- Lean fuel mixture with too little fuel
- Rich fuel mixture with incomplete combustion (Correct answer)
- Normal combustion at full throttle
- Water contamination in the fuel system
Correct answer: Rich fuel mixture with incomplete combustion
Black exhaust indicates a rich mixture where excess fuel is not fully burned, often caused by clogged injectors, restricted air intake, or over-fueling.
Question 3: Which component in the fuel system prevents air from entering the injection lines?
- The fuel strainer
- The priming pump
- The check valve (Correct answer)
- The fuel pressure regulator
Correct answer: The check valve
Check valves maintain line pressure and prevent air ingestion by allowing fuel flow in only one direction.
Question 4: When must a locomotive engineer report a fuel oil leak discovered during pre-trip inspection?
- Only if the leak is larger than a slow drip
- Only after completing the trip if minor
- Immediately before moving the locomotive (Correct answer)
- At the end of the work shift
Correct answer: Immediately before moving the locomotive
Any fuel oil leak must be reported immediately before the locomotive is moved, as fuel leaks create fire and environmental hazards.
Question 5: What happens to diesel fuel viscosity as fuel temperature increases?
- Viscosity increases, making atomization harder
- Viscosity decreases, improving atomization (Correct answer)
- Viscosity remains constant regardless of temperature
- Viscosity increases only above 150°F
Correct answer: Viscosity decreases, improving atomization
Higher fuel temperature lowers viscosity, which improves atomization through the injector nozzle but can reduce lubricity.
Question 6: A locomotive's fuel system develops a vapor lock. What is the most likely cause?
- Fuel temperature is too cold
- Fuel temperature is too high, causing fuel to vaporize in lines (Correct answer)
- The fuel tank is overfilled
- The injector return line is blocked
Correct answer: Fuel temperature is too high, causing fuel to vaporize in lines
Vapor lock occurs when fuel overheats and vaporizes in the supply lines, interrupting liquid fuel flow to the injection pump.
Question 7: What is the function of the injector return line (spill line) in a diesel fuel system?
- It supplies fuel to the turbocharger cooling circuit
- It returns excess pressurized fuel from injectors back to the tank or cooler (Correct answer)
- It bypasses the primary fuel filter during high demand
- It delivers fuel directly to the governor
Correct answer: It returns excess pressurized fuel from injectors back to the tank or cooler
Injector return lines carry unused high-pressure fuel back to the tank or a cooler, maintaining proper injector temperature and system pressure.
LEC Fuel Systems & Injection 2
What is the primary purpose of the fuel injection pump on a diesel locomotive?