LEC Fuel Systems & Injection 3 — Questions and Answers
Question 1: Which type of fuel injector delivers fuel directly into the combustion chamber at very high pressure?
- Port injector
- Carburetor nozzle
- Common-rail direct injector (Correct answer)
- Wick-type vaporizer
Correct answer: Common-rail direct injector
Common-rail direct injectors spray atomized fuel directly into the cylinder at pressures exceeding 20,000 psi for efficient combustion.
Question 2: What does a high fuel temperature alarm on a locomotive indicate?
- The fuel tank is below minimum level
- The fuel cooling system may be malfunctioning (Correct answer)
- Fuel injection timing is advanced too far
- Water has entered the fuel system
Correct answer: The fuel cooling system may be malfunctioning
A high fuel temperature alarm signals that the fuel cooler or heat exchanger may not be removing enough heat, risking vapor lock and injector damage.
Question 3: What effect does a worn injector nozzle tip have on combustion?
- It improves atomization by increasing orifice size
- It causes poor atomization, leading to incomplete combustion and power loss (Correct answer)
- It has no effect unless the needle is also worn
- It increases injection pressure automatically
Correct answer: It causes poor atomization, leading to incomplete combustion and power loss
A worn nozzle tip enlarges or distorts spray holes, producing large fuel droplets that do not burn completely, reducing efficiency and increasing emissions.
Question 4: When bleeding air from a diesel fuel system after filter replacement, where should the engineer begin?
- At the injectors, working backward to the tank
- At the fuel tank vent
- At the primary filter, then the secondary filter, then the injection pump (Correct answer)
- At the injection pump only
Correct answer: At the primary filter, then the secondary filter, then the injection pump
Air bleeding proceeds from the low-pressure side (primary filter) toward the high-pressure side (injection pump) to systematically purge all trapped air.
Question 5: Which HAZMAT regulation primarily governs the transport of bulk diesel fuel on railroad property?
- 49 CFR Part 172
- 49 CFR Part 174 (Correct answer)
- 49 CFR Part 179
- 49 CFR Part 195
Correct answer: 49 CFR Part 174
49 CFR Part 174 covers the carriage of hazardous materials by rail, including requirements for handling flammable liquids like diesel fuel.
Question 6: A locomotive engineer notices the fuel pressure gauge reading is lower than normal at idle. What is a probable cause?
- The fuel tank is overfilled
- A clogged fuel filter restricting flow (Correct answer)
- Injection timing set too late
- Excessive cooling water temperature
Correct answer: A clogged fuel filter restricting flow
A clogged filter creates a restriction that reduces fuel supply pressure, which can cause rough running, misfires, and eventual shutdown.
Question 7: What is the purpose of the governor's fuel rack linkage in a diesel locomotive engine?
- To control the speed of the fuel transfer pump
- To vary the amount of fuel delivered per injection stroke based on load and speed demand (Correct answer)
- To regulate the temperature of return fuel
- To switch between primary and secondary fuel filters
Correct answer: To vary the amount of fuel delivered per injection stroke based on load and speed demand
The fuel rack linkage connects the governor to the injection pump, physically moving the rack to increase or decrease fuel delivery as the governor responds to load changes.
LEC Fuel Systems & Injection 3
Which type of fuel injector delivers fuel directly into the combustion chamber at very high pressure?