RRB ALP Mechanic Diesel Trade — Solved Practice Question Bank

Q: What ignites the fuel in a diesel engine, since there is no spark plug? Sol: The heat generated by compressing air to a very high ratio (16:1 to 22:1) — this raises air temperature enough that injected fuel self-ignites on contact (compression ignition). Q: What is the main advantage of Common Rail Direct Injection (CRDI) over older mechanical injection pumps? Sol: Much more precise, electronically-controlled fuel timing and quantity for each injection event, improving efficiency and reducing emissions. Q: Why is diesel fuel contamination particularly damaging to the injection system? Sol: Injection pumps and injectors operate at very fine tolerances and extremely high pressure — even small contaminant particles can cause rapid wear or blockage of these precision components.

Q: What component in a liquid cooling system regulates when coolant flows to the radiator? Sol: The thermostat — it stays closed until the engine reaches operating temperature, then opens to allow coolant circulation through the radiator. Q: What does excessive black smoke from a diesel exhaust typically indicate? Sol: Incomplete combustion — often from an overly rich fuel mixture, a dirty/restricted air filter, or a worn/faulty fuel injector. Q: What should be checked FIRST when a low oil pressure warning appears? Sol: The engine oil level — it is the most common and simplest cause to check before investigating the oil pump or bearing wear.