Diesel fuel system — injector function In a compression-ignition (Diesel) engine, what is the principal function of the fuel injector?

Introduction / Context:
Diesel engines rely on compression-ignition. The injector's spray quality and timing dominate combustion efficiency, emissions, and noise.

Given Data / Assumptions:

• Air-only is compressed; fuel is injected near the end of compression.
• Injector may be mechanical or electronically controlled (common-rail).
• High-pressure atomization is required for rapid mixing with hot air.

Concept / Approach:
The injector meters, times, and atomizes fuel into fine droplets with an appropriate spray pattern and penetration so that self-ignition occurs due to the high temperature of compressed air. It does not intentionally pre-mix fuel with air before compression nor provide spark.

Step-by-Step Solution:
High-pressure pump/rail supplies injector.Injector opens per control signal/pressure → atomized spray enters cylinder.Spray interacts with hot, compressed air → auto-ignition and combustion.

Verification / Alternative check:
Engine starts and runs without spark system; combustion phasing tracks injection timing, confirming injector’s primary role.

Why Other Options Are Wrong:
Mixing before compression is a petrol engine carburation/port injection concept.

Diesels do not use a spark or separate flame front provider.

Fuel return lines exist but are not the injector’s principal function.

Common Pitfalls:
Poor atomization (worn nozzles) causes smoke and rough running; incorrect timing elevates noise and NOx.

Final Answer:
spray atomized fuel into the cylinder at the correct timing