Diesel engine intake process During the suction (intake) stroke of a compression-ignition (Diesel) engine, what is drawn into the cylinder?

Introduction / Context:
Diesel (compression-ignition) engines differ from spark-ignition engines in when and how fuel is introduced. Understanding the correct intake charge is fundamental to diagnosing smoke, misfire, and starting issues.

Given Data / Assumptions:

• No external mixture formation device (no carburettor).
• Fuel is injected directly (or into a pre-combustion chamber) near the end of the compression stroke.

Concept / Approach:
In a Diesel engine, the intake stroke draws in clean air only. This air is then compressed to a high pressure and temperature. Near the end of compression, fuel is injected and auto-ignites due to the hot air, starting combustion.

Step-by-Step Solution:

Verification / Alternative check:
Component layout confirms no carburettor in Diesels; fuel system comprises high-pressure pump, injectors, and lines.

Why Other Options Are Wrong:

• Air and fuel premixed or carburetted air–fuel (A/E): that is spark-ignition practice.
• Only fuel (B): intake cannot draw only fuel; airflow is required.
• Exhaust–air mixture (D): not normal; residuals may remain but intake is intended to be fresh air.

Common Pitfalls:
Assuming visible black smoke means fuel is drawn during intake; in reality, smoke is a combustion quality issue, not intake composition.

Final Answer: