Diesel engine intake process During the suction (intake) stroke of a compression-ignition (Diesel) engine, what is drawn into the cylinder?
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AAir and fuel (premixed)
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BOnly fuel
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COnly air
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DExhaust–air mixture
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EAir with atomized fuel from a carburettor
Answer
Correct Answer: Only air
Explanation
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:
Intake stroke: intake valve opens; piston moves down; only air is inducted.Compression stroke: both valves close; air is compressed, raising temperature sharply.Injection: fuel is sprayed near top dead center into the hot air.Combustion: auto-ignition occurs without a spark plug.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:
Only air