1
Given below are two statements
Statement (I) : Premixed combustion is smoother and quieter than diffusion combustion
Statement (II) : The longer the ignition delay, the higher percentage of the fuel that burns in premixed combustion and lower
the percentage that burns in diffusion combustion
In light of the above statements, choose the most appropriate answer from the options given below.
EXPLANATION
Engine Fuel & Air Induction Systems
- Combustion Phases in Compression Ignition (CI) Engines:
- Statement (I): Premixed combustion is smoother and quieter than diffusion combustion. $\implies$ Incorrect.
- Premixed (uncontrolled) combustion is rapid and explosive, producing an extremely steep rate of pressure rise ($dp/d\theta$), which causes diesel knock and combustion roughness. Diffusion (controlled) combustion is smooth and quiet.
- Statement (II): The longer the ignition delay, the higher percentage of the fuel that burns in premixed combustion and lower the percentage that burns in diffusion combustion. $\implies$ Correct.
- prolonged ignition delay allows more injected fuel to vaporize and mix with air before autoignition; when ignition occurs, this large accumulated charge burns simultaneously in rapid premixed combustion.
- Conclusion: Statement (I) is incorrect but Statement (II) is correct (Option 4).
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