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In a SI engine very high compression ratio cannot be used because
- a)the engine efficiency would be unmanageable high
- b)the power required for compression would be high
- c)cylinders will required very thick walls
- d)self-ignition may takes place before the spark occurs
Correct answer is option 'D'. Can you explain this answer?
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In a SI engine very high compression ratio cannot be used becausea)the...
Explanation:
Compression ratio is defined as the ratio of the volume of the cylinder when the piston is at the bottom dead center to the volume of the cylinder when the piston is at the top dead center. In a spark ignition engine, the compression ratio is limited due to the following reasons:
1. Auto-ignition:
If the compression ratio is too high, the temperature and pressure inside the cylinder will increase, causing the air-fuel mixture to ignite before the spark plug fires. This is known as auto-ignition or knocking. Auto-ignition can cause engine damage and reduce efficiency.
2. Power required for compression:
The higher the compression ratio, the more power is required to compress the air-fuel mixture. This can reduce the engine's overall efficiency.
3. Thick walls:
If the compression ratio is too high, the pressure inside the cylinder can cause the cylinder walls to deform or crack. To prevent this, the cylinder walls would need to be made thicker, which would increase the weight of the engine.
4. Engine efficiency:
While higher compression ratios can increase engine efficiency, there is a limit to how high the compression ratio can be before the drawbacks outweigh the benefits.
Therefore, the correct option is D – self-ignition may take place before the spark occurs.
Compression ratio is defined as the ratio of the volume of the cylinder when the piston is at the bottom dead center to the volume of the cylinder when the piston is at the top dead center. In a spark ignition engine, the compression ratio is limited due to the following reasons:
1. Auto-ignition:
If the compression ratio is too high, the temperature and pressure inside the cylinder will increase, causing the air-fuel mixture to ignite before the spark plug fires. This is known as auto-ignition or knocking. Auto-ignition can cause engine damage and reduce efficiency.
2. Power required for compression:
The higher the compression ratio, the more power is required to compress the air-fuel mixture. This can reduce the engine's overall efficiency.
3. Thick walls:
If the compression ratio is too high, the pressure inside the cylinder can cause the cylinder walls to deform or crack. To prevent this, the cylinder walls would need to be made thicker, which would increase the weight of the engine.
4. Engine efficiency:
While higher compression ratios can increase engine efficiency, there is a limit to how high the compression ratio can be before the drawbacks outweigh the benefits.
Therefore, the correct option is D – self-ignition may take place before the spark occurs.
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In a SI engine very high compression ratio cannot be used becausea)the engine efficiency would be unmanageable highb)the power required for compression would be highc)cylinders will required very thick wallsd)self-ignition may takes place before the spark occursCorrect answer is option 'D'. Can you explain this answer?
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