Question:
The compression ratios of petrol engines lie in the range of
The compression ratios of petrol engines lie in the range of
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To remember the compression ratios:
- Petrol (Spark Ignition) engines: Low ratio (5 to 10) to prevent knocking.
- Diesel (Compression Ignition) engines: High ratio (15 to 22) to enable self-ignition.
- Petrol (Spark Ignition) engines: Low ratio (5 to 10) to prevent knocking.
- Diesel (Compression Ignition) engines: High ratio (15 to 22) to enable self-ignition.
Updated On: Jul 23, 2026
- 3 to 6
- 5 to 8
- 15 to 20
- 30 to 40
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Verified By Collegedunia
The Correct Option is B
Solution and Explanation
Step 1: Understanding the Concept:
The compression ratio (\(r\)) is a key design parameter of internal combustion engines.
It represents the ratio of the volume of the cylinder when the piston is at Bottom Dead Center (BDC) to the volume when it is at Top Dead Center (TDC).
Step 2: Detailed Explanation:
Let us analyze the compression ratios for different engine types:
- Petrol (Gasoline) engines: These engines operate on the Otto cycle, where a mixture of air and fuel is compressed and then ignited by a spark plug.
- If the compression ratio is too high, the temperature of the air-fuel mixture will rise above its auto-ignition point during the compression stroke.
- This causes premature detonation (knocking), which can damage the engine.
- To prevent knocking, the compression ratio of petrol engines is restricted to lower values, historically ranging between 5 to 8 (and up to 10 to 12 in modern engines with high-octane fuels).
- Diesel engines: These engines operate on the Diesel cycle, where air alone is compressed to high pressures and temperatures, and fuel is injected to auto-ignite.
- They require high compression ratios, typically in the range of 15 to 20, to ensure the air reaches a high enough temperature to ignite the fuel.
Evaluating the options, the standard textbook range for petrol engines is 5 to 8.
Step 3: Final Answer:
The compression ratio of petrol engines lies in the range of 5 to 8. Hence, the correct option is (B).
The compression ratio (\(r\)) is a key design parameter of internal combustion engines.
It represents the ratio of the volume of the cylinder when the piston is at Bottom Dead Center (BDC) to the volume when it is at Top Dead Center (TDC).
Step 2: Detailed Explanation:
Let us analyze the compression ratios for different engine types:
- Petrol (Gasoline) engines: These engines operate on the Otto cycle, where a mixture of air and fuel is compressed and then ignited by a spark plug.
- If the compression ratio is too high, the temperature of the air-fuel mixture will rise above its auto-ignition point during the compression stroke.
- This causes premature detonation (knocking), which can damage the engine.
- To prevent knocking, the compression ratio of petrol engines is restricted to lower values, historically ranging between 5 to 8 (and up to 10 to 12 in modern engines with high-octane fuels).
- Diesel engines: These engines operate on the Diesel cycle, where air alone is compressed to high pressures and temperatures, and fuel is injected to auto-ignite.
- They require high compression ratios, typically in the range of 15 to 20, to ensure the air reaches a high enough temperature to ignite the fuel.
Evaluating the options, the standard textbook range for petrol engines is 5 to 8.
Step 3: Final Answer:
The compression ratio of petrol engines lies in the range of 5 to 8. Hence, the correct option is (B).
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