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Compression Ratio Formula:
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The compression ratio (CR) of an engine is the ratio of the volume of the cylinder and combustion chamber when the piston is at the bottom of its stroke to the volume when the piston is at the top of its stroke. It's a fundamental specification in internal combustion engines.
The calculator uses the compression ratio formula:
Where:
Explanation: The formula compares the maximum and minimum volumes in the cylinder to determine how much the air-fuel mixture is compressed.
Details: Compression ratio affects engine efficiency, power output, fuel requirements, and thermal efficiency. Higher ratios generally mean more power but may require higher octane fuel.
Tips: Enter swept volume and clearance volume in cubic centimeters. Both values must be positive numbers. The result is expressed as a ratio (e.g., 10.5:1).
Q1: What's a typical compression ratio for gasoline engines?
A: Modern gasoline engines typically have compression ratios between 8:1 and 12:1. High-performance engines may go higher.
Q2: Why do diesel engines have higher compression ratios?
A: Diesel engines use compression ignition and typically have ratios between 14:1 and 25:1 to achieve the high temperatures needed for ignition.
Q3: How does compression ratio affect fuel efficiency?
A: Higher compression ratios generally improve thermal efficiency, but there are practical limits due to fuel octane ratings and engine knocking.
Q4: Can I increase my engine's compression ratio?
A: Yes, through methods like milling the cylinder head or using higher-dome pistons, but this requires careful consideration of fuel requirements and engine management.
Q5: What's the relationship between compression ratio and octane rating?
A: Higher compression ratios require higher octane fuels to prevent premature combustion (knocking or pinging).