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Compression Ratio Formula:
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The compression ratio (CR) in an Otto cycle engine is defined as the ratio of the maximum volume to the minimum volume in the cylinder. It's a critical parameter that affects engine efficiency, power output, and fuel economy.
The calculator uses the compression ratio formula:
Where:
Explanation: The formula calculates the ratio between the total cylinder volume when the piston is at bottom dead center (V1 + V2) and the volume when the piston is at top dead center (V2).
Details: Higher compression ratios generally lead to better thermal efficiency and power output, but are limited by fuel octane rating and engine knocking considerations. Modern engines typically have compression ratios between 8:1 and 12:1.
Tips: Enter swept volume and clearance volume in liters. Both values must be positive numbers greater than zero for accurate calculation.
Q1: What is the typical range for compression ratios?
A: Most gasoline engines have compression ratios between 8:1 and 12:1, while diesel engines typically range from 14:1 to 25:1.
Q2: Why can't we use extremely high compression ratios?
A: High compression ratios can cause engine knocking (pre-ignition) which can damage the engine, especially when using lower octane fuels.
Q3: How does compression ratio affect fuel efficiency?
A: Higher compression ratios generally improve thermal efficiency, leading to better fuel economy, but this must be balanced against knocking risks.
Q4: What's the difference between swept volume and clearance volume?
A: Swept volume is the volume displaced by the piston movement, while clearance volume is the remaining volume when the piston is at top dead center.
Q5: Can I calculate compression ratio if I know the cylinder dimensions?
A: Yes, swept volume can be calculated from cylinder bore and stroke measurements using the formula: V1 = π × (bore/2)² × stroke.