Engine displacement is measured by calculating the total volume swept by all the pistons inside the cylinders of an engine.
Understanding Engine Displacement Measurement
Engine displacement refers to the combined volume of air that all the pistons displace as they move from the bottom of the stroke to the top within the cylinders. It is a key specification that indicates the engine's size and potential power output.
The measurement of engine displacement is a straightforward calculation based on the physical dimensions of the engine's cylinders and the movement of the pistons.
The Calculation Method
Based on the provided reference, engine displacement is precisely determined by:
calculating the engine cylinder bore area multiplied by the stroke of the crankshaft, and then multiplied by the number of cylinders.
This calculation directly results in the overall volume of air displaced by the engine during its operation.
Let's break down the components of this calculation:
- Cylinder Bore Area: The bore is the diameter of the cylinder. The area of the circle formed by the bore is calculated using the formula for the area of a circle: π (bore/2)² or π radius².
- Stroke: The stroke is the distance the piston travels up or down within the cylinder, from the bottom dead center (BDC) to the top dead center (TDC). This distance is determined by the crankshaft.
- Number of Cylinders: The total engine displacement is the sum of the displacement of each individual cylinder. Therefore, the volume displaced by one cylinder (bore area * stroke) is multiplied by the total number of cylinders in the engine.
The Formula
The formula for calculating engine displacement can be represented as:
Displacement = (π × (Bore/2)² × Stroke) × Number of Cylinders
This volume is typically measured in cubic centimeters (cc), cubic inches (ci or cid), or liters (L). 1 liter is equal to 1000 cubic centimeters.
Example Calculation (Simplified)
Imagine a simple engine with the following specifications:
- Bore: 8 cm
- Stroke: 9 cm
- Number of Cylinders: 4
- Calculate Cylinder Bore Area: π × (8 cm / 2)² = π × 4² cm² = π × 16 cm² ≈ 50.27 cm²
- Calculate Volume per Cylinder: ≈ 50.27 cm² × 9 cm ≈ 452.43 cm³
- Calculate Total Displacement: ≈ 452.43 cm³ × 4 ≈ 1809.72 cm³
This engine would have a displacement of approximately 1810 cc, or roughly 1.8 liters.
Units of Measurement
Engine displacement is commonly expressed in different units depending on the region or historical context:
| Unit | Abbreviation | Equivalent | Notes |
|---|---|---|---|
| Cubic Centimeters | cc or cm³ | Common for smaller engines (motorcycles) | |
| Cubic Inches | ci or cid | 1 in³ ≈ 16.39 cm³ | Historically common in the US |
| Liters | L | 1 L = 1000 cm³ | Common for automotive engines |
Understanding how engine displacement is measured provides insight into one of the fundamental specifications used to describe and compare engines.
