Question

Compression ratio in an internal combustion engine denotes

• A. (Total cylinder volume + Clearance volume) (Clearance volume)
• B. (Swept volume + Clearance volume) (Clearance volume)
• C. (Swept volume - Clearance volume) (Total cylinder volume)
• D. (Swept volume + Clearance volume) (Swept volume)

Hint:

Typical compression ratios:
Petrol engines (SI): 6:1 to 10:1
Diesel engines (CI): 14:1 to 22:1.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
The compression ratio (\(r\)) of an internal combustion engine is a geometric parameter defined as the ratio of maximum cylinder volume (when the piston is at Bottom Dead Center, BDC) to the minimum cylinder volume (when the piston is at Top Dead Center, TDC).
Key Formula or Approach:
\[ r = \frac{V_{\text{max}}}{V_{\text{min}}} = \frac{V_{\text{total}}}{V_c} = \frac{V_s + V_c}{V_c} \]
where \(V_s\) is swept (displacement) volume and \(V_c\) is clearance volume.

Step 2: Detailed Explanation:
When the piston reaches Bottom Dead Center (BDC), the total volume occupied by air/fuel mixture inside the cylinder is the sum of swept volume and clearance volume:
\[ V_{\text{total}} = V_s + V_c \]
When the piston reaches Top Dead Center (TDC), the enclosed volume is reduced to the clearance volume \(V_c\).
The compression ratio is the ratio of these two volumes:
\[ r = \frac{V_s + V_c}{V_c} \]

Step 3: Final Answer:
Thus, compression ratio is (Swept volume + Clearance volume) (Clearance volume), corresponding to option (B).