Question

Which of the statements for engine are true?
• [A.] The C.I Engines have high thermal efficiency
• [B.] The compression ratio of SI engines is 5:1 to 8:1
• [C.] In 4 stroke engine the crank case is air tight
• [D.] Crankshaft converts reciprocating motion into rotary motion
• [E.] Camshaft has twice speed than crankshaft in four stroke engine Choose the correct answer from the options given below:

• A. A, B, D Only
• B. B, C, D Only
• C. A, C, D Only
• D. B, D, E Only

Hint:

Important engine facts: \[ \text{CI Engines} \rightarrow \text{Higher thermal efficiency} \] \[ \text{Crankshaft} \rightarrow \text{Reciprocating to rotary motion} \] In a four-stroke engine: \[ N_{\text{camshaft}} = \frac{1}{2}N_{\text{crankshaft}} \]

Answer 1

The Correct Option is C

Concept: Internal combustion engines are classified mainly into Spark Ignition (SI) engines and Compression Ignition (CI) engines. The working mechanism, compression ratio, thermal efficiency and component motion are very important concepts in engine theory. To solve this question correctly, each statement must be analyzed carefully using standard engine principles. Important concepts used are:
• CI engines generally possess higher thermal efficiency because of higher compression ratio.
• Four-stroke engines require proper sealing of crankcase.
• Crankshaft converts reciprocating motion into rotary motion.
• In four-stroke engines, camshaft rotates at half the speed of crankshaft.

Step 1: Checking Statement A. Statement A says: \[ \text{``The C.I Engines have high thermal efficiency''} \] Compression Ignition (CI) engines operate at much higher compression ratios than SI engines. Due to higher compression ratio:
• combustion is more efficient,
• fuel utilization improves,
• thermal efficiency becomes higher. Diesel engines are therefore more fuel efficient than petrol engines. Hence Statement A is: \[ \boxed{\text{True}} \]

Step 2: Checking Statement B. Statement B says: \[ \text{``The compression ratio of SI engines is 5:1 to 8:1''} \] Typical SI engine compression ratios generally range approximately from: \[ 6:1 \text{ to } 10:1 \] Modern SI engines may even exceed this range. Thus the range \(5:1\) to \(8:1\) is not considered the standard accepted range in this context. Hence Statement B is: \[ \boxed{\text{False}} \]

Step 3: Checking Statement C. Statement C says: \[ \text{``In 4 stroke engine the crank case is air tight''} \] In four-stroke engines:
• the crankcase stores lubricating oil,
• it must remain sealed properly,
• leakage of gases and oil should be prevented. Therefore the crankcase is designed to be air tight. Hence Statement C is: \[ \boxed{\text{True}} \]

Step 4: Checking Statement D. Statement D says: \[ \text{``Crankshaft converts reciprocating motion into rotary motion''} \] Inside the engine cylinder:
• piston moves in reciprocating motion,
• connecting rod transfers motion,
• crankshaft converts this reciprocating motion into rotary motion. This is the fundamental working principle of IC engines. Hence Statement D is: \[ \boxed{\text{True}} \]

Step 5: Checking Statement E. Statement E says: \[ \text{``Camshaft has twice speed than crankshaft in four stroke engine''} \] In a four-stroke engine:
• one working cycle requires two revolutions of crankshaft,
• camshaft operates valves once per cycle,
• therefore camshaft rotates at half the speed of crankshaft. Hence statement E is incorrect because it says camshaft rotates at twice the speed. Actually: \[ N_{\text{camshaft}} = \frac{1}{2} N_{\text{crankshaft}} \] Therefore Statement E is: \[ \boxed{\text{False}} \]

Step 6: Selecting the correct combination. The true statements are: \[ A,\; C,\; D \] Thus the correct option is: \[ \boxed{\text{Option (C)}} \] Verification Summary: \[ \begin{array}{|c|c|} \hline \text{Statement} & \text{Result} \hline A & \text{True} \hline B & \text{False} \hline C & \text{True} \hline D & \text{True} \hline E & \text{False} \hline \end{array} \] Therefore: \[ \boxed{A,\; C,\; D \text{ Only}} \]