Question

Consider the following statements regarding C.I. engine and S.I. engine

(A) C.I. engines are more bulky than S.I. engines

(B) C.I. engines are more efficient than S.I. engines

(C) Lighter flywheels are required in C.I. engines

Choose the correct answer from the options given below:

• A. (A) and (C) only
• B. (B) and (C) only
• C. (A) and (B) only
• D. (A), (B) and (C)

Hint:

Think about compression ratio, structural strength and turning moment variation for each engine type.

Answer 1

The Correct Option is C

Step 1: Statement (A) says CI engines are more bulky than SI engines. CI engines run at much higher compression ratios and combustion pressures than SI engines, so their cylinder blocks, pistons and other parts must be built stronger and heavier to withstand this stress. This makes CI engines more bulky, so (A) is true.

Step 2: Statement (B) says CI engines are more efficient than SI engines. Because CI engines run at higher compression ratios, they extract more work from the same amount of fuel, giving them higher thermal efficiency than typical SI engines. So (B) is true.

Step 3: Statement (C) says lighter flywheels are required in CI engines. In reality, CI engines have a more uneven turning moment through the cycle, so they actually need HEAVIER flywheels than SI engines to smooth out the speed fluctuations, not lighter ones. So (C) is false.

Since only (A) and (B) are correct, the answer is option 3, (A) and (B) only.