Subtopic: Calculation of power, torque, fuel consumption, heat load and power losses
Question Statement:
Which of the following statements regarding the performance parameters and energy balance of a compression ignition (CI) diesel engine is/are CORRECT?
Options:
(A) Brake specific fuel consumption (BSFC) decreases with increasing engine load up to rated capacity due to improved mechanical efficiency
(B) Indicated thermal efficiency is strictly higher than brake thermal efficiency for any operating internal combustion engine
(C) Morse test can be directly used on a single-cylinder engine to determine indicated power
(D) In an engine heat balance sheet, cooling water and exhaust gases typically account for approximately $55\text{--}70\%$ of the total fuel energy
Answer Key:
A, B, D
Step-by-Step Solution & Explanation
- Statement A is correct: BSFC reaches a minimum near rated load because fixed mechanical friction losses represent a smaller fraction of total work (mechanical efficiency increases).
- Statement B is correct: Since Brake Power $BP = IP - FP$ and $FP > 0$, $\eta_{bth} = \eta_{ith} \times \eta_m < \eta_{ith}$.
- Statement C is incorrect: The Morse test requires cutting off ignition/injection in individual cylinders while remaining cylinders maintain engine speed, so it is strictly applicable only to multi-cylinder engines.
- Statement D is correct: Standard IC engine energy balances show ~30-35% converted to useful brake work, ~30% carried by exhaust, ~25-30% by cooling water, and ~5-10% by radiation and unaccounted losses.