Subtopic: Thermodynamic principles of I.C. engines
Question Statement:
A 4-cylinder, 4-stroke compression ignition engine has piston stroke of 10.5 cm and cylinder bore of 11 cm. At a mean piston speed of 7 m s⁻¹, the developed brake mean effective pressure is 650 kPa. The brake power in kW developed by the engine is
Options:
(A) 39.40
(B) 43.24
(C) 86.48
(D) 172.96
Official Answer Key:
B
Step-by-Step Solution & Explanation
Mean piston speed = 2×L×N ⇒ N (rps) = 7/(2×0.105) = 33.33 rev/s.
Piston area, A = (π/4)(0.11)² = 0.009503 m².
For a 4-stroke engine, BP = (bmep × A × L × N × n_cyl)/2 [the /2 accounts for one power stroke every 2 revolutions]
= (650,000 × 0.009503 × 0.105 × 33.33 × 4)/2 = 86,480/2 = 43.24 kW. Answer: (B).
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