Project ForgeThermodynamics
First Law of Thermodynamics
GATE 2015
Hard
Air enters a diesel engine with a density of 1.0 kg/m³. The compression ratio is 21. At steady state, the air intake is 30×10⁻³ kg/s and the net work output is 15 kW. The mean effective pressure (in kPa) is __________.
525 kPa(± 3 accepted)
Explanation
Total intake volume flow rate = ṁ/ρ = 0.03/1.0 = 0.03 m³/s (this fills the cylinder volume V1 at BDC). Swept-volume flow rate = V1_rate×(1−1/r) = 0.03×(1−1/21) = 0.03×(20/21) ≈ 0.02857 m³/s. mep = power/(swept-volume flow rate) = 15000/0.02857 ≈ 525,000 Pa = 525 kPa.
Source: GATE ME 2015 (Session 1) (2015)
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