Project ForgeThermodynamics
First Law of Thermodynamics
GATE 2020
Hard
The indicated power developed by an engine with compression ratio of 8, is calculated using an air-standard Otto cycle (constant properties). The rate of heat addition is 10 kW. The ratio of specific heats at constant pressure and constant volume is 1.4. The mechanical efficiency of the engine is 80 percent. The brake power output of the engine is __________ kW (round off to one decimal place).
4.5 kW(± 0.15 accepted)
Explanation
η = 1−r^(1−γ) = 1−8^(−0.4) ≈ 1−0.4353 ≈ 0.5647. Indicated power = η×Qin = 0.5647×10 ≈ 5.647 kW. Brake power = IP×ηmech = 5.647×0.8 ≈ 4.52 kW.
Source: GATE ME 2020 Session 1 (ME-1) (2020)
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