Problem Set #6

ME354 Thermodynamics 2

Problem Set #6: IC Engines


Problem 6: 1
Calculate the ideal air standard cycle efficiency based on the Otto cycle for a gas engine with a cylinder bore of 50 mm, a stroke of 75 mm and a clearance volume of 21.3 cm3.

Answer: n = 56.3%

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Problem 6: 9-79
An idealized air-standard diesel cycle has a compression ratio of 15. The energy input is idealized as a heat transfer of 700 Btu/lbm. The inlet conditions are 70 oF at 1 atm. Find the pressure and temperature at the end of each process in the cycle and determine the cycle efficiency.

Answer: n = 56.3%

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Problem 6: 3
An oil engine takes in air at 1.01 bar, 20 oC and the maximum cycle pressure is 69 bar. The compressor ratio is 18:1. Calculate the air standard thermal efficiency based on the dual-combustion cycle. Assume that the heat added at constant volume is equal to the heat added at constant pressure.

Answer: n = 68.2%

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Problem 6: 4
A four-stroke Otto-cycle has a crankshaft speed of 2000 rpm, a compression ratio of 8, and a displacement volume of 1.5 liters. At the start of compression the air is at 293 K, 0.1013 MPa. The peak cycle temperature is equal to the 2000 K source temperature. The compression and expansion processes are each reversible and adiabatic. Assuming constant specific heats, make a complete thermal analysis of the engine. Find the energy transfer per unit mass for each process in the cycle.

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Problem 6: 5
At the start of the compression process in a Diesel-cycle engine the air is at 530 R, 14.7 psia. The compression ratio is 16. The peak cycle temperature is equal to the 4000 R source temperature. The adiabatic compression and expansion processes are reversible. Even though high temperatures are involved, assume that specific heats are constants at their low-temperture values. Find the energy transfer per unit mass for each process in the cycle

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