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Unformatted text preview: Homework Set 18 Problem 1 At the beginning of compression in a cold air standard diesel cycle T = 300 K, P = 200 kPa and after combustion (heat addition) is complete T = 1500 K and P = 7.0 MPa. Find: a.) the compression ratio, (r=12.67) b.) the thermal efficiency and (η=58.7%) c.) the mean effective pressure(kPa) (mep= 997 kPa) Problem 2 An air‐standard Diesel cycle has a compression ratio of 18. The cut‐off ratio varies from 2.0 to 5.0 in 0.5 increments.. The state at the beginning of compression is fixed by P= 90 kPa and T=300 K. Determine the net work per unit mass of air, the thermal efficiency, the maximum pressure in the cycle (kPa), the mean effective pressure (kPa). How does variation of cut‐off ratio ratio affect the thermal efficiency of the cycle? Solve and analyze using EES. Problem 3 The compression ratio of an air standard Diesel cycle is 17 and the condition at the beginning of compression are P1= 14 psi, V1= 2 ft3 and T1 = 520°R. The maximum temperature in the cycle is 4000°R. Calculate: a.) b.) c.) d.) net work for the cycle (Btu) (W=54.87 Btu) thermal efficiency (η=53.1 %) mean‐effective pressure (psi) (mep=157.5 psi) the cut‐off ratio (rc=2.61) Problem 4 The displacement volume (V1‐V2) of an internal combustion engine is 5.6 liters. The processes within each cylinder of the engine are modeled as an air standard Diesel cycle with a cut‐off ratio of 2.4. The state of the air at the beginning of compression is fixed by P1 = 95 kPa, T1= 27°C, and V1 = 6.0 liters. Determine the net work per cycle (kJ), the power developed by the engine (kW) and the thermal efficiency if the cycle is executed 1500 times per minute. Ans: Wcycle = 4.901 kJ, = 122.53 , η=52.5% ...
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This note was uploaded on 01/03/2011 for the course MEEN 315 taught by Professor Ramussen during the Fall '07 term at Texas A&M.
- Fall '07