Thermodynamics and Ideal Air Standard Cycles
Explore the principles of Carnot for achieving high thermal efficiency, differences between ideal air-standard cycles and actual cycles, calculations for engine parameters, and more in the field of thermodynamics and ideal air standard cycles.
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Presentation Transcript
Sheet No. 2 Ideal Air Standard Closed Cycles
1- What are the Carnot`s principals to get the highest thermal efficiency. 2- What is the thermal efficiency of an engine develops 22.4 kW and consumes 10.25 litres of fuel per hour, the calorific value being 46000 kJ/kg and the specific gravity 0.72. 2- Solution: Potential heat supplied per hour = 10.25 0.72 46 000 = 339 300 kJ. Since 1 W = 1 J/s, work done per hour = 22.4 60 60 = 79 950 kJ. The thermal efficiency = 79 950/339300 =23.6%
3- How an ideal air-standard cycle differs from the actual cycle? 3- Solution: An ideal air-standard cycle differs from the actual by the following: i- The gas mixture in the cylinder is treated as air (an ideal gas with constant specific heats) for the entire cycle treated as. ii- The real open cycle is changed into a closed cycle. iii- The combustion process is replaced with a heat addition. iv- The open exhaust process, which carries a large amount of enthalpy out of the system, is rep. laced with a closed system heat rejection process
4- In a certain engine the cross-sectional area of the piston crown is 80 cm2and the stroke length is 120 mm. The swept volume is: (a)9600 cm3 (b) 120 cm3 (c) 960 cm3 5- A certain engine has a swept volume of 400 cm3and a clearance volume of 50 cm3. Calculate the compression ratio. 6- A petrol engine operating on the Otto cycle has a compression ratio of 8:1. Given the adiabatic index for air = 1.4, calculate the air standard thermal efficiency.
7- A certain diesel engine has a compression ratio of 14:1. The fueling factor (cut-off ratio or load ratio) = 1.78. Calculate the air standard efficiency; take = 1.4. 8- A compression ignition engine operating on the dual combustion cycle has a compression ratio of 16:1. The cut-off ratio for this engine is 1.6 and the pressure ratio rp=1.2 . Calculate the ideal thermal efficiency of this engine and take = 1.4.
9- The pressure and temperature of air standard dual combustion cycle are given below, i. T1 = 290 K ii. P1 = 1.01 bar iii. T2 = 871.1K iv. T3 = 1087.5 K v. T4 = 1236.3 K vi. T5 = 429.3 K and ratio of compression is 16:1. Calculate the thermal efficiency for this dual cycle engine.
