Reference no: EM133064667

5MA034 Engine Design and Thermodynamics - University of Wolverhampton

Question 1: (a) With respect to the thermodynamic analysis, explain the following terms:
(i) Polytropic process.
(ii) Adiabatic process.
(iii) Isothermal process.
(iv) Isochoric process.
Q1(b) A gas is compressed from the initial pressure and volume of 200 kPa and 120 cm³ respectively to 30 cm³ and the resulting pressure is 1 MPa. If the process obeys the general equation, PVn = C, calculate the index of compression n.
1(c) A gas is expanded from the initial pressure and temperature of 1MPa and 1000 °C respectively to 200 kPa by the law PV1.3 = C. Calculate the final temperature in Kelvin.

Question 2: An engine, operating on an Otto cycle, has a compression ratio of 10/1. The pressure and temperature of the air at the start of the compression process are 140 kPa and 45 °C respectively. The heat input on to the cycle is 710 kJ/kg. Given that Cv = 0.718 kJ/kgK and γ = 1.4, determine:
(i) The thermal efficiency.
(ii) The maximum temperature in the cycle.
(iii) The maximum pressure.
(iv) The network output per kg of air.

Question 3:
With the aid of suitable P-V and T-S diagrams, discuss the main characteristics of the Diesel cycle, including all the processes involved.

(b) An engine using the diesel cycle has a compression ratio of 25 and a cut off ratio of 2. At the start of the compression process, the air is at 1.01325 kPa and 20°C. Given that Cp = 1.005 kJ/kg K and γ = 1.4, calculate:
(i) The temperature at points 2 and 3 in the cycle.
(ii) The maximum pressure in the cycle.
(iii) The heat input, q_in.

Question 4: (a) With the aid of suitable sketches, differentiate between a nozzle and a diffuser.

(b) A steady flow air compressor draws in air at 30° C and compresses it to 140°C at the outlet. The mass flow rate is 0.85 kg/s and 8.5 kW of heat is transferred into the system. Given that Cp = 1.005 kJ/kg K, using your knowledge from the application of the first law of thermodynamic, calculate:
(i) The change in enthalpy per second.
(ii) The work transfer rate.

Question 5: (a)
Discuss four problems with the Carnot steam cycle and suggest at least a solution that can be used to mitigate these problems.

(b) A gas turbine uses the joule cycle. The inlet pressure and temperature to the compressor are respectively 1 bar and -20°C. After constant pressure heating, the pressure and temperature are 8.5 bar and 750°C respectively. The flow rate of air is 0.5 kg/s. Given that γ = 1.4 and C_p = 1.005 kJ/kgK , calculate:
(i) The cycle efficiency.
(ii) The heat transfer into the heater.
(iii) The net power output.