HEAT ENGINE CYCLES

Use the following values for air:  γ = 1.4; c_p = 1.005 kJ kg^-1 K^-1; c_v = 0.718 kJ kg^-1 K^-1

Question 1. Is an internal combustion engine a heat engine? Explain your answer.

Question 2. What is the fundamental equation, in terms of heat supplied and rejected, for calculating the thermal efficiency of a heat engine?

Question 3. A gas turbine uses the Joule cycle to deliver an output power of 1 MW. The inlet and exit temperatures to the turbine are 1017°C and 500°C respectively. The temperature at inlet to the compressor is 50°C .
(a) Sketch a p-V and T-S diagram for the cycle

(b) Calculate:

(i) the pressure ratio

(ii) the thermal efficiency of the cycle

(iii) the mass flow rate of gas in the cycle.

Question 4. A diesel cycle is to be designed to create a pressure ratio of 15:1 during the compression stroke. If the total volume at the start of compression is to be 2 m³, the mass of air contained in the cylinder during compression is 3 kg and the temperature at the start of compression is to be 50°C,

(a) Draw a p-V diagram for the cycle.

(b) Calculate:

(i) the volume after compression

(ii) the maximum temperature in the cycle if 1 MJ of heat is transferred to the air in the cylinder per cycle during the constant pressure heating process.

(iii) the thermal efficiency of the cycle

Question 5. In a dual combustion cycle the inlet temperature, pressure and volume are 40°C, 120 kN m^-2 and 0.3 m³ respectively. The volume after compression is 0.02 m³, and the maximum pressure and temperature for the cycle are 8 MN m^-2 and 1400°C.
(a) Sketch a p-V diagram for the cycle showing the appropriate values given
(b) Calculate:

(i) the efficiency of the cycle

(ii) the work output per cycle.