1. Mechanical Engineering
Thermodynamics
2nd year Petrol dept.
2011-2012
Lecture (7) Gas Power Cycles
Lecturer : Dr. Esmail Bialy

2. Background
 1- Ideal Gas Relation
 2- 1st Law of Thermodynamics (Closed Systems)

3. Ideal Gas Relation

4. Forms
 1- PV=mRT
Pressure Volume mass Gas Const. Temperature
(kPa) (m3) (kg) (kJ/kg.K) (K)

5. Forms
 2- Pv=RT
Pressure Specific Volume Gas Const. Temperature
(kPa) (m3/kg) (kJ/kg.K) (K)

6. Forms
 3- PV=nRuT
Pressure Volume no. of Universal Temperature
kmoles Gas Const.
(kPa) (m3) (kmole) (kJ/kmole.K) (K)

7. Specific Heats

8. Specific Heats

9. Specific Heats
γ γ

10. Specific Heats
 From the last two relations, we can drive another two
relations
 Cp=γR/(γ-1) For Air= 1.0035 kJ/kg.K
 Cv=R/(γ-1) For Air= 0.716 kJ/kg.K

11. Note:
1-For Ideal Gases
 Δ h= CpΔT
 Δu = Cv ΔT
2- For Steam
 Δ h= h2-h1
 Δu = u2-u1 from steam tables

12. 1st Law of Thermodynamics
(Closed Systems)
(Revision)

21. Note!!!
rp, r, rc
rp: Pressure ratio (Brayton Cycle)
r: Compression ratio (Otto & Diesel Cycles)
rc: Cutoff ratio ( Diesel Cycle)

22. Example (5-10):
A Diesel engine has a compression ratio of 20:1 with an inlet
state of 95 kPa, 290 K, and volume 0.5 L. The maximum cycle
temperature is 1800 K. find the maximum pressure, the net
specific work, and the thermal efficiency.