Discussion
An ideal Diesel cycle has a compression ratio of 20 and cut-off ratio of 1.5. At the beginning of the compression stroke, air is at 100 kPa, 300 K. Use the cold-air-standard assumptions with property value \(c_{p}\) = 1.005 kJ/kg-K. Assume \(c_{p}/c_{v}\) = 1.4. For this cycle, the net work output per unit mass is
Answer: A
The net work output is about 335 kJ/kg.
With \(c_{v} = 1.005/1.4 = 0.7179\) kJ/kg-K, follow the cycle:
\[ \begin{aligned} T_{2} &= 300 \times 20^{0.4} = 994.3\ \text{K} \\ T_{3} &= 1.5\,T_{2} = 1491.5\ \text{K} \\ T_{4} &= T_{3}\left(\tfrac{1.5}{20}\right)^{0.4} = 529.2\ \text{K} \end{aligned} \]
Heat is added at constant pressure and rejected at constant volume:
\[ \begin{aligned} q_{in} &= 1.005(1491.5 - 994.3) = 499.7 \\ q_{out} &= 0.7179(529.2 - 300) = 164.6 \\ w_{net} &= 499.7 - 164.6 \approx 335\ \text{kJ/kg} \end{aligned} \]
The distractors are the intermediate quantities: 500 kJ/kg is the heat added and 165 kJ/kg the heat rejected. The thermal efficiency, \(335/500 = 0.67\), is a check.
Post your comment
Please log in or register to post a comment.
Examination Categories
- SSC Exams
- Banking Exams
- Teaching Exams
- Civil Services Exams
- Railways Exams
- Engineering Recruitment Exams
- Defence Exams
- State Government Exams
- Police Exams
- Insurance Exams
- Nursing Exams
- Other Government Exams
- NRA CET
- PG Entrance Exams
- Campus Placement
- MBA Entrance Exams
- CUET and UG Entrance
- Judiciary Exams
- Regulatory Body Exams
- Software Development