For a semi-diesel cycle with fixed compression ratio and heat input, how does thermal efficiency respond to a higher pressure ratio_______________?
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Answer: A. increase
Explanation
The semi-diesel cycle combines elements of both constant volume Otto and constant pressure Diesel thermodynamic cycles. Holding the compression ratio and total heat input constant, increasing the pressure ratio raises peak cycle temperatures. According to second law thermodynamic principles, higher peak operating temperatures improve overall thermal efficiency. Thermal efficiency equations for semi-diesel and dual combustion cycles depend directly on compression and pressure expansion ratios. The pressure ratio is defined as the maximum combustion pressure divided by the compression pressure at the end of the stroke. Optimizing the pressure ratio extracts more expansion work from the working fluid before exhaust blowdown occurs.
Decrease is incorrect because raising the pressure ratio at fixed heat input always improves the theoretical thermal efficiency. Remain unaffected contradicts the fundamental thermodynamic laws governing heat engine cycle efficiencies. Options D and E suggest variable or dual trends, whereas standard cycle analysis yields a clear, direct efficiency increase.
- Subject
- Engineering
- Category
- Mechanical Engineering
- Topic
- —
- Difficulty
- medium
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