Otto Cycle MCQ – Objective Questions with Answers
Mechanical Engineering › Thermodynamics | Free practice MCQs with detailed explanations
Last Updated: June 2026
📌 About this MCQ Set
The Otto cycle is the ideal cycle for spark-ignition (petrol) engines. Heat is added at constant volume.
These MCQs cover the four processes, efficiency, and dependence on compression ratio.
8 questions • every answer comes with a worked explanation. Click Show Answer to check yourself.
📖 New to this topic? Read the full concept guide: Otto Cycle →
Otto Cycle MCQs
Q1. The Otto cycle is the ideal cycle for:
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Answer: B. Spark-ignition (petrol) engines
The Otto cycle models spark-ignition (petrol) engines.
Q2. In the Otto cycle, heat is added at constant:
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Answer: B. Volume
Heat addition and rejection in the Otto cycle occur at constant volume.
Q3. The air-standard efficiency of the Otto cycle depends on:
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Answer: A. Compression ratio and γ
η = 1 − 1/r^(γ−1), depending on compression ratio r and specific heat ratio γ.
Q4. As the compression ratio increases, the Otto cycle efficiency:
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Answer: B. Increases
Higher compression ratio gives higher thermal efficiency.
Q5. The Otto cycle consists of two adiabatic processes and two:
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Answer: B. Constant-volume processes
Two reversible adiabatics plus two constant-volume heat transfer processes.
Q6. Compression ratio in the Otto cycle is the ratio of:
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Answer: B. Total cylinder volume to clearance volume
r = V_max/V_min = (clearance + swept)/clearance volume.
Q7. Practical petrol engine compression ratios are limited by:
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Answer: B. Detonation / knocking
Too high a compression ratio causes auto-ignition (knocking), limiting practical petrol-engine ratios.
Q8. For the same compression ratio, the Otto cycle is ____ than the Diesel cycle.
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Answer: B. More efficient
At the same compression ratio the Otto cycle has higher efficiency than the Diesel cycle.
Frequently Asked Questions
What is the Otto cycle used for?
It is the ideal air-standard cycle for spark-ignition (petrol) internal combustion engines.
How is Otto cycle efficiency calculated?
η = 1 − 1/r^(γ−1), where r is the compression ratio and γ is the ratio of specific heats.
Why are petrol engine compression ratios limited?
High compression ratios cause knocking (auto-ignition of the fuel-air mixture), which limits how high the ratio can go.