Thermodynamic cycle of a petrol (gasoline) engine On which idealized thermodynamic cycle is a conventional spark-ignition petrol engine modeled for analysis and instruction?
Correct Answer: Otto cycle
Introduction / Context:Ideal cycles provide a simplified framework to analyze engine performance. Spark-ignition petrol engines are classically associated with the constant-volume heat-addition Otto cycle.
Given Data / Assumptions:
- Four-stroke spark-ignition engine with near-stoichiometric fueling.
- Ideal analysis (no pumping, friction, heat losses).
- Constant-volume heat addition approximation during combustion.
Concept / Approach:The Otto cycle consists of isentropic compression, constant-volume heat addition, isentropic expansion, and constant-volume heat rejection. This approximates combustion that occurs quickly near top dead center in SI engines.
Step-by-Step Solution:
Match engine type (SI) to constant-volume heat addition model.Recognize that diesel engines align with the constant-pressure Diesel cycle.Select Otto cycle for petrol engine modeling.Verification / Alternative check:Textbooks and engine courses consistently pair petrol engines with the Otto cycle in idealized analyses.
Why Other Options Are Wrong:
- Carnot: theoretical maximum efficiency, not a practical engine cycle.
- Diesel: constant-pressure addition fits CI engines.
- Rankine: steam power plants.
- Miller: a valve-timing-modified variant; not the baseline teaching cycle.
Common Pitfalls:Assuming real combustion exactly matches constant volume; in practice, it is neither perfectly constant-volume nor instantaneous.
Final Answer:
Otto cycle