In a petrol engine, specific fuel consumption drops initially and then rises with an increasing air-fuel ratio; within what range does the minimum occur__________________?
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Answer: A. lean mixture
Explanation
Specific fuel consumption measures the mass of fuel consumed per unit of power output produced by an internal combustion engine. As the air-fuel ratio increases from rich toward lean, combustion becomes more complete and thermal efficiency improves. Minimum specific fuel consumption occurs slightly on the lean side of the chemically correct stoichiometric ratio. Stoichiometric air-fuel mixtures provide complete chemical reactions, but lean mixtures utilize excess oxygen to burn fuel more efficiently. Operating an engine at peak fuel efficiency requires precise electronic fuel injection mapping within the lean mixture zone. Exceeding the optimum lean limit causes misfires, erratic combustion, and a sharp drop in engine thermal efficiency.
Chemically correct stoichiometric mixtures emit lower pollutants but do not yield the absolute minimum specific fuel consumption. Rich mixtures consume excessive fuel to generate power, resulting in high specific fuel consumption values. Unpredictable is incorrect because engine fuel consumption follows repeatable thermodynamic and chemical combustion laws.
- Subject
- Engineering
- Category
- Mechanical Engineering
- Topic
- —
- Difficulty
- medium
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