In a petrol engine, M.E.P. initially rises with air-fuel ratio before dropping; within what mixture zone does maximum M.E.P. occur________________?
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Answer: C. rich mixture
Explanation
Mean effective pressure represents the theoretical constant pressure acting during a power stroke to produce measured engine work. As the air-fuel mixture becomes richer, flame propagation speed and combustion pressure increase up to an optimum point. Maximum mean effective pressure occurs within a slightly rich mixture because it ensures complete oxygen consumption and higher cylinder pressures. Stoichiometric air-fuel ratios provide complete chemical combustion, but slightly rich mixtures yield maximum power output. Carburetors and fuel injection maps are calibrated to supply rich mixtures during heavy acceleration and high engine loads. Excessively rich mixtures beyond this peak cause incomplete combustion, black smoke, and a rapid drop in engine power.
Lean mixtures maximize fuel economy and combustion efficiency but fail to produce the highest possible mean effective pressure. Chemically correct stoichiometric mixtures provide optimal emissions control rather than maximum engine power output. Unpredictable and none of the above are incorrect because engine power response curves follow well-established thermodynamic laws.
- Subject
- Engineering
- Category
- Mechanical Engineering
- Topic
- —
- Difficulty
- medium
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