How does the thermal efficiency of a two-stroke cycle engine compare to a four-stroke engine_________________?
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Answer: B. less
Explanation
Two-stroke engines lose a portion of fresh air-fuel charge directly into the exhaust pipe. Incomplete scavenging leaves residual burnt exhaust gases inside the combustion cylinder volume. These scavenging inefficiencies reduce overall fuel conversion effectiveness compared to four-stroke designs. Four-stroke engines have dedicated exhaust and intake strokes that clear cylinders thoroughly. Thermal efficiency compares useful work output against the total chemical energy of fuel supplied. Two-stroke cycles deliver power on every revolution but sacrifice some volumetric and thermal efficiency.
Small lawn equipment often uses two-stroke engines for simplicity despite lower fuel efficiency. Large marine two-stroke diesel engines use advanced port timing to minimize scavenging losses. Automotive applications overwhelmingly favor four-stroke cycles due to strict fuel economy standards. Stating two-stroke efficiency is higher ignores the well-documented penalty of charge short-circuiting. Equal efficiency is incorrect because mechanical scavenging processes differ fundamentally between cycles. Load-dependent variations do not negate the general baseline lower efficiency of standard two-strokes.
- Subject
- Engineering
- Category
- Mechanical Engineering
- Topic
- —
- Difficulty
- medium
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