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Magazine Chapter 4: Q. 4.19 (page 133)
The amount of work done by each stroke of an automobile engine is controlled by the amount of fuel injected into the cylinder: the more fuel, the higher the temperature and pressure at points 3 and 4 in the cycle. But according to equation 4.10, the efficiency of the cycle depends only on the compression ratio (which is always the same for any particular engine), not on the amount of fuel consumed. Do you think this conclusion still holds when various other effects such as friction are taken into account? Would you expect a real engine to be most efficient when operating at high power or at low power? Explain.
Short Answer
The real engine is most efficient in low power than the high power.
Step by step solution
Concept Introduction
The cycle of operation is Otto cycle why because the efficiency depends only upon the compression ratio.
In practice, there are several losses such as:
1. Time loss
2. Heat loss
3. Blow down losses
4. Friction loss
5. Pumping loss
Explanation
Actual P-V Diagram of Otto Cycle
Maximum efficiency condition may occur in ideal cycle but because of losses in the cycle, the efficiency decreases.
So, taking in consideration all the losses, the real engine will be most efficient when operating at low power because at high power, losses will be high too andhence , the efficiency will decrease.
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