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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

Expert verified

The real engine is most efficient in low power than the high power.

Step by step solution

01

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

02

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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Most popular questions from this chapter

Why must you put an air conditioner in the window of a building, rather than in the middle of a room?

Use the definition of enthalpy to calculate the change in enthalpy between points 1 and 2 of the Rankine cycle, for the same numerical parameters as used in the text. Recalculate the efficiency using your corrected value ofH2, and comment on the accuracy of the approximationH2≈H1.

Imagine that your dog has eaten the portion of Table 4.1 that gives entropy data; only the enthalpy data remains. Explain how you could reconstruct the missing portion of the table. Use your method to explicitly check a few of the entries for consistency. How much of Table 4.2 could you reconstruct if it were missing? Explain.

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