How Efficient is a 100-hp Car Engine Compared to Carnot Efficiency?

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SUMMARY

A 100-hp car engine operates at approximately 15% efficiency, with a cold-temperature exhaust reservoir at 85°C and a thermal intake temperature of 500°C. The Carnot efficiency can be calculated using these temperatures, revealing the maximum possible efficiency for the engine. The discussion also emphasizes the need to estimate the power output in watts and the heat exhausted in joules and kilocalories over one hour of operation.

PREREQUISITES
  • Understanding of Carnot efficiency calculations
  • Basic thermodynamics concepts
  • Knowledge of horsepower to watts conversion
  • Familiarity with heat energy units (joules and kilocalories)
NEXT STEPS
  • Calculate Carnot efficiency using the formula: 1 - (T_cold/T_hot)
  • Convert horsepower to watts for accurate power output assessment
  • Learn how to convert energy units between joules and kilocalories
  • Explore real-world applications of thermodynamic efficiency in automotive engineering
USEFUL FOR

Engineers, automotive technicians, and students studying thermodynamics or mechanical engineering will benefit from this discussion, particularly those interested in engine efficiency and performance optimization.

mmg0789
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A 100-hp car engine operates at about 15 percent efficiency. assume that the engine's water temperature is 85deg C is its cold-temperature (exhaust) reservoir and 500deg C is its thermal "intake" temperature (the temperature of the exploding gas/air mixture)

a)calculate its efficiency relative to its maximum possible (Carnot) efficiency

b) estimate how much power (in watts) goes into moving the car, and how much heat, in joules and in kcal, is exhausted to the air in 1 h.

--i'm not sure how to go about this problem any help is appreciated


Thanks in Advance
 
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mmg0789 said:
A 100-hp car engine operates at about 15 percent efficiency. assume that the engine's water temperature is 85deg C is its cold-temperature (exhaust) reservoir and 500deg C is its thermal "intake" temperature (the temperature of the exploding gas/air mixture)

a)calculate its efficiency relative to its maximum possible (Carnot) efficiency

b) estimate how much power (in watts) goes into moving the car, and how much heat, in joules and in kcal, is exhausted to the air in 1 h.

--i'm not sure how to go about this problem any help is appreciated


Thanks in Advance
The Carnot efficiency is easily calculated. What percent of the maximum possible efficiency (the Carnot efficiency) is the engine achieving?

The 15% efficiency tells you what fraction of the input energy is going into moving the car. The rest goes out in the exhaust.
 

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