How do you show the efficiency of an engine is x?

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SUMMARY

The efficiency of a hypothetical engine operating with an ideal gas is defined by the formula n = 1 - 1/γ ((1 - (P3/P1))/(1 - (V3/V1))). The discussion emphasizes the importance of understanding the processes involved in the engine cycle, specifically the transitions between states 1, 2, and 3. Key equations include ΔU = Qout - Qcold - Work and PV = nRT, with γ representing the ratio of specific heats (Cp/Cv). Clarification on the types of processes (constant volume, constant pressure) and heat flow during transitions is essential for accurate calculations.

PREREQUISITES
  • Understanding of thermodynamic cycles and efficiency calculations
  • Familiarity with the ideal gas law (PV = nRT)
  • Knowledge of specific heat capacities (Cp and Cv) and their significance in thermodynamics
  • Ability to interpret and analyze adiabatic processes in thermodynamic systems
NEXT STEPS
  • Study the derivation of the efficiency formula for thermodynamic cycles
  • Learn about adiabatic processes and their implications in engine efficiency
  • Explore the concepts of constant volume and constant pressure processes in thermodynamics
  • Investigate the role of specific heats (Cp and Cv) in calculating engine performance
USEFUL FOR

Students of thermodynamics, mechanical engineers, and anyone involved in the design or analysis of engine efficiency will benefit from this discussion.

lilliebeth
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Homework Statement


A hypothetical engine, with an ideal gas as the working substance, operates in the cycle shown in the diagram, show the efficiency of an engine is :

n= 1 - 1/[itex]\gamma[/itex] ((1-(P3\P1))/(1-(V3/V1)))

The diagram is basically a section the bottom left quadrant of a circle with an adiabatic process for 3 to 1 to make it a cycle

Homework Equations


ΔU = Qout -Qcold - Work
PV=nRT
gamma = Cp/Cv

The Attempt at a Solution


I really have no idea how to start this
 
Last edited:
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Hi lilliebeth. Welcome to PF. To be sure of how you are labeling the states 1, 2, and 3 could you please answer the following?

The process from 1 to 2 is what type of process? (constant volume, constant pressure, or what?)
Does heat flow in or out of the engine in going from 1 to 2?

The process from 2 to 3 is what type of process?
Does heat flow in or out of the engine for this process?

To get started, you should add another relevant equation: the equation for the efficiency of an engine. That will help you decide what you need to calculate.
 

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