Compressed Air Engine Calculations

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SUMMARY

This discussion focuses on the calculations for power and torque values in a single-cylinder compressed air engine operating at a constant inlet pressure of 9 bar. The user is attempting to validate their calculations against MATLAB results and seeks formulas for determining torque at various RPMs and the rate of air tank depletion. Key insights include the need for a more accurate model of the engine's operation, specifically recognizing that the expansion process is more accurately described as polytropic rather than adiabatic, with a k value of approximately 1.35.

PREREQUISITES
  • Understanding of polytropic and adiabatic processes in thermodynamics
  • Familiarity with MATLAB for simulation and validation of calculations
  • Knowledge of reciprocating engine mechanics and slider-crank mechanisms
  • Basic principles of fluid dynamics related to compressed air systems
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  • Research polytropic expansion calculations in compressed air engines
  • Learn how to model reciprocating engine performance using MATLAB
  • Investigate flow dynamics in compressed air systems and their impact on performance
  • Explore torque calculation formulas specific to single-cylinder engines
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Engineers, mechanical designers, and researchers involved in the development and optimization of compressed air engines, particularly those focusing on performance metrics like power and torque.

karan_s
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TL;DR
I have done some calculations to obtain power from the engine but don't think they are correct. Also need some help calculating torque at different rpms and air tank emptying time.
Hi, I posted a question a while ago which I have managed to do some more calculations for. I need a bit of help to see if they are correct. I am trying to obtain power and torque values at different rotational speeds of a single cylinder compressed air engine. The inlet pressure into the engine is a constant 9 bar and the air is discharged from the chamber as the piston reached BDC rather than a conventional cam valve design. My calculations below for power do no seem right compared to MATLAB and experimental results.

I have attached screenshot as it will not let me post equations into this.

I would like to get torque values at different rpms and also any formulas to calculate how quickly a air tank would empty at a specific rpm.

Much appreciate the help.
 

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What sort of engine do you have in mind? Is it a reciprocating machine employing a slider-crank mechanism or a continuous flow machine like an air turbine? You need to tell us more about what you are contemplating before much can be said about your calcs.
 
Dr.D said:
What sort of engine do you have in mind? Is it a reciprocating machine employing a slider-crank mechanism or a continuous flow machine like an air turbine? You need to tell us more about what you are contemplating before much can be said about your calcs.
It would like a reciprocating engine
 
You use of the constant k = 1.4 seems to imply an adiabatic expansion. In fact, it will be more nearly a polytropic expansion, k = 1.35 roughly.

The other problem I see is that you have assumed a very idealized cycle, with instantaneous fill and exhaust; this is not how it actually happens.
 

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