Sound Intensity of Piston in Engine at 8000 RPM

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SUMMARY

The discussion focuses on the sound intensity produced by a piston in an engine operating at 8000 RPM, with a stroke of 86 mm. The calculated frequency of the sound is 133 Hz, and the wavelength is 2.57 m. The pressure amplitude is determined to be 20000 Pa, resulting in a sound intensity of 479000 W/m². Participants question the validity of this intensity level, prompting a review of the calculations using the formulas for pressure amplitude and sound intensity.

PREREQUISITES
  • Understanding of sound wave properties, including frequency and wavelength
  • Familiarity with the concepts of pressure amplitude and intensity of sound
  • Knowledge of the bulk modulus and its role in sound propagation
  • Basic principles of engine mechanics and piston dynamics
NEXT STEPS
  • Review the calculation of sound intensity using the formula: intensity of sound = pressure amplitude²/(2*density of air*speed of sound)
  • Explore the relationship between pressure amplitude and bulk modulus in sound waves
  • Investigate the effects of engine RPM on sound frequency and intensity
  • Learn about sound wave propagation in different mediums, focusing on air density and speed of sound
USEFUL FOR

Engineers, acoustics researchers, and automotive professionals interested in sound analysis and engine performance optimization.

sid_galt
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consider a piston in an engine with a stroke of 86 mm and RPM 8000 which gives the frequency of sound it is producing(due to compression and decompression) to be 133 Hz and wavelength 2.57 m.

Then the pressure amplitude turns out to be 20000 Pa and the intensity of the sound wave to be 479000 W/m2.

Is it just me or is the intensity of the sound much too high? Am I going wrong somewhere?
 
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Well, any takers? Is the sound intensity produced really that high or am I going wrong somewhere with my calculations. I used the following two formulas

pressure amplitude = bulk modulus * wave number * displacement amplitude

intensity of sound = pressure amplitude^2/(2*density of air*speed of sound)
 

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