How does a reciprocating engine muffler decrease engine noise?

How does a reciprocating engine muffler decrease engine noise?

• A. By increasing the exhaust velocity.
• B. By combining cylinder exhausts into a common manifold with an expansion chamber and diffusing the flow.
• C. By releasing exhaust directly to ambient.
• D. By adding a secondary combustion chamber.

Answer: (B)

The muffler slows and disperses the exhaust sound by shaping the flow of the exhaust pulses. It gathers the pulses from all cylinders into a common path (a collector or shared manifold), so the individual pressure spikes reinforce less and the overall pulsation is reduced. An expansion chamber gives the high-pressure gas room to expand, lowering peak pressures and converting some of the sound energy into heat as the gas decelerates and interacts with the chamber walls. Diffusing the flow spreads the exhaust, reducing jet noise and allowing more of the sound energy to be absorbed or canceled by the muffler’s internal surfaces. In short, combining cylinder exhausts, expanding the gas, and diffusing the flow work together to smooth out pressure waves and dissipate acoustic energy, producing quieter exhaust.

The muffler slows and disperses the exhaust sound by shaping the flow of the exhaust pulses. It gathers the pulses from all cylinders into a common path (a collector or shared manifold), so the individual pressure spikes reinforce less and the overall pulsation is reduced. An expansion chamber gives the high-pressure gas room to expand, lowering peak pressures and converting some of the sound energy into heat as the gas decelerates and interacts with the chamber walls. Diffusing the flow spreads the exhaust, reducing jet noise and allowing more of the sound energy to be absorbed or canceled by the muffler’s internal surfaces. In short, combining cylinder exhausts, expanding the gas, and diffusing the flow work together to smooth out pressure waves and dissipate acoustic energy, producing quieter exhaust.