Exhaust System Basics
Purpose of an Exhaust System Exhaust system design specifications are typically defined by the OEs. They are looking for a solutions that can redirect engine exhaust, reduce exhaust noise and most recently, reduce emissions (hydrocarbons, carbon monoxide, soluble organic fraction (SOF)). Diesel engines are a reliable and efficient power source for vehicle and equipment manufacturers. Governmental regulations across the globe are driving diesel engine users to consider buying new vehicles or retrofitting their existing engines to meet the new emissions regulations. Muffler Design & Performance Donaldson mufflers are designed and tested with specific focus on three performance variables: attenuation, backpressure and structural. Attenuation For exhaust systems, attenuation refers to the reduction in sound level measured between an engine without a muffler and the same engine with a muffler. This sound level is typically measured in a decibal scale (dBAs). Traditional mufflers use tubes, baffles, and expansion chambers and insulation to help control noise. Newer applications include emissions reduction devices installed in the exhaust system. Many of the devices also provide the needed noise attenuation either in part or in total. Sound quality is an additional noise characteristic that is important to the end user. An example of a sound quality concern is the sound of fingernails on a chalk board – this screeching sound makes people wince, yet the measured sound level would not be significant. A low throaty rumble may seem even quiet (and almost desirable) but may be amplified and become annoying if it reverberates within the operator's cabin.
Heavy-duty mufflers typically employ one of four sound reduction techniques including: Reactive silencing What's important: the ratio of the body diameter to the tube
Resistive silencing Exhaust flow is forced through a small area. It removes energy to reduce noise level.
Absorptive silencing Transforms wave energy into thermal energy. Uses acoustic packing (or wrap) just inside the outer shell of the muffler.
Engine manufacturers generally expect a reduction in engine exhaust sound level of 15-25 dBA. The overall noise level of a vehicle or piece of stationary equipment is the actual regulated value. The overall noise level is typically measured while driving past a microphone at a specific speed and distance. Maximum noise levels in the U.S. are regulated by the U.S. EPA (Environmental Protection Agency).
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