Engine Exhaust Noise Control

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ASHRAE TC 2 6,Engine Exhaust Noise Control,nReactive Mufflers. nAbsorptive Silencers,nReactive Absorptive Mufflers. nTail Pipe Design,nTuned Resonators,nProject Examples. The above are the subjects that we will discuss,Some data will also be presented from field tests. One an example of a project failure and the other a. big success,ASHRAE TC 2 6,Engine Exhaust Considerations.
The exhaust system of a generator has,several inherent design problems that must. be considered These characteristics impose,severe limitations on what can be done to. silence the engine exhaust noise,nVery High Noise 100 to 120 dBA 1 m. nHigh Temperatures 950 to 1050 F,nHigh Velocities 5 000 to 15 000 fpm. nCombustion By Products soot corrosion,nPipe Thermal Expansion.
ASHRAE TC 2 6,Performance Characteristics,n Insertion Loss dB. depends on design size and frequency,n Pressure Drop inches H 2O or Hg. depends on velocity design,n Self Generated Noise dB ref 1 picowatt. depends on velocity design, Insertion loss IL is defined as the reduction of noise level. that occurs when a silencing element is inserted into the. system Because engines generate strong tonal, components the IL of any one muffler will not be the same.
with different engines different loads or different piping. configurations Pressure drop is more predictable however. Specific data on self noise is generally not available. ASHRAE TC 2 6,Engine exhaust noise varies significantly. with loading Typically the noise level at,full load is about 10 dB higher than the. no load condition The next slide shows,typical engine exhaust sound levels at. different loads,The curves also show that the majority of. the engine exhaust noise is at low,frequencies,ASHRAE TC 2 6.
Unsilenced Exhaust Noise,Sound Pressure 1 m dB,n Unlike engine block 125. noise exhaust noise 120,increases significantly,with engine load. n Graph at right shows 105,noise level vs load 100. for a 16 cyl 2000 KW,engine 1800 RPM Octave Band Frequency Hz. 25 50 75 100,ASHRAE TC 2 6,The overall noise level from most unsilenced.
engine exhaust systems varies from about 110,dBA to 120 dBA when measured 1 meter from. the pipe outlet,The noise level does not always align with the. power rating of the generator as you can see by,this next graph. Exhaust noise can also be affected by engine,turbochargers and after coolers It is best to. obtain exhaust noise data from the engine,manufacturer.
ASHRAE TC 2 6,Unsilenced Exhaust Noise,Sound Pressure 1 m dB. n Unsilenced engine 125,exhaust noise is 120,broad band with 115. highest levels at low,frequencies,n Data compares 6 cyl 100. 150 KW and 500 KW,engines with a 16 cyl Octave Band Frequency Hz. 2000 KW engine all 150 KW 114 dBA 350 KW 110 dBA,1800 RPM diesels 500 KW 113 dBA 2000 KW 120 dBA.
ASHRAE TC 2 6,The exhaust noise spectrum will always contain. strong tones associated with the rate of cylinder,firings In 4 cycle engines each cylinder fires. once every other revolution of the drive shaft,Cylinders fire once every rev in 2 cycle engines. The lowest tone is always the CFR which is the,firing rate for any one cylinder. The engine firing rate is generally the strongest,tone in the exhaust spectrum.
ASHRAE TC 2 6,Engine Exhaust Tones,n Cylinder Firing Rate CFR. CFR RPM 60 for 2 cycle engines,CFR RPM 120 for 4 cycle engines. n Engine Firing Rate EFR,EFR N CFR where N cylinders. n Harmonics of CFR and EFR,ASHRAE TC 2 6,This graph shows a narrow band spectrum of the. exhaust noise of a 6 cylinder diesel engine,running at 1800 RPM in a 500 kW generator The.
data was collected with the microphone placed 1,meter from the exhaust outlet with the engine. running at full load,Note the strong tone at 90 Hz which is the EFR. Note that the second and third harmonics are,also prominent in the spectrum. ASHRAE TC 2 6,500 KW Engine Exhaust Tones,30 Hz 60 Hz 90 Hz 180 Hz. 2xCFR 4xCFR 1xEFR 2xEFR,Sound Pressure Level dB,1 24th Octave Band Center Frequency Hz.
No Silencer 6 Pipe 113 dBA,ASHRAE TC 2 6,The most common element used to silence. generator exhausts are reactive mufflers, Reactive mufflers are available in a wide range of. cost and performance The noise is reduced by,forcing the exhaust air to pass through a series. of tubes and chambers,Each element in the muffler has sound reduction. properties that vary greatly with acoustic,frequency and it is the mixing and matching of.
these elements that constitutes muffler design,ASHRAE TC 2 6. Reactive Mufflers,n 2 3 or 4 chamber,n All metal construction. with no sound,absorptive materials,n Maximize ratio of body. diameter to pipe,diameter volume,ASHRAE TC 2 6,Over the years a series of muffler grades have. evolved to describe the approximate insertion,loss performance for engine exhaust mufflers.
The words do not necessarily imply where the,mufflers should be used Note that better quality. e g higher insertion loss mufflers will be,physically larger than lower quality units. Although size is not the only factor you cannot,get good acoustical performance without it. Engine Exhaust Noise Control nReactive Mufflers nAbsorptive Silencers nReactive Absorptive Mufflers nTail Pipe Design nTuned Resonators nProject Examples The above are the subjects that we will discuss Some data will also be presented from field tests One an example of a project failure and the other a big success ASHRAE TC 2 6 Engine Exhaust Considerations The exhaust system of a generator

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