Generator quieting

MEXICOWANDERER wrote:
I believe a person will find COMBUSTION DETONATION is a major culprit of radiated noise. Example? Diesel. That knocking and clatter is an example and reduction of the noise because of water jacketing is a perfect example.

Because of "chain link association", my work with generators led me howling and fuming to problems with prime movers and it is impossible to isolate noise issues from customer complaints.

Take a 36-turn Wisconsin 37.5 horsepower 15Kw generator PM and compare it to an Onan 4cyl 36-turn 15-Kw generator.

The Wisconsin is deafening. The Onan is merely loud. The Wisconsin is air-cooled.

It's like a speaker. Only the voice coil actually is the origin of the noise -- the fabric is a sympathetic resonator. In an engine, cylinder combustion is the origin of BOTH exhaust AND resonating noise. The surface of the engine acts like the sympathetic resonator.

Water transmits noise, yes? But water in a chamber can also diffuse noise through an intricate physics of echo cancellation. Noise bouncing off a far side wall cancels frequency waves and this action is definitely selective.

I fiddled with sound proofing although I did not want to.

A thin foil of lead absorbs higher frequency emissions. Soft foam with pyramid protrusions is the most effective sound absorbsion for middle and low frequencies.

I had to deal with generator noise while building trawlers. It isn't fun. A diesel genset can turn the hull and bulkheads into giant resonators. Stick a stethoscope against concrete block of a generator shed and hear the effects of this.

Suppress sound. Then stick your stethoscope against the outside wall once again -- amazing eh?

It would cost a moderate fortune for me to clad the inside of my gen shed with 3" suppressor foam. Then there is the issue of flammability. Not feasible with auto extinguishing suppressors like Halon. Beyond my budget.

If you want real life examples of generator sound suppression, movie set tow trailer gen sets are perfect. A 20 Kw unit (diesel) is quieter with an ear a foot from the enclosure than a Honda 2000 watt inverter generator is at 10ft distance. Not bad for a DIESEL versus gasoline comparison. All's it takes is lots of money, lots of space and a significant reduction in engine efficiency due to increased exhaust back pressure. And keep in mind those movie set units have to deal with radiator cooling air flow.

Mex,

Yeah, in my haste to post..

I did omit the idea of the detonation in the cylinder as a plausible source of noise. What you have in a sense is a controlled burn, not exactly an explosion but a controlled burn in the cylinder which happens incredibly fast.

This spikes the pressure in the cylinder and head which slightly deforms the cylinder and head. In a nutshell the cylinder and head expand/contract with the pressure increase and decrease.

That vibration also can be transferred to the rest of the engine.

However, one should note that most of the "noise" is generated internally and radiated out through the engine case.

Air cooled engines do tend to be a bit noisier than water cooled, part in due to air cooled cylinders unlike water cooled are exposed.

Water cooled engines by design have a water jacket around the cylinder and head which can help dampen some of the harshness.

Sound control is a science all to it's self but in reality it comes down to dampening and absorption rather than trying to attack it with a huge exhaust muffler.

My video does clearly show a difference in the exhaust note vs the rest of the gen and that is what I set out to demonstrate in hopes that someone else on the wobbly web might bounce across my video before setting out going the wrong direction. :)