In answer to Peters interest in this, here is a simple cheap design for silencing a stationary motors exhaust. Dig a hole about 600mm deep 600mm wide and about 1200mm long. Hold the walls up with dry wall stone or bricks or whatever will do the job (non combustable material) Build 3 short walls with old bricks 2/3rds of the way across the hole dividing it into 4 equal 'rooms' with an opening at the ends. Put the exhaust into the first 'room' and an outlet stack into the far end 'room'. Make a lid from an old sheet of roofing iron and cover it with dirt. The way it works is that noise travels in straight lines and looses energy each time it goes around a corner, in this contraption it is forced to go around at least 5 corners. If it works well you could make it more permanent with better materials. However the main thing is to make it so it wont fall in or become a mantrap or fill up with water when it rains. The diagram if it loads up should explain better.

Attached Thumbnails

 

__________________
Johnnojack
4WD Isuzu Jackaroo 3.1 68,000km on WVO 2 tank home built system 6 solenoids. Mk. 8 version.

When I was much younger, still in high school, my dad installed a diesel engine for pumping water for our orchard, in place of the electric motor.
It was a diesel engine out of a land rover, which was fitted with starter motor, generator etc and so was easy for mum to start while dad was at work.

As a silencer, he got a 44 gallon drum and cut the top and bottom out, buried in in the ground, put the exhaust pipe to the bottom and filled it almost all of the way with large blue metal (crushed rock), then took the old lid and screwed a 2" pipe into the large bung hole, then put thel id on and covered it with dirt.

Exhaust noise was negligible, but the engine was not quiet as it rattled away pumping water thru the 4" centrifugal pump to the tank 50M higher or the orchard 25 - 35M higher then the pump.

Dad did lose the ends of 3 fingers due to tensioning the Vee belts while it was running.

It was still working, every day, 3 years later when we sold the orchard (only 2 km from where we now live).

This is the same principle as JohnnoJack's buried muffler, causing the exhaust gas to change direction and with different path lengths through the rock, the noise was muffled to be quieter than the engine itself.

I hope this helps anyone considering such a silencer.

Regards,
Tony

__________________
Searching the Biofuels Forum using Google
Adding images and/or documents to your posts

This may help for making a noise proof box for the engine of the genset.
One of the best noise dampening things I have come across was coruated iron with lots of holes (about 4mm) drilled in it (about every 40mm) with fiberglass insulation behind it. (it was in a machine room so got rid of a lot of noise on the inside) I think the holes stopped pressure waves building up on the noisy side and causing the metal to vibrate (therby transferring the noise) and being corugated and waves that reflected off it were dispersed.

__________________
cheers
Chris.
1990 landcruiser 80, 1HD-T two tank, copper pipe HE+ 20 plate FPHE, toyota solenoids and filters. 1978 300D, elsbett one tank system. 1979 300D veg oil/ diesel blend for now.

Noise suppression enclosures which need to be ventilated as well are quite technically sophisticated. I could explain but it would take far more time on this computer than I can afford and a heap of drawings which I am not that good at. To get started here are a few points.
1.To contain noise within an enclosure you need both a barrier and an absorber .
2. A noise barrier is any solid material rigid enough to not be set vibrating by the noise source, eg sheet steel, brickwall, plasterboard, concrete, thick composite board (MDF) etc
3. Insulation like compressed fibreglass batts are not a noise barrier. They are an absorber, they are there to stop noise reflecting off a hard surface.
4. Noise travels in straight lines.
5. To stop noise while allowing airflow you need a ventilator which has a Z path for the air and which has that path lined with absorbent material. Tricky.

To learn more study acoustical engineering, or probably easier to go to a decent library and find some reference books on the subject.

A lot of people think they know how to reduce noise but end up wasting their money on things which don't work eg. Brush fences, or hedges, to stop traffic noise or a expensive generator enclosure with big holes at each end to let air in and out.

__________________
Johnnojack
4WD Isuzu Jackaroo 3.1 68,000km on WVO 2 tank home built system 6 solenoids. Mk. 8 version.

Very informative, thankyou!

MORE Reading

Peter<><

Intake air has a similar problem in the engine takes it in in "gulps" which causes noise similar to the exhaust, (not as bad as there is less intake air) but of course needs to be cool and not restricted.
Would another hole like johnojack has suggested for exhaust be the way to go?
If this thread also has a way to combat the smell of the exhuast (move next to a hungy jacks, or use water?) I think I many buy one.....

__________________
cheers
Chris.
1990 landcruiser 80, 1HD-T two tank, copper pipe HE+ 20 plate FPHE, toyota solenoids and filters. 1978 300D, elsbett one tank system. 1979 300D veg oil/ diesel blend for now.

Intake noise is not difficult to suppress. You just install a solid air cleaner with a Humboltz chamber (funny looking bulgy plastic thing you find under modern diesel car bonnets before the aircleaner) or you can use an exhaust muffler before the aircleaner.

To combat the smell of the exhaust you need the motor running very clean. That may be difficult to do with some motors. To disperse the smell of exhaust put it into a stack which goes as high as practical say 4 or 5 metres. If you have neighbours next door, say less than 20metres away, and especially if they have a double story house then, sorry, you're project is doomed.

__________________
Johnnojack
4WD Isuzu Jackaroo 3.1 68,000km on WVO 2 tank home built system 6 solenoids. Mk. 8 version.