critical mufflers?

I know the term "critical muffler", but does this imply a design, or a
performance standard?

Are critical mufflers available for small engine applications, ie., in
compact packages for 1.5" exhaust pipes on small air-cooled diesels?

Suppose I add a critical muffler to a small, unbaffled, aircooled diesel
rated at 77dB/23 feet?
Will it provide significant additional quieting, given that the engine block
radiates significant noise?

 

I dont know the term Critical but yes a good muffler will significantly
reduce noise. Not all mufflers are the same. Db reduction varies on
size and design. Some power will be lost.

 

I have never seen a critical silencer/muffler on small engines. Mostly 40 kw
and above for applications where noise is an issue. The housing and the
muffler work together to quiet the produced sound. Check out one of your
local rental yards look at the towed gensets from Mulitquip. Mulitquip has
some that I have rented that are really quiet even under full load.

 

to revive a previous theme of mine re active noise reduction

there has been some work on an active noise reduction system applied to
mufflers

such technology should be cabable of reductions on the order of 10 to 15
dBa since the system is somewhat closed for the electronic control
volume which is then modified.

One need to basically take care to two things, the hot air flow exiting
the pipe and the round or elliptical type surface that could propagate
sound of its surface. one needs to modulate or control both the air
flow and the surface features.

However this could be done and maybe has

cost is another issue and likely the critical issue (no pun intended) as
one needs to obtain the technology at some kind of reasonable cost.

however nerual network and fuzzy control technology have advanced and
there maybe is good hardware these days to do the job.

Paul (EE)

 

I have a 5.5 kw Chinese 3600 rpm aircooled diesel, in a tight baffled
enclosure, which is actually in the class of "quiet" diesels. I have been
told by an independent source that in that case, just throwing some flex
hose on the exhaust will make it very unobtrusive. Therefore, with
sufficient intricateness, an aircooled diesel can be quieted, but I would
agree with you that it is virtually impossible to do as a home project.

The question, however regards a military 2KW aircooled open frame unit,
quite a number of which are being surplused now. Because my "stationary" AGM
batteries do not like to be bulk charged, preferring instead constant
voltage, it's very difficult to get them to float in a reasonable period of
time. This 2KW unit would fill a gap in my lineup, providing better fuel
economy.

The unit is rated at 77 dB @ 7 meters, and is optimistically described as
"noise attenuated." The particular unit is 28VDC, which is attractive to me.

I suppose they are being surplused in favor of quieter units. Does anybody
know what the military is using for field power these days?