Exhaust Muffler Design

[ibdennyak]

Dang it.........A couple of years ago, I was trying to build a super silent standby power system for areas affected by hurricanes and other natural disasters.....kind of an emergency...emergency power system. The unit ran fine, but I couldn't get the noise level low enough to suit me. One of my sources for engine quieting was a website for Swedish ultralights. Apparently Sweden flat out grounds an ultralight that produces more than a set amount of noise pollution. When Kerf mentioned Rotax, that reminded me to search for the very helpful site again. They were using megaphone shaped tubes lined with fiberglass roving (kind of a giant glasspack) and airboxes to quiet their engines, and very effectively. Unfortunately the size of the system was becoming prohibitive. Maybe some one else has better search techniques.

 

[happycheapskate]

I searched for 2 Stroke Baffle and came up with this website
http://motorcycleproducts.co.uk/catalogue/exhaust-baffles-c-90_354.html

The page lists guaze packing for mufflers, and various baffles in many sizes, for replacements or DIY muffler builds.

 

[happycheapskate]

Has anyone tried an air swirler, similar to the idea of the Gas Saver Tornados and things like it?

 

[kerf]

Fix A Problem - Create A Problem

I hope everyone had a good Christmas and now it's back to business. My air box has some more miles on it and it's doing what it was supposed to do as to noise reduction. The engine is running very well but probably needs to be leaned a little more for peak performance. One issue I've had with the R460, is fuel blow back through the carburetor. This engine has very aggressive port timing and I'm running a pretty high gear ratio of 18.75:1, this combined with too much throttle at low speeds creates issues.

At 30 mph, in high gear, the engine is only turning 7175 rpm and it doesn't reach full torque until 8000 rpm and max HP at 11,000 rpm. Applying too much throttle at speeds below 25 mph, creates lots of blow back and I've actually clogged the air filter to the point the engine wouldn't even start. I thought the air box would help as the blow back isn't going straight into the air filter. I took a test run over some pretty hilly roads on Friday and noticed fuel leaking down on my muffler. When I removed the air box cover fuel poured out of the box and took some of my newly applied paint off the muffler. It seems that while I solved one issue I created another, maybe a project killer.

I pondered the problem of getting any blow back out of the air box. A drain would be of little use as the air box has negative pressure while running so nothing would drain. After more thought, I decided that reintroducing the fuel back into the carburetor air stream would be the only solution. To this end, I fashioned, for lack of a better term, an atomizer tube. This is a short length of small diameter brass tubing, silver brazed to the air box reinforcing plate, so the lower end of the tube almost touches the bottom of the air box. The upper end extends just into the carburetor air stream and this end is beveled back toward the engine. The idea was, air being drawn into the engine would move over the end of the tube, creating negative pressure within the tube and pulling any blow back fuel into the carburetor.

Does it work? This morning, at 5:30 (30 degrees) I set out on a hilly 15 mile run. On getting back I pulled the air box cover and the results are shown in the attached jpg.

Mission accomplished.

 

[ibdennyak]

I hope everyone had a good Christmas and now it's back to business. My air box has some more miles on it and it's doing what it was supposed to do as to noise reduction. The engine is running very well but probably needs to be leaned a little more for peak performance. One issue I've had with the R460, is fuel blow back through the carburetor. This engine has very aggressive port timing and I'm running a pretty high gear ratio of 18.75:1, this combined with too much throttle at low speeds creates issues.

At 30 mph, in high gear, the engine is only turning 7175 rpm and it doesn't reach full torque until 8000 rpm and max HP at 11,000 rpm. Applying too much throttle at speeds below 25 mph, creates lots of blow back and I've actually clogged the air filter to the point the engine wouldn't even start. I thought the air box would help as the blow back isn't going straight into the air filter. I took a test run over some pretty hilly roads on Friday and noticed fuel leaking down on my muffler. When I removed the air box cover fuel poured out of the box and took some of my newly applied paint off the muffler. It seems that while I solved one issue I created another, maybe a project killer.

I pondered the problem of getting any blow back out of the air box. A drain would be of little use as the air box has negative pressure while running so nothing would drain. After more thought, I decided that reintroducing the fuel back into the carburetor air stream would be the only solution. To this end, I fashioned, for lack of a better term, an atomizer tube. This is a short length of small diameter brass tuning, silver brazed to the air box reinforcing plate, so the lower end of the tube almost touches the bottom of the air box. The upper end extends just into the carburetor air stream and this end is beveled back toward the engine. The idea was, air being drawn into the engine would move over the end of the tube, creating negative pressure within the tube and pulling any blow back fuel into the carburetor.

Does it work? This morning, at 5;30 (30 degrees) I set out on a hilly 15 mile run. On getting back I pulled the air box cover and the results are shown in the attached jpg.

Mission accomplished.

hey, looks like ya done good Kerf. Wonder if the same thing could be accomplished by having the floor of the air box at the bottom of the carb inlet.

Anyways...pretty ingenious.

 

[Danny3xd]

Amazing! Gonna have to reread this. Been wondering how to reduce intake noise. Purty work Kerf