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| Exhaust Mufflers for 2 cycle engines |
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Message |
    
barry
Member
Username: barry
Post Number: 29
Registered: 02-2006
| | Posted on Sunday, December 24, 2006 - 05:09 pm: | 
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I’m interested in obtaining design/construction information for exhaust mufflers suitable for 2- cycle engines.
4-cycle engines have the force provide by upward piston travel to push exhaust gases out of the cylinder whereas 2-cycle engines exhaust during downward piston travel . Thus exhaust back pressure decreases available propulsion power and can add to starting difficulties.
I am wondering if there is a minimum back pressure muffler design that is best for 2 cycle application.
I would like to build and test mufflers using my test bench and try to discover a design that minimizes power loss.
Thanks
Barry |
jb_castagnos
Senior Member
Username: jb_castagnos
Post Number: 205
Registered: 07-2002
| | Posted on Monday, December 25, 2006 - 07:32 am: |
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Barry, exhaust scavenging on two cycles is critical to performance and has been known for some time. The old bateaus around here ran a straight exhaust, but the old timers all have they're idea of the ideal length, usually around 68". In reallity the ideal length would depend on the rpm range you wanted to make the most power. Modern expansion chambers are designed so that when the pulse leaves the cylinder it draws a vacuum behind it purging the cylinder and actually drawing a charge of fuel and air into the exhaust while both ports are open. The exhaust expands in the funnel shaped pipe, hits the back with the small opening and bounces back, forcing the fuel mixture back into the cylinder after the intake ports are closed and the exhaust are starting to close, giving a supercharged effect. The timing on this is critical and the pipes will only work in a certain rpm range, the slower the engine the longer the pipes have to be. I would think you could figure the length with the speed of sound. |
jb_castagnos
Senior Member
Username: jb_castagnos
Post Number: 206
Registered: 07-2002
| | Posted on Monday, December 25, 2006 - 07:39 am: |
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See this patent for an interesting idea, he injects water to change the timing of the pulses, would work well on a marine engine.
http://www.google.com/patents?vid=USPAT3385052&id=PmlgAAAAEBAJ&pg=PA1967#PPA1967,M1 |
barry
Member
Username: barry
Post Number: 30
Registered: 02-2006
| | Posted on Wednesday, December 27, 2006 - 10:08 am: |
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JB,
Thanks for your reply. This has encouraged me to experiment using my test bench to attempt to achieve the power burst characteristic of a tuned exhaust. There is an excellent explanation of this including a very useful animation at
http://www.southernskies.net/page_info/runningtwostrokeengine.html
Anyone who is operating two cycle engines will find this site very interesting.
You referred to a patent in your Dec 25 post. Would you please let me know the patent number.
Thanks again and regards
Barry |
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