tag:blogger.com,1999:blog-411220736004281930.post2852411056057292684..comments2023-11-16T02:33:36.383-08:00Comments on Yorkshire Ferret: Geoffrey Roe: The Annular Discharge SilencerThe Yorkshire Ferrethttp://www.blogger.com/profile/18230250521199517256noreply@blogger.comBlogger11125tag:blogger.com,1999:blog-411220736004281930.post-61671535526140436162023-03-19T05:34:05.296-07:002023-03-19T05:34:05.296-07:00This comment has been removed by the author.GespannFahrerhttps://www.blogger.com/profile/16779310802547278606noreply@blogger.comtag:blogger.com,1999:blog-411220736004281930.post-68933522646783588002022-08-30T10:04:06.986-07:002022-08-30T10:04:06.986-07:00This comment has been removed by the author.GespannFahrerhttps://www.blogger.com/profile/16779310802547278606noreply@blogger.comtag:blogger.com,1999:blog-411220736004281930.post-68823899846219511752022-02-17T02:43:20.860-08:002022-02-17T02:43:20.860-08:00Further to my earlier comments (as Ken) - I have j...Further to my earlier comments (as Ken) - I have just re-read the article: Drs. Roe and Thorpe presented their "motorcycle improvements from research" to the Liverpool University Motorcycle club in 1974 - or 75. This stimulated a design I produced for a 400kV circuit breaker silencer: To silence an air motor that was discharging 28bar of air to atmosphere from a 10in diameter x 5 in stroke cylinder. I managed to drop 9dBA from the "open pipe" to "Silenced" condition - as a comparison at 1m from the exit orifice. (similar to the 1m stick the Noise adjudicator used at Aintree!). But I did not use Helmholtz resonators: The air passed into the central larger tube, thence via 4 sets of holes into the outer annulus, and by "pressure wave chopping" and the different speeds of sound inside the large central tube (from exhaust pipe) and the outer annulus (to atmosphere) caused a higher frequency and lower peak magnitude noise: A rifle shot instead of a cannon "boom". So the circuit breaker could not be heard at the nearest village to the sub-station. (unlike previous designs!). I am not an acoustics engineer, so actually cannot calculate what was happening. But there was some adiabatic expansion cooling of the air blasting down the silencer tubes, as they always has a good layer of condensation develop on the outside of the cold steel tubes after an operation. I suspect the Bike silencers also had this effect, though not so cold as the start temperature was much higher.<br />KenAnonymoushttps://www.blogger.com/profile/17587384450961202599noreply@blogger.comtag:blogger.com,1999:blog-411220736004281930.post-24393224299064402892022-01-10T06:01:43.507-08:002022-01-10T06:01:43.507-08:00This comment has been removed by the author.GespannFahrerhttps://www.blogger.com/profile/16779310802547278606noreply@blogger.comtag:blogger.com,1999:blog-411220736004281930.post-39273583920999433332022-01-10T05:55:26.991-08:002022-01-10T05:55:26.991-08:00This comment has been removed by the author.GespannFahrerhttps://www.blogger.com/profile/16779310802547278606noreply@blogger.comtag:blogger.com,1999:blog-411220736004281930.post-78833201363427891122022-01-10T05:23:13.785-08:002022-01-10T05:23:13.785-08:00This comment has been removed by the author.GespannFahrerhttps://www.blogger.com/profile/16779310802547278606noreply@blogger.comtag:blogger.com,1999:blog-411220736004281930.post-29519477213735225782021-08-07T23:27:44.114-07:002021-08-07T23:27:44.114-07:00Further memories of racing bike silencing: Between... Further memories of racing bike silencing: Between 1973 and 1979 I was a volunteer marshall at Aintree race course with the dubious pleasure of managing the the exit from pits and start zone (grid positioning of riders). (Waterloo and District MCC meetings). This meant I spent all day alongside bikes that were being revved to warm them up.... while the ACU Noise-meter-man checked random bikes with his meter and notched stick. I think the lads had to rev their engines to 3000rpm or 50% of the red-line on their tacho, whichever was higher. - Or something like that. I was curious to note that from the earliest meetings to a couplke of years later, how silencers appeared first on the tail-pipe of expansion boxes of the 2-strokes, but also the short large cans (annular disharge types?) on 4-stroke exhaust pipes. I didn't have a comparison between unsilenced and silenced bikes, and my hearing today is well knackered... perhaps in part due to the 105 dBA I experienced for most of a 10 hour shift at Aintree? - Those were the days before we heard of Elf and Safety....Anonymoushttps://www.blogger.com/profile/17587384450961202599noreply@blogger.comtag:blogger.com,1999:blog-411220736004281930.post-88010311124798923342021-08-07T23:15:47.938-07:002021-08-07T23:15:47.938-07:00My curiousity was originally aroused in 1972 when ...My curiousity was originally aroused in 1972 when I owned an Honda CB77 motorcycle - bought second-hand without baffles. after a few months of "loud" exhausts, I was advised by another motorcyclist (doing a Mech. Eng. degree) that the back pressure was wrong for initial carburation and I should buy and fit replacement baffles. He was right, not only was the bike as quiet as new, but low speed torque certainly felt better and economy improved. I can't say the top speed was changed. I understand the Honda design uses 2 or 3 external annular chambers in the silencers, with the central exhaust pipe passing these. The inner wall of these chambers is made by the baffle pipe, having strategically placed holes that align with each outer resonant chamber. Each resonant chamber - both on the Honda design and the annular disharge silencer - acts as an Helmholtz resonator: I think?<br />This is not new technology in principle: (see GM paper https://www.jstor.org/stable/44437706?read-now=1&seq=3#page_scan_tab_contents). <br />However, I understand that the Annular discharge silencer has some other advantages. If the main exhaust stream is passing down the centre of the silencer, then there is less opportunity for the gas to lose energy (heat) because it is surrounded by chambers of hot exhaust - acting as insulation. Although some heat is lost by the pressure wave entering then later leaving the chamber, this is small in comparison to the conducted heat from the hot gas, through the metal to atmosphere. But this conducted heat is also small in comparison to the heat dumped out of the tail-pipe. However, with the annualr discharge silencer, the hottest gas of the exhaust stream is changing prerssure to velocity in the thin annulus, of which the outer shell is exposed to atmospheric temperature. Thus heat from the exhaust gas main stream, as well as frictional heating from the fast gas stream adjacent to the silencer outer wall, heats the silencer wall and thus loses this heat to the outside atmosphere. This in turn has an extra sound deadening effect as it is extracting energy from the exhaust stream. While I am not clever enough to crunch the numbers, it would be interesting to know if my postulations are correct? Any thoughts?<br />KenAnonymoushttps://www.blogger.com/profile/17587384450961202599noreply@blogger.comtag:blogger.com,1999:blog-411220736004281930.post-43342059061533186592020-04-19T03:44:47.964-07:002020-04-19T03:44:47.964-07:00Essentially, the exhaust gases do something very s...Essentially, the exhaust gases do something very simple: (1) expand into the first chamber, then 2 Pass into the annulus: After that they pass 3 more chambers that contain "absorption" material. Each chamber is tuned for a frequency: based on the hole size and volume of the chamber. If you look inside original part car manufacturers' silencers, some of them do the same science. just the box is a different shape. If you look at the intake of most modern cars, there are "plastic boxes" stuck on the side of the air intakes to do the same "resonant damping" to reduce noise. For the air intake, dampers are fitted at the engine revs and load (i) for the drive-by noise test, (ii) for cruising at 70mph or 120kph. in top gear. These 2 phases are particularly quiet when driving and make the car more saleable. Which is what Dr. Roe was doing. The torque change was a bonus from "resonance" I guess? Where the "noise" dissipated and pressure either sucked-in more mixture, or allowed more exhaust out, or pushed some exhaust back into the cylinder to alter combustion and energy exchange for the gases.... just as happens today in your average car or motorcycle. In fact, Velocette, Villiers et al were all doing this from 1930s onwards, especially with 2-strokes. But - not to ignore 4-strokes - Brough and others used fish-tails the same way. Please correct me if I have got this wrong - I love to learn!Anonymoushttps://www.blogger.com/profile/17587384450961202599noreply@blogger.comtag:blogger.com,1999:blog-411220736004281930.post-87493275565826849882020-04-19T01:04:20.428-07:002020-04-19T01:04:20.428-07:00Hi,
I was inspired by a lecture in '73 or '...Hi,<br />I was inspired by a lecture in '73 or '74 by Dr. Roe., attended by the Liverpool University Motorcycle Club. The design was later shown in a bike magazine - and I kept a copy of the article. Understanding the principle of gas Velocity and Pressure relationship, down a pipe with a series of holes... and being shown by Dr. Roe that the CSA of holes per length of travel down the tube needs to follow an hyperbolic function... I followed a sort-of copy of the silencer when I worked on Circuit Breakers at Reyrolle Power Switchgear. The air exhaust (A few litres of air at 28bar) down a pair of 3in diameter pipes was a bit like the single opening of an exhaust valve from a "big single" - at least in my imagination. I managed to get a reduction on 136dBA to 124dBA at 1m from the outlet with the silencers I copied from Dr. Roe's work. This meant we achieved the certification for noise at 30m and 100m from the circuit breaker when operated. I now use this knowledge to design diffuser tubes for gas burners as a hobby.. THANKS Dr. Roe! A Great Tutor and Engineer.Anonymoushttps://www.blogger.com/profile/17587384450961202599noreply@blogger.comtag:blogger.com,1999:blog-411220736004281930.post-19528120176891119652016-12-12T23:38:47.289-08:002016-12-12T23:38:47.289-08:00Interesting, thanks again.Interesting, thanks again.GreginAdelaidehttps://www.blogger.com/profile/11700327727868020300noreply@blogger.com