Page 12 of 33 FirstFirst ... 2101112131422 ... LastLast
Results 166 to 180 of 492

Thread: the clean two-stroke thread

  1. #166
    Join Date
    22nd November 2013 - 16:32
    Bike
    STRIKE trike & KTM300 EXC TPI
    Location
    Perth, Western Australia
    Posts
    878
    A compression ratio question. For my initial phase UHV project where:
    -106 cc aircooled
    -test rpm of around 3800 rpm
    -power level around 2 hp (low I know, but gotta start somewhere and if it 2 strokes at light load then that is a good thing)

    Just wonder what CR I should be looking at. Have been using 15:1 (total), but thought it may be wise to get some opinions. This would be based on the volume calculated to the end of the plug thread, ie where the thread is flush with the chamber face.
    "Success is the ability to go from one failure to another with no loss of enthusiasm.”

  2. #167
    Join Date
    20th January 2010 - 14:41
    Bike
    husaberg
    Location
    The Wild Wild West
    Posts
    11,823
    Quote Originally Posted by ken seeber View Post
    A compression ratio question. For my initial phase UHV project where:
    -106 cc aircooled
    -test rpm of around 3800 rpm
    -power level around 2 hp (low I know, but gotta start somewhere and if it 2 strokes at light load then that is a good thing)

    Just wonder what CR I should be looking at. Have been using 15:1 (total), but thought it may be wise to get some opinions. This would be based on the volume calculated to the end of the plug thread, ie where the thread is flush with the chamber face.
    I am not wise but i remember something somewhere about squish and pollution.
    I can't remember why but maybe its due to the unburnt area. It was counter intuitive what would have the best hpmight not have being the best burn.
    Quote Originally Posted by Katman View Post
    I reminder distinctly .




    Kinky is using a feather. Perverted is using the whole chicken

  3. #168
    Join Date
    4th September 2017 - 10:39
    Bike
    Daelim besbi 2008
    Location
    España
    Posts
    300
    Quote Originally Posted by ken seeber View Post
    A compression ratio question. For my initial phase UHV project where:
    -106 cc aircooled
    -test rpm of around 3800 rpm
    -power level around 2 hp (low I know, but gotta start somewhere and if it 2 strokes at light load then that is a good thing)

    Hi Ken
    His work together with that of Katinas, are very useful if you want to make a pump driven by crankcase fluctuation.
    Thank you

  4. #169
    Join Date
    20th April 2011 - 08:45
    Bike
    none
    Location
    Raalte, Netherlands
    Posts
    3,341
    Quote Originally Posted by ken seeber View Post
    A compression ratio question. For my initial phase UHV project where:
    -106 cc aircooled
    -test rpm of around 3800 rpm
    -power level around 2 hp (low I know, but gotta start somewhere and if it 2 strokes at light load then that is a good thing)
    Just wonder what CR I should be looking at. Have been using 15:1 (total), but thought it may be wise to get some opinions.
    Two-stroking at light load is a good thing indeed. The two-stroking means no unburned HC emission due to misfiring caused by insufficient mixture quantity, purity or igniteability, and the light load means no NOx-production and low thermal stresses for the engine. In the case of Ken's UHV it specifically means low thermal and pressure stresses for the reeds.

    A low compression ratio would contribute to reducing these stresses, but it would also reduce the engine's thermal efficiency. Its specific fuel consumption would go up and the environment would suffer (I remember the times when we did't yet have an environment and petrol cost 40 cents a liter. Those were the days).

    As in any engine, combustion should be rapid, which requires squish and a compact combustion chamber. Or Homogeneous Charge Compression Ignition, but HCCI requires a high BMEP, which could be detrimental to the reeds, so unfortunately I cannot see a combination of UHV and HCCI.

    Squish then. The present UHV layout seems to permit a fairly tight squish gap; the reeds only need room to move when the piston is away from TDC. And anyway, if the reeds were closing too slowly, the piston would help them, like it would 'help' the exhausts valves in a four-stroke.

    The reed layout that Ken showed us the other day, might produce something other than squish, namely tumble. In a four-stroke, tumble is a welcome substitute for squish. But for a two-stroke I'm not so sure, because tumble will give a thorough mixing of fresh charge and exhaust gases. Four-strokes nowadays thrive on Exhaust Gas Recycling. In a two-stroke it would rather be Exhaust Gas Retention and I've always tried to avoid that. But then I've always tried to find power, while Ken's goal is to save the environment. Maybe it's time to reconsider my goals.

  5. #170
    Join Date
    10th February 2005 - 20:25
    Bike
    1944 RE 1
    Location
    Auckland, New Zealand.
    Posts
    2,243
    Quote Originally Posted by Frits Overmars View Post
    Two-stroking at light load is a good thing indeed. The two-stroking means no unburned HC emission due to misfiring caused by insufficient mixture quantity, purity or igniteability, and the light load means no NOx-production and low thermal stresses for the engine. ................................................. But then I've always tried to find power, while Ken's goal is to save the environment. Maybe it's time to reconsider my goals.
    FRITS
    Although I have not mentioned the word "tumble" ( only found it when I started delving into what other people were thinking and found that was what it was being called!), so now I realize I have been an advocate for "tumble" for quite some time -maybe a couple of years, to be more precise!.

    However, you are discussing it in terms of the "normal" two stroke operation ( Schnurle transfer, tuned exhaust, expansion chamber, squish etc etc) where I feel it will only introduce more problems. - but contrary to your view as encouraging mixing of fresh and used gases. In the OP engine layout I see it also as a means of peventing mixing, by forming a slower self contained moving plug - could that be considered a possibility??

    So for quite a while I have been proposing OP type despite its PAL (potentially awkward layout) but suitable for using HCCI, combined with my own ideas on how to introduce a "tumble" type fresh charge to the cylinder, also variable compression for startup, no more crankcase pumping (to give it the chance of proper lubrication), using a turbocharger etc. - this whole layout being (to my mind) much more useful than the "mixing pot" that the common (successful till now) Schnurle system tends to produce by swirling at high speed through the used charge still in the cylinder! - some people may make claims to the contrary!

    Not at all meaning to decry other peoples' ideas and efforts of course - all ideas valid for rearranging the two stroke for its survival do need to be considered!

    My big problem of course is that relatively speaking, I am a layman here (and not trying to compete with anyone) - I realize that most of you guys could shoot me down in flames if you felt like it! - (if you do feel that way, do so - then I'll have learnt a bit more!) ............ I'm willing to take that risk, but it sometimes feels like..... and then sometimes, am I right or wrong? .....
    Last edited by WilDun; 13th August 2020 at 15:28. Reason: addition (end of 2nd paragraph)
    Strokers Galore!

  6. #171
    Join Date
    22nd November 2013 - 16:32
    Bike
    STRIKE trike & KTM300 EXC TPI
    Location
    Perth, Western Australia
    Posts
    878
    Quote Originally Posted by Frits Overmars View Post
    Two-stroking at light load is a good thing indeed. The two-stroking means no unburned HC emission due to misfiring caused by insufficient mixture quantity, purity or igniteability, and the light load means no NOx-production and low thermal stresses for the engine. In the case of Ken's UHV it specifically means low thermal and pressure stresses for the reeds.

    A low compression ratio would contribute to reducing these stresses, but it would also reduce the engine's thermal efficiency. Its specific fuel consumption would go up and the environment would suffer (I remember the times when we did't yet have an environment and petrol cost 40 cents a liter. Those were the days).

    As in any engine, combustion should be rapid, which requires squish and a compact combustion chamber. Or Homogeneous Charge Compression Ignition, but HCCI requires a high BMEP, which could be detrimental to the reeds, so unfortunately I cannot see a combination of UHV and HCCI.

    Squish then. The present UHV layout seems to permit a fairly tight squish gap; the reeds only need room to move when the piston is away from TDC. And anyway, if the reeds were closing too slowly, the piston would help them, like it would 'help' the exhausts valves in a four-stroke.

    The reed layout that Ken showed us the other day, might produce something other than squish, namely tumble. In a four-stroke, tumble is a welcome substitute for squish. But for a two-stroke I'm not so sure, because tumble will give a thorough mixing of fresh charge and exhaust gases. Four-strokes nowadays thrive on Exhaust Gas Recycling. In a two-stroke it would rather be Exhaust Gas Retention and I've always tried to avoid that. But then I've always tried to find power, while Ken's goal is to save the environment. Maybe it's time to reconsider my goals.
    Good stuff Frits,

    Yes, there is a bit of a dichotomy between power and emissions. Interestingly, in some situations, the improvements of one can benefit the other.

    At the end of the day, one just doesn’t want to lose any unburnt fuel out the exhaust, unless for some obscure reason like post combustion heating up of the exhaust for tuning or catalyst reasons.

    Not sure at all what pressure the reeds will take under running conditions, but time will tell. It will also tell of the “asymmetric “ layout (the cactus) that I am currently preparing will also be of any benefit. When completed, I intend to do a proper back to back shootout, on same day, of all the combinations and lay bare the results.

    One possibly secondary benefit of the UHV is that it will allow additional cylinder charging after exhaust port closure, say using a blower or turbo.
    "Success is the ability to go from one failure to another with no loss of enthusiasm.”

  7. #172
    Join Date
    4th December 2011 - 22:52
    Bike
    Yamaha XJ750 1982
    Location
    South Africa
    Posts
    219
    Quote Originally Posted by WilDun View Post
    FRITS
    Although I have not mentioned the word "tumble" ( only found it when I started delving into what other people were thinking and found that was what it was being called!), so now I realize I have been an advocate for "tumble" for quite some time -maybe a couple of years, to be more precise!.

    However, you are discussing it in terms of the "normal" two stroke operation ( Schneurle transfer, tuned exhaust, expansion chamber, squish etc etc) where I feel it will only introduce more problems. - but contrary to your view as encouraging mixing of fresh and used gases, in the OP engine layout I see it also as a means of peventing mixing, by forming a slower self contained moving plug - could that be considered a possibility??
    Two things:
    1. A loop scavenged engine is using tumble - the loop flow by its very nature is the tumble motion, the trick is to control the tumbling speed.
    2. OP engine has a serious issue with scavenging, you pretty much have to choose between swirling flow and plug flow or come up with something new.

    Swirling flow by its centrifugal motion displaces the fresh charge to the outside and can create a down flowing central column of burn gas, leading to low scavenging efficiencies. There are a large number of publications available on this topic.

    Plug flow in an OP engine seems to be a neglected topic.

  8. #173
    Join Date
    20th April 2011 - 08:45
    Bike
    none
    Location
    Raalte, Netherlands
    Posts
    3,341
    Thank you Neels. I was contemplating a response to WilDun's remarks, but you said it all.
    I would try to avoid swirl in any engine that has circumferential exhaust ports. I think swirl only makes sense in engines like the giant marine diesels with overhead exhaust valves that offer a way out for the trapped central column of burnt gas.

    I try to approach plug flow in conventional two-strokes and I use proper plug flow in my FOS symmetrical scavenging system. By the way, Neil Hintz has cylinders with this same scavenging laying about, from his sleeve valve engine .
    Click image for larger version. 

Name:	HVG 2011-11-02-02.jpg 
Views:	77 
Size:	75.7 KB 
ID:	346763 Click image for larger version. 

Name:	FOS @ JWSPORT-06.jpg 
Views:	79 
Size:	48.4 KB 
ID:	346762

  9. #174
    Join Date
    12th March 2010 - 16:56
    Bike
    TT500 F9 Kawasaki EFI
    Location
    Hamilton New Zealand
    Posts
    2,764
    Quote Originally Posted by Frits Overmars View Post
    Thank you Neels. I was contemplating a response to WilDun's remarks, but you said it all. I would try to avoid swirl in any engine that has circumferential exhaust ports.
    I think swirl only makes sense in engines like the giant marine diesels with overhead exhaust valves that offer a way out for the trapped central column of burnt gas.

    I try to approach plug flow in our conventional two-strokes and I use proper plug flow in my symmetric scavenging FOS system. By the way, Neil Hintz has cylinders with this same scavenging suystem layout about .
    And I have a new cylinder with a new layout.

    I'm desperately trying to find time finish and test this new concept, but work keeps getting in the way bugger it. We might be in for another Covid lock down here in NZ shortly,
    What Im really missing is a heat treating oven, then Im largely self sufficient, trade me time.

  10. #175
    Join Date
    20th April 2011 - 08:45
    Bike
    none
    Location
    Raalte, Netherlands
    Posts
    3,341
    Quote Originally Posted by Frits Overmars View Post
    I would try to avoid swirl in any engine that has circumferential exhaust ports. I think swirl only makes sense in engines like the giant marine diesels with overhead exhaust valves that offer a way out for the trapped central column of burnt gas.
    Come to think of it, with scavenging ports at one end of a cylinder and circumferential exhaust ports far, far away at the other end, swirl might not be quite so bad. Still, I think I'd prefer plug scavenging.

  11. #176
    Join Date
    10th February 2005 - 20:25
    Bike
    1944 RE 1
    Location
    Auckland, New Zealand.
    Posts
    2,243
    I'll have to sit down and digest all that properly! - well, after all, I did ask for it really! - now you guys have gone and upset my rythm!

    Frits, on your FOS cylinder - could it be that the (normal) curvature of the transfer ports creates something akin to "swirl" like situation, causing the oil, petrol and air to separate in the passage with the oil and petrol being introduced perilously close to the outgoing exhaust gases? - the oil then becoming (as it were ) the "boundary layer" between the fresh and spent gases moving in opposite directions?

    Anyway, as I said I guess I'll have to sit down and ponder everything in the last few posts a bit more! - but tomorrow - it's bedtime here!

    BTW. we are in stage 3 lockdown in Auckland ..... again!
    Strokers Galore!

  12. #177
    Join Date
    20th April 2011 - 08:45
    Bike
    none
    Location
    Raalte, Netherlands
    Posts
    3,341
    Quote Originally Posted by WilDun View Post
    Frits, on your FOS cylinder - could it be that the (normal) curvature of the transfer ports creates something akin to "swirl" like situation, causing the oil, petrol and air to separate in the passage with the oil and petrol being introduced perilously close to the outgoing exhaust gases? - the oil then becoming (as it were ) the "boundary layer" between the fresh and spent gases moving in opposite directions?
    For clarity: swirl is a gas rotation around the longitudinal cylinder bore axis. Generating swirl would require tangentially-aimed ports, but I took great care in aiming all six of my transfer ducts radially, so I don't think there is any swirl in the FOS cylinder; at least I hope not.

    Because of the curvature of just about every transfer duct there will be a tendency to fling the heavy petrol and oil droplets to the duct's outer walls. Lubricating the opposite gas movements in the boundary layer is an amusing thought, I must say Will. It's one of those things that I hadn't thought of until you pointed me at it .

  13. #178
    Join Date
    12th October 2016 - 01:24
    Bike
    1964 Vespa GS
    Location
    San Francisco
    Posts
    101
    If the OP has a smaller exhaust piston then the swirl would be contained somewhat from flowing out of the radial exhaust.
    Patrick Owens
    www.OopsClunkThud.com

  14. #179
    Join Date
    12th March 2010 - 16:56
    Bike
    TT500 F9 Kawasaki EFI
    Location
    Hamilton New Zealand
    Posts
    2,764
    Quote Originally Posted by OopsClunkThud View Post
    If the OP has a smaller exhaust piston then the swirl would be contained somewhat from flowing out of the radial exhaust.
    My boat uniflow engine utilized differential size pistons, exhaust smaller. 50 against 56, so made for a small squish area, also makes the combustion chamber a less awkward shape. This engine would run to 9500 rpm under load, non tuned pipe.
    It has six transfers, two from one crankcase creating a small amount of swirl with the other four creating a central plume. Interestingly the central plume fuel was overly rich, 66%, outside swirl at 33%. This was to help fuel cool the exhaust pistons.
    This was all done 25 years ago.

  15. #180
    Join Date
    12th October 2016 - 01:24
    Bike
    1964 Vespa GS
    Location
    San Francisco
    Posts
    101
    Quote Originally Posted by Flettner View Post
    This was all done 25 years ago.
    and still seems highly relevant
    Patrick Owens
    www.OopsClunkThud.com

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •