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Converting 4 stroke to 2 stroke

Ideas on Converting 4 stroke engine to 2 stroke for power or economy
  [vote for,

My logic is you could use the same cam of a 4 stroke to make it run a 2 stroke cycle.

The order of operations (starting at TDC) of a 4 stroke is 1.suck 2.squeeze 3.bang 4.blow.

If you change the order so it is 1.bang 2.blow 3.suck 4. squeeze or the ideal of 1.bang 2.suck/blow 3. squeeze with timings of 1.0-90deg 2.90-270deg (exhaust opening just before intake opens and intake closing just after exhaust closes) 3.270-360 you would have a 2 stroke cycle from a two stroke engine. A supercharger would be required to push air in and exhaust out.

For higher efficiency a rotating tube with hole in at the correct times could be used as a camshaft/valve system. This idea was used on the Norton 500cc motorbike engines and was thought of by Lawie Bond and developed by Norton.

Any ideas on my theory? thanks Nick

randylandy666, Aug 25 2007

(?) Norton Rotary Overhead Valve http://www.dself.ds...aryValveIC.htm#nort
See the Norton section to see what im on about. It could be chain or gear driven like todays camshafts are instead. [randylandy666, Aug 25 2007]

(?) Lawrie Bond http://web.ukonline...e/Racing%20cars.htm
He sounds like a halfbaker. [normzone, Aug 25 2007]

The idea of using a supercharger to make a clean two stroke High_20performance_...4_20stroke_20engine
Needless to say, halfbaked. [acurafan07, Aug 25 2007]

Miller Cycle http://en.wikipedia.org/wiki/Miller_cycle
How it works [acurafan07, Aug 25 2007]

(?) Ram Air Exhaust Ram_20air_20exhaust
My idea for a way to create an exhaust blower using the venturi effect. [acurafan07, Aug 26 2007]

Steam/exhaust hybrid Steam_20Anti_20Turbo-Lag_20System
steam turbo [randylandy666, Aug 28 2007]

Steam/exhaust hybrid Steam_20turbo
and again! [randylandy666, Aug 28 2007]

Variable Displacement http://en.wikipedia...riable_displacement
Similar, but baked, idea [Spacecoyote, Jan 13 2008]


       wouldn't work. you have dangerous left over gas inside the cylinder after the exhaust because the airflow is only going from the intake to the exhaust valves, a very show distance. also even if you were able to get the airflow just right how do you suppose your going to to get air in and out of the cylinder in the very small fraction of a secant after the power stroke?
F_R_O_G, Aug 25 2007

       See link. The problem with using any type of compressor to scavenge a 4-stroke and make it a 2-stroke, you see, is that you must first create a compressor that allows the engine to make more power as a 2-stroke with scavenger and no boost than a 4-stroke with boost.
acurafan07, Aug 25 2007

       "The order of operations ... of a 4 stroke is 1.suck 2.squeeze 3.bang 4.blow.   

       .. change the order so it is 1.bang 2.blow 3.suck 4. squeeze or the ideal of 1.bang 2.suck/blow 3. squeeze"   

       ... that's what she said.
globaltourniquet, Aug 25 2007

acurafan07, Aug 25 2007

       The idea needs some work, but not bad for a first post.   

       No need to sigh like "OMG you SHOULD have known SHEESH" if your idea is already thought of.   

       Don't let rudeness from posters discourage further posts, btj I urge you to read the help and not listen to negative nancy's like we got on this site.   

       Welcome randylandy666
Giblet, Aug 25 2007

       Thanks for the comments guys F_R_O_G: maybe if there was a vacuum on the exhaust? it could pull the exhaust gasses out and incourage the fuel/air or just air for a diesel into the combustion chamber?   

       acurafan07: I am aware of whats on the halfbakery already but no one mentioned any timings or cycles so i was presenting those for comment.   

       globaltourniquet: i didnt quite see the meaning of the post unless you were highlighting the point i just made to acurafan07   

       Giblet: thanks for the warm welcome any suggestions to perfect the recipe so we can bake? lol Thanks Nick
randylandy666, Aug 25 2007

       [randy] - it's a sexual innuendo, a joke. People of certain... mindsets shall we say... occasionally see what are called "double meanings" in certain turns of phrase, and it's a common method of humorously drawing attention to said double meaning, or innuendo, by following the said phrase with the response "That's what she said", indicating that in an imagined recent sexual encounter, your lover had said the same phrase in response. It's fun and amusing. Try it yourself the next time someone says something like "My, how you've grown!"
globaltourniquet, Aug 25 2007

       Sorry if my comments were interpreted as overly negative. I agree that for a first post this is very good.
acurafan07, Aug 25 2007

       thanks global i am normally of tht mindset but it was 4am when i posted this and i had just woken up when i had read your first annotation and missed the last line however due to my comic nature and certain mindset i use the sexual innuendos commonly and i now am wetting myself laffing at the other other meanings but pray tell my do u prefer 2 or 4 stroke cycle? o btw names nick the randylandy666 just random junk lol   

       acura thanks for the appology and the praise but any more comments on how to improve the idea??   

       thanks Nick
randylandy666, Aug 25 2007

       Well for starters the least restrictive exhaust possible would be good to aid in the scavenging (see my idea for a Ram Air Exhaust for one possibility). Also, you might want to make the camshafts such that they create a Miller Cycle effect (and I assume you're talking about either a roots-type or twin-screw supercharger for the engine). Since the supercharger has no time to actually compress the air into the cylinder (it is busy scavenging the exhaust and replacing), making it a Miller Cycle will help a lot. (See link). Oh, and direct injection is a must.
acurafan07, Aug 25 2007

       Thanks acura is there a link to your exhaust? would a centrifugal supercharger work? they are lighter and more efficient and also more compact so they will fit a variaty of engines?   

       The line im thinking along are for diesel because they already have an injection system and can be used with veg oil and the like for cheaper running on agricultural machines that need higher power outputs   

       any ideas on order of operations so we can have another giggle?   

       thanks Nick
randylandy666, Aug 26 2007

       Sorry Nick but if you wanted to use diesel as your fuel you'd be working on an already baked concept. 2-stroke diesels exist, and in a way quite like this. Actually pretty much exactly like this. As for the scavenging I'm pretty sure I've read somewhere that only positive displacement blowers (not centrifugal) work for scavenging. I could be wrong, however.
acurafan07, Aug 26 2007

       i do know they exist they are built by detroit but i was just thinking that i havent seen 4 strokes converted before thanks Nick
randylandy666, Aug 26 2007

       I don't think there are any showstoppers for converting a four-stroke diesel to a two-stroke. You'd have to change the heads and obviously change the camshaft(s).   

       I strongly recommend adding a turbo to a two-stroke anything - pressurizing the intake cycle gives that much more bang per unit swept volume, and in a diesel gives much, much better scavenging of the cylinder. Upside of this is: virtually all the diesel engines that are expected to run long times at moderate to high outputs are already turbocharged. In your proposed agricultural application, that describes your idea to a T.   

       One last bit about converting: the cooling passages of a four-stroke are not engineered for the heat load of a two-stroke, and I guarantee you that a two stroke is going to be much hotter than a four-stroke of similar displacement. Generally, the idea of using a two-stroke is to make more power from a similar volume, or the same power from a much smaller engine package. Generating more power also means generating more waste heat, but as far as the engine goes, so far all you've changed is valve timing. Switch out heads to one that is designed with more and bigger coolant passages, and increase the size of the radiator.   

       Or better yet, get a Detroit Diesel that was designed as a two-stroke in the first place.
elhigh, Aug 27 2007

       [elhigh], but wouldn't adding a turbo create too much backpressure for the scavenging?
acurafan07, Aug 27 2007

       thanks guys elhigh: i was thinking about that as it will be roughly twice the heat (twice the amount of explosions) and i saw this water pump that cools at the same time so if used in conjuction with the original cooling system could bring the heating part right down to where manufacturers designed it and it i was too use the rotary valves then a new head would be in order so thanks for highlighting the larger cooling passages needed   

       acura: on the backpressure front on halfbakery there is talk of injecting water into the exhaust so it will expand and spoool up the turbo so if you did this wouldnt it create a vacuum and give me more power?   

       thanks Nick
randylandy666, Aug 27 2007

       Eh... not exactly a vacuum. You see, the pressure from the steam will choose the path of least resistance. When the exhaust valve is closed, that is the turbocharger. But as the steam is expanding (and this is unavoidable), the exhaust valve will open and the pressure will try to get into the cylinder. I'm sure there could potentially be a way to create enough boost to make this not a big problem, but I'm not sure how well it would work.   

       What idea are you talking about exactly with the backpressure?   

       A supercharger would definately be better. If you want to use steam, make something like a steam turbine alternator that doesn't cross the exhaust's path to create electricity for an electric motor that could perhaps aid the supercharger in create boost.
acurafan07, Aug 27 2007

       [acurafan07]"that only positive displacement blowers (not centrifugal) work for scavenging."   

       I can't see why this would be true. However, both models of 2stroke I've worked on, the 6-series Detroit and the Fairbanks O-P, use positive displacement superchargers. Really all you have to do to scavenge is create a good breeze, which a centrifugal will do. Also, a centrifugal is more efficient and can move more volume, but won't be able to make as much pressure (assuming valve timing would allow for supercharging). I think the biggest problem here is that the scavenging air isn't going to sweep much spent gas from the cylinder. Many two-cycle gasoline engines use specially shaped piston crowns and head chambers to 'loop' the intake charge through as much of the cylinder as possible to remove spent gas. If it were possible to design the intake port as a sort of 'air jet' that could force the scavenging charge directly at the crown of the piston, perhaps the piston could be shaped to direct this charge toward the exhaust valve. This may also help with cooling of the crown (as would oil spray to the underside of the piston coupled with an oil cooler). I suggest you forget the turbo, as I believe that it would create too much backpressure for efficient two-cycle operation. Certain amounts of backpressure are neccessary in gas 2-cycles to prevent the fuel/air charge from blowing right out with the scavenge, but this is not a factor with Diesel cycles.
wittyhoosier, Aug 28 2007

       All these anno's and I was the first to vote!?
wittyhoosier, Aug 28 2007

       thanks guys shall i open an idea on the most efficient design for a 2stroke as its startin to seem like im redesigning the whole engine?   

       acura: if the exhaust grew larger where the water injector was then the path of least resistance is definately outwards would this work?   

       witty: seeing as a majority of diesels have turbos wouldnt be better to keep it? mind you if you replaced the exhaust section with a pully and put it on the ancillery belt then you would have a centrifugal charger for almost free   

       thanks Nick
randylandy666, Aug 28 2007

       Yes it would, but making it grow larger would also have to make the entire turbocharger larger to keep it as the path of least resistance. Like I've said, I'm sure it can be done, I just think a supercharger would be better.   

       I also see that you linked to my idea. You'll note that the steam is injected onto the pistons to expand out of the cylinder with the rest of the spent gasses to prevent steam backpressure, and there's the added bonus of capturing more heat than was otherwise possible (since the pistons would almost certainly have more heat than the exhaust system would absorb).
acurafan07, Aug 28 2007

       accura: it would also cool things down wouldnt it? thanks Nick
randylandy666, Aug 28 2007

       Sure would. In fact the Crower 6-stroke engine doesn't need any cooling system because it uses a steam cycle.
acurafan07, Aug 28 2007

       yea good idea that miller cycle 2stroke diesel with crower last two cycles with turbo and scharger runnin on veg oil on turned up injectors and water injection and hydrogen injection lol that would be pure power it could be a 1l with the power of a 3l thanks Nick
randylandy666, Aug 28 2007

       It is a good idea. Although I've already halfbaked the 2-stroke diesel Miller Cycle, and the last part is baked by Bruce Crower. The problem with water injection on a 2-stroke diesel (or any diesel) is that they actually use heat and compression for ignition, so it might actually interfere with your combustion abilities.   

       For the hydrogen injection, you could choose to run a steam turbine alternator off of the engine's waste heat and use the electricity for electrolysis. Although this is sure to be much less efficient than electric motors for a hybrid or an electric supercharger.   

       However I garuntee you that with this kind of thinking, it won't be long before you come up with a really good halfbaked engine idea.
acurafan07, Aug 28 2007

       @[acura] - there would be an increase in backpressure if he were to add a turbo, yes. But the turbo provides a much higher intake pressure, too: the better to force the old cylinder charge out and replace it with fresh. Putting the intake path under pressure makes it one heckuva lot more efficient than asking it to suck in an air charge from ambient pressure.   

       It's a generalisation - which means that under certain conditions it is probably incorrect - that turbocharging and diesels go hand in hand. I've yet to see an application where a turbodiesel's performance wasn't in every way superior to an otherwise identical NA diesel. I think even the specific fuel consumption goes down. Lord knows, with a higher output you can get by with a smaller engine.   

       Just think, a two-cylinder two-stroke turbodiesel should have comparable performance to a conventional diesel of twice the cylinders and displacement. The actual engine could be slightly more than half the size. The radiator would have to be the same, though. Imagine how tiny an engine bay you could get by with. Or better still, replace the engine in what you're driving now, with this thing. There'd be an awful lot of extra space under the hood.
elhigh, Aug 28 2007

       Actually [elhigh], my comments about diesels were in relation to the Crower Cycle, not turbocharging in general. I was getting at the fact that it isn't necessarily a good thing to remove heat in a diesel using steam, since it uses it for compression ignition. I very much agree that the performance of a turbodiesel is superior to a naturally aspirated or supercharged one.   

       As to replacing a car engine with a 2-stroke diesel, as efficient as they may be, I'm not sure I could live without the thrilling high revs of a gasoline engine.
acurafan07, Aug 28 2007

       That's what she said.   

       thanks guys gd ideas all round!
randylandy666, Aug 28 2007

       that's what she said
F_R_O_G, Aug 29 2007

acurafan07, Aug 29 2007

       lol back to that are we? thanks Nick
randylandy666, Aug 29 2007

       Okay, I can see the fact of the "thrilling high revs" going away might be a bad thing - but I've never been big on high revs, though with strong turbocharging you could maybe shorten a diesel's stroke and get a buzzier engine. Don't forget though that valve float becomes a serious problem in two-strokes at around 3000-4000 rpm and only gets worse.   

       Could you make do with mountains of torque at off-idle speeds? Use of the first three gears is optional.   

       Crower himself said the steam cycle wouldn't do much for the diesel - it boosts output by about 40% on spark ignited engines, but only 5% on diesel. Probably for exactly the reason you mentioned, [acura].
elhigh, Aug 29 2007

       yea but elhigh it would spool the turbo up by some and give you more power it would also mean the two stroke would not be soo difficult to coool thanks Nick
randylandy666, Aug 29 2007

       But with a diesel you really don't have all the cooling issues.
acurafan07, Aug 29 2007

       dont you? i would of thought you would as you use high heat to make fuel self combust? thanks Nick
randylandy666, Sep 10 2007

       I got an idea. What if you get creative with the use of the cylinders?   

       I wonder if you can use 2 cylinders like pumps to make it into a positive pressure intake? You would throttle the exhaust or fuel/spark to control revs....   

       You are going to get a lot more charge into the cylinder, but I guess there is the risk of a big explosion in the intake manifold unless you go with careful timing and direct injection.
curado, Jan 13 2008

       This one is baked. There's a race-engine builder in California (can't remember his name, Google him yourself) who converted a 4-stroke Mercedes to 2-stroke just because he wondered what it would sound like. He also built a cool 6-stroke; 1-4: conventional, 5: water is sprayed onto hot piston head, 6: resulting steam not only expands to power additional stroke, but cleanses cylinder, promoting engine longevity.   

       (later) The guy's name is Bruce Crower. Thanx [RunnerPack]
Alterother, Mar 27 2008


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