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8 stroke engine
For all those people that want to make a 2 stroke engine... | |
The main purpose of this is to shorten the rod length and still have high compression without the use of slow turbos and week superchargers. A shorter rod would also help in engine stability. Because of this and the shorter rod, the rod can be made of a cheaper lighter material being able to make more
power.
Click the link to bring up the 8 stroke diagram... So it would go suck, squeeze, suck, squeeze, bang, blow, squirt, blow. I know the last two strokes have already been baked but I would need these to keep the 8 stroke engine cool because of little airflow at times and adding the two strokes would be more effective than adding them to a four stroke engine because of the large heated surface area and small stroke.
Another benefit of this design is the high pressure reservoir. By simply opening the reservoir valve while on the forth stroke you can cause a lot of turbulence.
One thing about the pictures is that the reservoir valve would be big enough to not cause any disruption in airflow. So it would not be as small as it shows.
diagram
http://s237.photobu...lbums/ff67/F_R_O_G/
ofcorce it didn't display them in the right order. you just have to look at them backwords [F_R_O_G, Aug 29 2007]
[link]
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Interesting, turning the cylinder into its own piston supercharger by adding a reservoir chamber. |
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Unfortunately, I think you lose any peformance gains from that one supercharged power stroke to the extra intake and compression stroke. You gain a small advantage by adding the Crower stroke, but I don't think it would be enough. Here's why: |
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Conventional four-stroke: four strokes, one of which is power. Power delivery = 25%
F_R_O_G cycle: eight strokes, two are power. Power delivery = 25%. But two of the idling strokes are loaded, as opposed to just one of the four-stroke. One of those is a light load, but still. And the delay between power strokes is longer, so the running quality of the engine would be very choppy. |
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Sorry. I don't think it's a goer. It probably would go, but not very well. |
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High compression is still attainable with a shorter rod length and stroke. Just look at any F1 engine. |
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And the fact that the Miller Cycle exists and works very well indicates that a "week" supercharger is, in fact, more efficient at compressing air than a piston. |
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I don't know, I like the completist idea that you could eventually select an engine with as many strokes as tickle your fancy. Regardless of the efficiency merits of this idea, I appreciate the "let's do it because we can" aspect of it. |
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Bunned to counteract a bone only. |
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Perhaps someone can come up with a 7-stroke engine with one big piston that is actually a small rotary engine, all driving a pump that feeds fuel and water into a steam boiler. |
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Think this would self-destruct after 3000 rpm, but it would be fun just because it's (probably) possible. |
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I want to know more about this week supercharger thing. My week is kind of dragging along and could really use a charge. |
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I just thought if the 8 was sideways, it would be an infinity stroke engine... I don't know how it would work though. |
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Are steam piston engines one stroke? |
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/My week is kind of dragging along and could really use a charge/ |
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It looks like 8 strokes is just what you need. |
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elhigh- on the first compression stroke there is very little resistance because of the large area to the stroke length, on the second compression stroke there is the same resistance as a normal 4stroke engine but for a shorter stroke meaning a shorter time. this would cause less power to be used to compress the same amount of air. |
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The engine would run very smooth because there much shorter strokes. |
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Your right that this 8stroke engine would be 2 power strokes to 8 strokes. 2 to 8 or 25% but consider this. I obviously haven't built and tested one of these so i don't know how much power i would get out of it but the 2 power strokes should provide more power than the power stroke of a comprable 4stroke engine. Also remember that because these strokes are shorter you could have a screaming engine running over twice as many RPMs as a normal 4stroke engine could. |
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acurafan07-
//a "week" supercharger is, in fact, more efficient at compressing air than a piston.//
that may be so, but don't forget the power loss in transferring the power to the supercharger. |
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BrauBeaton look at it again your missing a few things |
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The problem with the extra area where you plan to store this extra 2-stroke of air is that it adds to the overall displacement of the engine. So right when the engine goes through the 2nd compression stroke, this new area is opened for combustion to affect and transfer heat to (flatheads were not very thermally efficient). Sure you can try to use valve timing to keep combustion gasses from getting in, but it sounds like it would be almost impossible to prevent some problems. |
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So when you inject the water into that extra storage area, it has to first expand into the relatively large chamber before it can "push" the piston down. |
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You can't spin the engine "twice as fast" just because you have a short stroke. Yes, that reduces piston speed and reduces reciprocating weight, so there are certain increases in top speed to be had, but there are also valve float to consider. I could cheerfully run every engine out there (unless it says Ducati on it somewhere) right up to the redline until the valves started to bounce, and then all the fun stops. Sometimes it stops with a crunch. |
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Your short stroke design loses torque, so you have to rev it twice as fast to get the same output torque as before. Remember, it's torque that actually moves the car. "Horsepower" is a measurement that calculates the amount of torque generated vs. the rotational speed of the output shaft. |
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After the first compression stroke, the compressed charge is stored until TDC on the second compression stroke. Net result: effectively two low-compression charges in one cylinder, that have only one stroke's time to expand, which they cannot begin to fully do in a single short-stroke expansion cycle. So the extra work of compressing the extra charge is never really rewarded with sufficient extra output to justify it and the much higher complexity of the engine. |
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Your valvetrain is going to have to be 1/4 crankspeed. You could conceivably run everything off of one shaft, but in the spirit of jumbling a relatively simple process up even further, I recommend you go with three. And for the higher revs, make it a VTEC system that switches lobes to open the intakes a little sooner. |
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I've had time to consider this idea further, and it's time to bone it. Sorry. |
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Excess pressure in the cylinder at the beginning of the exhaust stroke is generally worse than useless in terms of providing power. Something like a Miller cycle is good because it reduces the ratio of exhaust pressure to intake pressure. In your engine, the pressure in the reservoir will be quite high when you vent it. |
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This is not a flat head it's a L-head. Also the reservoir valve would not open till there was slightly less pressure in the reservoir than in the piston area meaning less overall pressure on the piston. |
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You can add top speed to this OR you can keep the engine in the same gear longer to provide more torque longer. |
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valve float is a nominal factor that can be fix in may ways. Like what you suggested, make it like a Ducati. I also believe that there is sufficient time to fully take in most of the benefits of a combustion. I can always change the size of the reservoir and the piston chamber. (remember this is only the half-bakery) |
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The longer the stroke is the more energy your losing because now the engine has to compensate for that inertia. a shorter stroke will loose less energy. that and the fact that 1 in 4 strokes is a powerstroke, just like a 4stroke engine, means that less energy is wasted on inertia. this makes for a more powerful engine. |
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A large size reservoir would mean more heat meaning the more water could be put in for more gas, not that it needs to be big either. There is also a water injector right between the intake and reservoir valves to inject water into the cylinder. This engine would do well at self rectifying, a key part in engineering anything. If there was heat left over from the first power stroke than the second power stroke would be stronger than if there wasn't as much heat leftover. This would be controlled by the Engine Management System. |
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VVT on almost any engine would be better than no VVT but since this is normally a high reving engine i don't see the benefits of it's use beond what would benefit a 4stroke engine would have. i would however recommend a VVT system on this engine because of it's long rev range but this is not what my idea is about. |
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I really see this working well. Most ideas i have will last all of a minuet until i find something wrong with them. Some of my good ideas have lasted a day. But this has lasted over 3 days and the more and more i look at it the more i see the benefits. I am very optimistic that this would actually work well and could be put into production. |
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one stroke engine = cannon? |
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"Some of my good ideas have lasted a day." Uh... that's kind of a sign that an idea isn't actually a good one. |
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if thats your only responce than i'm good... |
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Well I've already established that I don't agree with the concept, no point in arguing. But since you commented... |
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The thing about this is that you need to do twice the work for twice the compressed air, and therefore theoretically twice the "bang" (two compression cycles for twice as big a combustion cycle). Using this knowledge, it would seem you could, at best, break even with a 4-stroke engine. Only because of the losses associated with the extra area in the storage chamber and pumping, breaking even is optimistic. |
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I like the way you think [F_R_O_G], you seem to have a pretty good idea of how things work. It would just seem that this isn't a winner. |
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If i could convince you that you could do 1 1/2 times the work for twice the air would you consider the engine to be more effective than a 4 stroke? |
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No, because it takes twice as many strokes to get 50% more work. Engine wear increases, parasitic losses increase, engine size stays the same. All other factors being equal, your concept is more complex and produces less power than a four-stroke of similar size. |
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A four-stroke engine which closes the intake valve at BDC cannot be very efficient, because the only way to get any power is to have the pressure at BDC going into the exhaust cycle exceed the pressure at BDC of the intake, and any pressure differential there is wasted. |
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From what I can tell, using two compression strokes is exactly the wrong approach to improving efficiency. What would improve efficiency (were it not for the technical difficulties and frictional losses) would be to have one compression stroke, then fire the combustion chamber and let about half of the gas from the chamber into the cylinder. Then do an exhaust stroke (not through the chamber) and let the other half of the gas from the chamber into the cylinder. |
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This isn't the best way to add an extra expansion stroke to an engine, but at least it should shift the compression/expansion ratio in the right direction. |
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crap, was just about done with what i was typing and the computer looses it.... round2 |
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You would have an average of 4.5atmospheres for 100mm on a 4 stroke engine with 100mm stroke and compression ratio of 10 to 1 with perfect volumetric efficiency. (yes, i know this would cause knock but lets make it easy to work the numbers) Then with my engine you would have 2.00atmospheres on the first stroke. (remember there's the reservoir space) with a 50mm stroke and a "compression ratio" of 5 to 1. for over half of the second commission stroke the reservoir chamber will be closed so for the first half 25mm there would be an average of 2.00atmospheres and the second half, 25mm, a average of ~7.50atmospheres. So we avrage the second stroke up. 2.00atmospheres + 7.50atmospheres = 9.50atmospheres divide that by 2 and we get 4.25atmospheres for the second 50mm commpresion stroke. we then avrage the first and the seond commpression stroke so 2.00atmospheres + 4.25atmospheres = 6.25 and devide that by 2 and we get 3.125atmospheres for an average of 100mm that is less than 4.50atmospheres for 100mm. |
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The average compression ratio of the 4 stroke engine is 4.50atmospheres where as the equivalent 8 stroke engine is 3.125atmospheres . But both have the same results in the end. Mechanical advantage come to mind. |
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*edited to clarify and correct my math |
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A big 'ole bun for the CONSTANT VOLUME BURN,
which has been a unicorn for many engineers in the
field. |
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I still have doubts about the losses, though. You're
asking a lot out of those valves. They're not very
patient, you know. They only work as well as they do
in an IC engine because they don't have a lot of time
to leak. |
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// it would go suck, squeeze, suck, squeeze, bang, blow,
squirt, blow.// Reminds me of a ...ah, nevermind. |
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