h a l f b a k e r y"Look on my works, ye Mighty, and despair!"
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The first idea I ever posted here was the first version of this. Within about 10 minutes I got my first MFD for bad science. After all, it called for the use of a supercharger, that essentially would have ended up blowing all its boost out the exhaust and in doing so would have sucked out any intake
air the engine would be trying to breathe. The second version of this idea used butterfly valves and got a neutral response, although it was pointed out that butterfly valves really aren't practical. Well, today being my half aniversary, I figured I'd try my first idea again.
Note: for this to work, the engine would have to be inline since there isn't a very practical way of fitting an intake and exhaust manifold in the center of a V engine.
Okay, out of each valve the runners split into two tubes (one directly on top of the other making a Y shape) and there is a sliding valve (up and down) controled by a camshaft to restrict one tube and open the other (when the valve uncovered one tube, it would automatically cover the other). Cooling passages can be designed so that the exhaust heat wont directly be transferred to the intake air.
Losses: The camshafts for the valves that control the up-and-down valve would undoubtebly require some power. But the fact that there would be 4 camshafts total throughout the engine would mean that they would essentially only require as much power as a DOHC V12. Also, when each passage is restricted by the valve, this would probably create a slightly less efficient than normal flow path (but I'm sure the double valve area would way more than make up for it).
Gains: Double the valve area for both intake and exhaust.
[Edit: I've removed everything about the flexitube bit]
Rotary Valve System 1
Rotary_20Valve_20System_201
This is close to what elhigh described. [BJS, May 15 2007]
Better Illustration
http://s210.photobu...4-Stroke-Engine.jpg
Just thought I'd post it [acurafan07, Jul 26 2007]
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I know I say this a lot, but I'll need a picture to understand this. From what I can gather, you're talking about moving this tube up and down between the intake and exhaust valves. It might work, but I'm not sure how you would lubricate the camshafts or keep the flexible tube from breaking. I think that this is basically the same thing as a lot of rotary valve setups, and I'm not sure how well those work. |
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A flexible tube capable of handling the exhaust temperatures will be a tall order. High mass of the reciprocating tube might limit the engine speed as well. |
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Yeah, I guess each tube would have to have its own cooling jacket with hoses to pump the water from each tube to a small radiator. If the valve used a type of system like ducati's Desmodromic, they would at least be springless meaning that the cams would require less power since they wouldn't have to overcome extremely tight springs, and the danger of valve float wouldn't be an issue. |
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Also, I know it is possible to make flexible tubing that can withstand the high temperatures of an engines exhaust since cars often have flexible tubes hooked up to their exhaust pipes when they are on a dynamometer. |
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Yah, but that's at the end of the entire exhaust system, where the gases have had oodles of room and time to cool off. You're talking about a flexible tube attached directly to the exhaust port, where the exhaust gases are fresh off of combustion--temperatures won't be much lower than they are in the cylinder itself. And it has to be flexible both when the engine is hot and cold. I mean, I'm sure it can be done, but we're looking at seriously exotic materials. |
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He mentioned the Desmo drive, so he gets a bun regardless of the practicality of the idea. |
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Well there are other ways of doing this. For example, the runner could split into two tubes (one directly on top of the other) and there could be a sliding valve (up and down) controled by a camshaft to restrict one tube and open the other. The problem with every way of doing it is simply that no matter what, the intake gases will have to pass through at least some of the space that the exhaust gases pass through, heating the intake air. But still, the split tubes with an up and down restictor valve is probably more practical. |
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//Happy half anniversary.// Thank you. |
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I don't know if this would be an improvement on the reciprocating mass, but wouldn't a ball valve work better? Rather than completely closing off the passage, the ball would rotate enough to connect one passage one way, then rotate back to connect the other way. The intake and exhaust plenums have to cross each other at the ball valve. |
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Size the ball right and time its speed right, and you wouldn't have to have reciprocating motion; it could just rotate. Exhaust would be immediately followed by intake, while the ball rotated through a long enough inactive space to allow the compression and expansion strokes to complete. |
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I think I just took your idea to an already-baked valve concept. |
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My bad. Okay, back to wiggling the pipes! |
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Does this idea include poppet valves for the cylinders? Or does it only have the flexi-tube valves? |
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Yes unfortunately, there would be poppet valves for the cylinders. But in total, there would be 36 valves (24+12), only 4 more than a 4-valve V8. |
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Wow, thats a lot of valves, do you think it would really be worth it? |
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For double the valve area for both the intake and exhaust? You tell me. But I can tell you that in comparison (and as I mentioned in a previous version of this idea) Ford once updated their 2-valve 5.4L to having 3-valves per cylinder and it gained 52HP just from one intake valve. Imagine that times 2 plus the added flow of the 2 extra exhaust valves. |
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I'm pretty sure you're over-hyping the benefit based on one data point. As has been mentioned before, it's intake area that is important as (for a non-turbo engine) you've only got atmospheric pressure filling the cylinders. As for the exhaust, the rising piston will drive the pressure up and up until the cylinder _IS_ empty. Bigger exhaust valves will help, but have only a second-order effect by comparison with the intakes. |
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I don't think this one is a goer: |
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- You don't have a sealed connection between intake (filter) and engine. Not too much of a problem. |
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- You don't have a sealed connection between engine and exhaust, so you'll run into major badness on emissions. |
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- Exhaust temperatures are about six hundred degrees. Flexible plastics won't stand that. Trying to achieve this degree of flex in a metal part will certainly cause it to crack and break up very quickly. If you water-cool it, you might lower the temperature but you will also massively increase the stresses as you try to move the water around too. |
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In theory, the physics works, but in practice you couldn't build it and have it run for more than five minutes. You'd be better off fitting a turbo to increase the pressure in the inlet and overcome the inlet flow restriction that way. |
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Separately though, you seem to think in a structured manner, with a goal to achieve. It's good. |
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what did a valve ever do to you that you are driving so heavily for their extinction. They are such happy dependable and well understood pieces of metal that I am simply blown away by your intense desire to get rid of them. |
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[jhomrighaus] was that annote to me or someone else?
[david_scothern] What if instead the runners could split into two tubes (one directly on top of the other) and there could be a sliding valve (up and down) controled by a camshaft to restrict one tube and open the other (when the valve uncovered one tube, it would automatically cover the other)? I thought in depth about both this way and the way listed on the idea and chose the one with flexitube, perhaps a bad choice. |
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It was pointed at you MR. Death to Valvesanator. |
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Trying to get rid of valves? Au contraire. I'm simply trying to use the ones available to their fullest. I mean the way I think of it, it just doesn't make sense to have a 4-valve head with 2 intake valves and 2 extra potential intake valves when the engine is sucking air in (and not be able to use them). And with companies like Ferrari and Volkswagen making engines with 5-valves per cylinder just to get an extra intake valve, if they could simplify the head and just use the valves already there, that would be much better. |
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Incidentally, most companies (notably Ferrari) are back to 4-valve heads. From what I've heard, the performance gains of switching from 4 to 5 are questionable. Complex airflow issues start coming up. |
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//Complex airflow issues start coming up.// Yeah that's true, in the old Ferrari F355 with 5 valve heads, the middle intake valve opened and closed 10 degrees before the other two. I think for some reason that helped. |
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