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Post by freegan on Nov 9, 2012 23:24:43 GMT
Cyber, your post on page 1 gave us this site with a list of auto-ignition temperatures for a variety of fuels and a few woods. Gasoline is listed at 280 oC and generic wood at 300 oC. I tried to find some info about lignum vitae but sadly it is unavailable. However, verawood, an Argentinian equivalent, is available but I have yet to find its auto-ignition temperature. Both of the above woods have the advantages that they are self lubricating (they have been used for bushings and bearings) and so dense that they are unlikely to splinter. I expect that verawood would present the best material for manufacturing an internal combustion engine using gasoline/air/water or DME/air/water. A drawback is that working such dense woods is rough on tools.
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Post by memeengine on Nov 9, 2012 23:34:24 GMT
Out of interest, could you make a 'steam' engine using something with a far lower boiling point than water - say alcohol? Maybe something that you could boil using electric heating elements (cobbled together maybe from a cars electrical system) that is powered by a car battery? If the boiling point of the liquid was low enough you *might* be able to extend the running time of the battery to an hour. I mean, all we are looking for is enough power to allow the vehicle to move under its own power at a very low speed for an hour. So would an alternative 'steam' engine work? It would certainly remove the need for a cooling system, even with friction in the cylinders. While using another liquid might help solve the thermal problem, you'd still have to cope with creating a pressure vessel to hold the pressurized gas that the boiler created. It is possible to make low-pressure steam engines but the down side is that they have to be much larger for the same power output. If Boulton and Watt had been successful in convincing people that high-pressure steam was too dangerous, then we probably would not have had the steam locomotive, as we know it, at all. Also with a "steam" engine, I think you're still going to face the problem of the pressurized gas/vapour penetrating the walls of the wooden cylinder and the piston head. If that happens then those parts will expand. So you'll need to engineer a solution that can cope with that expansion. In fact, it might be better to avoid the cylinders altogether and go for a steam turbine. That would do away with the need for tricky things like valve timing.
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Post by chriso on Nov 10, 2012 1:58:51 GMT
Steam turbine was my first thought too. But, to get those small enough for a car it seems you need really high rpm.. something wood would not handle too well. Not to mention the precise blade fabrication the myth busters would have nowhere near the time to do. I think we are firmly stuck with pistons.
Noticed a lot of talk about water d of water-injection cooling and did a little research. I used the temperature of 350 degrees as the temperature wood starts to smolder at (not at which autoignition occurs) and looked up how much pressure water can be under before it vaporizes above that point. For those that don't know, as the pressure goes up, the temperature at which a substance boils goes up too, and vice versa. It seems that in order to allow our coolant to continue working (Assuming enough is being injected), the pressure needs to be kept below 148 PSI. Low... but possible. (note: the increased partial pressure of the oxygen that occurs during compression might lower the acceptible PSI. Cannot remember enough chemistry to know for sure.)
If I was doing this, I have come up with a method of cooling I think I would try to use. Going back to my first post here, I would use a mixture of alcohol and water as my fuel and my coolant. I am going to describe it with a four stroke engine, as that is all I am familiar with, no idea how a two stroke works.
My idea involves a specially tuned engine and the aforementioned fuel-coolant. The stroke starts by letting a mixture of air, alcohol, and water in on the intake stroke of the engine. Following this, the compression stroke begins. Compression will increase the heat, causing the mixture to start to vaporize. Now alcohol boils lower than water, meaning it will start to vaporize first, resulting in the alcohol vaporizing and removing heat, keeping most of the water liquid.
This would continue until the compression stroke is over, at which point the engine, which is specially tuned to this, will have vaporized almost all the alcohol, leaving most of the water in a liquid form, where it will not interfere (much) with combustion. Then, a spark ignites the mixture, and the power stroke starts. The water kicks in, and absorbs the excess heat produced by the combustion of alcohol while it itself turns to vapor, expanding and providing much of the kick of the engine. Meanwhile, as long as their is enough water and the pressure is below 148 PSI, the vaporizing of the water takes enough of the heat away to prevent the cylinder walls from being scorched. From here,
The engine itself is tuned so that the mixture of alcohol, air, and water, and the amount of compression that occurs, means that the alcohol will finish vaporizing at the end of the compressions stroke and their will be enough water to finish the power stroke.
I have actually been trying to figure out if this is practical, as my fear is you are going to need a insane amount of water and alcohol in the engine for any decent level of compression, but have not been able to find the relevant equations. Been too long since chemistry...
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Post by freegan on Nov 10, 2012 2:19:17 GMT
[glow=red,2,300]Chriso[/glow] A two-stroke engine can obviate the need for valves as it uses the piston as an exhaust port opener/closer and can use the crankshaft similarly for the mixture inlet port. It is less efficient in mpg than a four-stroke but is simpler to manufacture.
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Post by chriso on Nov 10, 2012 2:37:57 GMT
Any idea whether the same cycle would work? That's the main reason I stuck to four strokes. And thanks for the animation: I think I finally "get" it.
The less valves the better, any wood engine would have abysmal fuel efficiency anyhow.
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Post by freegan on Nov 10, 2012 6:53:50 GMT
Any idea whether the same cycle would work? That's the main reason I stuck to four strokes. And thanks for the animation: I think I finally "get" it. The less valves the better, any wood engine would have abysmal fuel efficiency anyhow. It's still suck, squeeze, bang, blow; it's just that the labor is split above and below the piston, so any fuel cycle that would run in a four-stroke system will work in a two-stroke.
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Post by chriso on Nov 10, 2012 7:37:32 GMT
I don't see any additional timing system as a problem for what I proposed. The engine is calculated mathematically to do it for you. Although, the same "going up in smoke problem" applies for all of these...
Honestly, I suspect that you are going to need a ICE system with cooling of some sort. Both the points about steam and compressed air are exactly why I have not bothered much with them.
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Post by freegan on Nov 10, 2012 7:52:55 GMT
I don't see any additional timing system as a problem for what I proposed. The engine is calculated mathematically to do it for you. Although, the same "going up in smoke problem" applies for all of these... Honestly, I suspect that you are going to need a ICE system with cooling of some sort. Both the points about steam and compressed air are exactly why I have not bothered much with them. I'm quite hopeful that, with water mist, we can reduce the fuel burn temperature (even that of gasoline) below the ignition point of a good dense hardwood. Scorching may occur but considering that our ancestors used (and 'primitive' tribesmen still use) scorching in an open flame to harden the points of wooden spears and arrows, I don't think that would present too much to worry about.
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Post by Cybermortis on Nov 10, 2012 15:06:22 GMT
What we really need is someone with too much time on their hands to try making one....
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Post by trakmec on Nov 10, 2012 16:43:07 GMT
I actually threw together a 3d graphic for a very simplistic all wood design.
If someone could point me in the right direction to get the image uploaded. Then you all could review it, make suggestions on needed changes and maybe I could cob it together.
The design is done in Google SketchUp 8, I just don’t know how to upload it as an image, any suggestions?
of course if it works it's not a myth is it?
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Post by Cybermortis on Nov 10, 2012 17:26:03 GMT
You should be able to upload images to a site like photobucket and link from there.
If Photobucket isn't accepting an upload, you may want to save the image as a JPEG file
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Post by trakmec on Nov 10, 2012 19:42:03 GMT
thanks I'll play around and see if that works
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Post by chriso on Nov 10, 2012 22:05:58 GMT
What we really need is someone with too much time on their hands to try making one.... That sounds like so much fun... What? Haven't you seem my profile? Honestly, If I had the technical know-how, I would love to try it.
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Post by Cybermortis on Nov 10, 2012 23:24:05 GMT
Well the MB don't really have any technical know-how when it comes to car engines either - other than how to turn a perfectly usable vehicle into a wreck.
That said I am NOT asking if anyone would be willing to do any at home testing. Apart from anything else this is would be very dangerous.
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Post by trakmec on Nov 11, 2012 4:45:24 GMT
Chris O: Here is a quick wiki link with a good animated graphic of how a 2 stroke works, it is less efficient than a 4 stroke but also much less complicated. en.wikipedia.org/wiki/Two-stroke_engineAlcohol and water vapor sounds good to me, I believe that alcohol is still used in drag racing so there should be some usable information available. Now as to this picture; it’s a 2 stroke with multiple ports 4 intakes and 4 exhausts. the exhaust ports are ¾” and the intake ports ½” that should help with air flow thru the cylinder during the exhaust stroke. The directly opposed pistons on this should give great compression due to the long stroke length and corresponding cylinder volume approximately 2 5/8” under power and another 3” on vacuum as the flywheel brings it to the bottom of the cycle. For a total piston movement of 5 5/8”each. I am not counting the full chamber volume because pressure is not built before the piston passes the exhaust ports closing them This BIPOLAR design should prevent blowing a cylinder head off of it and the long vacuum stroke should help remove exhaust gases, draw in more cool air and help to keep it running cooler. I’ll have to do the math for the fuel quantity but am going with freegan’s idea of less being more. The fuel system is not shown here I am planning on using a plunger type of injector activated by the piston cranks return stroke. It will allow for consistency and isolate the fuel system from the combustion chamber during ignition. Ignition will be accomplished by both compression, and if necessary the insertion of a wooden glow plug (the red stick in the photo) basically it will have a burning ember inserted into it, then it is inserted into the engine. Initial cylinder volume is 37.68, reduced to 4.71, that’s 8:1 I think, so the temperature ought to be good for fuel ignition without the plug. Once the fuel system is draw up I’ll use the same setup for the water injected cooling system again I’ll have to do the math for the correct volumes. If anyone else wants to help with that part feel free, I hate math. the fluid chamber to the left represents a gravity fed oil well for lubrication, it’s not much but better than nothing. the construction is as we’ve said plywood on the outside for cross grain strength and a hard wood for the cylinder, the pistons are hard wood and capped with plywood to prevent fracturing along the grain at the head, the oil ring will be leather as suggested earlier. As always, I await your slings and arrows OK photo not as good as hoped Orange is the piston cylinder; Brown the pistons; Blue is the air intake ports, and yellow the exhaust ports
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Post by silverdragon on Nov 11, 2012 11:04:42 GMT
I am struggling with a problem.
Speed..... and sudden brick walls?.... You got it... Brakes.
Conventional braking ideas.... Would YOU trust wooden disk brakes?.... Or Drums?...
There is a bonfire in the making.
Someone give me an idea to thing (Edit...: Thing?.. typo... THINK...) on for this one please... parachutes are not multi-use, I will admit air-brakes and Flaps to do that (Like that thing on the Veyron) are plausible, but low-speed (less than 20mph) repeated use "Heavy Traffic" situations?....
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Post by freegan on Nov 11, 2012 11:40:55 GMT
How about a turbine (connected to the drive-shaft) driving an hydraulic fluid around a cyclic flow-path? When in normal use the fluid would be free-flowing but under braking it's flow-path restricted.
The clutch could also be by hydraulic connection between the engine shaft and the drive shaft.
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Post by silverdragon on Nov 11, 2012 11:48:47 GMT
^^ Thanks Freegan... thats worth thinking on?.. Hydraulic clutch idea... Hmmm..... you got a good idea there.
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Post by Cybermortis on Nov 11, 2012 15:27:09 GMT
Because of the complex nature of this idea, it was decided to concentrate on designing and building a wooden engine rather than a whole 'car'. One of the reasons for this is that all the other important parts of a car could be made from wood given the time to design and build them.
However no one is entirely sure if a wooden engine is possible on any level. So we are looking at the one debatable part of the larger idea.
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Post by trakmec on Nov 11, 2012 17:04:16 GMT
My attempt is just an engine at this point and to be quite honest I have no idea how the contraption I’ve concocted would fit under the hood of a real vehicle. I do agree with cybermortis that most systems could be done over time and that limiting to the engine keeps it less complicated, so more testable.
That said Silverdragon; how would engine breaking sound to you? I had already planned on air flow control to stop the engine operation. Shouldn’t be too much trouble to use the pistons compression to stop the vehicle depend upon its weight. Not necessarily street worthy but certainly operable and there for testable.
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