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Post by Cybermortis on Nov 7, 2012 14:44:04 GMT
One advantage of inserting cylinders into a larger block would be that you could, presumably, pull them out and replace them. You *might* even be able to use this to try and create a cooling system, a network of shallow groves cut into the outer surface of the cylinder would allow a cooling solution to be run through them. (This would probably have little or no effect to be honest. But I thought I'd note that possibility).
As far as cooling and the overall design goes. We seem to be working on the assumption that your engine has to be an ICE engine with high compression and running off gasoline (or similar).
First there is nothing about the myth that specifies that gasoline has to be used as the fuel. There are alternative fuels that have lower ignition points than gasoline, and it *may* be that one of these potential fuels has such a low ignition temperature that even with friction the overall internal temperature will remain below the ignition point of wood*. (Which is to say that we *might* not need a cooling system). Likewise we may not need a high compression engine.
High compression and gasoline would result in a more powerful and efficient engine. But then we are only looking to make this move at walking pace (around 3 mph), so less powerful fuels and low compression might may prove adequate for obtaining this type of performance - as well as allowing the engine to run for much longer.
One note/reminder; We shouldn't look at designs that are too complex, either in terms of design or build. It should ideally be a something that the Cast can design and build with little or no outside (expert) help.
(*Someone on Discovery even suggested that compressed air/gas was used rather than conventional fuels.)
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Post by GTCGreg on Nov 7, 2012 15:30:02 GMT
(Which is to say that we *might* not need a cooling system) It's still a thermodynamic engine and has to follow a thermodynamic cycle. It's been 40 years since my last thermodynamics class in college, but is is my understanding that with all the IC engine thermodynamic cycles, you have to have heat flowing in order to produce work. If you don't have some form of heat sink to remove the heat, the engine will not produce work. I could be wrong, it's been a long time but that's the way I understand it to work. |
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Post by Cybermortis on Nov 7, 2012 15:37:44 GMT
The exhaust might be good enough for this, wood is after all an insulator so the gasses in the cylinder may be removing heat faster than the wooden walls could absorb it - IF the fuel being used has a low ignition temperature.
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Post by freegan on Nov 7, 2012 16:06:51 GMT
Although the internal combustion engine traditionally uses the exothermic reaction of igniting gasoline vapor in the presence of oxygen, I am given to understand that there are a number of endothermic gas producing reactions which might be worth exploring as a means of cooling.
Unfamiliar as I am with this branch of chemistry, could someone with a deeper understanding investigate the possibilities of either
(a) adding extra cycles to the normal 4-stroke ICE to exploit the endothermic reaction or
(b) adding the reactants of the endothermic reaction to the fuel/air mixture?
I understand that this would limit the power of the engine but a useful amount may still be achievable.
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Post by GTCGreg on Nov 7, 2012 19:02:19 GMT
What about something like a wooden Sterling engine that uses ambient temperature air for the heat source and dry ice or liquid nitrogen for the sink? Maybe some type of hard wood would be able to transfer heat well enough for it to work. At least you wouldn't have to worry about your engine catching on fire.
Another option would be to stay away from the piston type engine altogether and use some spring type energy storage system such as a large wooden bow or maybe a heavy dropping wooden weight. Well, it works for a cuckoo clock.
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Post by chriso on Nov 7, 2012 19:13:08 GMT
I know that a Stirling engine relies on heat differences traveling between parts of its cylinder, and is a closed system, so as wood is a strong insulator I suspect that it would operate too slowly to be useful.
Also, ignition temperatures and burn temperatures are two completely different things. Alcohol's autoignition temperature is around 350 degrees, below wood's 451, but can reach temperatures of 2000 degrees while burning, well above what wood starts burning at. So the ignition temperature is not a very good indicator of whether you need a cooling system or not.
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Post by GTCGreg on Nov 7, 2012 19:33:50 GMT
I don't know how well a heat insulator a hard wood, such as Oak is but my thought is that if you kept the cylinder walls fairly thin...
Not sure it would work, just doing some brainstorming.
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Post by Cybermortis on Nov 7, 2012 19:34:10 GMT
What about using Dimethyl ether as the fuel? en.wikipedia.org/wiki/Dimethyl_etherThis is already used as an alternative to propane - so could be argued to be a fuel you might have lying around in the middle of no where - has a boiling point of - 24C and an autoignition point of some 350C (higher than wood according to the figures I've seen). So this might be a cool-running fuel, especially if you could rig the engine so that there was no ignition spark on every-other cycle - allowing the gas to both absorb heat from the cylinder and act as a coolant while still allowing for expansion of gas and therefore some power to be produced. I have no idea what effect this stuff would have on wood, or if such as coolant system would work, but this could be a viable way to make a wooden ICE engine work. |
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Post by memeengine on Nov 7, 2012 22:24:47 GMT
I think the trouble with some of the more exotic choices of fuels is that you're simply trading one set of engineering problems for another.
If we're sticking to the concept of creating a wooden engine to fit in an existing vehicle, then most of the components that you're connecting to (fuel system, ignition system, drive train) will be geared (if you pardon the pun) to a given engine type with a certain power output. If your new engine differs significantly from that design then you're going to have to redesign those components too.
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Post by silverdragon on Nov 9, 2012 8:48:38 GMT
Off Topic... Coal gas?....
If you are going a wooden car, as Coal when burnt gives off a combustible gas, could we go Coal powered then Steam?...
This is presuming the engine of an IC is out of the question.
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Post by freegan on Nov 9, 2012 13:32:29 GMT
I don't think that gasoline fuel is quite out of the door yet.
Further to my post about endothermic reactants (above), I found that water mist (H2O) is a viable additive for reducing the combustion chamber temperature with the added advantage that as it flashes to steam, absorbing its latent heat of evaporation from the fuel/air reaction, it expands in volume, giving a little more bang for your buck.
[Anyone recall the discussion about this over at Disco'?)
By experimenting on a standard engine fitted with pyrometers, the MBs could test that myth to provide data regarding the optimum H2O/fuel/air mix for the wooden engine.
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Post by Cybermortis on Nov 9, 2012 14:13:04 GMT
I do recall that discussion on Disco yes, WW2 fighters used to inject water into their engines to give a short-term power boost.
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Post by trakmec on Nov 9, 2012 15:23:22 GMT
Cybermortis: The DME sound interesting as a fuel, but how to handle and deliver it? Could this be run thru a carburetor or does the gas have to be injected into the cylinder.
Also please consider this, if DME is the fuel it will be harder to use as a coolant introduced into the cylinder because the residual heat from combustion may well cause it to ignite. It may be better to stick with injected water, because it’s an established technology.
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Post by freegan on Nov 9, 2012 15:26:47 GMT
I do recall that discussion on Disco yes, WW2 fighters used to inject water into their engines to give a short-term power boost. Indeed. This old post on an old forum mentions that methanol was included in the mix for the power boost. (The rest of the thread discusses the engine cleaning properties of H 2O in the fuel/air mix.) Another advantage that occurs to me is that the fuel/air mix could be reduced to a level that puts less stress on the wooden components. It would result in a lower power engine but still viable, nonetheless. Edit: The test engine for data gathering would need to be an old-school non-electronic type as the engine management systems in modern engines would hinder the experiment. |
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Post by Cybermortis on Nov 9, 2012 15:53:42 GMT
Cybermortis: The DME sound interesting as a fuel, but how to handle and deliver it? Could this be run thru a carburetor or does the gas have to be injected into the cylinder. Also please consider this, if DME is the fuel it will be harder to use as a coolant introduced into the cylinder because the residual heat from combustion may well cause it to ignite. It may be better to stick with injected water, because it’s an established technology. DME is used as an alternative to propane in some domestic products - including camping stoves. So the handing part is taken care of, since it is shipped in gas bottles. You can replace gasoline with types of gas in ICE engines with minimal modifications - and Mythbusters managed to get a car engine running using Hydrogen gas with no modification at all. DME's autoignition temperature is around 350C, which means that the engine would have to be on fire before the DME would ignite in the chamber. It's boiling point is only 24C, which means that it should be possible to ignite it at much lower temperatures than you can with gasoline. |
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Post by trakmec on Nov 9, 2012 20:06:44 GMT
Cybermortis: that was kind of what I meant, if we have combustion within a wooden cylinder along with wooden moving parts isn’t the possibility of very small splinter or fragments of either the piston or the cylinder to be present after a few cycles? Most of the engines I’ve worked on show signs of burn residue on the pistons and plugs. Now this may have been particular to the fuels used, or the engines themselves. My concern is that this combustion or friction residue may be enough to ignite the fuel as you’re injecting it into the cylinder to act as coolant. Unless I have misunderstood the process suggested, or the timing sequence that you have in mind.
As for DME as the fuel if we are going with more modern parts and not all natural, then yes I agree it could easily be set up.
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Post by freegan on Nov 9, 2012 20:17:00 GMT
Most of the engines I’ve worked on show signs of burn residue on the pistons and plugs. Now this may have been particular to the fuels used, or the engines themselves. My concern is that this combustion or friction residue may be enough to ignite the fuel as you’re injecting it into the cylinder to act as coolant. from the same old forum that I referenced earlier, should allay your fears. |
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Post by trakmec on Nov 9, 2012 21:35:00 GMT
Freegan: I read the post and see how water injection would work as a coolant. I have friends in aviation who are familiar with the old water injection systems and they’ve told me some about them. My question was about using the fuel DME as the injected coolant. If DME has such a low ignition temp wouldn’t it just ignite within the hot cylinder creating more heat? I get that the water would drop the temperature as it used the energy to flash to steam, but that’s basically a phase change and not a chemical reaction which would put more heat into the system. Plus if the timing was off you’d have all sorts of problems with this engine. I wonder what a blown wooden piston and rod would look like With a four stroke engine here is the problem as I see it intake: DME would basically be fuel waiting to ignite, on the first few cold cycles not a problem but once the cylinder heated up could the DME cool it off enough or would it just ignite from the ambient temperature of the exhaust gasses that have just left? . Compression: well compression is going to cause heat check the link to the fire piston www.boyscouttrail.com/library/firepistons.asp There is not much gained by injecting here, unless you plan on using pressure as your ignition spark like a diesel. This is an idea I actually like. But do not see a lot of cooling likely Power: well for obvious reasons your just adding fuel to the fire Exhaust: possibly while the valves are open, but with the low ignition temp and the fact that there is hot exhaust gases present wouldn't that make the risk of premature detonation high? I do think DME would be a great fuel, and with the right timing you could ignite it like a diesel removing the need for plugs and distributor. Not so convinced it would work as a coolant A reduced amount of fuel per cylinder would help reduce heat, a great idea Freegan Think that injected water would solve the temperature issue nicely and would not be too complicated to rig; you might even be able to use a reworked existing fuel system What are your ideas? |
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Post by freegan on Nov 9, 2012 22:09:37 GMT
I'd say you've thought about this rather more than I have.
I suspect that a fair bit of experimentation would be required to get some useful data regarding the proportions and amounts of water, fuel and air needed to find a balance between the needs for reliable ignition, cool burn and a viable power output.
Getting the MBs to try out DME in a test rig might be more problematic than getting them to test the proportions etc using gasoline when we have an existing 'myth' regarding the use of water in gasoline engines that could serve to supply data for the wooden engine.
Perhaps they could use the test rig for the first myth to try DME if the data they get for gasoline precludes its use in a wooden engine.
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Post by Cybermortis on Nov 9, 2012 22:14:06 GMT
So far the ideas are good, but we are running the risk of getting too complex for something that could be tried by the Mythbusters.
What we need is a very simplistic design that they can put together without outside assistance in a week, which would include small-scale testing.
There seem to be a number of options here. Conventional ICE, external engine - steam power, a flywheel/spring engine or compressed air/gas.
The most straightforward one is to try and build a conventional ICE engine using wood, but looking for a fuel that isn't going to incinerate the cylinders or have an effective coolant system. Of the two options for an ICE, fuel seems the better and faster way to go as it would be simpler to design and test - Small scale wooden engines running on different fuels would very quickly show which fuels are likely to be best suited for this.
Designing a cooling system would be a nightmare. Given that wood is an insulator, any such system would either have to be so complex it would take months to build or in-cylinder cooling that would require a more complex timing system. Such a timing system adds to complexity and hence build and testing time - get it wrong and the big engine you just built is going up in smoke rather quickly.
Steam has its own set of problems, starting with it simply not being safe to make a pressurised container from wood - especially not since you'd have to make at least one of the walls rather thin to heat up the water.
The other problem with a steam engine design is endurance and fuel loading. You'd either need someone there to shovel the fuel in (very dangerous as they'd be next to the engine), or an auto-loader that adds complexity and weight and is unlikely to be capable of running for an hour without refuelling.
Then there is a flywheel or spring engine. But no such engine would give you continuous power for an hour without being absurdly large and heavy.
Compressed air (or gas) without any ignition is the last option. But I doubt you could carry enough pressured gas containers to give the required endurance of an hour, without having so many gas tanks that it wouldn't be capable of moving under its own power.
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.
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