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Suppose one has an engine with a Crower six-stroke engine, with a dedicated steam exhaust valve in each cylinder, and a steam condenser.
Why should we be restricted to water and steam for the 5th and 6th strokes?
Why not use an alternative working fluid, such as gasoline? This would allow the
use of only one fuel tank (gasoline), instead of two (gasoline and water).
Any gasoline vapor which isn't completely evacuated from the cylinder by the end of the 6th stroke would simply get mixed with the incoming air of the 1st stroke.
This "loss" of gasoline vapor is harmless. Firstly, the loss of fluid from the Rankine cycle portion of the system would be replenished from the fuel tank. Secondly, the vapor which gets into the fresh air is as combustible as any other gasoline, and can simply be burnt during the engine's regular power stroke. Since the "lost" vapor is being burnt usefully, it's not being wasted.
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I wonder what you'd do with the boiled gas. Once a
good part of it is vaporized, you'll lose a lot of room
you'd ordinarily have for fresh air, and if you plan on
getting rid of it, you're ruining Crower's purpose of
efficiency anyway. |
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I'm assuming that each cylinder has a separate vapor exhaust valve, leading to a vapor manifold (leading to a condenser) that's separate from the exhaust manifold. On each cylinder's 6th stroke, it is this vapor exhaust valve, not the air exhaust valve, that is opened. |
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At the end of each cycle's 6th stroke, only the vapor in the combustion chamber of the cylinder remains, which is a small fraction the cylinder's maximum volume. |
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Considering the typical boiling points for gasoline, it's not unreasonable to assume that the pressure in the condenser will be below that of the atmosphere. |
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If this is so, then at the end of the 6th stroke, the pressure of the vapor remaining in the cylinder will also be below atmospheric, and when the vapor valve closes and the intake valve opens, air will be pushed in by the atmosphere, compressing the remaining vapor to an even smaller volume. |
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Thus, the residual gasoline vapor will not displace enough fresh air to prevent the first four strokes of the next cycle from operating efficiently. |
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pretty neat if it works... but it's at least as much work in the plumbing department. |
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Would there be any advantage of gasoline over water, from an expansion point-of-view ? Gasoline vapour is much heavier than water vapour I presume, so that's not a plus, but it has a lower boiling point. |
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The downside of gasoline is that necause it has a lower latent heat of vaporization, a larger amount would be needed to be injected on each cycle's fifth stroke for cooling... about 7x as much as if we were using water, I think. |
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The upsides of gasoline are that it doesn't require antifreeze, it doesn't require corrosion inhibitors, and it won't run out as long as the engine has fuel. |
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I don't see how the boiling point is relevant, as long as the liquid's boiling point is below the temperature of the hot surfaces onto which it's being sprayed. |
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The expansion ratio is relevant, but even if the ratio is lower for gasoline than for water, it will balanced out by the fact that we'd be injecting about 7x as much gasoline as we would be injecting water. |
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actually, for a downside, an oopsy in the valvetrain means your exhaust system explodes. |
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This is more a 4stroke + a 2stroke expansion (which I suppose the Crower is also) seeing as you *really* need to clear the vapour out before the next cycle. |
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[edit]: unless you want to put a chiller on the exhaust... then you could make it into a 2 or 4-stroke (diesel mebbe) by injecting it right after combustion ("Atkinson" type cycle required to harness the extra oomph, rich or stochiametric mixture to start with) |
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An oopsy in the valve train would result in lots of gasoline going out the exhaust, but it would surely be too rich to burn. It wouldn't explode in the exhaust system, but rather would result in flames coming out the tailpipe. |
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Yes, it is a 4 stroke + 2 stroke expansion, much like Crower's. |
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As for reducing the number of strokes by injecting right after combustion... then you would not only need to cool and condense the vapor, but you also need to cool all of the other components of the exhaust gas. |
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To cool the entire exhaust stream enough to condense the vapor in it would add hugely to the weight, overall size, and cost of the engine, making it unsuitable for use in an automobile. |
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Plus, even after you'd condensed *most* of the gasoline, there would still be some gasoline vapor left in the incondensible gasses. This would go out the tailpipe, resulting in wastage of fuel, and air pollution. |
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Furthermore, you would need to remove a significant amount of water from the condensed gasoline. And particulates, too. |
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so we have Intake, Compression, Combustion, Exhaust, Expansion, Recycle... may need to "rinse" at TDC between Recycle and Intake (ie: both Intake and R-Exhaust valves open to flush out the vapour), also what do you do if some of the gas is still liquid ? |
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At the end of the "Recycle" (vapor exhaust) stroke, the pressure of the vapor remaining in the cylinder will be very similar to the pressure of the condenser, which in turn will be below atmospheric pressure. Thus, the total mass of remaining gasoline vapor will be quite small. |
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There are two possible procedures that we could choose to take: |
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First option: First close the vapor exhaust valve, then open the air intake valve, thus mixing that residual gasoline vapor with incoming atmospheric air. The gasoline vapor gets burnt (usefully), and the cooling system will need to be replenished with gasoline from the fuel tank. The downside is that the gasoline vapor adds heat to the air, reducing it's density, which in turn will power. The more heat added to the air, the more power lost -- fortunately, it's only a small amount of vapor, so it's a small amount of heat added, and a small amount of power lost. |
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Second option: Open the intake valve while the vapor exhaust valve is still open. Air rushes in through the intake and out through the vapor exhaust valve, forcing the residual vapor out of the cylinder and into the vapor exhaust manifold, and thence to the condenser. Shortly after, before too much air goes out the vapor exhaust valve, the vapor exhaust valve closes. Little or no gasoline vapor is "lost", and little or no heat gets added to the intake, *but* more air ends up in our condenser than otherwise would. This air needs to be removed from the condensor via a vacuum pump, which consumes power, which is lost from the engine. |
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Given the choice between losing a bit of power due to warmer intake air, and losing power due to running the vacuum pump more than we otherwise would need to (not to mention, using a larger vacuum pump than we would otherwise need), I would choose to lost a bit of power due to warmer intake air. |
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As for some of the gasoline still being liquid -- that's silly, if we inject the correct amount, all of the gasoline will boil, and none will be left as a liquid. On the contrary, it's likely the vapor produced will be moderately superheated, not saturated. |
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Using excess heat to help make fuel might be better. |
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wjt, It's hard enough to turn a vehicle's waste heat into mechanical energy... if you can think of a way to turn a vehicle's waste heat into usable chemical energy... post it on the HB :) |
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