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Engine Oil Viscosity Management System
By evaporating off lighter elements in a constantly evacuated crankcase and cooling/storing them in a remote reservoir we can ensure constant viscosity at all temperatures | |
Over their operating cycle, car engines require various viscosity ratings at different points: while starting the VR needs to be low to get all the moving parts lubricated as quickly as possible and stay lubricated while the engine is warming up. When the engine (thus the oil) is warmed up a higher
VR is required to keep the actual viscosity in a usable range. While the engine is not in use a *very*high VR is optimal to coat and thereby protect surfaces against rust, also to provide a persistent lubrication for when the engine is started next.
As the engine warms up we're going to evacuate the crankcase[1] more and more until it's a vacuum[2]. After the boiled-off lighter oil is returned to normal pressure outside the crankcase it is cooled, filtered of any soot then stored in a remote reservoir. Thus as the engine temperature increases, the viscosity rating of the working oil increases. The low viscosity distillate can of course be returned to the sump as required (eg: the load decreases).
When the engine is turned off, the pump continues to occasionally spray the internal engine surfaces and the lighter elements are still drawn off: as the engine cools this results in a coating of heavy oil on the inside of the engine. Eventually the crankcase is allowed to return to atmospheric pressure and the content of the light-oil reservoir is returned into the sump.
This means that when you go to start the engine next, the bearings will be pre-lubricated with heavy oil and the sump will be full of light oil until increased temperature causes the heavy oil to flow back into the common sump.
[1] Crankcase evacuation is used on high-performance cars and dragsters to reduce pumping losses, but since engines aren't originally designed with CE in mind, the aftermarket kits available only evacuate a quarter atmosphere or so. This idea provides a mechanism for dealing with boiled-off oil (which is of course the main idea) but also provides the benefits of an evacuated crankcase (say 5pct more hp).
[2] Blowby is the stuff that sneaks through the piston rings into the crankcase from the cylinders; it comprises of exhaust and some uncombusted HC's. In a normal (unevacuated) crankcase it is returned via the PCV valve to the air intake to be recombusted. Since we're evacuating the crankcase the blowby would be mixed in with the evaporated oil, but since water, oil and gasoline have pretty disparate boiling points we can take the oil off first then toss the water out the back and return the HC vapour to the PCV valve fairly easily.
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Random Product Link [bigsleep, Aug 27 2009]
[link]
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Hmm - I'm not sure about the premise with regard to viscosity requirements. |
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The only reason you'd ever want a high viscosity is to limit the rate at which the pump needs to supply oil to plain bearings. |
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Low viscosity is better for performance and economy as it offers lower friction at the bearing. |
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Modern engines are manufactured to sufficiently tight tolerances to permit the use of very low viscosity oils. |
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Multigrade oils achive what you are suggesting to some degree. |
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Oil addatives such as suspended PTFE leave a lubricating residue on bearing surfaces after the engine is stopped. |
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There is value in a non crank driven (i.e. electric) oil pump which can pressurise the whole oil system before the engine is started. An electric pump may also be driven according to demand, using less power than the conventional oversize pump and bypass valve arrangement. |
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In order to seperate light oil from water and unburnt hydrocarbons, you would need a temperature controlled fractional distillation plant, which is not trivial, especially when the unburnt HC's will be quite similar to the light oil. |
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I wonder what the effective life of the oil would be.. would you have to top up the light oil frequently as some of it would inevitably be lost past the scraper rings and valve guides? |
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All that said, this gives me an idea for a completely different application - so (+) for that! |
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If you're going to mess about with cooling oil and storing it in separate reservoirs I'm concerned at the weight penalty it will confer. |
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[Twizz] you think too much ;) the object is to have nice thick oil covering everything including the bearings while the engine is off and a consistently thin oil running through the system no matter what the temperature when the engine is on. Title's a bit misleading, granted: while the engine's running we're trying to get a consistant working viscosity through all temperature/load ranges. (my nomenclature's a bit shaky; I'll clean it up as I get more familiar with it) |
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For storage and pre-lubrication purposes, the internal engine surfaces and bearings are covered with heavy oil in between operations: it's already pre-oiled when you start the vehicle, ie: no pre-oiler or PTFE needed. |
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During warm-up, light oil is running through the system because the heavier oil is still stuck to internal surfaces. |
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As the engine warms up, the light oil is gradually evaporated out and the heavier oil gradually comes unstuck and flows back into the sump. Done right the heavier oil is now thin because of the higher temperature. |
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I don't think the lighter oil components would be lost; I'm more concerned that waxes will end up stuck in some obscure corner that doesn't get heated much; that's up to engine design. |
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Yes, a different pumping system would be required, not so much due to the extra plumbing but because of the crankcase vacuum. |
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If an HC distills out at the same temperature as oil... it's oil :) |
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[UB] It's just one oil, but the lighter fractions get proportionally stored in a separate reservoir when they're not needed (ie: at high engine temperature). More plumbing but I don't think the weight increase would be that much on a car engine. |
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I'm suspicious of being told that I think too much - read 1984 lately? :-) |
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I'm not sure the oil will behave as you expect, seperating itself neatly into thick and thin fractions. |
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When the engine is stopped, all will remain hot for some time. If the higher viscosity fractions had thinned enough at running temperature to be useful, they will run quickly into the sump. When the engine cools, the lower viscosity fractions will condense on the surfaces, helping to wash off any remaining heavy ol deposits. |
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PTFE works, electric pumps are light and effecient. Have you had a stab at the size and weight of your distillation plant? |
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Oil coolers are baked.
Dry sumps are baked.
So are scavenger pumps. |
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That makes this idea pretty much redundant, I figure. Farting about with an onboard fractionating plant seems a lot like shifting deck chairs on a sinking ship. |
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I was referring more to having to respond to a long, multipointed annotation not your actual cognitive duration. That being said I think oil *will* separate such that generally speaking lighter oil will evaporate more than heavier oil: neatness doesn't matter much. Note that per the post the crankcase is still being evacuated for awhile after engine-off: the lighter fractions still being pulled out. As far as fractional distillation is concerned I'd be just as happy to toss the lot into a cold tank, let it settle out then treat the stuff in the middle as the "light oil" (assuming water is heavier than oil is heavier than random liquid light HC's). |
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[+], for your spirited defence. |
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//[+] for your spirited defence//
well thanks but looking at what your offense is: |
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//weight//
a few kilos - a vacuum pump, a supplementary electric oil-pump or two, a reservoir, couple hoses and a not-too-mysterious device that separates oil, water and HC's. |
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//oil coolers, dry sumps, scavenger pumps are baked//
then it's a good thing this idea isn't any of those, isn't it. |
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can't say as I deserve it. |
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They're an integral part of your design, whether you like it or not. What you've described is a dry sump lubrication system. It's just that you didn't specify that or scavenger pumps in your description. |
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Oil coolers are part of almost every racing car, to prevent oil overheating and foaming. |
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I think you'll need upwards of 20 litres of oil for your engine lubrication, based on what you specified. That's a lot more than the usual 4 or 5 litres most road cars require. |
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I don't see where you're getting "upwards of 20 litres" of engine oil. A few quarts to make up for the portion that's not being used, and another quart or two for good luck is all. |
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It's not necessarily a dry-sump system: thought out as wet-sump actually. |
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Neither is it an oil-cooling system. The evaporation of the lighter oils is just a transport mechanism for the oil, and as the engine warms up it's mostly a one-way trip to the reservoir. Once the engine is warmed up some light oil will be returned but just enough to make up for incidental evaporation and spray recycling. So cooling would be transient, and anti-foaming a byproduct of an evaporated crankcase. |
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Scavenging isn't well covered because it isn't the main purpose of the system. Also not covered are the changes that would have to be made in the pre-existing oiling design. |
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