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When engine is shut down heat conserving measures (insulation, reduce cooling by convection),would help maintain the engine at it's normal (and most efficient) operating temperature; then, a car that has been sitting all day or night would reach it's maximum efficiency more quickly. An engine that was
still warm would also start easier and last longer in addition to getting better mileage.
Aircraft Version
http://www.aircraft...s/ezheatblanket.php
[jurist, Nov 02 2004]
Engine Blanket
http://www.descmath.com/sponsors/jc.html
Here's one non-electrical version supposedly available from J.C. Whitney for $9.99 USD. [jurist, Nov 02 2004]
[link]
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Electric engine and radiator blankets used to be quite common for cars garaged in cold climates, but I was surprised to be unable to find any currently displayed in Google. Perhaps too many people forgot to remove and unplug them before starting their car and attempting to drive away. Or perhaps they were found to damage the paint job on car hoods. You can still get Engine Block Heaters, and Oil Pan Heaters, and Battery Warmers, however, which accomplish much the same task. I did manage to find a photo of an engine blanket in use for aircraft. [link] |
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An excellent idea. What's to lose? If the car sits for so long that the engine cools right down, you're only back to the situation we have currently. + |
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{-jurist] As I see this idea it would be a characteristic of the engine compartment installed by the manufacturer. The firewall and sides of the engine compartment could have fairly efficient thin insulation. The hood would be insulated and sealed similar to the trunk. I am sure that these simple measures would give the average commuter a worthwhile saving in gas and afford other advantages as well. |
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[hangingchad], you seem to have missed the need for cooling an IC engine, and supplying it with oxygen. Sealing and insulating the hood would prevent your engine running. |
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However, a system that only insulated the engine when it was switched off would reduce wear on cars used mainly for short journeys which otherwise run cold. |
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Sealing is not a problem as long as you put the air intake someplace where it can get air. And most (all?) modern cars use water cooled engines, so airflow around he engine isn't necessary. Of course the radiator has to be outside the sealed part of the engine compartment. I imagine that some engines might rely slightly on the extra cooling from the airflow through the engine compartment, but since water cooling is so much more effective, it would only take minor changes to make it rely 100% on the liquid cooling system. |
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This design may help to slightly increase the life of the engine and maybe save some gas, but if we take it one step further, it may be possible to simplify the design of the engine. Aren't there a lot of design decisions made to allow an engine to run when cold? What if the engine was designed never to be run when cold? If the insulation from this idea was good enough, the energy necessary to keep the engine at full temperature might be pretty small. There could be an onboard gasoline powered heater to keep the engine warm (optional electric heater for cars parked in garages). If the car was going to be left off for a week, it could be allowed to cool, then be reheated using the heater before it was started. |
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[david-scothern], By "The hood would be insulated and sealed similar to the trunk." I meant to say that heated air rising from the engine would be blocked by the hood. To me the word "hood" denotes that part of the car's body you lift up when you want access to the engine. Sealing the engine compartment would certainly only be feasable when the engine was not running. |
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Good... in which case I agree with you totally and entirely. |
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Would it work to have a parking spot which had a big hunk of metal over which you position your engine? The engine heat would warm the metal mass and the whole thing would retain heat longer . . . maybe? Of course, heat rises which might make my idea suck. |
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Maybe a mass on the bottom of the hood that absorbs the engine heat and a heat pump that moves the heat to a radiator under the engine. I guess you'd have to plug something like that in, though. |
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[jurist], look up "winterization." My car still has an electric block heater, battery heater, and transmission/gearbox heater from its tenure in Alaska. |
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[scad mientist] I think you would find that most of the measures to allow an engine to start and run while cold involve giving it more gas. On a fuel injection engine the coolant temperature sensor is a major input to the system with low temperature resulting in a richer mixture and faster idle speed. On carburetor engines low temperature causes the choke to close (slurps gas) and the idle speed to increase. If someone out there has a car with a miles-per-gallon meter I would like to hear what they find - cold engine vs warm engine. |
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This stuff is my bread and butter. |
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Airflow around the engine is *certainly* necessary and a well-studied component in modern engine compartment design. While I'm just a lowly heater hose engineer, I've spent enough time in the aerothermal group to tell you this. |
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[RayfordSteele] While the radiator fan is running or the car is moving the air circulation around the engine would be the same as any other car. The air would still come in through the radiator and exit through the underside and back of the engine compartment. When the car is parked the changes I described would prevent the loss of engine heat by convection through the hood and heat transfer by conduction would be slowed by insulation on the sides and firewall. With a sealed hood and the cooling air inlet located low, as it is on most cars now, a "bubble" of hot air encompassing the engine and radiator could be maintained for some time. The changes I propose are about equivalent to throwing a large airtight insulated blanket over the hood of your car when you park it. |
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Baked but not implemented: VW developed a canister full of eutectic salts that would hold a heat charge of at least 168 deg. F for eight hours - enough to cut the warm-up period of an engine to about a third of its previous time. |
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Baked / kind of. My Toyota Prius does this. On shut-off, it pumps the fluids into an insulated area so they stay hot. |
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I think it would be easier/better to just keep the fluids hot rather than keep the whole engine hot. Methods to keeping the engine hot will likely hurt its normal need to be cooled. |
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[sophocles] Surely my measures are considerably simpler and less trouble prone than any scheme that involves draining and then restoring the coolant to retain heat. |
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Sealing the hood where it contacts the body of the vehicle and insulation on the sides and firewall of the engine bay would not inhibit the cooling system. Air would still flow through the radiator and then over and around the engine and exit the bottom of the engine bay. |
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Recently I got home (engine block nice and hot), and knew I wouldn't be using it again for a while. Leaving the heat to dribble away into the world is a great shame. |
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As it happens, my neighbour was just leaving. It would have been neat to string a flow/return hose coupling across and bring his block up to running temperature. Thermal jump start? |
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That's the pass-the-hot version... |
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The hot-stash version says I could dump the heat into my domestic hot water tank. |
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Domestic hot water hovers around 50C because the boiler runs cold, so it can condense. Ten (?) litres of engine water at 83C plus 100kg of hot (>100C?) engine block would tickle the temperature of the 150 litre (?) tank up nicely, and save running the boiler. Optimisation: f I knew I was about to bring all that heat home &the boiler not to run, we get better transfer because the thermal gradient is bigger. |
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In reverse: next time I'm starting on a cold day, I can run the process in reverse. The hot water tank holds a lot of energy, and flowing water can move it fast. |
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Being fast, it should beat electric engine block heaters because it doesn't have to fight convection under the bonnet [hood] for the 30 (?) minutes it takes to warm up. |
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Major disadvantage for be entirely useless in the car park at work, of course. Heat arrives, dissipates. Finish work, engine is cold. |
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there is a heat regulation issue. If the engine itself was
insulated extensively the radiator would need to be much
larger and the intake and exhaust manifolds would be much
hotter. Lets say we install radiator slats (very much baked)
and a complete underbody pan with some sort of closing
vent (also easily done) how many hours of extra engine
heat would you expect to retain? I think you could easily
test this using half inch aluminum backed thermal
insulation. |
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Anybody have a small inboard engine boat? The engine is in a box, and even the exhaust manifold is water cooled, so the box can be insulated for sound. Do they stay warm for longer after shutdown, Than say a car with the same engine? 1 hour? 1 day? |
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