Phase-change material for down-sizing cooling system

[Galane]

IIRC, Volvo experimented with phase change materials in an insulated container, heated by engine coolant. Something about it in the early 1980's in Popular Science or Popular Mechanics.

They abandoned the idea due to size and weight and the insulation materials available had to be too thick to make it practical.

But with advances in insulation technology, the overall size and weight can be reduced while making the amount of PCM large enough to be useful.

For a vehicle used every day, there needs to be enough PCM with good enough insulation to keep it liquid at least 24 hours. Another thing is the vehicle must be driven long enough each time to "recharge" the PCM.

If you don't run long enough to fully heat up the PCM tank, then it's just wasted weight.

[Ecky]

Originally Posted by meelis11

Anyone has good examples to show how to set up exhaust heat exchanger?
Basically you need to wrap copper pipe around exhaust and coolant flows through that spiral? How many wraps around exhaust?
How much is it possible to make warmup time quicker?

That autospeed idea seems really good to use it as heat battery - to preserve waste heat that in the morning you get engine warm sooner.

I'd be wary of adding any weight to my car, but an exhaust heat exchanger sounds like a great idea, if you could overcome some practical problems. I'd be interested in how Toyota overcame some of them - specifically, you don't want the exhaust heat exchange to be part of the cooling loop once the engine is up to temperature... however, simply changing how the thermostat functions (instead switching from exhaust heat exchanger to radiator loop once up to temperature) would not work, as the liquid in that part of the loop would quickly reach astronomical temperatures. Instead, you would need to somehow decouple the heat exchanger from the exhaust at some point.

[Galane]

Use a two path exhaust pipe with flaps to route the heat through the exchanger or not. Another possibility is have the heat exchanger near the exhaust pipe and use air heated by the exhaust pipe to blow through the coolant heat exchanger.

That would need something like an "air stove" around part of the pipe, similar to the old heat risers that used to be ducted to the air filter housing with carbueretors. Probably would need to cover more of the exhaust pipe. A length of double wall pipe, with the gap sealed at the ends and a fan blowing circulating air around through the space between the pipes and the coolant heat exchanger would allow for cutting off the heat.

[oil pan 4]

Water mist injection on my diesel seems to really help keep the electric cooling fans off.
The water pump uses a tiny amount of power compared to running a fan.

[niky]

I've always wondered about using sodium acetate as a heat sink for car engines... Phase-changes to liquid when hot, but stays liquid when cooled down, so it could be used to bring an engine partially up to temperature when you trigger phase-change back into solid state (occurs at some 50 degrees C).

[oil pan 4]

Got anything proven to work?

So far with water injection I can keep my electric fans off with my diesel. Driving around town when I use to need my fans the most I need the least water, maybe about 2gph around town moving at slow speed. When stopped less than 1gph will keep it cool.
I didn't expect water injection to be any use at all at low speed or when stopped.

[Tesla]

Read the article a while back, nice idea for a niche application.
For everyday operation wouldn't the first step be to remove all heat sensative equipment from the engine bay, like battery & electronics, then completely seal & insulate the engine bay so the entire engine including coolant is a heat sink. Have a cool air intake, coolant in & out controlled by thermostat & exhaust out.

[Air-Hybrid]

Originally Posted by Tesla

Read the article a while back, nice idea for a niche application.
For everyday operation wouldn't the first step be to remove all heat sensative equipment from the engine bay, like battery & electronics, then completely seal & insulate the engine bay so the entire engine including coolant is a heat sink. Have a cool air intake, coolant in & out controlled by thermostat & exhaust out.

If you insulated the engine bay completely (you'd need to manufacture new cowling to pipe the air exiting the rad) the header and exhaust heat would quickly raise the temps around the engine and then the coolant system would need to deal with quite a considerable additional thermal load. And even if the car was driven gently the extra need to radiate heat via the coolant through the radiator would not do anything but bad things for efficiency, and may still boil the coolant.

[Air-Hybrid]

Water injection for cooling Diesels is nice, but the water still has to be carried, even if the consumption is quite low. (I assume the 1gph stated above is 1 gallon an hour, which still adds up).
The idea of having such a massive overhead, in terms of sizing a cooling circuit and radiator for sustained full-on driving in the hottest & driest climates is, I guess, what car mnftrs have to build for, but it would be nice if, like a hybrid-electric car around town 'borrows' power from its batteries, the cooling system could borrow heat-sinking capacity at the moment when the driver needs it (say to climb a long hill) against a later time when the engine is working much less hard.... That was my original thinking and I still have little doubt it would make no difference at all to all but the most lead-footed of driver.

[oil pan 4]

For a large vehicle like what I have, I am going to try to put a used 40 gallon plastic side fuel tank under there and use that for holding water. I would only fill it to capacity before a long trip because 40 gallons of water will weigh something like 330 pounds.
On the open road I would be using about 2 gallons of water for every gallon of water.
40 gallons of water to 25 gallons of fuel on a road trip would make a pretty good match.

A diesel car could get away with using far less water.