Mimicking Gen3 Prius Exhaust Heat Recovery

[Daox]

Well, it does make sense for me. My wife drives around a lot during the day servicing different companies. The dang aluminum block cools off pretty quick in that car and this may allow very fast warm ups which would really help out in my case. I've also noted temperature drops of up to 35 degrees when going from highway to slow city driving.

[Daox]

Interesting presentation Bearleener, thanks for sharing. Of course, exhaust heat will be much more plentiful on a gas engine vs diesel due to it being less efficient. Also, they didn't show their setup. I wonder how they did it...

[Daox]

I did the test the other night. It didn't turn out so great, but I think it still gives you an idea of how much energy there is to capture. The outlook isn't so bright.

For the testing, I used the Paseo. I took exhaust pipe temperatures from just behind the cat. The exhaust manifold on the car comes out the front of the engine, then wraps around and goes toward the back. The cat is probably a good 5 feet from the head. The main problem I encountered was the new exhaust. It is so shiny, that my IR thermometer had problems getting consistent readings. I got as accurate of readings as I could. The coolant temperature was measured with the scangauge.

It took 3.5 minutes for the exhaust pipe temperature to exceed the coolant temperature. At this point the temperature does rise up above coolant temps pretty quickly. However, this is also just sitting and idling. If we were to be actually driving, both coolant and exhaust pipe would heat up much faster. Unfortunately, I have no way of testing this.

On the other end of the stick. I did take one temperature reading of the exhaust manifold right after the test with the engine still running. It was right around 580F, so roughly twice as hot as the pipe behind the cat. This I do think would be a viable area to extract heat from. However, the result would be the cat warming up slower and increased emissions.

Here is the graph I made. Temperature is in degrees fahrenheit. Time is the bottom scale and is in seconds.

[blueflame]

Directing intake air from the exhaust manifold may work as well with less cost or work.

A hood blanket/belly pan will also retain engine warmth and reduce warm up times.

[Daox]

That is probably quite true.

[basslover911]

About the exhaust manifold vs the cat.

It would take longer for the cat to warm up, but the engine would also be warming up MUCH faster which I think would offset that downtime of the cat... ? Get what I am saying?

[dremd]

I can tell you from my supra experiences that EGT's are with in 200 deg of where the will be at full temp in 30 seconds (Say 700F in 30 seconds of light driving).

Also had an idea in regards to drain back.
How about a drain back + heat exchanger?

Basin/ tank low mounted, submersible pump in tank, pump water up to exaust manifold heat collector, through a exhaust heat water -> coolant water heat exchanger, then back to the tank.

If we could weld some tubing on to the exhaust manifold we'd get way better heat transfer.

For the Drainback/ exhaust heat -> coolant heat exchanger perhaps a heater core with engine coolant flow ruining inside it with a box around it containing drain back water. Just an idea.

Issue will be how much heat can we steal off the exhaust stream before the catalytic converter has issues.


I *think* that would all work.

Other question is how much gain will you get out of it? very cold climate + pulse an glide probably a good bit. Warm climate + turbo diesel probably not a lot.

[basslover911]

What do you think would be a good enough gain if this works?

The car warming up 30 seconds faster? would that justify itself? Or would 2 minutes faster warm up be the minimum...

[dremd]

Originally Posted by basslover911

What do you think would be a good enough gain if this works?

The car warming up 30 seconds faster? would that justify itself? Or would 2 minutes faster warm up be the minimum...

I think that has to depend on the car, your driving style, and your goals.

[MetroMPG]

Originally Posted by Daox

For the testing, I used the Paseo. ... It took 3.5 minutes for the exhaust pipe temperature to exceed the coolant temperature. ... However, this is also just sitting and idling.

Oh, how it must have pained you to idle your car like that.

But we appreciate your reduced fuel economy in the pursuit of science!