Idea: Use engine exhaust to heat coolant for quicker warm ups? - Fuel Economy, Hypermiling, EcoModding News and Forum

ps2fixer · 03-09-2012, 04:40 AM

I have read about ideas of using the exhaust to heat the coolant with no good solution to clear out the coolant when up to temp. I have been thinking since a block heater helps when plugged into the wall, that maybe using some of the engine's work ability to help heat up the coolant faster might result in better average MPG for a given trip. Of course there are a ton of inefficencies which probably kill off this from being useable, but figured it never hurts to suggest an idea.

Bad setup:
200-500w (or maybe larger with a larger alternator?) block heater
inverter that can handle the constant 200-500w draw

Better setup:
Some sort of DC based block heater with no inverter losses.

What do you think? Winter vs Summer use?

wheel_of_steel · 03-09-2012, 06:18 AM

I think you would find that the inefficiencies of even a decent DC system would just consume even more power, however I'm open to ideas/solutions.

What about a grille block mang? Although you are still 'wasting' the exhaust gases, it will assist with warm-up times for very little outlay.

On second thoughts, coolant temperature usually follows block temperature pretty well. Remember that most of the coolant is circulating inside of the block, apart from the stuff that is kept in your radiator and heater core by the thermostat. I'm not sure how much you would gain by adding more capacity to the cooling system to warm it faster... hmm. Good question.

ps2fixer · 03-09-2012, 07:30 AM

Might be an odd idea, but it would seem a coolant system that has less coolant would be better for faster warmups.

If memory servs me correct, in my corolla, the heater core gets constant circulation when the valve is open (controlled via heater controls). If that is true, a in coolant heater setup seems to be ideal.

Going off the deep end here, but someone with good fab skills could make some sort of flap in the exhaust pipe to reroute the exhaust though some sort of heat exchanger to the coolant only durning warmup, and when it is warm have some way to close the flap and have it completely bypass the "coolant heater". Image below is my crappy paint skills via laptop

. I think this would be the most ideal setup, but I think it would be quite a lot of work.

I guess to really figure how possible the block heater idea would be is to look at current fuel usage when cold starting and driving the first say 5 miles vs how much extra fuel it would use to power the heater and how much shorter the warmup time ends up being. I'm guessing this probably wouldn't have any benefit at all for short trips since a good share of the trip would be with higher than normal loads, and for a long trip... if it did inprove the average, I would guess it would be a small amount, maybe 1-2%.

If only there was a really efficent way to store heat energy when the engine was turned off, then there wouldn't be "cold starts" any more

.

oil pan 4 · 03-09-2012, 03:44 PM

Quote:

Originally Posted by ps2fixer

but someone with good fab skills could make some sort of flap in the exhaust pipe

Check out "exhaust cutouts" on summitracing.com for a valve like you are talking about.

ps2fixer · 03-09-2012, 08:09 PM

Interesting, didn't know the prius has something already along the lines of a exhaust heated coolant.

Post #8 has a photo.
how good is the heater? - PriusChat Forums

The electric flaps would be nice from summitracing, but seem a bit high priced to me. I guess if it saved enough fuel it would be well worth it though.

A fairly simple way to build a heat exchanger could be to run coolant though a 2nd heater core first that is on the exhaust manifold, and when the engine is up to temp, some how move it away so it isn't overworking the oversized cooling system. Maybe a driver controlled heat shield would work.

pete c · 03-09-2012, 08:42 PM

I really think folks put a little too much importance on getting the coolant to temp very quickly. In the dark ages before FI, it was more important, but, still not as big a deal as it's made out to be.

A block heater is a good idea, but doing it any other way with rerouting exhaust through a heat exchanger is silly, IMO. And the idea about using electric resistance heating from the alternator is beyond silly. Just think about how much hp it would take to spin the alternator to provide this heating.