Exhaust Heat Recovery - Steam Power - Fuel Economy, Hypermiling, EcoModding News and Forum

Daox · 06-30-2010, 03:14 PM

I was thinking about new mods the other day. Of course, one of the first ideas that always pops into my mind is waste heat recovery. It is a hugely untapped area since only approx 1/3rd of the energy from burning gas is used to propel the vehicle. Massive amounts of heat energy are just blown out the tail pipe. So, for kicks I calculated it. To keep the Paseo going 55 mph down the road (the majority of my commute) it takes roughly 9.5 hp. That means 19hp is going out the radiator or tail pipe.

19hp is a lot of power. About half of that is exhaust heat and half is absorbed into the coolant. So, we have 9hp available for the taking out of the exhaust. How do we capture it though? We've talked about a bunch of ways of doing it on EM over the years, peltiers/TECs, turbos, quicker coolant heat up, and more. So, the next question becomes, how do you capture it without spending a small fortune? I think I have an idea that might work.

My idea is to capture the heat energy as pressure by heating water with the exhaust heat. With this pressure, we can spin mechanical devices or generators/alternators as is my current idea.

The implementation is relatively simple, you weld a sleeve around the exhaust pipe (depending on the pressures you may need a thicker pipe). Fill it with water, and route a line to something that will do work for you. I was thinking of routing the outlet to a turbine that spins an alternator. All the benefits of an alternator delete, but no plugging in to recharge. Depending on the efficiency, you very well may even have excess power. I haven't even really thought of how else to use this yet.

I know this sounds a lot like the BMW turbosteamer or something like that. But, I think its completely doable and for pretty cheap. I just need a bit of help polishing the idea.

Frank Lee · 06-30-2010, 04:10 PM

First quick impressions:

1. If spinning a turbine, the water is nothing more than a transfer medium, with it's own complexities, weight, and losses. I'd stick the turbine in the exhaust stream.

2. This is probably way out there and not viable, but I think it would be neat to be able to bottle up all that heat energy and use it to help heat the house or garage via quick-connect xfer lines or something.

Daox · 06-30-2010, 04:32 PM

I agree the turbine in the exhaust is a probably a more efficient approach and I have thought about it. The problem I find is that its hard to deal with something spinning as fast as a turbo is to convert it into usable energy. If you have ideas on this I'm all ears.

The heat transfer would be cool too. Storage of that heat energy is a problem as it would require much added weight I'd imagine.

Frank Lee · 06-30-2010, 04:37 PM

Yeah. All these things have problems... or we'd see them already right?

brucey · 06-30-2010, 04:47 PM

What about just using thermo-plates that generate electricity when heated up? The same kind that they use in wimpy coolers that cool one side and heat up the other when electricity is applied. If you apply heat to one side and keep the other cool, it will generate electricity. I believe.

Daox · 06-30-2010, 04:49 PM

That would be the peltiers/TECs I mentioned earlier. Their efficiency is horribly low, 8% or less I think.

ShadeTreeMech · 06-30-2010, 05:02 PM

Quote:

Originally Posted by Daox

I agree the turbine in the exhaust is a probably a more efficient approach and I have thought about it. The problem I find is that its hard to deal with something spinning as fast as a turbo is to convert it into usable energy. If you have ideas on this I'm all ears.

That's an easy one. gear it down. Adapting the gearbox of a drill to a turbo should be simple enough which will bring down the rpms, then pick your application I suppose.

Frank Lee · 06-30-2010, 05:06 PM

Re: alt: I wonder if the alt magnets and whatnot could be built right into the perimeter of the turbo itself? No gearbox, no separate alt.

Daox · 06-30-2010, 05:08 PM

Quote:

Originally Posted by ShadeTreeMech

That's an easy one. gear it down. Adapting the gearbox of a drill to a turbo should be simple enough which will bring down the rpms, then pick your application I suppose.

Sorry, that would not work. Turbochargers spin incredibly fast. Smaller turbos can spin over 100,000 rpm, and some up to 200,000 rpm. Gearing it down is a big pita, you'd have to make your own journal bearings to take that kind of rpm input. Then you have to find something that will spin that fast without blowing up. It gets complex really fast.