Use for exhaust heat?

[hattymender]

Been playing 'hunt the oil leak' (again). While lying under a warm 110 with the exhaust 6" from my nose waiting for the next drip (it's the transfer box) I got to thinking about something that's been troubling me for some time; how much energy is 'wasted' through the exhaust? And can I recover some of it?

(as an aside, how many other's find lying under a Land Rover strangely therapeutic? Or is it just me? )

I seem to remember reading somewhere that about 50% of the energy in fuel goes out of the exhaust pipe, and a fair bit through the radiator. Now 50% of a V8's fuel is a lot of energy. Has there been any successful attempts at capturing some of this?

I'm thinking something like a supplementary steam engine driven by a flash boiler in the exhaust pipe (closed loop system?).

Or a Stirling heat engine driven by hot exhaust?

Or directly driving ancillaries via a turbine?

Possibly simpler, and more relevant with winter coming, is to use it for extra heating (wrap a copper pipe around the exhaust and pump it through an extra heater)?

Presumably it's not that simple or mainstream manufacturers would all be doing it?

[gsr341]

dont have any ideas for your ''spare heat'' but watched a program a few weeks back on building the bugatti veron , it acctally produces 3000 BHP 2000 of which is heat , cant rember the exact figuers but an hour running could provide the heating needs of up to 100 houses

[rtbarton]

Putting something such as a turbine in the exhaust pipe is a no-no as the back pressure will be increased which could affect the tuning and you'd need more pwer from the engine to overcome the resistance.

A Stirling engine likes all the heat concentrated in one place so that wouldn't work.

I'd favour the water jacket, but again taking heat from the exhaust may affect the tuning.

[Briarston]

Been playing 'hunt the oil leak' (again). While lying under a warm 110 with the exhaust 6" from my nose waiting for the next drip (it's the transfer box) I got to thinking about something that's been troubling me for some time; how much energy is 'wasted' through the exhaust? And can I recover some of it?

(as an aside, how many other's find lying under a Land Rover strangely therapeutic? Or is it just me? )

I seem to remember reading somewhere that about 50% of the energy in fuel goes out of the exhaust pipe, and a fair bit through the radiator. Now 50% of a V8's fuel is a lot of energy. Has there been any successful attempts at capturing some of this?

I'm thinking something like a supplementary steam engine driven by a flash boiler in the exhaust pipe (closed loop system?).

Or a Stirling heat engine driven by hot exhaust?

Or directly driving ancillaries via a turbine?

Possibly simpler, and more relevant with winter coming, is to use it for extra heating (wrap a copper pipe around the exhaust and pump it through an extra heater)?

Presumably it's not that simple or mainstream manufacturers would all be doing it?

VW were using exhaust heat (warm/hot air) for cabin heating years ago with air cooled

engines. Perhaps you could make up a hot air system. Would need a fan, a fresh air intake, and make VERY VERY sure you don't have an exhaust leak in the crucial area!

[Aragorn]

Turbocharger....

[disco2hse]

VW were using exhaust heat (warm/hot air) for cabin heating years ago with air cooled

engines.

Yes and it was pretty effective too. But you are taking the engine heat via a fan and just redirecting it through ducts into the cabin.

I would think that for this to be effective the place to capture the heat would be at the manifold, where it is most intense. On salt water cooled marinised engines it is common to put in a heat exchanger into the exhaust system. This has a fresh water and salt water component in which the fresh water is circulated through the water jacket in the same way that water is run through the car's radiator. The heat in the fresh water is carried off by the salt water, which is then discharged through the exhaust. This has the added benefit of cooling the exhaust too. In one vessel I had the salt water was carried around the exhaust in a water jacket before it was discharged so that the exhaust fumes were significantly cooler when expelled.

With the caution about carbon monoxide and other nasty gases in mind, what you could do is construct a water jacket around the exhaust manifolds that could be used to reticulate heat into the cabin. Rather than having the heat used to warm up cold air you could either plumb it into a modified heater box to increase the heat presence in the existing heater or run pipes, say, under the floor or around the cabin roof to create ambient warmth like a radiator in a house. A simple tap or shut-off valve could be used to control the circulation of water. Circulation can be aided, if necessary with a small pump, otherwise I suspect the natural tendency for heat to rise and cool water to fall would be enough to circulate water throughout the system.

All been done before. Nothing new there, just in the application.

Alan

[reb78]

make VERY VERY sure you don't have an exhaust leak in the crucial area!

That would be my worry - you may not notice a leak early and may end up with CO poisoning. The copper coil and water jacket it a better idea i think - safer and will probably work out easier in the end.

Also, i guess the VW systems were also good as they were air cooled engines werent they? - so more heat than with ours perhaps. I hear that they were apalling when the flap setup went bad, but that is the same as a poorly set up heater on a defender!

[Mr Bean]

You could weld a larger diameter pipe around your exhaust to make a jacket around it.

This jacket you would pump water through it to heat the water up and in turn this would go through a radiator/heater matrix to warm the interor.

If the gain (delta - t) is large enough it may even work as a shower in the wild when on overland.

How is your pipe welding skills?

[dirtyninety]

I believe a petrol engine is only 26% (?) efficient, meaning only 26% of your fuel is actually converted into a rotating motion, the rest is noise and heat!

A diesel is a better 36% (?)

(my percentages seems wrong... but there very close, its a long time since i learnt about this at uni! and i was hungover or drunk most of my uni life)

[disco2hse]

You could weld a larger diameter pipe around your exhaust to make a jacket around it.

This jacket you would pump water through it to heat the water up and in turn this would go through a radiator/heater matrix to warm the interor.

If the gain (delta - t) is large enough it may even work as a shower in the wild when on overland.

How is your pipe welding skills?

Yeah, that's the kind of thing I had in mind. The important difference between heating water and air (apart from the transmission of noxious gases) is that water takes a lot longer to cool down than air so you can also store it for later use.

Try this for size

[TheHarv]

http://en.wikipedia.org/wiki/Crower_six_stroke 

[nicks90]

i have this mental image of pictures of his 110 appearing on here with a whopping big white household radiator strapped behind the front seats on the bulkhead and copper pipes running all over the cabin into the engine bay

[landroversforever]

On a related note... How about having the Radiator in the cab? Get some warmth from that . Would worry about it springing a leak and the resulting pain though.

That 6 stroke is rather interesting .

Would taking the heat directly from the manifold affect performance for the better/worse/no effect? Any effect on the turbo if its getting much cooler gasses (assuming a Tdi)?

[Superpants]

There are such things as turbo generators- as far as I know the only real world use for them (other than the odd foray into motorsport) is combined heat and power plants where the system can be designed to cope with the required flows through the exhaust and the associated back pressure.

With modern engines, the deign of the exhaust system is critical to the emissions of the vehicle, so it isn't very practical to add items into the system without a lot of development work.

Having said that, you can get power out of a junction of disimilar metals- the seebeck effect. This is the way a thremocouple works, generating a voltage from the heat input. With enough junctions you could extract maybe a few watts of electricity- this is horrendously inefficient!

[Mr Bean]

Or fit a turbo and instead of using the impeller wheel giving you extra power you could use it to drive as an air compressor filling a reservoir to run air tools.

[FridgeFreezer]

I can see a few issues around the practicaility of doing this:

- As has been stated, exhaust leaks / carbon monoxide are a risk. When VW did it they were operating in less safety-conscious times.

- The exhast is quite high temperature, so you may boil water in the jacket if there's not enough cooling/flow to keep it within spec.

- Trying to fit a water jacket round a manifold / manifold into a water jacket would be tricky to do without b*ggering up the manifold's characteristics and losing more than you gain.

- If you want a better heater, remember the engine is already throwing away huge amounts of heat through the radiator, your standard heater is only using a tiny bit of this. Just hijacking the existing coolant circuit and adding a better heater matrix (or two, or three) would gain you loads of readily available heat, with the bonus of being regulated and cooled by the main rad so as not to boil over when you don't want a sauna in the cab.

[Bush65]

With larger diesel engines there is a class known as compound engines. The simple description is; they are like a conventional diesel with an exhaust driven turbine, like a turbocharger, but instead of the turbine driving a compressor, it is compounded with the drive train.

From memory, many of the well known manufactures of diesel engines also produce compound engine.

Edit: the purpose is to increase efficiency.

[Phils truck]

Another possibility is to convert the exhaust heat into refrigeration.

There were some trucks using this system to refrigerate food goods during transport.

From memory the ejector tube concept was used, and latter the ammonia/hydrogen concept.

Wood ant bee too difficult to design a system to cool down the air intake for more horse power.

Then again,,, if you can at least achieve COP 1.5 conversion efficiency, pumping snow flakes out the exhaust would be a trip.

Phil...

[Dave W]

Many years ago our house heating was done with storage heaters and I often wondered if the same principal could be used to provide or supplement a warm start system by storing the heat overnight and then using it to warm the engine at a pre-determined time in the morning. Essentially storing the heat from the engine's last run to warm it up prior to starting it. It would also be a safe option to supply a source of cab heating when the engine is turned off if you are sleeping in the vehicle overnight.

I did play around with it and the main drawback was the weight and bulk of the bricks that are used in household systems but it did kind of work in theory at least. I always had the suspicion though that transporting the bricks around would cost more than any potential fuel saving !

[reb78]

BMW have a latent heat storage system in some of their vehicles for heat storage - much less bulky than bricks and very effective. It is some kind of chemical reaction that stores engine heat so when you jump in the next morning you have warm air from the second you turn on the engine. Its quite nice on a winters morning trouble is, if it is icy, i wont be in the BMW, i'll be freezing my bits off in the defender! Just gotta get the eberspacher fitted, then that wont be a problem anymore

[ian_s]

Water Cooled exhaust manifolds are pretty much standard on boat engines, but they usually look to be quite innefficient.

the water jacket has two main functions:

1) it reduces the temperature within the engine compartment, as these often have limited circulation.

2) it reduces the EGT to a point where rubber exhaust tubing can be used, making it much easier to route the exhausts through bulkheads and through the hull.

neither of these has any real advantage on a car though

[FridgeFreezer]

BMW have a latent heat storage system in some of their vehicles for heat storage - much less bulky than bricks and very effective. It is some kind of chemical reaction that stores engine heat

Are you sure this isn't just a fuel-powered heater like an eberspacher, as a lot of modern cars have these fitted now - even the diesel Freebies.

[reb78]

Are you sure this isn't just a fuel-powered heater like an eberspacher, as a lot of modern cars have these fitted now - even the diesel Freebies.

No definately not. That is another option on the BMW - they use webasto heaters. The latent heat system is a salt chemical of some sort that that traps heat somehow and releases it in the reverse chemical reaction. I found a paper on it earlier - its on my work PC, can email it if anyone is interested. They can hold heat for up to 7 days in cold climates.