Capturing waste heat from diesel engine....

[DaltonASU]

I'm looking to capture waste heat to generate electricity. my first idea was to use a centrifugal supercharger but in effect use it in reverse, by changing out the compressor blade for a turbine blade and using the pulley to drive a generator.

One of my concerns is that the centrifugal supercharger will not be able to deal with the heat, and break down very quickly.

Another concern is that the geometry inside of the supercharger won't allow for proper flow.

I have tried doing research to see if something like this has already been done, but so far i haven't been able to find anything. If you have ny knowledge it will be extremely helpful. thank you very much

 

[Bribyk]

I don't think your supercharger is gonna be worth the time. If it was easy to use the waste heat from an engine every engine would do it. Look up "cogeneration" on the web.

 

[chicopee]

You would be better off to have the diesel exhaust gases go thru a FT or WT boiler to generate saturated steam which in turn would operate a saturated steam turbine- generator set,however,you'll need a lot of hot gases.

 

[KiwiMace]

Or pre-heat feed water is more likely.

 

[DaltonASU]

yeah and the preheated water can just come from the coolant system as long as its pure h20. then a condenser will needed to be added it line after the steam turbine, but that idea is definitely achievable. I'd still like to explore the options of using a exhaust driven generator. i've herd of a system used on old aircraft and big rigs that use turbo compounding that there is an exhaust driven turbine that actually attaches to the crankshaft of the engine to aid in power. but those units seem to big for my application of a 1L diesel engine.

 

[Bribyk]

Is this just something for you to tinker with? If you look at your energy savings for a 1L diesel it's probably not economical.

I've run some quick numbers based on a lean burn 32:1 AFR natural gas engine (cause I have the data).

The recoverable power (without condensing the water in the exhaust, which leads to other issues) coming out the exhaust is about 9 kW (12 hp). Based on a natural gas delivery rate of $6/GJ (current wholesale is ~$4/GJ) your cost savings is about $4 or $5 per day, meaning it would take you ~2 years to payback the centrifugal supercharger (if it works). Or you could save about $18 per day in electricity.

Running some quick numbers can save you from some really good bad ideas.

 

[Bribyk]

I should mention the engine used above is turbocharged, lean-burn and at full load/speed to approximate diesel performance. It is based on a 142L engine and then scaled down to 1L by dividing the power by displacement (142L).

 

[DaltonASU]

thank you for calculating that out, but not really looking to save anytype of money. the 1L diesel engine is strictly a APU for our experimental hybrid, and we are just trying to suck as much electricity from anywhere that we can. and so far we have utilized almost every system in the car to generate power except this exhaust gas thats going unused, so in the old engineering fashion if its there and hot and being unused make it do work.

 

[Bribyk]

The details about your application make it easier for posters to help.

You could try to use the turbine half of a turbocharger to drive a generator. The turbine side is different aerodynamically than a compressor side (such as in a centrifugal) You would have to carefully match the turbine to the engine and your generator choice though. If the engine is turbocharged already there's going to be less available energy to drive a second turbine. You'll also have to pay attention to the turbo bearing type/loading and the speed at which you're driving your generator.

 

[MintJulep]

BWM was playing with using exhaust gas heat to produce steam to turn a generator a few years ago.

http://www.gizmag.com/go/4936/

I haven't seen anything on it recently.

 

[DaltonASU]

yeah your right, i was kind of vague with my description, and that's something need to work on. i was thinking about using the a stripped down turbocharger, but i would have to go through at least a 10:1 gear ratio reduction being that the turbo charger will spool to RPM's of 100,000 and the generator should be >10,000. i need to pick out a generator before i do any optimization of gearing.

I've never stripped down a turbo, but would it really be as easy as just pulling it apart to get an exposed shaft to put on a pulley?

 

[Bribyk]

Tearing down a turbo is pretty straight-forward, just remove the bolts/nuts.

Bearings are going to be an issue with this. Turbo bearings likely won't handle the radial load that a pulley or gearset will place on the shaft. Balancing your assembly is also going to be critical and I don't think a belt will handle the speeds. You could see how it's done on a centrifugal supercharger though, maybe use the gearing and bearings from one of those and adapt it to fit the turbine.

 

[DaltonASU]

yeah i never really thought about the belt not being able to handle those types of speeds, there could be lots of stretching and too many inertial loads. thanks for helping through that.

so i guess i need to research steam generation more using diesel exhaust to turn at a lower speed.

 

[IRstuff]

I think, in general, the problem is that turning an electric generator requires mechanical work from the exhaust. This can only be achieved by manifesting as a backpressure on the exhaust, which increases the load on the engine.

That's why cogeneration typically uses only the waste heat.

TTFN

FAQ731-376

 

[KiwiMace]

A stirling cycle engine/gen can use this sort of heat to generate electricity.

 

[enginead]

What about thermo electric generation using peltier effect ceramics? Not sure how much power would be available but the concept is heating doped ceramics creates a current. Might be worth a look.

 

[DaltonASU]

yeah i have looked up thermo electric generation, seems to be viable, but also very expensive. looking to do this as cheaply as possible.

 

[chief]

Consider using the exhaust side of an exhaust turbocharger and using a magnet drive to power your Generator end. You will not have a physical connection and can easily regulate speed of Generator by varying the magnet field gap.

Offshore Engineering&Design

 

[DaltonASU]

hmmm im trying to imagine what your suggesting, a magnetic drive would transfer the spinning of the turbine shaft to the generator via a magnetic field?

 

[DaltonASU]

is there anywhere that you know of that sells these magnetic drives? or what the technical name is?