Exhaust Waste Heat / Preussre Wave, Energy Recovery?

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Brent Hasty
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Exhaust Waste Heat / Preussre Wave, Energy Recovery?

Post by Brent Hasty » Fri Feb 17, 2012 8:30 am

On my bike build, the Gluppity Glup (A dr suse reference), I am planning on doing significant exhaust energy recovery coupled into the electric hybrid drive. Current thoughts are tiling the 2" square .065" thinwall tubing with TEG, that are liquid cooled with a binary rankine cycle expanding through a scroll compressor / expander alternator. The flywheel alternator will have a selective switch to enable and disable it.

So take a 10hp chinese engine
free up one hp from the crankshaft by eliminating the alternator, replace with TEG (thermal electric generators) on the exhaust
free up one hp from the crankshaft by eliminating the cooling fan, replace with electric cooling fan.
turbocharge to add 3 hp
Store the excess electricity in the hybrid drive and have a 5 mile reserve power booster.
Once the hybrid drive is full shunt excess electricity directly through the electric motor to the final drive.

All that and a custom tailored dr suse colorful riding suit......

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Re: Exhaust Waste Heat / Preussre Wave, Energy Recovery?

Post by Dougy » Fri Feb 17, 2012 9:44 am

The only problem is though mate is its been done to death, saying that though if the whole kit drops below £10, I may give it a go. :wink:

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Re: Exhaust Waste Heat / Preussre Wave, Energy Recovery?

Post by tappy » Sat May 05, 2012 1:10 pm

I agree with your principles but think you might need a spot of help with the calculations.

1hp= 745W, so unless you're constantly using 700W electrical power (over 50A) then you won't get an extra hp by deleting the alternator.

If you remove the crank mounted cooling fan you might gain 1hp, but then you need to provide power for a 1hp electric fan, AND the losses in the motor, and the losses in the generation of the electrical power.

By TEGs do you been thermopiles or Peltier devices? Their efficiency is shocking - often less than 10%. So for every 10 watts of heat being radiated from the exhaust, you'll only get 1W electrical power. To get 700W electrical power (that's what you've assumed for your alternator) you'd need to be losing 7KW of heat through the exhaust.
Internal combustion engines are typically 25% efficient so a machine producing 12hp, actually consumes about 48hp of chemical (fuel) energy, or about 35KW. It's not unreasonable therefore to assume that 7KW of heat is disappearing out of the exhaust, but if you try to remove that 7KW then you'll be sucking so much temperature and pressure out of the flow that you'd cause a lot of back-pressure and ruin the performance of the actual engine.

I really don't want to dismiss your ideas and often think along similar lines myself, but think you need to do some basic thermodynamic calculations. I'm happy to help :)

My own conclusions on the issue go like this:
Much of the problem with small diesel motorbikes is poor acceleration.
Much of the energy wasted is in deceleration against the brakes.
Hybrid drive with energy recouperation is a potential answer to both - store the braking energy when decelerating, and then add it to the engine power for good acceleration.
For steady cruising (12hp would get you about 60mph) you just use the engine power.

The difficulty actually comes in the transmission efficiency. A direct mechanical coupling from engine to rear wheel could be 98% efficient. A generator, converter, battery and motor would have a combined efficiency of about 60%. So for maximum performance you need mechanical coupling AND electrical coupling - this is where it starts to get a bit complicated!

When I've looked at it for my own project I'm slightly hamstrung by having a 24hp engine, but for a small engine like yours I'd use a CVT coupling between engine and jack-shaft, and a chain drive to the rear wheel. Then I'd also couple an electric motor/generator to the same jack-shaft.

Again, I'm happy to help / mull over ideas / calculations.

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