Electric supercharger for efficiency?

[California98Civic]

Originally Posted by sendler

The Mercedes F1 engine runs at 50% thermal efficiency due to the electric turbo harvesting all of the available waste heat and gas velocity in the exhaust.
.
https://youtu.be/anLDCVD6v1s
.

Thanks for that, sendler. Really interesting.

Here is an overly complex setup that allows a very small engine for greater fuel economy: a small, light-weight car, with an engine that is smaller than 1.0L. It would use a combination of a BAS-type eAssist, an exhaust turbo, and a very small electric supercharger for low end torque in the turbo lag seconds. Set up with the ability to harvest heat and kinetic waste energy in a battery with a grid charging ability too... Seems likely to win a Rube Goldberg design award!

[Ecky]

A belt-attached electric assist would do everything an electric supercharger would do, only more efficiently. This is the principle behind nearly every hybrid.

And, it only really works in conjunction with downsizing an engine and regearing. So, not something you can really bolt onto an existing engine.

[niky]

Originally Posted by sendler

The Mercedes F1 engine runs at 50% thermal efficiency due to the electric turbo harvesting all of the available waste heat and gas velocity in the exhaust.
.
https://youtu.be/anLDCVD6v1s
.

While true (and indeed, Mercedes have a fantastic engine, with their innovative Hot-Vee electric turbo assist system), that's a $12 million dollar engine.

[sendler]

The Mercedes F1 engine serves as an advanced proof of concept for an electricity harvesting turbocharger in a hybrid vehicle.

[California98Civic]

Originally Posted by Ecky

A belt-attached electric assist would do everything an electric supercharger would do, only more efficiently. This is the principle behind nearly every hybrid. ...

I understand, but there is something the e-turbo or e-supercharger does that the eAssist does not: reduce pumping losses. So if the eAssist is more efficient than a small e-Supercharger (is it?), we could imagine making the eAssist a little more efficient with a properly sized and tuned e-Supercharger to reduce pumping losses. I know it is not practical for ecomodders because it is way beyond bolt-ons and such. This discussion is just about conceptualizing. And yeah, we would want to downsize the engine, as well as capture waste heat in the battery. I noted that above, too. I get your point.

Originally Posted by sendler

The Mercedes F1 engine serves as an advanced proof of concept for an electricity harvesting turbocharger in a hybrid vehicle.

Yeah, that's what I see too. Of course it is too expensive and complex for a Prius bolt-on. Greater range is more cheaply accomplished with a bigger battery. Greater power is more cheaply accomplished with a more powerful hybrid engine/motor or different tuning. But I like thinking about these combinations.

[Ecky]

I'm not certain I follow the logic with reduced pumping losses - you're pumping more air through the engine, not less, right? That energy is still coming from somewhere.

Pumping loss in spark-ignition piston engines is the power required to perform their intake and exhaust pumping functions.

^ I mean, if you using grid power to run the supercharger, sure, the energy being used isn't coming from gasoline, but you could also just use that power to directly drive the wheels. The fewer steps between, the better. Ideally you'd have the electric assist after the transmission to reduce losses even further, but fabrication gets difficult. Maybe you could put a pullet on one of the CV axles?

What am I missing?

[California98Civic]

Originally Posted by Ecky

... What am I missing?

I am assuming we are downsizing the ICE engine and want to get similar power out of the total set up. Pump losses are parasitic. It is the energy the engine uses trying to suck air past the throttle plate. The boost from a turbo or supercharger reduces that loss. Yes, it uses other energy to do that, but that energy comes from capturing waste energy in heat and braking (plus the grid, sure). I have no idea, really, if simply the eAssist is good enough, better, or equivalent to an eAssist + e-supercharger. I am wondering about it. We'd need to know how much power would be gained from the supercharger and how much power it would cost to run it. Maybe a simple eAssist is better.

[Ecky]

I'm under the impression you'd get more power increase from an e-supercharger but in terms of total efficiency, it would be less than a straight e-assist.

[jamesqf]

Originally Posted by Ecky

I'm not certain I follow the logic with reduced pumping losses - you're pumping more air through the engine, not less, right? That energy is still coming from somewhere.

Exactly! With a turbocharger, the energy comes from exhaust heat. It's energy that would otherwise be lost out the tailpipe. With a supercharger, the energy comes from the engine, robbing power that would otherwise propel the car, and ultimately reducing fuel efficiency.

Originally Posted by California98Civic

The boost from a turbo or supercharger reduces that loss. Yes, it uses other energy to do that, but that energy comes from capturing waste energy in heat and braking...

NO! That's the fundamental difference between a turbocharger and a supercharger. The turbo uses energy from waste heat, the supercharger takes energy from the engine.

[Ecky]

Originally Posted by jamesqf

NO! That's the fundamental difference between a turbocharger and a supercharger. The turbo uses energy from waste heat, the supercharger takes energy from the engine.

To be fair, there are still energy losses associated. Intercoolers exist for that reason. They add exhaust restriction and there's also added friction, but I imagine it to be a net gain.