Electric supercharger for efficiency?

[sendler]

The most advanced F1 engines have electric turbos/ superchargers along with regenerative braking which make them the most fuel efficient gas engines in the world. Getting close to 50%.
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https://youtu.be/I7MOlYhLZDY
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[Angel And The Wolf]

How about spinning your turbocharger through an air conditioner compressor clutch with an electric motor until exhaust gas pressure can take over, then de-clutching the electric motor? Low end grunt, AND high end boost.

[Ecky]

Originally Posted by Angel And The Wolf

How about spinning your turbocharger through an air conditioner compressor clutch with an electric motor until exhaust gas pressure can take over, then de-clutching the electric motor? Low end grunt, AND high end boost.

Or, directly assist the engine with that electricity. Electric torque is 100% from 0rpm, don't even need to spin the engine.

[hayden55]

Originally Posted by ProDigit

An electric supercharger or turbo would generally not work, unless,
Mercedes has been doing some research...

Instead of a Turbo compressing incoming air, Mercedes equipped their car exhaust with turbo-like turbines; powering a small generator; feeding a battery, that goes straight to an electric motor.

You could even do without the battery, and just install an electric motor to one of the rear wheels, and directly connect it to the generator powered by the exhaust turbine.
It would only be bad if you'd be pressing the brake at the same time as the accelerator.

Anyway, you'd be surpassing 50% engine efficiency like that, or add about 30% of MPG.

If you do install a battery pack, or supercapacitor pack, you could harvest kinetic energy on one wheel (if engineered well).


The simpler solution is use one of those turbo exhaust blades and electric generator, to power an electric supercharger. The exhaust would be making a few HP in most cases.


Just adding a 12V supercharger would probably increase HP by 1% or less, and isn't worth it.

Its a big maybe on the exhaust turbine spinning an electric motor. It is the next low hanging fruit but Physics comes into play. Since (the best) turbines are only 30% efficient and then it has to go to an e motor then to charge a battery you have a very inefficient complex system. F1 has decided its too expensive and failure prone and are voting as a whole to get rid of what they call the "MGU-h" for the next rule set.

[RustyLugNut]

Originally Posted by Ecky

Or, directly assist the engine with that electricity. Electric torque is 100% from 0rpm, don't even need to spin the engine.

I remember seeing their plans to capture the remaining energy post turbo in their large diesel engines as they realized there was still much remaining energy in the exhaust stream. A large turbo electric generator drove an electric motor with about 50 hp rating. It wasn't much on a 500 hp diesel engine but it did recover some of that wasted energy. I don't remember them using a battery storage bank, just a smoothing capacitance. For all intents and purposes, it was a direct energy to the crank scheme. I'm not sure what happened to the project.

[ProDigit]

Originally Posted by hayden55

Its a big maybe on the exhaust turbine spinning an electric motor. It is the next low hanging fruit but Physics comes into play. Since (the best) turbines are only 30% efficient and then it has to go to an e motor then to charge a battery you have a very inefficient complex system. F1 has decided its too expensive and failure prone and are voting as a whole to get rid of what they call the "MGU-h" for the next rule set.

Not for Mercedes. Aside from their F1 engine, they now also have a similar engine in a high end, luxury coupe sedan.
It's just scavenging exhaust energy, and re-converting it to kinetic energy.
Energy that normally would be lost.
Unlike a turbo, which adds a lot of load on the engine (an engine is basically a big air pump), an exhaust turbine powering a generator, can have a fixed, or variable load, that will be much gentler on engines.
The excess power can easily be routed to an electric motor to one of the rear wheels (in case of a Front wheel drive car).
It's a workable upgrade for econocars, that don't cost a lot, and don't significantly lowers engine life. In fact, it could actually increase it, if used right.

Then again, the power output of such generator will be low. The excess power will do pretty much nothing to 0-60 time, due to the additional weight of motor and battery pack. However, it definitely can improve MPG!
It's basically a hybrid, driven on exhaust, rather than having a gasoline engine charge the batteries; while driving the car.

[pgfpro]

https://www.autosport.com/f1/news/13...step--mercedes

[niky]

Originally Posted by Ecky

Or, directly assist the engine with that electricity. Electric torque is 100% from 0rpm, don't even need to spin the engine.

10 Kw of electric motor equals 10 Kw of assist going to the ground.

10 Kw of electric motor spinning a turbo equals more than double that.

The only issue is the specialized high speed heat resistant motor you need to turn the turbine.

[ProDigit]

Originally Posted by niky

10 Kw of electric motor equals 10 Kw of assist going to the ground.

10 Kw of electric motor spinning a turbo equals more than double that.

The only issue is the specialized high speed heat resistant motor you need to turn the turbine.

Interesting idea,
However, with 10kW you're probably bringing the engine into serious overboost.
With risk of blowing the engine, or, a waste gate will be opened and energy lost, or just a fraction of the electric motor's power .
Electric supercharging from an electric exhaust turbine might be an option..

[Ecky]

Originally Posted by niky

10 Kw of electric motor equals 10 Kw of assist going to the ground.

10 Kw of electric motor spinning a turbo equals more than double that.

The only issue is the specialized high speed heat resistant motor you need to turn the turbine.

Where do you prefer the power in a daily driver? 20kw at high rpm and very little below 2000, or 10kw from a dead stop, with built-in ability to auto-stop, silently restart the engine, and creep along on electricity alone in traffic?

Adding boost requires changes to an engine which make it less efficient while out of boost. I'd take a high compression N/A engine with electric assist over an electrically supercharged one for a DD any day of the week. On a track or for racing purposes it might be another story, of course.

An anecdote, a Honda Insight weighs in at ~1850lbs, has a ~66hp gas engine with tall gearing, and takes around 10.5 seconds to 60 with a healthy engine and battery. Without electric assist, 0-60 time is closer to 13.5 seconds, with most of the additional time happening in the 0-30mph range. Torque is improved from around 55ft-lbs to 90ft-lbs at 2000rpm with assist, even though peak HP at 6000rpm only improves from 66 to 73.

How much boost would it take to improve torque at 2000rpm from 55ft-lbs to 90ft-lbs? In an engine with a nearly 11:1 compression ratio, how much would compression need to be reduced? How much boost would it take to match electric assist's 0-30mph time?