
Electric Turbochargers: The Next Big Thing in Fuel Efficiency - nkurz
http://www.navigantresearch.com/blog/electric-turbochargers-the-next-big-thing-in-fuel-efficiency
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Animats
It's just a supercharger, not a "turbo" anything. A turbo-supercharger is
driven by an exhaust turbine. Mechanically driven superchargers for cars go
back to 1921, and were widely used on aircraft.

As with most things electrical, the control is better with an electric motor.
That seems to be the main advantage here. It's something else the engine
control computer can use to optimize the engine.

There's an argument for electric oil pumps, too. You can have full oil
pressure before engine start. A sizable portion of engine wear comes during
the first few turns when the engine is cold and dry.

IC cars seem to be heading towards a power package where the outputs and
auxiliaries are all electrical, like Diesel-electric locomotives.

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sologoub
Thought the same thing as soon as I read this - this is not a turbocharger,
it's an electric air compressor.

The efficiency of the turbo comes from the use from the otherwise wasted
exhaust gas energy being used to compress the intake air. Superchargers use
main engine energy via the accessory belt, thereby consuming some of the
energy they help produce.

Benefits of injecting compressed air into an internal combustion engine is
well documented and supported by physics. The main problem is how to do it for
free or nearly free. One option that the article seems to imply is to separate
power generation and compression, perhaps using some sort of dynamo in exhaust
and running generated power to compressor?

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paddy_m
Look at what F1 teams are doing this season. They have an electric dynamo on
the turbos, and on the driveshaft. They can recover energy out of the turbo or
put energy into it, the same with the driveshaft.

Mercedes has the best engine by far this year. They put the exhaust turbine of
the turbocharger on the back of their v6 engine, it is connected to the
compressor via a long driveshaft that goes in the V of the cylinder bank. This
separation between turbine and compressor allows them to keep a lot of heat
away from the intake side, which allows a denser charge, which allows more
power. The dynamo for the turbo also sits in the V, I think they have some
type of clutch there also so they can let either side of the turbo system
freewheel.

Note:I think dynamo is the proper term for an electric motor which can also be
a generator.

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error54
As a once and future car nut, the idea of electric superchargers have been
around for a while. What I'd like to see is how an electric supercharger is
better than a mechanical supercharger other than more fine grained control
over the motor.

For the non motor heads:

Turbo: exhaust spins a compressor which shoves more air into the engine
producing more power.

Supercharger: a pulley running off the engines main drive spins a compressor
which shoves more air into the engine producing more power.

Electric Supercharger: electricity powers a compressor which shoves more air
into the engine, producing more power.

One of the main reasons electric superchargers haven't really caught on is
that power to spin the supercharger has to come from the alternator which
itself derives its power from the engine. So in essence, a mechanical
supercharger does the same job but it cuts out the alternator as the middle
man. Granted, I tend to think in terms of what will generate the most HP and
torque for the least cost so suppose with the right programming and fine
tuning the ECM and the electric supercharger, one could achieve excellent fuel
mileage which seems to be their goal.

~~~
sparkman55
If you're already charging batteries for a hybrid electric drivetrain, perhaps
the electric supercharger makes more sense? After all, the electric motor
itself is used for extra torque when the gasoline engine is incapable. The
energy to drive the supercharger could be recovered during regenerative
braking...

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graycat
There's an issue here: For the air compressor, how does that work?

There is the _roots_ idea of two lobes, maybe a foot long each, interlocked
like two gears, inside of a housing that is so tight against the lobes that
there are no air leaks. So, talking a lot of friction. Then, roughly double
the RPM of the compressor and double the amount of air moved.

Corvette and Dodge are using roots.

Then there is a centrifugal compressor: It's simpler with less friction, but
double the RPM and roughly square the amount of air moved. So, at low RPM,
move too little air and at high RPM, move too much.

So, centrifugal air compressors, for supercharging, driven by a belt off the
front of the engine, had the compressor RPM directly proportional to the
engine RPM with too little boost at low RPM and too much boost, and too much
power to drive the compressor, at high RPM.

The beauty of the usual exhaust driven turbo charger is that the exhaust side
took the square root of the exhaust flow and the cold side squared it again
and, thus, moved air volume directly proportional to engine RPM -- great.

But with an electric motor, could have a centrifugal compressor, the simpler
mechanical option, always with the right RPM, not directly proportional to
engine RPM.

Of course, could also have a turbine, that is, with little blades like in a
turbojet engine -- these tend to be expensive.

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yason
This is just one step in a continuing development. Engines become smaller but
charged give the same amount of power or more than existing engines. The
engines are eventually only used for spinning a generator (with the rest of
the drive train being electric) which means the engines can be explicitly
designed to run short spurts at very high power output, very high efficiency
but also higher wear (but that's ok because it doesn't run for 10 hours
straight).

The engines probably end up being tiny but charged diesel engines (diesel
cycle is more efficient and diesel engines can easily run on various kinds of
renewable or recycled oils) that are designed to charge the car batteries with
the best possible efficiency in the shortest possible time. Most driving will
be powered by the battery only within 100-200 mile radius, and people are
probably fine with limiting the top speed of the vehicle on longer distances
so that the tiny engine can remain tiny and weigh less.

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ChuckMcM
This is part of Volvo's new engine design (see
[http://autoweek.com/article/car-news/volvos-new-electric-
sup...](http://autoweek.com/article/car-news/volvos-new-electric-supercharger-
explained)) And it is a valid question if it is a 'super' charger or a 'turbo'
charger. I go with 'super' as the motor powers a generator which provides the
electric power in concert with batteries. However if the batteries are simply
charged braking action (regenerative braking) and then that charge is used to
provide the low RPM compression boost its kind of a turbo and kind of not.
(otherwise wasted energy being recycled for better engine performance). I'm
guessing that an thermoelectric intercooler doesn't provide as much
improvement but it would be fun to have both working together.

~~~
205guy
Not turbo because the exhaust energy is lost. The comments above mention the
F1 solution: put an electric motor/dynamo on the turbo so you can drive the
intake earlier and regenerate from the exhaust side.

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graycat
There seems to be another point in the article but not emphasized: The
potential role of direct fuel injection.

So, go ahead and let the compression ratio go up through the roof, from the
piston in the cylinder and/or the supercharger. And, don't bother working hard
to cool the compressed air before letting it past the cylinder intake valve.

Why cool in the past? Because otherwise the heat of compression would cause
pre-ignition.

What's different with direct fuel injection? The fuel is not in the hot air in
time for pre-ignition. So, basically have a Diesel situation and, indeed,
might not need a spark plug! I'm not sure people are taking advantage of this
possibility now, but have to suspect that there is an opportunity here.

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readerrrr
I know it isn't comparable, but honestly, the next big thing in fuel
efficiency is an electric engine. Why improve the combustion engine if you can
skip the middle man, so to speak.

~~~
jwcooper
Baby steps.

There is a huge distribution network of gas stations, refineries, and (right
now) fairly cheap oil. I'd like to own a 100% electric vehicle right now for
the price of a Prius (with similar range, cold weather capabilities, comfort,
space, etc), but I'm not sure if that's possible yet.

I see no problem with making gas/diesel engines more and more efficient until
they are replaced by cheaper electric cars.

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rebootthesystem
Turbo/Super chargers do not improve engine efficiency (more power with the
same amount of fuel). They improve VOLUMETRIC efficiency. To put it plainly,
they allow you to shove more fuel into the same size engine. To burn more fuel
you need a lot more air, hence the compressor. The same engine produces more
power by burning more fuel per unit time.

As far as the 10% fuel economy improvement (i.e: 20 to 22 mpg) by combining
cylinder shutdown with electric turbo is concerned, well, I'll give them the
benefit of the doubt and remain very skeptical.

Do any of the claims account for non-trivial compressor motor power?

If we dig deep enough are we going to learn that this company got a huge grant
from the EPA? It feels like the whole business of solar bike paths in Holland.

It's been a long time since I studied Thermodynamics. From what I recall
engines are cycle limited and modern designs are optimized as far as you can
go without resorting to esoteric optimizations. In other words, as long as you
have an Otto cycle engine that's your limit. I seem to remember 18% max
thermodynamic efficiency for Otto cycle under ideal conditions. Stirling cycle
can do 90% efficiency, again, from memory.

~~~
drmilsurp
I think the theme is really power on demand. I don't like the idea of an
electric turbo/compressor for the same reasons I don't like quartz watches.
But maybe adding an electric compressor and upgrading the already taxed
alternator will offset the parasitic loss?.

Performance and economy are in opposition. It is still all down to
Air/Fuel/Spark. You just know that 10% was from DI and fuel cut on the odd
cylinder in spite of the eturbo. When you open the throttle plate 100% and get
that turbo of any kind running 100K+ rpms, ignition advance drops, fuel flow
jumps and there goes your fuel economy. Again, you cut the fuel when you don't
need it and/or stop spraying fuel everywhere else but directly in the chamber.
Where you fall on the curve before/after MBT can be changed but it's not
really possible to run after (lean side) the fuel curve with standard fuel
stocks and certainly not under boost, ie you can do it, but you won't be
making any power.

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jonah
Here's a little bit about Audi's implementation:
[http://www.worldcarfans.com/112092048467/audi-electric-bi-
tu...](http://www.worldcarfans.com/112092048467/audi-electric-bi-turbo-engine-
revealed)

It basically uses the high voltage electric supercharger to provide initial
boost while the turbocharger is still spooling up.

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sparkman55
This makes great sense! I'd guess this would be (relatively) easily integrated
with a standard hybrid system, although the powertrain would be quite
expensive (hybrid system PLUS turbocharger system).

I wonder if this would work well with a turbodiesel engine?

Also, I'm a bit confused: why is this not an electric supercharger? I thought
the 'turbo' name meant that there was a turbine that spins using the engine
exhaust gasses, which drives a compressor that compresses the intake air. This
appears to spin using an electric motor instead...

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maxerickson
The linked promotional material calls it a supercharger:

[http://www.valeo.com/en/page-transverses-gb/popin-
diaporama-...](http://www.valeo.com/en/page-transverses-gb/popin-diaporama-
en/popin-diaporama-pts-en/diaporama-electric-supercharger.html)

I guess the journalist (blogger?) isn't a car person (I'm not either, but I
think lots of people that aren't car people know the difference).

Edit: This page is more informative:

[http://www.valeo.com/en/our-activities/powertrain-
systems/te...](http://www.valeo.com/en/our-activities/powertrain-
systems/technologies/electric-supercharger-45.html)

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acd
I think you can eliminate turbo lag with electrical turbo chargers.

I wish we can take experimental engines and race them. So you could score
points not only for fastest time but also for cleanest engine.

Here is a 450hp 2.0Liter Volvo turbo engine
[http://www.speedhunters.com/2014/10/triple-boost-
volvos-450h...](http://www.speedhunters.com/2014/10/triple-boost-
volvos-450hp-2-0l-four/)

~~~
drmilsurp
I'd think the compressor would still have an efficiency range even if it's
electric. Would a compressor that can feed an engine at low rpms 25psi over
atmospheric be able to maintain that psi as rpms increase? I'm curious if the
electric compressors are turning at 100k rpms like the mechanical turbo they
are replacing.

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WalterBright
This is how a supercharger is done:

[https://www.youtube.com/watch?v=_pCOK1ezH6Q&feature=player_d...](https://www.youtube.com/watch?v=_pCOK1ezH6Q&feature=player_detailpage#t=153)

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lazylizard
how about running the internal combustion engine at constant rpm, and use the
electricity generated by the exhaust turbine to charge the batteries on a
hybrid?

~~~
limaoscarjuliet
Close. [http://en.wikipedia.org/wiki/Diesel-
electric_transmission](http://en.wikipedia.org/wiki/Diesel-
electric_transmission)

