Electric Turbochargers: The Next Big Thing in Fuel Efficiency

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.

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.

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.

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.

This is part of Volvo's new engine design (see http://autoweek.com/article/car-news/volvos-new-electric-sup...) 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.

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.

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.

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.

Here's a little bit about Audi's implementation: http://www.worldcarfans.com/112092048467/audi-electric-bi-tu...

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

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...

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...

This is how a supercharger is done:

https://www.youtube.com/watch?v=_pCOK1ezH6Q&feature=player_d...

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?