Electric Superchargers

So many definitions of "efficiency" will be applied to this that no one can tell.

Well basically what I'm getting at is the conversion efficiency....the engine driven supercharger uses about 20% of the engine output , now we know the electric power required to drive the electric supercharger is produced by the engine via alternator battery route, which is also taken from the engine...so which path is more efficient...what about bang for the buck? Is electric supercharging likely to be cheaper? So what are the tradeoffs for each?

Like this?

Mercedes R170 W202 SLK230 C230 GENUINE Supercharger Coupling Electric Clutch NEW

Yes I think a good strategy is for it to boost only when engine vacuum hits a certain point or perhaps only with full throttle....

Like this one....maybe with cowl induction

Although the claims here are a little fantastic.....the performance of a 6 psi boost for as long as 30 seconds would be fine....

I have a Mercedes AMG A45 which incredibly produces about 340 HP from a 2 litre engine (the latest ones claim 376 HP). However, the turbo lag is most noticeable, and with an automatic gearbox one cannot rev the engine and slip the clutch. I do wonder if an electrically-driven turbo would have been a better solution.

The only thing that TURBOcharger and SUPERcharger have in common is "charger"...I guess you could modify one to be run off something other than the exhaust but it would take a lot more work than with a supercharger. Superchargers are generally driven by a belt connected to the crank pulley. Turbo's are drive by the exhaust gasses. That's why you have "turbo lag"...no "instant" exhaust gasses.

Is it more efficient to drive it directly, with a belt drive, or drive a generator to charge a battery to drive it.

It takes the same amount of power input to get a certain level of boost out. It all comes down to the efficiency of the drive system.

What is a turbo fan?

Yes I would think the fan design becomes critical...

I would like to see something like this...

The problem is determining the most efficient range of power draw and matching it to the fan rpm range and fan blade design, size, speed and shape for proper air velocity and pressure....

cfm requirement...

http://www.csgnetwork.com/cfmcalc.html

Yes, but fan design is fairly mature now.

It's probably as much a matching problem as it is a design exercise.

The multi-stage type you show eats up a lot of space and may be too delicate for this application.

So, that leaves Roots or Paxton style blowers and the lobe clearances in a Paxton are a problem.

So, go with a centrifugal and be on your way.

The choice I think is to be between centrifugal and axial flow fans. The main reason axial flow was selected (a long time ago now) for jet engines for aviation was that axial flow compressors could be designed for much higher output without increasing diameter.

That ties back to the drag on the air frame.

In an auto engine, it is simply easily done with a single stage centrifugal that fits nicely within the compartment. I suppose one could use exhaust to power a steam generator, and have the steam output on high pressure, but by-passing steam at low flow to the condenser (radiator, air-cooled) during warm-up, then when the turbo is demanded, steam output could be switched 100% to drive the turbo fan, and still use exhaust heat as the source of power, and still be "instantly switchable". Perhaps my thinking is a bit steam-punk for the automotive crowd to accept, but it would in fact function well, except during the first few minutes of ice melting.

You also need to consider space & weight. Direct driven requires a pulley and a belt. Where would the generator and battery, or batteries go and how much power would be required to overcome the additional weight & possibly greater coefficient of drag if the vehicle increases in size?

Does the supercharger need to run all the time?
If not, then the electric should be more efficient, on the grounds that it need only be driven when needed.
Don't think we need a supercharger at tick over, as long as the whole system is designed to cope with that.

Del

I agree with Del, "on-demand" would be more efficient than something that has a continuous drag on the engine. You could have either mechanical or electric "on-demand" superchargers.

Maybe some supercapacitors to drive a high voltage on-demand system...

Smaller engine using "boost-on-demand" via CPU control to meet varying driving power needs.

I hadn't even thought about efficiency. I thought the reason for an electric turbocharger was to reduce the lag between pressing the accelerator and feeling the acceleration...

I'm NOT a drag enthusiast; I just have a TDI VW (yeah, one of those!)

How about 5 leaf blowers in a Chevy Monza with a 5.7L V-8? These guys bought a 5.0L V-8 Monza. First they put two leaf blowers in, next three, then they dropped the larger engine and added two more leaf blowers. Did it work? Yes and no. Yes, they got more HP out of the engine (a lot more) + more torque. Did the car go faster in a one mile run? Watch the video and see. https://www.youtube.com/watch?v=U81_0waqEWA

I think a computer controlled electonic supercharger would work better, because you can get more boost at very low rpms. If you can use regenerative braking or solar panels to charge a battery and use it to run the supercharger, it would also be more efficient.

So where are all my GAs you miserable bunch of tightwads?
Del (Kris made me ask)

Happy now?

Electric is much more efficient as described here. Here, a small displacement engine, WITH TURBOCHARGING, is being augmented with an "on demand" electric supercharger.

Fulltime electric supercharging would not be as efficient as turbo-powered. We know how inefficient gasoline engines are at converting the fuel-to mechanical-to electrical energy......A turbo uses exhaust heat to recover some waste thermal energy, for full time use.

What my company is working on is a way to recover vast amounts of the lost, wasted, thermal energy from the tailpipe to electrical energy. Lose the belt run alternator, the belt run a/c compressor, possibly the power steering pump.......

Well it seems the conventional turbocharger would also create some back pressure to the exhaust...can't help thinking a negative pressure exhaust would improve performance...pressure in, suction out = improved air flow...Has anyone ever tried a negative pressure exhaust? What would be the ideal suction boost... -6 psi?

This implies recompression of the exhaust by default. The exhaust stream exists normally under a pressure slightly greater than atmospheric ambient.

You have proposed adding a mechanical/physical device to (a) lower this pressure in the immediate area of the cylinder exhaust manifold, and then to (b) re-compress the exhaust to atmospheric flow conditions. I think it might be hard to extract sufficient energy per unit time (power) to drive this device from the exhaust itself, thus it will add a parasitic load to the engine. The question then becomes one of energy expended in producing the vacuum, and then forcing the exhaust out at a higher pressure.

I suppose one could introduce a cooler for the exhaust before this compressor device, thus lowering the amount of work required, however, usually this means intricate passageways that may or may not be conducive to high gas flow rates. It also means one more parasitic load added in the form of fans to drive air through the inter-cooler.

If a method could be found which recovered sufficient heat from the exhaust to condense a significant portion of the water vapor in that exhaust, the condensation process would produce the partial vacuum. Such a system would have to be placed after, or perhaps surrounding, the catalytic converter to avoid smog problems. The interior of the catalytic converter would still have to remain hot for the catalytic action to function.

I understand about there being a fair amount of water vapor in automotive exhaust...that seems interesting. I don't know how much vacuum that would produce based on excess air being utilized (lean burn conditions??). One needs the material balance to enable a back of envelope calculation, or at least an assumption about fuel mass to air mass flow. I suppose then one could recover this nasty condensate and evaporate it to steam and run the supercharger/turbocharger. It might only work in supercharger mode, since the amount of condensate/heat available could be limited.

There's more water vapor after the catalytic converter, if it is functioning as intended, than in the original exhaust.

Remember that the volume ratio of vapor to liquid is roughly 2000-1, so even a modest amount of condensation can reduce the pressure significantly. That process is what produces the low pressure at the center of storms. Have you never boiled water in a rectangular can, closed the top as you removed it from the heat, and then watched the can collapse as it cools?

Nasty condensate? It's distilled water with a tiny bit of dissolved crud. You can see it the first few minutes after you start most any vehicle engine while the exhaust is still cold. In humid tropical climates, you can see it any time you look close enough.

Evaporating it to steam would require a source of energy, and there went your savings...

I would not drink that condensate, much less feed it to a boiler cycle, without at least one intervention (carbon filtration). I work in a power plant, and I intimately know all about producing a vacuum at a condenser from steam turbine exhaust.

I appreciate your explanation, too. There is enough heat at the exhaust manifold to more than evaporate any condensate produced at sufficient pressure to drive or assist in driving a turbocharger. (If the turbo is only used on demand, the condensate can be stored until needed). The extra water vapor could be routed back into the engine intake for fuel preheating, and for the extra expansion in cylinder, without causing engine stall.

In post #21, Wolfie62 says: "What my company is working on is a way to recover vast amounts of the lost, wasted, thermal energy from the tailpipe to electrical energy. Lose the belt run alternator, the belt run a/c compressor, possibly the power steering pump......."

If they could extract that much energy from the exhaust, it seems like the gases and liquids would be exiting only a little above ambient, and much of the water would have condensed.

Definitely an admirable objective, but I'll be surprised if I live long enough to see it happen!

Basically, I agree with you, but there is an even better way:

Several years ago, a concept car was made by Ingo Valentin (INGOCAR). This car removed most all of the conventional drive train components, installed hydraulic accumulator, and installed new, small, efficient, light weight hydraulic motors on all four wheels. The chassis is one that is also less weight, but made to fit a range of body styles that "snap-on" and "snap-off" when a change is desired. The car was designed to have all the standard creature comforts. The engine/hydraulic pump combination is unique opposing piston type, where fuel injection timing allows a range of fuels from hydrogen, methane, etc., through gasoline, bio-diesel, diesel, kerosene, jet fuel, etc.

The high compression engine exhibits a very high compression ratio without any preignition issue due to advanced control of fuel injection. Due to weight savings, regenerative braking, etc., expected vehicle standard mileage was expected to be 160 miles per gallon, with a range of over a thousand miles. Hydraulic drive was reported to be very peppy indeed. Maybe it does not sound like a corvette, but it will go further on the same fuel volume. This is not to say that a sport variant could not be made that would be way more awesome that folks are accustomed to. If we are talking wasted thermal energy, this vehicle takes and gets rid of most of that at the source.

I don't believe I had heard about that one.

Generally speaking, I'm much more comfortable with electrics than with hydraulics, and consider hydraulics messy and dirty. Replace the pump with a generator/alternator, the accumulator with a battery (not very large), and put electric motors in all four wheels, and you'd have my version...

http://www.valentintechnologies.com/

I urge anyone to go to this link, and learn all they can and still tell me they think hydraulic is "messy"! I believe electric or even hybrid electric will still struggle to compete with the performance, range, and comfort of the car. Wait until you see the helicopter, the wind turbine, and the tank (armored vehicle propulsion), and don't forget the locomotive!

Whenever any hydraulic item springs a leak, it is messy. Keeping things clean for a short time does not guarantee a long time. Energy storage is also an issue.

Every application of hydraulic energy requires a balance between hydraulic accumulator, regenerative pressure-flow, rate of hydraulic power utilization, and instantaneous power demand. That is why the accumulator for a wind turbine installation of this technology is way different (or maybe non-existent) than that for a locomotive, a tank, or a helicopter or an automobile.

Would you rather be bathed in hydraulic oil in a severe collision (even though the accumulators are rated for G impulse levels no human could survive), or be bathed in bromine water???

I'll take Lilac water, if you please.

I suppose a car could be propelled using that. Why not? I would rather have something I could pull off tap, and mix a beverage with (not necessarily alcoholic, just saying).

I guess a car could even run off "Tang", especially since there should be enormous stockpiles of that now we are not going into space "as frequently". At least until passenger service kicks in.

The Tang fuel cell car. What an idea!

I don't see that you would produce any more pressure than normally experienced in the exhaust pipe post impeller, the only difference would be negative pressure from the manifold to the impeller...now the system may require a larger pipe size leaving the impeller for the system to work properly, but that is undetermined...Let's say this exhaust vacuum system was part of the electric on-demand supercharger system and would only be powered when the supercharger was running...at other times it would just freewheel....the flow characteristics of negative atmospheric pressure would facilitate better air flow from the exhaust ...

So what you want is an uber-supercharger....

No such thing as negative pressure....

Wouldn't that be a vacuum?

Vacuum still has a positive pressure greater than zero.

I heard once that the Chevy Power Glide transmission's predecessor was invented for use as a two speed drive system for the P-51 Mustang supercharger.

Have you ever heard of such?

No, I never had heard that. So what you are saying is that this transmission fed hydraulic power to the supercharger? Did it work even if not in drive, as in stationary? Or did it have to have power on the transmission output shaft?

No,

My understanding was that it drove the supercharger at two different speeds.

I think that as you went to high altitudes it shifted to spin the supercharger faster for more boost in thinner air.

I've looked a couple of times for this, again, and never found anything. You seem to know your way around airplanes, so I thought I'd ask.

I know enough to get in trouble. Yes, the P-51 Mustang is a lot different than a Ford Mustang, LOL! I did not know that GM made that supercharger, but it makes sense.

GM made a hot version of the F4F Wildcat for the Navy designation FM-2 that I think did have a supercharged engine. Still had sucky flight characteristics as a fighter, but better than other one, still lost to A6m0-A6m5 in vertical stall fight. It was a different story when the F6F Hellcat debuted. Zeros tried the same stall tactic and lost badly.

In later models of the P-51, and P-38 series the superchargers would spin faster at high altitude. Both series had improved flight range, and high altitude performance gets an A+ for WWII era piston engine aircraft, but only after all the mods were made. Merlin two-stage turbo-superchargers changed the P-51 from a modestly high performance aircraft into a high altitude air superiority aircraft. The Allison engines, not so much.

"The V-1710 has 12 cylinders with a bore and stroke of 5.5 by 6 inches (140 by 150 mm) in 60° V-format, for 1,710.6 cu in (28.032 L) total displacement, with a compression ratio of 6.65:1. The valvetrain has single overhead camshafts per bank of cylinders and four valves per cylinder......The accessory end had a one- or two-speed engine-driven supercharger that might have a second stage with or without anintercooler, the ignition magnetos and the customary assortment of oil and fuel pumps, all dictated by the application requirements." (source: Wikipedia)...same engine used on P-39, P-40, early P-51, and P-38 models.

I wonder what happened when they shifted to reverse or park.

They did not have reverse or park. Let me tell you this. I would not have spun the prop backward. At the worst case by stalling the supercharger to zero rotation, one would have had high manifold vacuum, and high exhaust pressure (from "normal military power"), and thus power for sustained flight would be at a minimum, and the standard procedure would have been immediate return to base (as long as that was possible), unless engine overheat condition from continued operation at a bad point resulted in overheat and seize up. Then the pilot had to look for open ground, if land was available, or contemplate a ditch in open water that might be shark infested.

http://www.wwiiaircraftperformance.org/mustang/mustangtest.html

the above link has a lot of flight test information from Wright Field USAAF (but the information although old, is accurate). Notice how much faster P-51H is than P-51B, and this of course is at a high altitude, but maximum speed is never at the service ceiling. That is where the balance between flying and falling takes over.

Still no mention of GM's involvement in the turbo-superchargers for these, although the first GM automatic transmissions precede the turbo-superchargers by date, and could have been employed thusly. Late war developments in armored vehicles including tanks made use of automatic transmissions from GM.

When any pressure is less than another, it can be said to be negative by comparison.

Except that in absolute terms there is zero (which technically is never really sitting on absolute zero), and positive pressure. In gauge pressure, there is positive pressure (a zero on the gauge and the needle can be on zero, meaning that pressure is practically the same as external pressure, and vacuum pressure which reads as a positive amount of vacuum is usually only goes to 15 tops, and many gauges seem to go to only 12 psig vacuum, or other reduced amount.

Comparison to what?
If you are are comparing to atmospheric then yes, you could pump out the exhaust, but could you pump it out faster than the piston pushes it out? You could also tune the exhaust, as is common in racing two strokes using gas momentum to help get pressure below atmospheric.
I'm not sure the benefit is worth it in a 4 stroke as the exhaust is a V high pressure compared to atmospheric in the first place.

Del

That's like saying there's no such thing as negative voltage. It depends on the reference.

"you can't get more negative than no pressure"

Maybe, but you can't get "no" pressure. At least not here on earth.

It takes mega suckage to get down to almost "no" pressure.

Not sure why you say "maybe" when as you say we can't even get to zero!
Del

I think I am the one that stated we can't get to 0 psia (or in any other unit of measure), since there is always that little something at 10^-7 mmHg even in some really hard core vacuum systems for basic research. Getting to 0 psig is very different, and can take place hundreds of times a minute, etc. There is a big difference. Most people are totally unaware of this as a concept, let alone have experience with "real" vacuum systems.

What really sucks is having words put in my mouth that I did not utter. Within the depths of your peristaltic pump the pressure is negative with reference to the inlet and positive with reference to the outlet.

Relative or differential pressure can be negative, yes. Absolute pressure (psia, for example), or gauge pressure (psig, for example) will always be positive, or at least should be. Sometimes one can find a gauge that reads something like -14 psi to +30 psi, with "0" in the middle somewhere, but I have not seen that in a while. Most of the time, a gauge where the expected pressure range will be from some vacuum (with respect to atmospheric local pressure), to some pressure above atmospheric local pressure, will have a range on the vacuum side that shows increasing vacuum, 0, and a range above ambient. On any absolute pressure reading device (manometer), there can only be 0, and positive numbers. No physical system exists anywhere such that there is a negative force per unit area at the boundary between two parts of such a system.

To state otherwise is something akin to stating that General Relativity only works on alternate Tuesdays in Vermont.

Since an ignition coil primary winding is +12 Volts and ground would not the spark produced by the secondary be negative voltage in relationship to ground?

That depends on which direction the two windings are wound, and on which end of each winding is connected to ground. It could also change depending on whether the two windings were wound on one side of a magnetic core loop (long, thin coil), or if the primary is on one side and the secondary is on the other side of the core loop (short, fat coil).

I'm under the belief that the ground connection is the "center tap".

Or in this design the secondary circuit runs through a pair of plugs one positive and one negative.

I hadn't seen this one! Of course it will only work if you have an engine that has 2 spark plugs that fire at exactly the same time.

If you google "ignition circuit", it comes up with lots of variations, many of which have nothing to do with vehicle engines. Virtually all of them have one end of the secondary grounded, but most do not have sufficient detail to be absolutely sure that the other end of the secondary is indeed the positive terminal.

So this only works with two simultaneous cylinders (if it works at all)! If you have anything more than two cylinders, you would have to have more than one ignition coil. Have never, ever seen that. Are you sure you didn't dream this up, trying to "stump the band?"

Perhaps you have heard of a Honda Goldwing? From 1975 to 1987 they were built with four cylinder engines using two coils. Starting with 1988 they have six cylinders with three coils. Each coil fires two cylinders simultaneously.

I have heard of, seen others with, and wanted a Gold Wing. This is something I did not know about them, but I suppose it makes sense now. I guess on a Gold Wing, if one cylinder misses, its partner cylinder also misses?

I'm not sure but I believe the cylinders are 180 degrees apart when they fire. IOW, one fires at the top of the compression stroke while the other is at the top of the exhaust stroke.

I guess an extra spark at the top of the exhaust stroke wouldn't hurt anything, except wear the plugs a bit faster.

That is exactly what happened on my two-cylinder four-stroke Honda m/c engine.

I am with DKWarner on this one. Why is spark at top of exhaust stroke even necessary, unless the engine is not able to efficiently burn the fuel in the power stroke? If there is that much left over fuel, then an additional spark might ignite it, and scavenge one little surge of power.

According to your circuit, it one spark plug misses, they both miss.

Goldwing engines are notorious for being bulletproof. Simple maintenance and they will run several hundred thousand miles. Our 2001 GL1800 has 105K miles and the plugs have only been replaced twice. Both times I replaced them the old ones looked very good and could have lasted much longer. The set I'm using now, E3 plugs, will probably last for years. I see no issue with Honda's design here.

They must indeed have a bulletproof ignition system upstream of the spark plugs! Apparently, this is from Japanese researchers paying utmost attention to details, just like sword makers.

Two things:

1. An ICE is pretty much just a positive displacement air pump.

2. Creating such a vacuum would require some type of power and exhaust systems operate best with some backpressure.

They do make dual stage exhaust systems for C7 corvettes ....

https://www.youtube.com/watch?v=zYrboFjc3VU

A supercharger takes energy from the engine. Theoretically you could supercharge an engine to thousands of HP, and be able to stop it with your hand. Their only advantage is they operate at low RPM's. Turbos OTH use waste energy from the exhaust, and theoretically are unlimited. They typically need 1700 RPMs or so to before there is sufficient exhaust pressure to drive the compressor, even then the exhaust must increase before the turbo can produce more boost. This is the delay. I see no way for a motor driven supercharger to be more efficient, you must add the weight of the motor, increased size of the alternator and the associated wiring.

For speed out of the starting block there is nothing that can beat 4WD electric. There is a Youtube video of some kind of Tesla beating all competition in 1/4 mile.

You suggest that turbos are free of any energy penalty.

This is not the case. Restrictions caused by the turbo also cost horsepower.

It's been 25 years since I dealt with exhaust system manufacturing engineers (and toured their test facility) but that much I remember.

It is definitely true that turbochargers restrict exhaust flow and get their energy from the engine, and so do initially reduce the power/energy available to go to propulsion, but as soon as they get up to speed, they increase the efficiency of the engine, providing more horsepower. I guess it's a matter of semantics...

Yes, both provide a net HP gain.

Otherwise, why bother?

Overall, turbochargers are better for general purpose driving, I agree.