Here's a question I've been mulling over and just out of idle curiosty thought I'd ask.

Now I know there are cheepy electric fans that claim to increase BHP. But I'm not talking about them, for FI you need something that compresses not blows.

BUT

A Centrifugal supercharger is mearly a compressor driven via a belt from the engine. So what if you connected that belt to a high powered elctric motor instead.

In the case of the LS1 the engine operates from 1500rpm to about 6000rpm. These are easy speeds for an electric motor to acheive. Obviosuly the motor would need to be powerful enough to counter the load of compressing the air.

Cons:
Now the down sides would be the electic motor. As it will be fairly large and heavy in its self. Also the power consumption of the thing. Would it require more BHP from the engine than the blower does being driven directly from the engine?

And maintance with the electric motor brushes. Although if you're into model cars you'll know the benifits of the brushless motors, which practically never wear out.

Pros:
That the blower is no longer driven directly by the engine. So as long as the electric motor was effiencent enough you would produce more BHP.

Also using an electronic control device you could have the blower producing maximum boost from a little above idle. Thus no longer being engine rpm dependant. Or indeed any lag as a turbo suffers from.

In addition I suppose by having full control of the blower rpms you could simply via a switch on the dash board alter the maximum boost instantly. Or indeed switch the blower off completly if you so desired. (fuel saving).

So far I have done NO research on this, so I don't know whether it has been tried before or not. Any comments or views on it are most welcome. Even if you think I'm bonkers!

 

The only problem I see is getting a motor strong enough to turn the blower however many rpms with that kind of load and have enough electricity to power it. Also I don't see how you would tune it precisely. Oh and how much boost are we speaking anyway? 9psi at 2k. that's crazy I'd figure you'd wouldn't gain much up top is the blower is at it's peak at 2k.

 

I'd need to find out more info about what electric motors are available. I think this kind of setup would be limited to shall we say 1 bar of boost or lower, as the power needed to power the blower will continue to increase with increased boost demands.

On a smaller blower on a 4 cylinder engine there may be larger scope.

And using an ECU related to the throttle postion there is no reason why you couldn't have infinate control over the boost provided it was within the operating range of the blower and electric motor.

I suppose the way to do this, would be to purchase a blower head unit like a P1 or D1 from Procharger, rig it up on a mock unit. And measure how much boost can be acheived with different electric motor setups running from a 12 or maybe 24v power supply.

 

an electric motor that has enough HP will require too many amps that the alternator will be able to deliever.

 

Its a good idea, but a little impractical to say the least. Lets go through it.

You need roughly 40 hp to drive a supercharger for our engines. So you need a 40 hp electric motor. Have you ever seen how large these can be? Probably about the size of a hybrid car's electric motor.

Then you need an alternator / generator. Its 744 watts/hp, so lets say you need a 35,000 watt generator. It does not matter if its 12 volts, 24 volts, or 120 volts, its still 35,000 watts, and thats huge.

Much simpler to just have the engine drive the compressor in the first place.

 

How much energy (bhp/kw) would a Procharger P1 require to delivery 8psi of boost to an Ls1 running stock CR?

I may be working this out wrong so please correct or advise as appropriate.

If a typical centrifugal supercharger can reach efficency levels of 85-90% and gives an Ls1 a boost of 100-150bhp @ approximatley 8psi. I work that out to be:

Minimal gain 100bhp with minimal loss of 10% (90% efficency) = 10bhp required to power the supercharger at 'x' rpm's.

Maximum gain at 8psi is 150bhp with 15% loss (85% efficency) = 22.5bhp required by the blower.

These are only very rough approximations, however if they are in the least bit realistic then finding an electric motor to produce circa 20-25bhp is not really out of this world or indeed that far fetched.

Idea's comments anyone?

 

Did I post when you were writing?

If so, look above.

I think 75% efficiency is about right.

How big is your alternator?

 

There is a company that does this by attaching high output motors to a roots blower and spinning that. It can run for 15 second intervals, and puts out ~8 psi on a 4 cylinder. Runs off of a bank of high output capacitors in your trunk that charge off the factory charging system over time. I think it's like 10 minutes between 15 second runs. I'll see if I can find a link.

 

Yeah I suppose to be safe you would need to factor in a lower efficency rate.

As for the alternator, I think you would have to custom fab the electrical source, rather than using the stock setup.

I guess the angles I'm looking at here are:

1. This being the main one. Boost availability and power delviery. There is no idea setup at present. Centrifugals are rpm dependant and positive displacement blowers are quite as efficent. Turbo's suffer from lag (no matter how minute it is there).

By powering the blower independantly it would negate all of this, thus allowing maximum boost from anywhere in the rev range and throttle position.

2. The power lost by either powering a supercharger from the main engine, or in the case of turbo's having to succum to lower CR engines to run the higher boost levels, thus dramatically effecting off boost performance. (also although only minor, there is still a bhp loss with a turbo as it is requireing exhaust gases to power this then cuases a slight restiction. As said its minor, but for the sake of correctness should probably be included).

 

This question is a revolving door on this site.....

For the record, supercharger load is a function of airflow and boost.

(CFM*PSI)/Eff = HP Required

For most applications this is in excess of 100 HP. I'll lay it out if there is some doubt.

An electrical supercharger will never be able to complete with a mechanical drive supercharger. The mechanical transmission efficiency between the motor and the supercharger is ~3%. That is some pretty stiff competition for electrical losses of transmission between generator and driver.

Also, a 100 HP DC motor weighs almost as much as your car.

There are better energy transfer methods out there other than electricity to remote mount the supercharger, ie hydraulic.

 

To start with some correct info and some bad info.

--- (CFM*PSI)/Eff = HP Required --- is incorrect
Efficiencies are in high sixties to low seventies not 75-90 the compressors are too small with large blade height to tip clearances. Also Procharger, Vortech, Paxton use vaneless diffusion which provides wider operating ranges, but with efficiency hit.

At least 20KW would be required achieve your goal. That’s allot power and then you need an inverter (speed control electronics), very bulky and expensive.

Mike

 

Apologies; I know your original comparison regards supercharging... but your untapped source of "free" power in an internal combustion engine is heated exhaust gases. For power and efficiency, turbo applications make the electrical approach an extremely moot point. And if you're worried about lag, I'll respectfully refer you to the very quick turbo cars represented on this site...

No offense meant to the blower guys; and my respect remains for thinking outside the box.

Rich

 

You should really look up something like this before correcting somebody. The above formula is correct. Your assumption of 20 KW is off by about 200%.

A good read with some basic centripital compressor calculations if you need to brush up on them: Design, Testin gand Installation of Supercharger Systems by Corky Bell

Example Calculation (from a 540 HP 8-rib D1)
11 psi boost
900 CFM air flow
60% Supercharger Efficiency (adiabatic)
97% Drive Efficiency (belt, pulley etc...)

Drive Power = (Boost x Airflow) / (Drive Eff * Adiabatic Eff)
Drive Power = (11 lb/in2 x 900 ft3/min x 144 in2/ft2) / (0.97 * 0.60 * 60 sec/min * 550 ft-lb/hp-sec)
Drive Power = 74.2 HP

74.2 HP = 53.69 KW

For my personal car at 700 HP, this works out to be 105 KW

An electric supercharger may be possible for small imports with low compressor flows. But as the flow and pressure increase the parasitic loss of the supercharger becoms staggering. For this reason, I doubt you will ever see an electric supercharger on one of our cars.

However, here is to thinking outside the box

 

Way too much math guys. Fact is. There's barely any room in there for the blower itself. Even a low hp motor if it would work wouldn't be able to fit anywhere in the engine bay.

 

How about a gas turbine powering a turbo compressor? No drag on your engine, no restriction of your exhaust, and I think that it would be pretty small.

 

www.boosthead.com
Thomas Knight Superchargers

 

Kevin,

No disrespect to you, but if that’s what “Supercharger Systems by Corky Bell” says then I guess you can put just about anything into print.

I think that it is a generic calculation, with results far too high for centrifugal or axial flow compressors. It also does not factor in temperature (absolute) and does not use mass flow, both of which are critical. Also any sound equation will not use CFM but use SCFM (S=standard, which accounts for temperature).

P= power in watts

P=m*cp*(T03-T01)
m=mass flow kg/s
cp=1005 J/kg K
T03-T01=(T01/nc)*((p03/p01)^((k-1)/k)-1)

Above calculation uses absolute values, which you must use. As an example, when it’s colder outside, air is denser (more mass) and HP required to spin compressor goes up. Does your car not make more power when it’s colder? That’s why Dyno results are corrected.

Mike

 

That would be kinda cool...until you hit the afterburner. But remember that a turbine engine is nothing but a big air compressor in itself.

 

Some guy in the sixties designed one, except it worked of a chemical reaction. It was supposed to be very simple, I don’t know how many seconds or minutes chemical charge would last.

Mike

 

[QUOTE=johnpate01 But remember that a turbine engine is nothing but a big air compressor in itself.[/QUOTE]
Show me an engine that's not! I was just trying to think of the most compact power unit. Skunkworks outdid me though. I forgot that rocket motors are smaller per output than jets. At least the turbine could run on gasoline. Maybe they sell rocket fuel at the same places where the NO2 guys shop, I wouldn't know.