A supercharger (or turbocharger) increases the compression within the cylinder. To compensate for increased compression, it also needs to add more fuel (otherwise the combustion will be too lean and that can lead to other problems). Any efficiency is due to the increased horsepower/torque, but not necessarily to mpg. Plus, higher compression means higher octane is required or you'll get detonation. So even if your mpg increases, so does your cost for a gallon of gas.
In my experience, most cars are tuned to give a rich mixture from the factory. Rich mixtures are safer than lean mixtures. Go too lean and you'll burn a piston. Getting an aftermarket tune using a wideband O2 sensor on a dyno will improve efficiency, and if done correctly, by adjusting fuel throughout the rpm range, mpg will improve without compromising the integrity of the engine. You'll also get more horsepower to boot, and if your engine currently runs on regular gas, you can still use the same octane.
But car manufacturers are just as concerned about warranty replacements on engines. Tuning an engine rich means fewer warranty issues. Tuning an engine leaner could mean more engine failures within the warranty period, so that probably won't happen from the manufacturer. Unfortunately, getting an aftermarket tune could void your warranty.
So, has anybody done the math? The peak air requirement for a 2.0 liter engine at 6,000RPM and 15psi boost is 230scfm. The minimum power required to run the super- or turbo-charger is approximately 12 HP. At 750 watts/HP, this would require approximately 9KW, exclusive of efficiency, which is way beyond the capacity of 12 volt automotive systems (2 KW more or less). Yes, it doable, but requires a high(er) voltage electrical system. From a weight and cost standpoint, the exhaust-driven turbocharger looks pretty good!
The article mentions fuel economy standards for light trucks. This device might be an OK option for some passenger cars (if it works in the first place, given the issues raised in other comments), but not in a truck. Any technology that provides only brief bursts of additional power is not useful for pulling a loaded trailer up a mountain when maximum power may be required for extended periods.
I agree as well. These over unity device claims are a tad far fetched, but there may be some merrit to this. Doubtful, but maybe. What they show looks to be a roots type compressor, or a lysolm screw type device. The later operates much more efficiently than a roots at lower rpm.
The electric motor attached to this looks to be fairly sizeable, so it might produce 10-20 HP peak for a short time, and then basically go back to loafing when the engine isn't being asked to perform at max capacity.
Another aspect to this operation that may be being overlooked is that you could in fact belt, chain or gear drive the blower to run from the engine crankshaft, but put the throttle butterfly ahead of it. When demand is not high, it's only going to compress as much air as is required. (we did this same thing on a 302 mustang, worked great. instant boot at idle, and from 1000 rpm to redline produced solid 13 PSI boost pressure.
I can hear the complaint of lost efficiency at maximum rpm with light load spinning that compressor needlessly... ok, fine.. put an electro hydraulic, or electro viscus coupling between the belt/chain/gear drive and the input shaft of the compressor, and let the ECU modulate it for best performance.
Only other option I can think of is borrow (yet again) some technology from the GM 2 stroke diesels used in locomotoives. Early units used huge roots blowers driven right from the engine, but the later turboed engines used a hyprid drive of their own.... gear driven at low speeds to be able to start and idle, but once engine speed was up a bit, the exhauste turbine overran a one way clutch from that gear drive and spun the compressor to higher RPM as needed by load demand. Again, your variable viscus coupling could be used here too.
There... problem solved! (although personally I'd rather have a real motor!)
Well said, Jon, I have the same reservations about the realized efficiencies in a system like this. It is similar to all the sites that boast of improved engine performance with electrolysis created H2 gas supplied to the engine intake. None of these discuss the amount of energy required to breakdown the water. So, I'm with a lot of the comments here. In the energy balance big picture, this electric blower system is more efficient compared to what?
This seems to be an attempt at looking to produce a product without fully researching it. And written by sales people who think they are engineers because they think they know how a graph works.
All a supercharger (or turbocharger) does for an engine is to stuff more air into the engine so that more fuel can be burned. It does not necessarily improve engine efficiency. So yes, a smaller displacement engine could replace a larger engine. But efficiency will likely not change much. You will still burn more fuel to get the extra power. But you might be able to tailor the boost pressure at any given RPM to maximize efficiency.
The benefit that the electric drive supercharger has over one mechanically driven by the engine is that there will be boost available at low engine speeds, and variable boost at any RPM.
I'm not sure that a low power (12V) motor can put out enough to properly drive a supercharger in an automotive setting--maybe thats why the article discussion wanders over to hybrids where some decent electrical power for the supercharger is available from the vehicle motive power battery bank. 1 hp at 12V is 60+ amps, at the high end of typical loads in an automobile. A blower will likely require 1-5+ hp??
They also have forgotten that the variable speed blower might be able to spread the "sweet spot" or highest effiency area over a broad range of RPM. Their simplistic graph doesn't reflect this. But they also have not presented any real engine test data to confirm any of this. Nor do they suggest how much power a supercharger blower needs to provide boost for a typical 1-2 liter engine.
I'm wondering if a small hydrostatic drive might make more sense to run a blower than the electric drive they are pushing.
A supercharger under the control of an optimally programed ECU could indeed be quite something. An electric motor driven supercharger could be quite useful on a serious dragster, where it would not matter if it completely drained a car-sized battery in just a few seconds. MY point is that the belt driven superchargers take several horsepower to drive the small engine types, and the larger ones take several tens of horsepowers, and that kind of power is quite a lot to get from a 12 or 24 volt motor.
MY point is that until there are some actual dynomoeter results, with actual numbers, that an electrically driven supercharger is just an interesting concept. Consider that at 760 watts per horsepower, a 12 volt motor would draw 63.3 amps, if it were 100% efficient. A ten horsepower motor would draw 633 amps, and it would not be a small motor. So while it might work for a five second run on a drag-race car, it does not seem like a usable product for other vehicles.
However, if they have been able to come up with a DC motor delivering much more than 100% efficiency, that is a very newsworthy achievement.
It would be interesting to see more details about how efficiency is improved. Is the electric motor more efficient that the typical belt drive? And more efficient compared to what? A larger displacement engine? What are the benefits and tradeoffs compared to a turbo, which really does increase efficiency by using heat energy from the exhaust that is otherwise wasted?
In many engineering workplaces, there’s a generational conflict between recent engineering graduates and older, more experienced engineers. However, a recent study published in the psychology journal Cognition suggests that both may have something to learn from another group: 4 year olds.
Conventional wisdom holds that MIT, Cal Tech, and Stanford are three of the country’s best undergraduate engineering schools. Unfortunately, when conventional wisdom visits the topic of best engineering schools, it too often leaves out some of the most distinguished programs that don’t happen to offer PhD-level degrees.
Focus on Fundamentals consists of 45-minute on-line classes that cover a host of technologies. You learn without leaving the comfort of your desk. All classes are taught by subject-matter experts and all are archived. So if you can't attend live, attend at your convenience.