The fundamental reason why Electric superchargers don't work is they aren't powerful enough!
My 944 is to have a 3 Litre engine fitted with a supercharger. The blower is a Vortech V5 to give the lowly 8PSI boost which will up 211BHPto around 300-320BHP the blower will take 37BHP or 27kW or around 2250Amps at 12 Volts! Since the alternator is around 110 Amps this just ain't gonna happen.
The Vortech is a centrifugal blower so the cold bit of a turbocharger. Blade revs are around 31,500RPM.
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>>The fundamental reason ..
Yes, looked at another way, the alternator is driven by a belt, why drive the blower electrically when a belt is available? Using a belt would save the losses in converting mechanical energy to electrical in the alternator, and then back to mechanical in the electric motor.
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>>How much energy does an engine waste in/through the exhaust?
With the broadest of brush strokes, about 1/3 of the energy in the fuel becomes mechanical power to drive the car, about 1/3 is lost as heat in the exhaust gas, and about 1/3 is lost as heat to the coolant.
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>>How much energy does an engine waste in/through the exhaust?
Most of it!
NC beat me to it.
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NC
'1/3 is lost in heat energy in the exhaust gas'
I am not disputing your figures, but surely what drives the turbo is the kinetic? energy of the expelled exhaust gases? You have accounted for 100% of the energy generated from the fuel, without leaving anything over to drive the turbo.
Based on the supercharger figures, a very significant amount of energy is required to drive the compressor, - approx 30 -50% of the energy gained from supercharging?
pmh
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pmh,
>>but surely what drives the turbo is the kinetic? energy of the expelled exhaust gases?
This post by RichardW of August 2005 puts the situation very well IMO.
--------8<--------
"Now, back to the temperature / pressure thing. The gas expands through the turbo, and as it does so its temperature goes down - not because it it is losing heat to the atmosphere, but simply because it is expanding, and temperature and pressure are inextricable linked by Boyle's law, and hence the power from the turbo comes both from the pressure and the temperature. When the air is compressed by the other end of the turbo, not only its pressure but also its temperature rises (which is why there's all that stuff about charge cooling) - which is just the opposite effect."
--------8<--------
That the temperature and pressure are "inextricably linked" means that for a given engine, you can express the ability of an exhaust gas stream to drive a turbo purely in terms of the temperature of the exhaust gas at the turbo inlet, and in some case, you can cascade turbos in series until the exhaust gas becomes too cool to drive another turbo.
If there's sufficient heat energy in the exhaust stream, you can also use the exhaust gas to drive a turbine that is connected to the crank nose, and use the torque directly.
I hope this explains the apparent anomaly.
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NC Ok thanks for that link, I supposed that that I was viewing it too simplistically, but I understand that explanation.
pmh
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I have no option but to view technical matters simplistically and I'm sure that when nc says
If there's sufficient heat energy in the exhaust stream, you can also use the exhaust gas to drive a turbine that is connected to the crank nose, and use the torque directly. >>
that's more complex than it sounds, but I'm beginning to see why small but turbo-charged diesels can put out so much power.
So is it the expense and complexity that prevents many more engines being turbo-charged and, if I've understood correctly, making more efficient use of the fuel used to generate the overall power in the first place?
And is the "waste" to the exhaust a sort of paradox in that in order to make an engine perform more efficiently you have to be able to sweep the exhaust out more rapidly?
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>>So is it the expense and complexity that prevents many more engines being turbo-charged and, if I've understood correctly, making more efficient use of the fuel used to generate the overall power in the first place?
There's much less to gain by fitting a turbo to a petrol car, because you soon run into the damaging phenomenon of combustion knock.
With a diesel, however, this isn't such a limitation, and you can, by fitting a turbo to a diesel, effectively get two engines with different charaters. Off boost, you have a tame, economical engine, and on boost, you have the performance.
>>And is the "waste" to the exhaust a sort of paradox in that in order to make an engine perform more efficiently you have to be able to sweep the exhaust out more rapidly?
The waste energy in the exhaust is simply energy that hasn't been captured during the expansion in the cylinder on the power stroke - towards the end of the power stroke, the temperatue of the gas in the cylinder is rapidly cooling (although it's still very hot!), and the amount of power that can be directly obtained by the piston is diminishing. At this point, the exhaust valve opens, and this gas with its residual energy gets blown down into the exhaust.
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Also the turbine in the turbocharger tends to smooth out pulses in the exhaust so that a less restrictive system can be used to achieve the same noise level.
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Does VW still make the 1400cc Golf with a turbo and an engine-driven blower?
One got the impression it went very well, but does anyone know what it is like in service? And was it any more powerful, or driveable, or economical, than a slightly bigger engine with just one blower?
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My 2003 MK4 Golf auto has a 1.6 SE petrol engine code BFQ. It's fitted with a thing called an air pump. Which i think is there to assist when the engine is cold
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