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Turbocharger power input (consumption)

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joeqsmith:
Scan down a couple of posts and you can see some data I posted from one of my bikes showing the lag.

https://www.theturboforums.com/threads/a-way-to-reduce-turbo-lag.367255/page-2

Mazo:

--- Quote from: firewalker on March 25, 2020, 06:00:16 pm ---
--- Quote from: Mazo on March 25, 2020, 05:22:39 pm ---Just another thought on the power required by a turbo to provide useful boost pressure.  Say you have a NA engine producing 200 BHP, for the
By the way I once made a rough calculation on the power needed for a pretty small boost of 0.3bar on a 1.6L engine and the number I got was around the 5kW mark of electrical power needed.Very difficult to supply on 12V and by a standard alternator.

--- End quote ---

Did you just calculated the mass and the speed of air per second? I did that and my result same as yours.

Alexander.

--- End quote ---
Yes but I also took compressor efficiency(increase in power needed) and volumetric efficiency(decrease in power needed) of the engine into account(you can say they cancel out if you got an efficient compressor).
Thought about modding a car with such a supercharger(I call it a supercharger as  the plan was to supply it with electricity using a belt driven alternator),while thinking that a boost available from ~idle will make for a really flat torque curve.TL;DR it isn't as useful as one might think,and it still comes worse power and money-wise than driving a normal supercharger by mechanical means.
I was considering the idea from performance standpoint and it seems it is a no go.
AFAIK the electric compressors are made so one can pass the emissions regulations of the future.
Ofcourse impemented the way garett will do it,enables them to function as normal turbochargers at higher RPM and even regenerate the energy of the exhaust gases to charge batteries,at the same time eliminating turbo lag from big turbos bolted on cars with the displacement of a soda bottle :).
All in all if you don't use the exhaust gas at all the idea is terrible.(can't say I wasn't excited doing all the math to prove my gutsense is right)
P.S If someone has an example that proves otherwise,I would be very interested so PM me.

unknownparticle:

--- Quote from: Mazo on March 25, 2020, 05:22:39 pm ---
--- Quote from: unknownparticle on March 25, 2020, 05:05:15 pm ---Just another thought on the power required by a turbo to provide useful boost pressure.  Say you have a NA engine producing 200 BHP, for the sake of discussion a 2Ltr 4 cylinder unit, and you want 300 BHP using a turbo. So, ignoring all the other stuff needed to accomplish this, and all the relevant  efficiencies, losses etc etc.  In simple terms, power in = power out, so to produce that additional 100 BHP the turbo needs at least 100 BHP from the exhaust gas off the engine to do that. In practice, due to losses, efficiency, etc, etc, it needs more than that. So, more than 75 KW of energy, regardless of the turbo used.  Unless I'm getting something very wrong!

--- End quote ---
To get more power you need more air/fuel mixture to burn.The turbo gets you more air than possible with NA and the FUEL gets you the energy input.Following your line of reasoning a supercharger(driven by the engine by a belt in most cases) is a completely useless device as it will take 100hp to "give"100hp,and yet superchargers exist and are useful.As langwadt says it seems you are getting it wrong.

By the way I once made a rough calculation on the power needed for a pretty small boost of 0.3bar on a 1.6L engine and the number I got was around the 5kW mark of electrical power needed.Very difficult to supply on 12V and by a standard alternator.

--- End quote ---

Superchargers do work but are inefficient as they are parasitic devices, so they require mechanical power from the engine to drive them.  For that reason they never even get near the capability of turbos.  They are typically used for low boost applications.  Top fuel drag racing doesnt count!!!

unknownparticle:

--- Quote from: langwadt on March 25, 2020, 05:21:59 pm ---
--- Quote from: unknownparticle on March 25, 2020, 05:05:15 pm ---Just another thought on the power required by a turbo to provide useful boost pressure.  Say you have a NA engine producing 200 BHP, for the sake of discussion a 2Ltr 4 cylinder unit, and you want 300 BHP using a turbo. So, ignoring all the other stuff needed to accomplish this, and all the relevant  efficiencies, losses etc etc.  In simple terms, power in = power out, so to produce that additional 100 BHP the turbo needs at least 100 BHP from the exhaust gas off the engine to do that. In practice, due to losses, efficiency, etc, etc, it needs more than that. So, more than 75 KW of energy, regardless of the turbo used.  Unless I'm getting something very wrong!

--- End quote ---

yes you got it wrong, the turbo doesn't need 100hp to add 100hp, it needs the power required to add enough air to burn ~300hp more worth of fuel

--- End quote ---

Well, yes, but the fuel requires the correct amount of air for it to burn at the correct AFR. To provide that air the turbo has to compress the atmospheric air to the necessary pressure to provide the CFM flow to burn the fuel. So, power in = power out, to compress the air AND at the necessary CFM, the turbo has to be powered from the exhaust gas flow of the engine.

mzzj:

--- Quote from: firewalker on March 25, 2020, 05:02:47 pm ---Is the amount of power a turbocharger need the main reason for not having electrically driven turbines?

Alexander.

--- End quote ---
Yes, that is THE reason.
Heavily boosted 2.3L turbo engine with ~450 hp output needs 70hp power on compressor shaft.
Borgwarner matchbot shows "turbo shaft power" , this is a 2.3L ethanol(E85) fueled example:

http://www.turbos.bwauto.com/aftermarket/matchbot/index.html#version=1.4&displacement=2.3&CID=140.346&altitude=500&baro=14.502&aat=75&fueltype=3&turboconfig=1&compressor=67x80&pt1_rpm=2500&pt1_ve=88&pt1_boost=13&pt1_ie=99&pt1_filres=0.08&pt1_ipd=0.2&pt1_mbp=0.5&pt1_ce=66&pt1_te=85&pt1_egt=1450&pt1_ter=1.48&pt1_pw=16.27&pt1_bsfc=0.62&pt1_afr=9&pt1_wts=300&pt1_wd=83&pt1_wd2=74&pt1_wrsin=69033&pt2_rpm=3000&pt2_ve=95&pt2_boost=22&pt2_ie=95&pt2_filres=0.1&pt2_ipd=0.2&pt2_mbp=1&pt2_ce=70&pt2_te=83&pt2_egt=1550&pt2_ter=1.87&pt2_pw=25.72&pt2_bsfc=0.68&pt2_afr=8&pt2_wts=320&pt2_wd=83&pt2_wd2=74&pt2_wrsin=73635&pt3_rpm=4000&pt3_ve=100&pt3_boost=21&pt3_ie=95&pt3_filres=0.12&pt3_ipd=0.3&pt3_mbp=1.3&pt3_ce=74&pt3_te=72&pt3_egt=1650&pt3_ter=2.11&pt3_pw=36.22&pt3_bsfc=0.68&pt3_afr=8&pt3_wts=340&pt3_wd=83&pt3_wd2=74&pt3_wrsin=78238&pt4_rpm=5000&pt4_ve=95&pt4_boost=23&pt4_ie=92&pt4_filres=0.15&pt4_ipd=0.4&pt4_mbp=1.5&pt4_ce=76&pt4_te=71&pt4_egt=1650&pt4_ter=2.37&pt4_pw=40.62&pt4_bsfc=0.68&pt4_afr=8&pt4_wts=368&pt4_wd=83&pt4_wd2=74&pt4_wrsin=84681&pt5_rpm=6000&pt5_ve=90&pt5_boost=27&pt5_ie=90&pt5_filres=0.18&pt5_ipd=0.5&pt5_mbp=1.8&pt5_ce=72&pt5_te=70&pt5_egt=1650&pt5_ter=2.88&pt5_pw=40.24&pt5_bsfc=0.7&pt5_afr=8&pt5_wts=400&pt5_wd=83&pt5_wd2=74&pt5_wrsin=92044&pt6_rpm=7000&pt6_ve=80&pt6_boost=27&pt6_ie=90&pt6_filres=0.2&pt6_ipd=0.6&pt6_mbp=2&pt6_ce=70&pt6_te=70&pt6_egt=1650&pt6_ter=2.96&pt6_pw=39.64&pt6_bsfc=0.72&pt6_afr=8&pt6_wts=400&pt6_wd=83&pt6_wd2=74&pt6_wrsin=92044&

We considered adding 48v system and electric charger to that motor but 7kW electric turbo was marginal even to cover the low end before the larger turbo wakes up. For smaller engine or milder tune the electric turbo would cover the low rpm boost just fine. (Like in some Audi models)

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