Electrically driven Turbo Charger

  1. Hi;
    In a regular 1900 TDI car engine,if the turbo were to be operated by an electric motor
    instead of by the exhaust gasses,how many HP would be the needed output of such motor in
    order to produce the same effect.
    Thks.
    J.D.
     
  2. jcsd
  3. I've seen this attempted several times with air-cooled VWs - and I've never seen it work successfully. It may be that it's possible but impractical, as the amount of torque required to force air into the engine requires an electric motor that's heavy, or it may simply be that the turbo (which, being driven by the exhaust, adjusts itself to the speed of the engine) needs to be driven at the same speed as the engine in order to help.

    Superchargers are also driven directly by the engine, and so would force air into the intakes at the correct speed. If you want to go with an electric engine to do this, you're going to have to have an accurate way of measuring the speed of the engine, and providing intake pressure that's comparable to what the turbo or supercharger would provide.
     
  4. Mech_Engineer

    Mech_Engineer 2,299
    Science Advisor
    Gold Member

    This sounds a bit like a homework problem...

    The basic calculation method is you need to determine the volumetric flow rate of the engine at a specific speed you're interested in (say 5000 rpm) and the pressure of the input air at that flow rate. Given those values you can use an isentropic compressor approximation to estimate the energy input required for that pressure and flow rate.

    Does this help? Keep in mind the power required is going to be big compared to the power capability of the engine's alternator; in fact it's unlikely a big enough alternator will be available for the required power input...
     
  5. Bandit127

    Bandit127 204
    Gold Member

    If this is not a homework question requiring a specific answer I will put it in a very simplified way, the turbo on a Peugeot XUD diesel engine adds very roughly 20-30 bhp to the power. It does this by using waste energy in the exhaust.

    20 hp = 15 kW.

    So the general order of power required is 10s of kW.
     
  6. Mech_Engineer

    Mech_Engineer 2,299
    Science Advisor
    Gold Member

    The proper way to calculate it is to look at the volumetric flow rate of the engine at a specific engine speed, estimate the intake pressure required at that engine speed, and calculate the power through an isentropic compressor model.

    1) In the case of a 1.9 l turbodiesel, if we estimate it generates peak power at about 4000 rpm, and taking into account a volumetric engine efficiency of maybe 85%, that gives a flow rate of about 170 l/s.

    2) A TDI engine will operate at maybe 20 psi max boost (P2 = 34.7 absolute) from atomspheric intake (P1 = 14.7 psi), so we can look up the enthalpy of the air at these two states. Basically you can use a T-S or P-V diagram from air, assume 300 K for intake temperature, and follow an isentropic line from P1, T1 to P2.

    3) Assuming the increase in enthalpy in these two states comes from the compressor's drive, you now have everything you need to calculate the power required on that drive (flow rate and enthalpy change).
     
  7. Hi:
    I thk. you all for your answers - which I found very useful,however at this point I'm kind of tied up - but as soon as I can I'll retake the issue.
    Thks. once again,
    J. D.
     
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