6 supercharging and turbocharging

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Internal Combustion Engines by John B. Heywood (Lecture Slides)

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  • 6TOPICSupercharging and turbochargingChapter 6Section 6.8

  • Term supercharging refers to increasing the air (or mixture) density by increasing its pressure prior to entering the engine cylinder

    Three basic methods of supercharging:mechanical superchargingturbochargingpressure wave supercharging

    We consider operating characteristics of turbines and compressorsMethods of power boosting

  • Mechanical supercharging

  • Turbocharging

  • Engine-driven compressor and turbocharger

  • Two-stage turbocharging

  • Turbocharging with turbocompounding

  • Turbocharger with intercooler

  • Centrifugal compressor

  • Basic relationshipsEnergy balance

    Stagnation properties

    Work transfer rate

  • Compressor isentropic efficiencyTotal-to-total isentropic efficiency

    With constant cp

  • Compressor isentropic efficiencySince kinetic energy of the gas leaving the compressor is not usually recovered, a more realistic definition of efficiency is based on exit static conditions

    This is termed the total-to-static isentropic efficiency

  • Power required to drive compressorThermodynamic power requirement:in terms of total-to-total isentropic efficiency

    in terms of total-to-static isentropic efficiency

    Power required to drive compressor

  • Schematic of radial flow turbine

  • Turbine isentropic efficiencyTotal-to-total isentropic efficiency

    With constant cp

    Note: cp for exhaust gas may vary significantly with temperature

  • Turbine isentropic efficiencySince kinetic energy at the exit of the turbocharger is usually wasted, a more realistic definition of efficiency is based on exit static conditions

    This is termed the total-to-static isentropic efficiency

  • Power delivered by the turbineIn terms of total-to-total isentropic efficiency

    In terms of total-to-static isentropic efficiency

    With a turbocharger, turbine is mechanically linked to compressor. Hence, at constant turbocharger speed

    where m is the mechanical efficiency of turbocharger. It is usually combined with the turbine efficiency

  • Dimensionless groups used to describe turbocharger performanceMost important dependent variables are mass flow rate , isentropic efficiency , and temperature difference across the machine T0Each of these are functions of independent variables

    By dimensional analysis, these eight independent variables can be reduced to four dimensionless groups

  • Dimensionless groups used to describe turbocharger performanceReynolds number has little effect on performance and is fixed by the gas, therefore they can be omittedFor a particular device, dimensions are fixed and value of R is fixed. So, it is convenient to plot

    is corrected mass flow, is corrected speed

  • Schematic of compressor operating map

  • Centrifugal compressor operating map

  • Radial turbine performance map

  • Radial turbine performance map

  • Characteristics of turbochargerSteady-state turbocharger operating lines plotted as constant T03 /T01 lines on compressor map.

    dash-dot-dash line is for p03 = p02to the left p03 < p02to the right p03 > p02

  • Thats all for today

  • For those who wants to know more

  • Centrifugal compressor

  • Positive displacement compressors

  • h-s diagram for flow through centrifugal compressor

  • Velocity diagrams

  • Schematic of radial flow turbine

  • h-s and velocity diagrams for radial turbine

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