# 6 supercharging and turbocharging

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

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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